David Fonseca Mota

• Verma, Anshul; Aluri, Pavan K.; Mota, David Fonseca & Obukhov, Yuri N. (2026). Cosmographic constraints on a Gödel-type rotating universe. Journal of Cosmology and Astroparticle Physics (JCAP). 2026(6). doi: 10.1088/1475-7516/2026/06/047. Fulltekst i vitenarkiv Vis sammendrag

  We investigate the possibility of global cosmic rotation using a Gödel-type rotating cosmological model, constrained through a cosmographic analysis of Type Ia supernovae (SNIa) from the Pantheon+ dataset. Employing a Taylor-expanded apparent magnitude–redshift relation derived via the Kristian-Sachs formalism, we analyze low-redshift SNIa data across five redshift bins (up to Z ≤ 0.5). Our results reveal a mild but consistent preference for cosmic rotation, with the dimensionless rotation parameter Ω0 peaking at 0.29+0.21-0.15 for Z ≤ 0.2, and a broadly aligned anisotropy axis centered around equatorial coordinates (243°, -49°). The inferred Hubble constant h0 ≈ 0.73 remains stable across all bins, while the deceleration parameter q0 trends from near-zero to mildly negative values with increasing redshift. Model comparison using the Akaike Information Criterion (AIC) indicates a statistically significant preference for the rotating model over the standard ΛCDM cosmology at intermediate redshifts. A new result presented in the current work is the derivation of “m-Z” relation up to 𝒪(Z2) using the Kristian-Sachs expansion. Parameter estimates thus obtained from the extended cosmographic expansion result in weaker estimates with broad posteriors. These results highlight the need for beyond-cosmographic approaches to robustly assess the possibility of cosmic rotation and its influence on late-time expansion history of the universe.

• Faucher, Adrian; Benisty, David & Mota, David (2026). Hubble-constant and -mass determination of Centaurus A and M83 from tip-of-red-giant-branch distances. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 705. doi: 10.1051/0004-6361/202556283. Fulltekst i vitenarkiv Vis sammendrag

  An independent determination of the Hubble constant is crucial in light of the persistent tension between early- and late-Universe measurements. In this study, we analysed the dynamics of the Centaurus A (CenA) and M83 galaxies, along with their associated dwarf companions identified via tip-of-the-red-giant-branch (TRGB) distance measurements, to constrain both the group mass and the local value of H0. By examining the motions of these galaxies relatively to the system’s barycentre, we applied both the minor and major infall models, which provide bounds on the true radial-velocity dispersion. From the overlap of these approaches, we obtain a virial mass estimate of (7.3 ± 2.0)×10^12 M⊙ and a Hubble-flow-based mass of (2.6 ± 1.4)×10^12 M⊙. Modeling the cold Hubble flow around the group centre of mass, we derive a corresponding value of the Hubble constant as (64.0 ± 4.6) km s−1 Mpc−1. These results offer an independent, dynamically motivated constraint on the local value of H0, explicitly accounting for the impact of peculiar velocities in the nearby Universe. We also discuss the ∼2σ tension between the virial and Hubble-flow-based mass estimates, which likely arises from the fact that M83 is close to the velocity surface and goes against the Hubble-flow-model assumptions. While the Hubble-flow fit emphasises galaxies that follow smooth expansion on the lower branch of the velocity-distance relation, the virial mass estimate is found to be in good agreement with the group mass derived from the K-band luminosity of its brightest members and the projected mass methods.

• Allahyari, Alireza; Davari, Mohammadreza & Mota, David (2025). Lorentz violation with gravitational waves: Constraints from NANOGrav and IPTA data. Journal of High Energy Astrophysics. ISSN 2214-4048. 49. doi: 10.1016/j.jheap.2025.100448. Fulltekst i vitenarkiv Vis sammendrag

  We explore a theoretical framework in which Lorentz symmetry is explicitly broken by incorporating derivative terms of the extrinsic curvature into the gravitational action. These modifications introduce a scale-dependent damping effect in the propagation of gravitational waves (GWs), governed by a characteristic energy scale denoted as MLV. Tightest constraints on MLV are achieved when we assume GWs have a primordial origin. In this scenario, we derive the modified spectral energy density of GWs and confront it with recent observational data from the NANOGrav 15-year dataset and the second data release of the International Pulsar Timing Array (IPTA). Our analysis yields a lower bound on the Lorentz-violating energy scale, finding MLV > 10^-19 GeV at 68% confidence level. This result significantly improves upon previous constraints derived from LIGO/VIRGO binary merger observations. Our findings demonstrate the potential of pulsar timing arrays to probe fundamental symmetries of spacetime and offer new insights into possible extensions of general relativity.

• Rezaei, Mehdi; Pan, Supriya; Yang, Weiqiang & Mota, David (2025). Is Dark Energy Changing? Probing the Universe’s Expansion with Present and Future Astronomical Probes. The Astrophysical Journal (ApJ). ISSN 0004-637X. 995(2). doi: 10.3847/1538-4357/ae1294. Fulltekst i vitenarkiv Vis sammendrag

  This study explores the possibility of a time-varying dark energy (DE) equation of state (EoS) deviating from −1. We employ a comprehensive data set of the usual astronomical probes (Type Ia supernovae, baryon acoustic oscillations, Big Bang nucleosynthesis, Hubble data, and Planck 2018 cosmic microwave background (CMB)) alongside future mock gravitational wave (GW) distance measurements from the Einstein Telescope. We utilize the Padé approximation, a versatile framework encompassing well-known DE models such as constant EoS, Chevallier–Polarski–Linder parameterization, and other time-evolving DE parameterizations. Within the Padé parameterization, we examine three specific forms (Padé-I, SPadé-I, Padé-II) applied to both spatially flat and nonflat universes. Padé-II exhibits particularly interesting features in terms of the evidence of dynamical DE at many standard deviations. Our results can be summarized as follows. Flat universe: when analyzing the combined data set of standard probes (including CMB) with Padé-II in a flat universe, we find a strong preference (6.4 σ ) for a dynamical (time-varying) DE EoS. This preference remains significant (4.7 σ ) even when incorporating future GW data. Nonflat universe: in a nonflat universe, the combined standard data sets (without or with CMB) also indicate a dynamical DE EoS at a high confidence level (6.2 σ and 6.4 σ , respectively). The addition of GW data slightly reduces the evidence (3.8 σ and 5.1 σ , respectively), but the preference persists. These results collectively suggest a robust case for dynamical DE in the dark sector. While a nonflat universe is not strongly favored, Padé-II hints at a possible closed universe when CMB data are included (with or without GW data).

• Rodrigues, G.; Santos, F.B.M. dos; Costa, S. Santos da; Rodrigues, J.G.; Marttens, R. von & Silva, R. [Vis alle 8 forfattere av denne artikkelen] (2025). Forecasting constraints on quintessential inflation from future generation of galaxy and CMB surveys. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(11). doi: 10.1088/1475-7516/2025/11/022. Fulltekst i vitenarkiv Vis sammendrag

  We investigate the constraining power of future CMB and galaxy surveys on models of quintessential inflation realized within the framework of α -attractors. We analyze how these future datasets will probe the parameter space of α -attractor quintessential inflation, specifically the inflationary potential parameters. Our results demonstrate that the synergy between CMB-S4, LiteBIRD, and Euclid can significantly tighten the bounds on the model parameters, achieving forecasted 1σ precisions of ∼8.5% for α , 0.15% for n s , and 0.1% for ln(10 10 A s ) in the CMB+GC sp case. This level of sensitivity will enable us to discriminate between different realizations of quintessential inflation and test the attractor behavior characteristic of these models.

• Wang, Deng & Mota, David (2025). Did DESI DR2 truly reveal dynamical dark energy? European Physical Journal C. ISSN 1434-6044. 85(11). doi: 10.1140/epjc/s10052-025-15076-y. Fulltekst i vitenarkiv Vis sammendrag

  A fundamental question in cosmology is whether dark energy evolves over time, a topic that has gained prominence since the discovery of cosmic acceleration. Recently, the DESI collaboration has reported increasing evidence for evolving dark energy using combinations of cosmic microwave background (CMB), type Ia supernova (SN), and their new measurements of baryon acoustic oscillations (BAO). However, our analysis reveals that these combinations are problematic due to clear tensions among the CMB, BAO and SN datasets. Consequently, DESI’s claim of dynamical dark energy (DDE) is not robust. A more reliable approach involves constraining the evolution of dark energy using each dataset independently. Through a statistical comparison for each dataset, on average, we find that DDE is strongly preferred over the $$\Lambda $$ Λ CDM model. This suggests that DDE likely exists, although its real parameter space remains elusive due to weak constraints on the dark energy equation of state and inconsistencies among the datasets. Interestingly, when considering DDE, none of the individual datasets – including CMB, DESI DR2, Pantheon+, Union3, and DESY5 – can independently detect cosmic acceleration at a significant level. Our findings not only clarify the current understanding of the nature of dark energy but also challenge the established discovery of cosmic acceleration and the long-held notion that dark energy exerts negative pressure. Both individual and combined datasets suggest that the ultimate fate of the universe is likely to be dominated by matter rather than dark energy.

• Puttasiddappa, Prajwal Hassan; Rodrigues, Davi C. & Mota, David (2025). Shadows of naked singularity in Brans–Dicke gravity. European Physical Journal C. ISSN 1434-6044. 85(9). doi: 10.1140/epjc/s10052-025-14721-w. Fulltekst i vitenarkiv Vis sammendrag

  We investigate exact vacuum solutions in Brans–Dicke (BD) gravity, focusing on their implications for black hole shadow imaging. Motivated by the Event Horizon Telescope (EHT) observations, we revisit a class of BD solutions that exhibit a naked singularity. These solutions, despite lacking a conventional event horizon, exhibit photon spheres and produce shadow-like features. We analyze null geodesics and perform ray-tracing simulations under an optically thin accretion disk model to generate synthetic images. Our results show that BD naked singularities can cast shadows smaller than those of Schwarzschild black holes of equivalent mass. This requires, however, negative values for the BD parameter $$\omega $$ ω (in the range $$-3/2< \omega < 0$$ - 3 / 2 < ω < 0 ). The lower bound on $$\omega $$ ω is compatible with the absence of ghosts. Although such $$\omega $$ ω range is outside the Solar System bounds, our results are relevant for a larger class of modified gravity models whose local behaviour can be approximated by Brans–Dicke gravity. These findings suggest that BD naked singularities are possible candidates for compact astrophysical objects.

• Baidya, Mainak; Ghoshal, Anish & Mota, David (2025). Complementary signatures of α-attractor inflation in CMB and cosmic string gravitational waves. Physical Review D. ISSN 2470-0010. 111(12). doi: 10.1103/81v4-pp8q. Fulltekst i vitenarkiv Vis sammendrag

  When cosmic strings are formed during inflation, they regrow to reach a scaling regime, leaving distinct imprints on the stochastic gravitational wave background (SGWB). Such signatures, associated with specific primordial features, can be detected by upcoming gravitational wave observatories, such as the LISA and Einstein Telescope (ET). Our analysis explores scenarios in which cosmic strings form either before or during inflation. We examine how the number of e-folds experienced by cosmic strings during inflation correlates with the predictions of inflationary models observable in cosmic microwave background (CMB) measurements. This correlation provides a testable link between inflationary physics and the associated gravitational wave signals in a complementary manner. Focusing on 𝛼-attractor models of inflation, with the Polynomial 𝛼-attractor serving as an illustrative example, we find constraints, for instance, on the spectral index 𝑛𝑠 to 0.962 ≲𝑛𝑠 ≲0.972 for polynomial exponent 𝑛 =1, 0.956 ≲𝑛𝑠 ≲0.968 for 𝑛 =2, 0.954 ≲𝑛𝑠 ≲0.965 for 𝑛 =3, and 0.963 ≲𝑛𝑠 ≲0.964 for 𝑛 =4, which along with the GW signals from LISA, are capable of detecting local cosmic strings that have experienced ∼34–47 e-folds of inflation consistent with current Planck data and are also testable in upcoming CMB experiments such as LiteBIRD and CMB-S4.

• Benisty, David & Mota, David (2025). Line-of-sight velocity projection impact on Local Group mass determinations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 698. doi: 10.1051/0004-6361/202553846. Fulltekst i vitenarkiv Vis sammendrag

  The mass of the Local Group (LG), which includes the Milky Way, Andromeda (M31), and their satellites, is crucial for validating galaxy formation and cosmological models. Traditional virial mass estimates, which rely on line-of-sight (LoS) velocities and simplified infall assumptions, are prone to systematic biases due to unobserved velocity components and anisotropic kinematics. Using the TNG cosmological simulation, we examined two limiting cases: the minor infall model – which ignores velocities perpendicular to LoS directions – and the major infall model – which assumes purely radial motion toward the center of mass (CoM). Our simulations demonstrate that geometric corrections are vital: the minor infall model underestimates the true mass, while the major infall model overestimates it. By applying these calibrated corrections to observed dwarf galaxy kinematics within 1 Mpc of the LG’s CoM, we derived a refined LG mass of M LG  = (2.99 ± 0.60)×10 12   M ⊙ . This finding resolves previous discrepancies as it aligns with predictions from the Λ cold dark matter model, timing arguments, and independent mass estimates. Our analysis highlights the importance of correcting for velocity anisotropy and offers a robust framework for dynamical mass estimations of galaxy groups.

• Yang, Weiqiang; Pan, Supriya; Valentino, Eleonora Di; Mena, Olga; Mota, David & Chakraborty, Subenoy (2025). Probing the cold nature of dark matter. Physical Review D. ISSN 2470-0010. 111(10). doi: 10.1103/physrevd.111.103509. Fulltekst i vitenarkiv Vis sammendrag

  A pressureless dark matter component fits well with several cosmological observations. However, there are indications that cold dark matter may encounter challenges in explaining observations at small scales, particularly at galactic scales. Observational data suggest that dark matter models incorporating a pressure component could provide solutions to these small-scale problems. In this work, we investigate the possibility that present-day dark matter may result from a decaying noncold dark matter sector transitioning into the dark energy sector. As the sensitivity of astronomical surveys rapidly increases, we explore an interacting scenario between dark energy and noncold dark matter, where dark energy has a constant equation of state (𝑤de), and dark matter, being noncold, also has a constant (non-zero) equation of state (𝑤dm). Considering the phantom and quintessence nature of dark energy, characterized by its equation of state, we separately analyze interacting phantom and interacting quintessence scenarios. We constrain these scenarios using cosmic microwave background (CMB) measurements and their combination with external probes, such as DESI-BAO and PantheonPlus. From our analyses, we find that a very mild preference for noncold dark matter cannot be excluded based on the employed datasets. Additionally, for some datasets, there is a pronounced preference for the presence of an interaction at more than 95% confidence level (CL). Moreover, when the dark energy equation of state lies in the phantom regime, the 𝑆8 tension can be alleviated. This study suggests that cosmological models incorporating a noncold dark matter component should be considered as viable scenarios with novel phenomenological implications, as reflected in the present work.

• Vikenes, Vetle Amundsen; Ruan, Cheng-Zong & Mota, David (2025). An emulation-based model for the projected correlation function. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 696. doi: 10.1051/0004-6361/202452174. Fulltekst i vitenarkiv Vis sammendrag

  Data from the ongoing Euclid survey will map out billions of galaxies in the Universe, covering more than a third of the sky. This data will provide a wealth of information about the large-scale structure of the Universe and will have a significant impact on cosmology in the coming years. In this paper we introduce an emulator-based halo model approach to forward-modeling the relationship between cosmological parameters and the projected galaxy-galaxy two-point correlation function (2PCF). Utilizing the large A BACUS S UMMIT simulation suite, we emulated the 2PCF by generating mock-galaxy catalogs within the halo occupation distribution (HOD) framework. Our emulator is designed to predict the 2PCF over scales 0.1 ≤  r /( h −1  Mpc)≤105, from which we derived the projected correlation function, independent of redshift space distortions. We demonstrate that the emulator accurately predicts the projected correlation function over scales 0.5 ≤  r ⊥ /( h −1  Mpc)≤40 given a set of cosmological and HOD parameters. We then employed this model in a parameter inference analysis, showcasing its ability to constrain cosmological parameters. Our findings indicate that the projected correlation function places only weak constraints on several cosmological parameters due to its intrinsic lack of information; additional clustering statistics are necessary to better probe the underlying cosmology. Despite the simplified covariance matrix used in the likelihood model, the posterior distributions of several cosmological parameters remain broad, underscoring the need for a more comprehensive approach.

• Rácz, G.; Breton, M.-A.; Fiorini, B.; Brun, A. M. C. Le; Winther, Hans Arnold & Sakr, Z. [Vis alle 277 forfattere av denne artikkelen] (2025). Euclid preparation: LXIII. Simulations and non-linearities beyond Lambda cold dark matter. 2. Results from non-standard simulations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 695. doi: 10.1051/0004-6361/202452185. Fulltekst i vitenarkiv Vis sammendrag

  The Euclid mission will measure cosmological parameters with unprecedented precision. To distinguish between cosmological models, it is essential to generate realistic mock observables from cosmological simulations that were run in both the standard Λ-cold-dark-matter (ΛCDM) paradigm and in many non-standard models beyond ΛCDM. We present the scientific results from a suite of cosmological N -body simulations using non-standard models including dynamical dark energy, k -essence, interacting dark energy, modified gravity, massive neutrinos, and primordial non-Gaussianities. We investigate how these models affect the large-scale-structure formation and evolution in addition to providing synthetic observables that can be used to test and constrain these models with Euclid data. We developed a custom pipeline based on the Rockstar halo finder and the nbodykit large-scale structure toolkit to analyse the particle output of non-standard simulations and generate mock observables such as halo and void catalogues, mass density fields, and power spectra in a consistent way. We compare these observables with those from the standard ΛCDM model and quantify the deviations. We find that non-standard cosmological models can leave large imprints on the synthetic observables that we have generated. Our results demonstrate that non-standard cosmological N -body simulations provide valuable insights into the physics of dark energy and dark matter, which is essential to maximising the scientific return of Euclid .

• Mellier, Y.; Abdurro’uf, .; Barroso, J.A. Acevedo; Achúcarro, A.; Adamek, J. & Adam, R. [Vis alle 1 138 forfattere av denne artikkelen] (2025). Euclid I. Overview of the Euclid mission. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 697. doi: 10.1051/0004-6361/202450810. Fulltekst i vitenarkiv Vis sammendrag

  The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015–2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14 000 deg2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

• Verma, Anshul; Aluri, Pavan K. & Mota, David (2025). Anisotropic universe with anisotropic dark energy. Physical Review D. ISSN 2470-0010. 111(8). doi: 10.1103/PhysRevD.111.083508. Fulltekst i vitenarkiv Vis sammendrag

  We investigate the anisotropic parametrization of the dark energy equation of state within the framework of an axisymmetric (planar) Bianchi-I universe. Using the latest Pantheon+ Type Ia Supernova dataset, augmented by SH0ES Cepheid distance calibrators, we constrain both the equation of state for anisotropic dark energy and other standard cosmological parameters. Additionally, we examine the presence of an underlying anisotropic axis. Our analysis yields a mean anisotropic dark energy equation of state as 𝑤 =−0.8⁢6+0.15−0.11 and a difference in the equation of states in and perpendicular to the plane of the axisymmetric Bianchi-I space-time as 𝛿𝑤 =−0.12⁢9+0.090−0.064. We also identify an axis of anisotropy at approximately (27⁢2°,2⁢1°) in galactic coordinates. Through a comparative study of different cosmological models, we find that the data favor a Bianchi-I universe with anisotropic dark energy, where the equation of state deviates from “−1” along the axis of anisotropy (the 𝑤𝑏⁢CDM model), over other anisotropic models considered and the standard flat Λ⁢CDM or 𝑤⁢CDM models.

• Adamek, J.; Fiorini, B.; Baldi, M.; Brando, G.; Breton, M.-A. & Hassani, Farbod [Vis alle 270 forfattere av denne artikkelen] (2025). Euclid preparation: LXII. Simulations and non-linearities beyond Lambda cold dark matter. 1. Numerical methods and validation. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 695. doi: 10.1051/0004-6361/202452180. Fulltekst i vitenarkiv Vis sammendrag

  To constrain cosmological models beyond ACDM, the development of the Euclid analysis pipeline requires simulations that capture the non-linear phenomenology of such models. We present an overview of numerical methods and N-body simulation codes developed to study the non-linear regime of structure formation in alternative dark energy and modified gravity theories. We review a variety of numerical techniques and approximations employed in cosmological N-body simulations to model the complex phenomenology of scenarios beyond ACDM. This includes discussions on solving non-linear field equations, accounting for fifth forces, and implementing screening mechanisms. Furthermore, we conduct a code comparison exercise to assess the reliability and convergence of different simulation codes across a range of models. Our analysis demonstrates a high degree of agreement among the outputs of different simulation codes, typically within 2% for the predicted modification of the matter power spectrum and within 4% for the predicted modification of the halo mass function, although some approximations degrade accuracy a bit further. This provides confidence in current numerical methods of modelling cosmic structure formation beyond ACDM. We highlight recent advances made in simulating the non-linear scales of structure formation, which are essential for leveraging the full scientific potential of the forthcoming observational data from the Euclid mission.

• Christiansen, Øyvind; Hassani, Farbod & Mota, David Fonseca (2025). Environmental cosmic acceleration from a phase transition in the dark sector. Journal of Cosmology and Astroparticle Physics (JCAP). 2025. doi: 10.1088/1475-7516/2025/01/043. Fulltekst i vitenarkiv Vis sammendrag

  A new degravitation mechanism within the framework of scalar tensor gravity is postulated and included by prescription. The mechanism eliminates all constant contributions from the potential to the Friedmann equation, leaving only the kinematic and the dynamic terms of the potential to drive cosmic acceleration. We explore a scenario involving a density-triggered phase transition in the late-time universe, and argue that the resulting effective energy density and equation of state parameter can explain late-time cosmology when extrapolated to a region of the parameter space.

• Christiansen, Øyvind; Adamek, J.; Hassani, Farbod & Mota, David (2025). Gravitational waves from dark domain walls. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(1). doi: 10.1088/1475-7516/2025/01/149. Fulltekst i vitenarkiv Vis sammendrag

  For most of cosmic history, the evolution of our Universe has been governed by the physics of a `dark sector', consisting of dark matter and dark energy, whose properties are only understood in a schematic way. The influence of these constituents is mediated exclusively by the force of gravity, meaning that insight into their nature must be gleaned from gravitational phenomena. The advent of gravitational-wave astronomy has revolutionised the field of black hole astrophysics, and opens a new window of discovery for cosmological sources. Relevant examples include topological defects, such as domain walls or cosmic strings, which are remnants of a phase transition. Here we present the first simulations of cosmic structure formation in which the dynamics of the dark sector introduces domain walls as a source of stochastic gravitational waves in the late Universe. We study in detail how the spectrum of gravitational waves is affected by the properties of the model, and extrapolate the results to scales relevant to the recent evidence for a stochastic gravitational wave background. Our relativistic implementation of the field dynamics paves the way for optimal use of the next generation of gravitational experiments to unravel the dark sector.

• Valentino, Eleonora Di; Said, Jackson Levi; Riess, Adam; Pollo, Agnieszka; Poulin, Vivian & Gómez-Valent, Adrià [Vis alle 540 forfattere av denne artikkelen] (2025). The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics. Physics of the Dark Universe. 49. doi: 10.1016/j.dark.2025.101965. Fulltekst i vitenarkiv Vis sammendrag

  The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. These new methods will become increasingly important in the coming years as the volume of survey data continues to increase, and as the degeneracy between predictions of different physical models grows. There are several perspectives on the divergences between the values of cosmological parameters, such as the model-independent probes in the late Universe and model-dependent measurements in the early Universe, which we cover at length. The White Paper closes with a number of recommendations for the community to focus on for the upcoming decade of observational cosmology, statistical data analysis, and fundamental physics developments.

• Bose, B.; Carrilho, P.; Marinucci, M.; Moretti, C.; Pietroni, M. & Carella, E. [Vis alle 232 forfattere av denne artikkelen] (2024). Euclid preparation: XLIV. Modelling spectroscopic clustering on mildly nonlinear scales in beyond-ΛCDM models. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 689. doi: 10.1051/0004-6361/202348784. Fulltekst i vitenarkiv Vis sammendrag

  Context. The Euclid space satellite mission will measure the large-scale clustering of galaxies at an unprecedented precision, providing a unique probe of modifications to the ΛCDM model. Aims. We investigated the approximations needed to efficiently predict the large-scale clustering of matter and dark matter halos in the context of modified gravity and exotic dark energy scenarios. We examined the normal branch of the Dvali–Gabadadze–Porrati model, the Hu–Sawicki f(R) model, a slowly evolving dark energy model, an interacting dark energy model, and massive neutrinos. For each, we tested approximations for the perturbative kernel calculations, including the omission of screening terms and the use of perturbative kernels based on the Einstein–de Sitter universe; we explored different infrared-resummation schemes, tracer bias models and a linear treatment of massive neutrinos; we investigated various approaches for dealing with redshift-space distortions and modelling the mildly nonlinear scales, namely the Taruya–Nishimishi–Saito prescription and the effective field theory of large-scale structure. This work provides a first validation of the various codes being considered by Euclid for the spectroscopic clustering probe in beyond-ΛCDM scenarios. Methods. We calculated and compared the χ2 statistic to assess the different modelling choices. This was done by fitting the spectroscopic clustering predictions to measurements from numerical simulations and perturbation theory-based mock data. We compared the behaviour of this statistic in the beyond-ΛCDM cases, as a function of the maximum scale included in the fit, to the baseline ΛCDM case. Results. We find that the Einstein–de Sitter approximation without screening is surprisingly accurate for the modified gravity cases when comparing to the halo clustering monopole and quadrupole obtained from simulations and mock data. Further, we find the same goodness-of-fit for both cases – the one including and the one omitting non-standard physics in the predictions. Our results suggest that the inclusion of multiple redshift bins, higher-order multipoles, higher-order clustering statistics (such as the bispectrum), and photometric probes such as weak lensing, will be essential to extract information on massive neutrinos, modified gravity and dark energy. Additionally, we show that the three codes used in our analysis, namely, PBJ, Pybird and MG-Copter, exhibit sub-percent agreement for k ≤ 0.5 h Mpc−1 across all the models. This consistency underscores their value as reliable tools.

• Asghari, Mahnaz; Allahyari, Alireza & Mota, David (2024). Gravitational wave probes of Barrow cosmology with LISA standard sirens. Journal of Cosmology and Astroparticle Physics (JCAP). 2024(6). doi: 10.1088/1475-7516/2024/06/044. Fulltekst i vitenarkiv Vis sammendrag

  We study the Barrow cosmological model, which proposes that quantum gravity effects create a complex, fractal structure for the universe's apparent horizon. We leverage the thermodynamics-gravity conjecture. By applying the Clausius relation to the apparent horizon of the Friedmann-Lemaître-Robertson-Walker universe within this framework, we derive modified field equations where the Barrow entropy is linked to the horizon. We assess the Barrow cosmology against current observations — cosmic microwave background, supernovae, and baryon acoustic oscillations data — and include projections for future Laser Interferometer Space Antenna (LISA) standard sirens (SS). Our numerical results suggest a modest improvement in the Hubble tension for Barrow cosmology with phantom dark energy behavior, compared to the standard cosmological model. Furthermore, incorporating simulated LISA SS data alongside existing observational constraints tightens the limitations on cosmological parameters, particularly the deformation exponent.

• Christiansen, Øyvind; Hassani, Farbod & Mota, David (2024). Asimulation: Domain formation and impact on observables in resolved cosmological simulations of the (a)symmetron. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 689. doi: 10.1051/0004-6361/202449188. Fulltekst i vitenarkiv Vis sammendrag

  The symmetron is a dark energy and dark matter candidate that forms topological defects in the late-time universe and holds the promise of resolving some of the cosmological tensions. We performed high-resolution simulations of the dynamical and non-linear (a)symmetron using the recently developed relativistic N-body code asevolution. By extensively testing the temporal and spatial convergence of domain decompositioning and domain wall stability, we determined criteria and physical intuition for the convergence. We applied the resolution criteria to run five high-resolution simulations with 12803 grids and a box size of 500 Mpc h−1 of the (a)symmetron. We considered the behaviour of the scalar field and the domain walls in each scenario. We find the effect on the matter power spectra, the HMFs, and observables computed over the past light cone of an observer, such as the integrated Sachs-Wolfe and non-linear Rees-Sciama effect and the lensing, compared to ΛCDM. We show local oscillations of the fifth force strength and the formation of planar structures in the density field. The dynamics of the field was visualised in animations with high resolution in time. The simulation code is made publicly available.

• Verma, Anshul; Patel, Sanjeet K.; Aluri, Pavan K.; Panda, Sukanta & Mota, David (2024). Constraints on Bianchi-I type universe with SH0ES anchored Pantheon+ SNIa data. Journal of Cosmology and Astroparticle Physics (JCAP). 2024(6). doi: 10.1088/1475-7516/2024/06/071. Fulltekst i vitenarkiv Vis sammendrag

  We study the Bianchi-I cosmological model motivated by signals of statistical isotropy violation seen in cosmic microwave background (CMB) observations and others. To that end, we consider various kinds of anisotropic matter that source anisotropy in our model, specifically Cosmic strings, Magnetic fields, Domain walls and Lorentz violation generated magnetic fields. These anisotropic matter sources, taking one at a time, are studied for their co-evolution with standard model (isotropic) sources viz., dust-like (dark/normal) matter, and dark energy modelled as cosmological constant. We constrain the Hubble parameter, density fractions of anisotropic matter, cold dark matter (CDM), and dark energy (Λ) in a Bianchi-I universe with planar symmetry i.e., which has a global ellipsoidal geometry, and try to find signatures of a cosmic preferred axis if any. The latest compilation of Type Ia Supernova (SNIa) data from Pantheon+SH0ES collaboration is used in our analysis to obtain constraints on cosmological parameters and any preferred axis for our universe. In our analysis, we found mild evidence for a cosmic preferred axis. It is interesting to note that this preferred axis lies broadly in the vicinity of other prominent cosmic anisotropy axes reported in the literature from diverse data sets. Also we find some evidence for non-zero (negative) cosmic shear and eccentricity that characterize different expansion rates in different directions and deviation from an isotropic scale factor respectively. The energy density fractions of two of the sources considered are found to be non-zero at a 2σ confidence level. To be more conclusive, we require more SNIa host galaxy data for tighter constraints on distance and absolute magnitude calibration which are expected to be available from the future JWST observations and others.

• Sharma, Mohit K.; Sami, M. & Mota, David (2024). Generic predictions for primordial perturbations and their implications. Physics Letters B. ISSN 0370-2693. 856. doi: 10.1016/j.physletb.2024.138956. Fulltekst i vitenarkiv Vis sammendrag

  We introduce a novel framework for studying small-scale primordial perturbations and their cosmological implications. The framework uses a deep reinforcement learning to generate scalar power spectrum profiles that are consistent with current observational constraints. The framework is shown to predict the abundance of primordial black holes and the production of secondary induced gravitational waves. We demonstrate that the set up under consideration is capable of generating predictions that are beyond the traditional model-based approaches.

• Rezaei, Mehdi; Pan, Supriya; Yang, Weiqiang & Mota, David (2024). Evidence of dynamical dark energy in a non-flat universe: current and future observations. Journal of Cosmology and Astroparticle Physics (JCAP). 2024(1). doi: 10.1088/1475-7516/2024/01/052. Fulltekst i vitenarkiv
• Hadi, H.; Akbarieh, Amin Rezaei & Mota, David (2024). Gravitational wave pulse and memory effects for hairy Kiselev black hole and its analogy with Bondi-Sachs formalism. Classical and Quantum Gravity. ISSN 0264-9381. 41(10). doi: 10.1088/1361-6382/ad3caf. Fulltekst i vitenarkiv
• Capozziello, S.; Zare, S.; Mota, David & Hassanabadi, H. (2023). Dark matter spike around Bumblebee black holes. Journal of Cosmology and Astroparticle Physics (JCAP). 2023(5). doi: 10.1088/1475-7516/2023/05/027. Fulltekst i vitenarkiv
• Mauland-Hus, Renate; Elgarøy, Øystein; Mota, David & Winther, Hans Arnold (2023). The void-galaxy cross-correlation function with massive neutrinos and modified gravity. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 674. doi: 10.1051/0004-6361/202346287. Fulltekst i vitenarkiv Vis sammendrag

  Massive neutrinos and f ( R )-modified gravity have degenerate observational signatures that can impact the interpretation of results in galaxy survey experiments, such as cosmological parameter estimations and gravity model tests. Because of this, it is important to investigate astrophysical observables that can break these degeneracies. Cosmic voids are sensitive to both massive neutrinos and modifications of gravity and provide a promising ground for disentangling the above-mentioned degeneracies. In order to analyse cosmic voids in the context of non-ΛCDM cosmologies, we must first understand how well the current theoretical framework operates in these settings. We performed a suite of simulations with the RAMSES -based N -body code ANUBISIS , including massive neutrinos and f ( R )-modified gravity both individually and simultaneously. The data from the simulations were compared to models of the void velocity profile and the void-halo cross-correlation function (CCF). This was done both with the real space simulation data as model input and by applying a reconstruction method to the redshift space data. In addition, we ran Markov chain Monte Carlo (MCMC) fits on the data sets to assess the capability of the models to reproduce the fiducial simulation values of fσ 8 ( z ) and the Alcock-Paczyǹski parameter, ϵ . The void modelling applied performs similarly for all simulated cosmologies, indicating that more accurate models and higher resolution simulations are needed in order to directly observe the effects of massive neutrinos and f ( R )-modified gravity through studies of the void-galaxy CCF. The MCMC fits show that the choice for the void definition plays an important role in the recovery of the correct cosmological parameters, but otherwise, there is no clear distinction between the ability to reproduce fσ 8 and ϵ for the various simulations.

• Amaro-Seoane, Pau; Andrews, Jeff; Sedda, Manuel Arca; Askar, Abbas; Baghi, Quentin & Balasov, Razvan [Vis alle 158 forfattere av denne artikkelen] (2023). Astrophysics with the Laser Interferometer Space Antenna. Living Reviews in Relativity. 26(1). doi: 10.1007/s41114-022-00041-y. Fulltekst i vitenarkiv Vis sammendrag

  The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.

• Pan, Supriya; Yang, Weiqiang; Valentino, Eleonora Di; Mota, David & Silk, Joseph (2023). IWDM: the fate of an interacting non-cold dark matter — vacuum scenario. Journal of Cosmology and Astroparticle Physics (JCAP). 2023(7). doi: 10.1088/1475-7516/2023/07/064. Fulltekst i vitenarkiv Vis sammendrag

  Abstract In most cosmological models, the equation of state of the dark matter is assumed to be zero, which means that the dark matter is pressure-less or cold. While this hypothesis is based on the abundance of cold dark matter in the universe, however, there is no compelling reason to assume that the equation of state of dark matter is exactly zero. A more general approach would be to allow for a range of values for the dark matter equation of state and use the observational data to determine which values are most likely. With the increasing accuracy of experimental data, we have chosen to explore the possibility of interacting non-cold dark matter - vacuum scenario, where the equation of state of the dark matter is constant but can take different values within a specific range. Using the Cosmic Microwave Background (CMB) anisotropies and the CMB lensing reconstruction from the Planck legacy release, plus other non-CMB measurements, namely, the baryon acoustic oscillations distance measurements, and the Pantheon catalogue from Type Ia Supernovae, we have analyzed this scenario and found that a non-zero value for the dark matter equation of state is preferred with a confidence level of over 68%. While this is not significant by itself, however, it does suggest that investigating the possibility of non-cold dark matter in the universe is worth exploring further to gain a better understanding of the nature of dark matter.

• Khodadi, Mosen; Mota, David & Sheykhi, Ahmad (2023). Harvesting energy driven by Comisso-Asenjo process from Kerr-MOG black holes. Journal of Cosmology and Astroparticle Physics (JCAP). 2023(10), s. 1–27. doi: 10.1088/1475-7516/2023/10/034. Fulltekst i vitenarkiv
• Banerjee, S.; Bera, S. & Mota, David (2023). Growth of linear perturbations in a universe with superfluid dark matter. I Ruffini, Remo & Vereshchagin, Gregory (Red.), The Sixteenth Marcel Grossmann Meeting: On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics, and Relativistic Field Theories. World Scientific. ISSN 9789811269769. s. 2101–2118. doi: 10.1142/9789811269776_0164. Fulltekst i vitenarkiv Vis sammendrag

  The Lambda-Cold Dark Matter (ΛCDM) model agrees with most of the cosmological observations, but has some hindrances from observed data at smaller scales such as galaxies. Recently, Berezhiani and Khoury proposed a new theory involving interacting superfluid dark matter with three model parameters in,1 which explains galactic dynamics with great accuracy. In the present work, we study the cosmological behaviour of this model in the linear regime of cosmological perturbations. In particular, we compute both analytically and numerically the matter linear growth factor and obtain new bounds for the model parameters which are significantly stronger than previously found. These new constraints come from the fact that structures within the superfluid dark matter framework grow quicker than in ΛCDM, and quite rapidly when the DM-baryon interactions are strong.

• Adamek, J.; Angulo, R. E.; Arnold, C.; Baldi, Marco; Biagetti, M. & Bose, B. [Vis alle 133 forfattere av denne artikkelen] (2023). Euclid: modelling massive neutrinos in cosmology - a code comparison. Journal of Cosmology and Astroparticle Physics (JCAP). 2023(6). doi: 10.1088/1475-7516/2023/06/035. Fulltekst i vitenarkiv Vis sammendrag

  The measurement of the absolute neutrino mass scale from cosmological large-scale clustering data is one of the key science goals of the Euclid mission. Such a measurement relies on precise modelling of the impact of neutrinos on structure formation, which can be studied with N-body simulations. Here we present the results from a major code comparison effort to establish the maturity and reliability of numerical methods for treating massive neutrinos. The comparison includes eleven full N-body implementations (not all of them independent), two N-body schemes with approximate time integration, and four additional codes that directly predict or emulate the matter power spectrum. Using a common set of initial data we quantify the relative agreement on the nonlinear power spectrum of cold dark matter and baryons and, for the N-body codes, also the relative agreement on the bispectrum, halo mass function, and halo bias. We find that the different numerical implementations produce fully consistent results. We can therefore be confident that we can model the impact of massive neutrinos at the sub-percent level in the most common summary statistics. We also provide a code validation pipeline for future reference.

• Cremonese, Paolo; Mota, David & Salzano, Vincenzo (2023). Characteristic Features of Gravitational Wave Lensing as Probe of Lens Mass Model. Annalen der Physik. ISSN 0003-3804. 535(6). doi: 10.1002/andp.202300040. Fulltekst i vitenarkiv Vis sammendrag

  Abstract To recognize gravitational wave lensing events and being able to differentiate between similar lens models will be of crucial importance once one will be observing several lensing events of gravitational waves per year. In this work, the lensing of gravitational waves is studied in the context of LISA sources and wave‐optics regime. While different papers before the studied microlensing effects enhanced by simultaneous strong lensing, the focus is on frequency (time) dependent phase effects produced by one lens that will be visible with only one lensed signal. It is shows how, in the interference regime (i.e., when interference patterns are present in the lensed image), one is able to i) distinguish a lensed waveform from an unlensed one, and ii) differentiate between different lens models. In pure wave‐optics, on the other hand, the feasibility of the study depends on the signal‐to‐noise ratio of the signal and/or the amplitude of the lensing effect. To achieve these goals, the phase of the amplification factor of the different lens models and its effect on the unlensed waveform is studied, and the signal‐to‐noise calculation to provide some quantitative examples is exploited.

• Banerjee, Shreya; Bera, Sayantani & Mota, David (2023). Prospects of probing dark matter condensates with gravitational waves. Journal of Cosmology and Astroparticle Physics (JCAP). 2023(3). doi: 10.1088/1475-7516/2023/03/041. Fulltekst i vitenarkiv
• Christiansen, Øyvind; Hassani, Farbod; Jalilvand, Mona & Mota, David (2023). Asevolution: a relativistic N-body implementation of the (a)symmetron. Journal of Cosmology and Astroparticle Physics (JCAP). 2023(5). doi: 10.1088/1475-7516/2023/05/009. Fulltekst i vitenarkiv Vis sammendrag

  We present asevolution, a cosmological N-body code developed based on gevolution, which consistently solves for the (a)symmetron scalar field and metric potentials within the weak-field approximation. In asevolution, the scalar field is dynamic and can form non-linear structures. A cubic term is added in the symmetron potential to make the symmetry-broken vacuum expectation values different, which is motivated by observational tensions in the late-time universe. To study the effects of the scalar field dynamics, we also implement a constraint solver making use of the quasi-static approximation, and provide options for evaluating the background evolution, including using the full energy density averaged over the simulation box within the Friedmann equation. The asevolution code is validated by comparison with the Newtonian N-body code ISIS that makes use of the quasi-static approximation. There is found a very small effect of including relativistic and weak-field corrections in our small test simulations; it is seen that for small masses, the field is dynamic and can not be accurately solved for using the quasi-static approximation; and we observe the formation of unstable domain walls and demonstrate a useful way to identify them within the code. A first consideration indicates that the domain walls are more unstable in the asymmetron scenario.

• Ferlito, Fulvio; Vagnozzi, Sunny; Mota, David & Baldi, Marco (2022). Cosmological direct detection of dark energy: Non-linear structure formation signatures of dark energy scattering with visible matter. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 512(2), s. 1885–1905. doi: 10.1093/mnras/stac649. Fulltekst i vitenarkiv Vis sammendrag

  Abstract We consider the recently proposed possibility that dark energy (DE) and baryons may scatter through a pure momentum exchange process, leaving the background evolution unaffected. Earlier work has shown that, even for barn-scale cross-sections, the imprints of this scattering process on linear cosmological observables is too tiny to be observed. We therefore turn our attention to non-linear scales, and for the first time investigate the signatures of DE-baryon scattering on the non-linear formation of cosmic structures, by running a suite of large N-body simulations. The observables we extract include the non-linear matter power spectrum, halo mass function, and density and baryon fraction profiles of haloes. We find that in the non-linear regime the signatures of DE-baryon scattering are significantly larger than their linear counterparts, due to the important role of angular momentum in collapsing structures, and potentially observable. The most promising observables in this sense are the baryon density and baryon fraction profiles of haloes, which can potentially be constrained by a combination of kinetic Sunyaev–Zeldovich (SZ), thermal SZ, and weak lensing measurements. Overall, our results indicate that future prospects for cosmological and astrophysical direct detection of non-gravitational signatures of dark energy are extremely bright.

• Hartman, Stian Thomas Heimdal; Winther, Hans Arnold & Mota, David (2022). Cosmological simulations of self-interacting Bose-Einstein condensate dark matter. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 666. doi: 10.1051/0004-6361/202243496. Fulltekst i vitenarkiv Vis sammendrag

  Fully 3D cosmological simulations of scalar field dark matter with self-interactions, also known as Bose-Einstein condensate dark matter, are performed using a set of effective hydrodynamic equations. These are derived from the non-linear Schrödinger equation by performing a smoothing operation over scales larger than the de Broglie wavelength, but smaller than the self-interaction Jeans’ length. The dynamics on the de Broglie scale become an effective thermal energy in the hydrodynamic approximation, which is assumed to be subdominant in the initial conditions, but become important as structures collapse and the fluid is shock-heated. The halos that form have Navarro-Frenk-White envelopes, while the centers are cored due to the fluid pressures (thermal + self-interaction), confirming the features found by Dawoodbhoy et al. (2021, MNRAS, 506, 2418) using 1D simulations under the assumption of spherical symmetry. The core radii are largely determined by the self-interaction Jeans’ length, even though the effective thermal energy eventually dominates over the self-interaction energy everywhere, a result that is insensitive to the initial ratio of thermal energy to interaction energy, provided it is sufficiently small to not affect the linear and weakly non-linear regimes. Scaling relations for the simulated population of halos are compared to Milky Way dwarf spheroidals and nearby galaxies, assuming a Burkert halo profile, and are found to not match, although they conform better with observations compared to fuzzy dark matter-only simulations.

• Allahyari, Alireza; Nunes, Rafael C. & Mota, David (2022). No slip gravity in light of LISA standard sirens. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 514(1), s. 1274–1281. doi: 10.1093/mnras/stac1445. Fulltekst i vitenarkiv Vis sammendrag

  ABSTRACT Standard sirens (SS) are the gravitational wave analogue of the astronomical standard candles, and can provide powerful information about the dynamics of the Universe up to very high z values. In this work, we generate three mock SS catalogues based on the merger of massive black hole binaries which are expected to be observed in the LISA operating frequency band. Then, we perform an analysis to test modifications of general relativity (GR) inspired by the no slip gravity framework. We find that in the best scenarios, we can constrain the free parameters which quantify deviations from GR to 21 per cent accuracy, while the Hubble parameter can be simultaneously fit to 6 per cent accuracy. In combination with CMB information, we find a 15 per cent accuracy on the modified gravity free parameters and 0.7 per cent accuracy on the Hubble parameter. The SS events at very large cosmological distances to be observed in LISA band will provide a unique way to test nature of gravity, but in the context of the analysis performed here, it will not be possible to distinguish the no slip gravity from GR.

• Mina, Mattia; Mota, David & Winther, Hans Arnold (2022). Solitons in the dark: First approach to non-linear structure formation with fuzzy dark matter. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 662. doi: 10.1051/0004-6361/202038876. Fulltekst i vitenarkiv Vis sammendrag

  We present the results of a full cosmological simulation with the new code SCALAR , where dark matter is in the form of fuzzy dark matter (FDM), described by a light scalar field with a mass of m B  = 2.5 × 10 −22 eV and evolving according to the Schrödinger-Poisson system of equations. In comoving units, the simulation volume is 2.5  h −1 Mpc on a side, with a resolution of 20  h −1 pc at the highest refinement level. While the resulting large-scale resolution prevents us from studying the general properties of the FDM structure formation, the extremely high small-scale resolution allows a detailed analysis of the formation and evolution of central solitonic cores, which are found to leave their imprints on dark matter density profiles, resulting in shallower central densities, and on rotation curves, producing an additional circular velocity peak at small radii from the centre. Despite the limitations on the large-scale resolution, we find that the suppression of structures due to the quantum nature of the scalar field reveals indications of a shallower halo mass function in the low-mass end compared to the case of a ΛCDM simulation, in which dark matter is expected to cluster at all mass scales even if it was evolved with the same initial conditions as used for FDM. Furthermore, we verify the scaling relations characterising the solution to the Schrödinger–Poisson system for both isolated and merging haloes, and we find that they are preserved by merging processes. We characterise each FDM halo in terms of the dimensionless quantity Ξ ∝  E halo / M halo 3 , and we show that the core mass is tightly linked to the halo mass by the core–halo mass relation M core / M halo  ∝ Ξ 1/3 . We also show that the core surface density of the simulated FDM haloes does not follow the scaling with the core radius, as observed for dwarf galaxies. This is a challenge for the FDM model as the sole explanation of core formation.

• Abdalla, Elcio; Abellán, Guillermo Franco; Aboubrahim, Amin; Agnello, Adriano; Akarsu, Özgür & Akrami, Yashar [Vis alle 203 forfattere av denne artikkelen] (2022). Cosmology intertwined: A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies. Journal of High Energy Astrophysics. ISSN 2214-4048. 34, s. 49–211. doi: 10.1016/j.jheap.2022.04.002. Fulltekst i vitenarkiv
• Dombriz, Álvaro de la Cruz; Torralba, Francisco José Maldonado & Mota, David (2022). Dark matter candidate from torsion. Physics Letters B. ISSN 0370-2693. 834. doi: 10.1016/j.physletb.2022.137488. Fulltekst i vitenarkiv Vis sammendrag

  The stable pseudo-scalar degree of freedom of the quadratic Poincaré Gauge theory of gravity is shown to be a suitable dark matter candidate. We find the parameter space of the theory which can account for all the predicted cold dark matter, and constrain such parameters with astrophysical observations.

• Hartman, Stian Thomas Heimdal; Winther, Hans Arnold & Mota, David (2022). Constraints on self-interacting Bose-Einstein condensate dark matter using large-scale observables. Journal of Cosmology and Astroparticle Physics (JCAP). 2022(2). doi: 10.1088/1475-7516/2022/02/005. Fulltekst i vitenarkiv
• Hartman, Stian Thomas Heimdal; Winther, Hans Arnold & Mota, David (2021). Dynamical friction in Bose-Einstein condensed self-interacting dark matter at finite temperatures, and the Fornax dwarf spheroidal. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 647. doi: 10.1051/0004-6361/202039865. Fulltekst i vitenarkiv
• Mota, David (2021). Probing Screening Modified Gravity with Non-linear Structure Formation. I Saridakis, Emmanuel N.; Lazkoz, Ruth; Salzano, Vincenzo; Moniz, Paulo Vargas; Capozziello, Salvatore; Jiménez, Jose Beltrán; Laurentis, Mariafelicia De & Olmo, Gonzalo J. (Red.), Modified Gravity and Cosmology: An Update by the CANTATA Network. Springer. ISSN 9783030837143. s. 583–614. doi: 10.1007/978-3-030-83715-0_37. Fulltekst i vitenarkiv
• Valentino, Eleonora Di; Anchordoqui, Luis A.; Akarsu, Özgür; Ali-Haimoud, Yacine; Amendola, Luca & Arendse, Nikki [Vis alle 93 forfattere av denne artikkelen] (2021). Snowmass 2021 - Letter of interest: Cosmology intertwined II: The Hubble constant tension. Astroparticle physics. ISSN 0927-6505. 131. doi: 10.1016/j.astropartphys.2021.102605. Fulltekst i vitenarkiv
• Valentino, Eleonora Di; Anchordoqui, Luis A.; Akarsu, Özgür; Ali-Haimoud, Yacine; Amendola, Luca & Arendse, Nikki [Vis alle 92 forfattere av denne artikkelen] (2021). Snowmass 2021 - letter of interest: Cosmology intertwined I: Perspectives for the next decade. Astroparticle physics. ISSN 0927-6505. 131. doi: 10.1016/j.astropartphys.2021.102606. Fulltekst i vitenarkiv
• Valentino, Eleonora Di; Anchordoqui, Luis A.; Akarsu, Özgür; Ali-Haimoud, Yacine; Amendola, Luca & Arendse, Nikki [Vis alle 91 forfattere av denne artikkelen] (2021). Snowmass 2021 - Letter of interest: Cosmology intertwined IV: The age of the universe and its curvature. Astroparticle physics. ISSN 0927-6505. 131. doi: 10.1016/j.astropartphys.2021.102607. Fulltekst i vitenarkiv
• Valentino, Eleonora Di; Mena, Olga; Pan, Supriya; Visinelli, Luca; Yang, Weiqiang & Melchiorri, Alessandro [Vis alle 9 forfattere av denne artikkelen] (2021). In the realm of the Hubble tension—a review of solutions. Classical and Quantum Gravity. ISSN 0264-9381. 38(15). doi: 10.1088/1361-6382/ac086d. Fulltekst i vitenarkiv Vis sammendrag

   The simplest ΛCDM model provides a good fit to a large span of cosmological data but harbors large areas of phenomenology and ignorance. With the improvement of the number and the accuracy of observations, discrepancies among key cosmological parameters of the model have emerged. The most statistically significant tension is the 4σ to 6σ disagreement between predictions of the Hubble constant, H0, made by the early time probes in concert with the 'vanilla' ΛCDM cosmological model, and a number of late time, model-independent determinations of H0 from local measurements of distances and redshifts. The high precision and consistency of the data at both ends present strong challenges to the possible solution space and demands a hypothesis with enough rigor to explain multiple observations—whether these invoke new physics, unexpected large-scale structures or multiple, unrelated errors. A thorough review of the problem including a discussion of recent Hubble constant estimates and a summary of the proposed theoretical solutions is presented here. We include more than 1000 references, indicating that the interest in this area has grown considerably just during the last few years. We classify the many proposals to resolve the tension in these categories: early dark energy, late dark energy, dark energy models with 6 degrees of freedom and their extensions, models with extra relativistic degrees of freedom, models with extra interactions, unified cosmologies, modified gravity, inflationary models, modified recombination history, physics of the critical phenomena, and alternative proposals. Some are formally successful, improving the fit to the data in light of their additional degrees of freedom, restoring agreement within 1–2σ between Planck 2018, using the cosmic microwave background power spectra data, baryon acoustic oscillations, Pantheon SN data, and R20, the latest SH0ES Team Riess, et al (2021 Astrophys. J.908 L6) measurement of the Hubble constant (H0 = 73.2 ± 1.3 km s−1 Mpc−1 at 68% confidence level). However, there are many more unsuccessful models which leave the discrepancy well above the 3σ disagreement level. In many cases, reduced tension comes not simply from a change in the value of H0 but also due to an increase in its uncertainty due to degeneracy with additional physics, complicating the picture and pointing to the need for additional probes. While no specific proposal makes a strong case for being highly likely or far better than all others, solutions involving early or dynamical dark energy, neutrino interactions, interacting cosmologies, primordial magnetic fields, and modified gravity provide the best options until a better alternative comes along.

• Valentino, Eleonora Di; Anchordoqui, Luis A.; Akarsu, Özgür; Ali-Haimoud, Yacine; Amendola, Luca & Arendse, Nikki [Vis alle 92 forfattere av denne artikkelen] (2021). Snowmass 2021 - Letter of interest: Cosmology intertwined III: fσ8 and S8. Astroparticle physics. ISSN 0927-6505. 131. doi: 10.1016/j.astropartphys.2021.102604. Fulltekst i vitenarkiv
• Martinelli, Matteo; Tutusaus, I.; Archidiacono, M.; Camera, S.; Cardone, V. F. & Clesse, Sébastien [Vis alle 94 forfattere av denne artikkelen] (2021). Euclid: Impact of non-linear and baryonic feedback prescriptions on cosmological parameter estimation from weak lensing cosmic shear. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 649. doi: 10.1051/0004-6361/202039835. Fulltekst i vitenarkiv
• Baker, John; Baker, Tessa; Carbone, Carmelita; Congedo, Giuseppe; Contaldi, Carlo R. & Dvorkin, Irina [Vis alle 22 forfattere av denne artikkelen] (2021). High angular resolution gravitational wave astronomy. Experimental astronomy (Print). ISSN 0922-6435. 51, s. 1441–1470. doi: 10.1007/s10686-021-09712-0. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Since the very beginning of astronomy the location of objects on the sky has been a fundamental observational quantity that has been taken for granted. While precise two dimensional positional information is easy to obtain for observations in the electromagnetic spectrum, the positional accuracy of current and near future gravitational wave detectors is limited to between tens and hundreds of square degrees, which makes it extremely challenging to identify the host galaxies of gravitational wave events or to detect any electromagnetic counterparts. Gravitational wave observations provide information on source properties that is complementary to the information in any associated electromagnetic emission. Observing systems with multiple messengers thus has scientific potential much greater than the sum of its parts. A gravitational wave detector with higher angular resolution would significantly increase the prospects for finding the hosts of gravitational wave sources and triggering a multi-messenger follow-up campaign. An observatory with arcminute precision or better could be realised within the Voyage 2050 programme by creating a large baseline interferometer array in space and would have transformative scientific potential. Precise positional information of standard sirens would enable precision measurements of cosmological parameters and offer new insights on structure formation; a high angular resolution gravitational wave observatory would allow the detection of a stochastic background and resolution of the anisotropies within it; it would also allow the study of accretion processes around black holes; and it would have tremendous potential for tests of modified gravity and the discovery of physics beyond the Standard Model.

• Christiansen, Øyvind; Jiménez, Jose Beltrán & Mota, David (2021). Charged black hole mergers: Orbit circularisation and chirp mass bias. Classical and Quantum Gravity. ISSN 0264-9381. 38(7). doi: 10.1088/1361-6382/abdaf5. Fulltekst i vitenarkiv Vis sammendrag

  We consider the inspiral of black holes carrying U(1) charge that is not electromagnetic, but corresponds to some dark sector. In the weak-field, low-velocity regime, the components follow Keplerian orbits. We investigate how the orbital parameters evolve for dipole-dominated emission and find that the orbit quickly circularises, though not as efficiently as for a gravitationally dominated emission. We then regard circular orbits, and look for modifications in the gravitational waveform from the components carrying small charges. Taking this into account we populate the waveform with simplified LIGO noise and put it through a matched filtering procedure where the template bank only consists of uncharged templates, focusing on the charges' effect on the chirp mass estimation. We find a consistent overestimation of the 'generalised' chirp mass, and a possible over- and underestimation of the actual chirp mass. Finally, we briefly consider the effect of such charges on hyperbolic encounters, finding again a bias arising from interpreting the generalised chirp mass as the actual chirp mass.

• Wang, Deng & Mota, David (2021). 4D Gauss–Bonnet gravity: Cosmological constraints, H0 tension and large scale structure. Physics of the Dark Universe. 32. doi: 10.1016/j.dark.2021.100813. Fulltekst i vitenarkiv
• Khodadi, Mohsen; Lambiase, Gaetano & Mota, David (2021). No-hair theorem in the wake of Event Horizon Telescope. Journal of Cosmology and Astroparticle Physics (JCAP). 2021(9). doi: 10.1088/1475-7516/2021/09/028. Fulltekst i vitenarkiv Vis sammendrag

  Thanks to the release of the extraordinary EHT image of shadow attributed to the M87* supermassive black hole (SMBH), we have a novel window to assess the validity of fundamental physics in the strong-field regime. Motivated by this, we consider Johannsen & Psaltis metric parameterized by mass, spin, and an additional dimensionless hair parameter epsilon. This parametric framework in the high rotation regimes provides a well-behaved bed to the strong-gravity test of the no-hair theorem (NHT) using the EHT data. Incorporating the epsilon into the standard Kerr spacetime enrich it in the sense that, depending on setting the positive and negative values for that, we deal with alternative compact objects: deformed Kerr naked singularity and Kerr BH solutions, respectively. Shadows associated with these two possible solutions indicate that the deformation parameter epsilon affects the geometry shape of standard shadow such that it becomes more oblate and prolate with epsilon<0 and epsilon>0, respectively. By scanning the window associated with three shadow observables oblateness, deviation from circularity, and shadow diameter, we perform a numerical analysis within the range a*=0.9∓0.1 of the dimensionless rotation parameter, to find the constraints on the hair parameter epsilon in both possible solutions. For both possible signs of epsilon, we extract a variety of upper bounds that are in interplay with a*. Although by approaching the rotation parameters to the extreme limit, the allowable range of both hair parameters becomes narrower, the hairy Kerr BH solution is a more promising candidate to play the role of the alternative compact object instead of the standard Kerr BH. The lack of tension between hairy Kerr BH with the current observation of the EHT shadow of the M87* SMBH carries this message that there is the possibility of NHT violation.

• Mitra, Ayan; Misfud, Jurgen; Mota, David & Parkinson, David (2021). Cosmology with the Einstein telescope: No Slip Gravity model and redshift specifications. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 502(4), s. 5563–5575. doi: 10.1093/mnras/stab165. Fulltekst i vitenarkiv Vis sammendrag

  The Einstein telescope and other third-generation interferometric detectors of gravitational waves are projected to be operational post 2030. The cosmological signatures of gravitational waves would undoubtedly shed light on any departure from the current gravitational framework. We here confront a specific modified gravity model, the No Slip Gravity model, with forecast observations of gravitational waves. We compare the predicted constraints on the dark energy equation of state parameters w0−wa ⁠, between the modified gravity model and that of Einstein gravity. We show that the No Slip Gravity model mimics closely the constraints from the standard gravitational theory, and that the cosmological constraints are very similar. The use of spectroscopic redshifts, especially in the low–redshift regime, lead to significant improvements in the inferred parameter constraints. We test how well such a prospective gravitational wave dataset would function at testing such models, and find that there are significant degeneracies between the modified gravity model parameters, and the cosmological parameters that determine the distance, due to the gravitational wave dimming effect of the modified theory.

• Sahlu, Shambel; Ntahompagaze, Joseph; Abebe, Amare & Mota, David (2021). Accelerating universe in modified teleparallel gravity theory. Proceedings of the International Astronomical Union. ISSN 1743-9213. 15(356), s. 397–399. doi: 10.1017/S1743921320003567. Fulltekst i vitenarkiv Vis sammendrag

  Abstract This paper studies the cosmology of accelerating expansion of the universe in modified teleparallel gravity theory. We discuss the cosmology of f ( T, B ) gravity theory and its implication to the new general form of the equation of state parameter w TB for explaining the late-time accelerating expansion of the universe without the need for the cosmological constant scenario. We examine the numerical value of w TB in different paradigmatic f ( T, B ) gravity models. In those models, the numerical result of w TB is favored with observations in the presence of the torsion scalar T associated with a boundary term B and shows the accelerating expansion of the universe.

• Hagala, Robert; Felice, Antonio De; Mota, David & Mukohyama, Shinji (2021). Non-linear dynamics of the minimal theory of massive gravity. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 653. doi: 10.1051/0004-6361/202040018. Fulltekst i vitenarkiv Vis sammendrag

  We investigate cosmological signatures of the minimal theory of massive gravity (MTMG). To this aim, we simulate the normal branch of the MTMG by employing the R AMSES N -body code and extending it with an effective gravitational constant G eff . We implement an environment-dependent G eff as a function of the graviton mass and the local energy density as predicted by MTMG. We find that halo density profiles are not a good probe for MTMG because deviations from general relativity (GR) are quite small. Similarly, the matter power spectra show deviations only at the percentage level. However, we find a clear difference between MTMG and GR in that voids are denser in MTMG than in GR. As measuring void profiles is quite a complex task from an observational point of view, a better probe of MTMG would be the halo abundances. In this case, MTMG creates a larger amount of massive halos, while there is a suppression in the abundance of small halos.

• Wang, Deng & Mota, David (2020). Can f(T) gravity resolve the H0 tension? Physical Review D. ISSN 2470-0010. 102(6). doi: 10.1103/PhysRevD.102.063530. Fulltekst i vitenarkiv Vis sammendrag

  Motivated by the discrepancy in measurements of H0 between local and global probes, we investigate whether teleparallel gravities could be a better model to describe the present-day observations or at least to alleviate the H0 tension. Specifically, in this work we study and place constraints on three popular f(T) models in light of the Planck-2018 cosmic microwave background data release. We find that the f(T) power-law model can alleviate the H0 tension from 4.4σ to 1.9σ level, while the f(T) model of two exponentials fails to resolve this inconsistency. Moreover, for the first time, we obtain constraints on the effective number of relativistic species Neff and on the sum of the neutrino masses Σmν in f(T) gravity. We find that the constraints obtained are looser than in ΛCDM. However, the introduction of massive neutrinos into the cosmological model alleviates the H0 tension for the power-law model. Finally, we find that whether a viable f(T) theory can mitigate the H0 tension depends on the mathematical structure of the distortion factor y(z,b). These results could provide a clue for theoreticians to write a more physical-motivated expression of f(T) function.

• Khodadi, Mohsen; Allahyari, Alireza; Vagnozzi, Sunny & Mota, David (2020). Black holes with scalar hair in light of the Event Horizon Telescope. Journal of Cosmology and Astroparticle Physics (JCAP). 2020(09). doi: 10.1088/1475-7516/2020/09/026. Fulltekst i vitenarkiv Vis sammendrag

  Searching for violations of the no-hair theorem (NHT) is a powerful way to test gravity, and more generally fundamental physics, particularly with regards to the existence of additional scalar fields. The first observation of a black hole (BH) shadow by the Event Horizon Telescope (EHT) has opened a new direct window onto tests of gravity in the strong-field regime, including probes of violations of the NHT. We consider two scenarios described by the Einstein-Maxwell equations of General Relativity and electromagnetism, to which we add a scalar field. In the first case we consider a minimally-coupled scalar field with a potential, whereas in the second case the field is conformally-coupled to curvature. In both scenarios we construct charged BH solutions, which are found to carry primary scalar hair. We then compute the shadows cast by these two BHs as a function of their electric charge and scalar hair parameter. Comparing these shadows to the shadow of M87* recently imaged by the EHT collaboration, we set constraints on the amount of scalar hair carried by these two BHs. The conformally-coupled case admits a regime for the hair parameter, compatible with EHT constraints, describing a so-called mutated Reissner-Nordström BH: this solution was recently found to effectively mimic a wormhole. Our work provides novel constraints on fundamental physics, and in particular on violations of the no-hair theorem and the existence of additional scalar fields, from the shadow of M87*.

• Mota, David (2020). Nonlinear astrophysical probes of screened modified gravity. Proceedings of the International School of Physics Enrico Fermi. ISSN 0074-784X. s. 331–372. doi: 10.3254/ENFI200014. Fulltekst i vitenarkiv
• Mina, Mattia; Mota, David & Winther, Hans Arnold (2020). SCALAR: an AMR code to simulate axion-like dark matter models. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 641. doi: 10.1051/0004-6361/201936272. Fulltekst i vitenarkiv Vis sammendrag

  We present a new code,SCALAR, based on the high-resolution hydrodynamics andN-body codeRAMSES, to solve the Schrödingerequation on adaptive refined meshes. The code is intended to be used to simulate axion or fuzzy dark matter models where theevolution of the dark matter component is determined by a coupled Schrödinger-Poisson equation, but it can also be used as a stand-alone solver for both linear and non-linear Schrödinger equations with any given external potential. This paper describes the numericalimplementation of our solver and presents tests to demonstrate how accurately it operates.

• Yang, Weiqiang; Pan, Supriya; Mota, David & Du, Minghui (2020). Forecast constraints on anisotropic stress in dark energy using gravitational waves. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 497(1), s. 879–893. doi: 10.1093/mnras/staa1859. Fulltekst i vitenarkiv Vis sammendrag

  It is always interesting to investigate how well can a future experiment perform with respect to others (present or future ones). Cosmology is really an exciting field where a lot of puzzles are still unknown. In this paper, we consider a generalized dark energy (DE) scenario where anisotropic stress is present. We constrain this generalized cosmic scenario with an aim to investigate how gravitational waves standard sirens (GWSS) may constrain the anisotropic stress, which, according to the standard cosmological probes, remains unconstrained. In order to do this, we generate the luminosity distance measurements from O(103) mock GW events that match the expected sensitivity of the Einstein Telescope. Our analyses report that, first of all, GWSS can give better constraints on various cosmological parameters compared to the usual cosmological probes, but the viscous sound speed appearing due to the DE anisotropic stress is totally unconstrained even after the inclusion of GWSS.

• Hartman, Stian; Winther, Hans Arnold & Mota, David (2020). Collapse of spherical overdensities in superfluid models of dark matter. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 639. doi: 10.1051/0004-6361/201937263. Fulltekst i vitenarkiv Vis sammendrag

  Aims. We intend to understand cosmological structure formation within the framework of superfluid models of dark matter with finite temperatures. Of particular interest is the evolution of small-scale structures where the pressure and superfluid properties of the dark matter fluid are prominent. We compare the growth of structures in these models with the standard cold dark matter paradigm and non-superfluid dark matter. Methods. The equations for superfluid hydrodynamics were computed numerically in an expanding ΛCDM background with spherical symmetry; the effect of various superfluid fractions, temperatures, interactions, and masses on the collapse of structures was taken into consideration. We derived the linear perturbation of the superfluid equations, giving further insights into the dynamics of the superfluid collapse. Results. We found that while a conventional dark matter fluid with self-interactions and finite temperatures experiences a suppression in the growth of structures on smaller scales, as expected due to the presence of pressure terms, a superfluid can collapse much more efficiently than was naively expected due to its ability to suppress the growth of entropy perturbations and thus gradients in the thermal pressure. We also found that the cores of the dark matter halos initially become more superfluid during the collapse, but eventually reach a point where the superfluid fraction falls sharply. The formation of superfluid dark matter halos surrounded by a normal fluid dark matter background is therefore disfavored by the present work.

• Banerjee, Shreya; Bera, Sayantani & Mota, David (2020). Growth of linear perturbations in a universe with superfluid dark matter. Journal of Cosmology and Astroparticle Physics (JCAP). 2020(07). doi: 10.1088/1475-7516/2020/07/034. Fulltekst i vitenarkiv Vis sammendrag

  The Lambda-Cold Dark Matter (ΛCDM) model agrees with most of the cosmological observations, but has some hindrances from observed data at smaller scales such as galaxies. Recently, Berezhiani and Khoury proposed a new theory involving interacting superfluid dark matter with three model parameters in [1], which explains galactic dynamics with great accuracy. In the present work, we study the cosmological behaviour of this model in the linear regime of cosmological perturbations. In particular, we compute both analytically and numerically the matter linear growth factor and obtain new bounds for the model parameters which are significantly stronger than previously found. These new constraints come from the fact that structures within the superfluid dark matter framework grow quicker than in ΛCDM, and quite rapidly when the DM-baryon interactions are strong.

• Sahlu, Shambel; Ntahompagaze, Joseph; Abebe, Amare; Dombriz, Álvaro de la Cruz & Mota, David (2020). Scalar perturbations in f(T) gravity using the 1+3 covariant approach. European Physical Journal C. ISSN 1434-6044. 80. doi: 10.1140/epjc/s10052-020-7961-3. Fulltekst i vitenarkiv
• Llinares, Claudio; Hagala, Robert & Mota, David (2020). Non-linear phenomenology of disformally coupled quintessence. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 491(2), s. 1868–1886. doi: 10.1093/mnras/stz2710. Fulltekst i vitenarkiv Vis sammendrag

  The quintessence model is one of the simplest and better known alternatives to Einstein’s theory for gravity. The properties of the solutions have been studied in great detail in the background, linear and non-linear contexts in cosmology. Here we discuss new phenomenology that is induced by adding disformal terms to the interactions. Among other results, we show analytically and using cosmological simulations ran with the code isis that the model possesses a mechanism through which it is possible to obtain repulsive fifth forces, which are opposite to gravity. Although the equations are very complex, we also find that most of the new phenomenology can be explained by studying background quantities. We used our simulation data to test approximate relations that exist between the metric and scalar field perturbations as well as between the fifth force and gravity. Excellent agreement was found between exact and approximated solutions, which opens the way for running disformal gravity cosmological simulations using simply a Newtonian solver. These results could not only help us to find new ways of testing gravity, but also provide new motivations for building alternative models.

• Vagnozzi, Sunny; Visinelli, Luca; Mena, Olga & Mota, David (2020). Do we have any hope of detecting scattering between dark energy and baryons through cosmology? Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 493(1), s. 1139–1152. doi: 10.1093/mnras/staa311. Fulltekst i vitenarkiv Vis sammendrag

  We consider the possibility that dark energy and baryons might scatter off each other. The type of interaction we consider leads to a pure momentum exchange, and does not affect the background evolution of the expansion history. We parametrize this interaction in an effective way at the level of Boltzmann equations. We compute the effect of dark energy-baryon scattering on cosmological observables, focusing on the cosmic microwave background (CMB) temperature anisotropy power spectrum and the matter power spectrum. Surprisingly, we find that even huge dark energy-baryon cross-sections σxb∼O(b)⁠, which are generically excluded by non-cosmological probes such as collider searches or precision gravity tests, only leave an insignificant imprint on the observables considered. In the case of the CMB temperature power spectrum, the only imprint consists in a sub-per cent enhancement or depletion of power (depending whether or not the dark energy equation of state lies above or below −1) at very low multipoles, which is thus swamped by cosmic variance. These effects are explained in terms of differences in how gravitational potentials decay in the presence of a dark energy-baryon scattering, which ultimately lead to an increase or decrease in the late-time integrated Sachs–Wolfe power. Even smaller related effects are imprinted on the matter power spectrum. The imprints on the CMB are not expected to be degenerate with the effects due to altering the dark energy sound speed. We conclude that, while strongly appealing, the prospects for a direct detection of dark energy through cosmology do not seem feasible when considering realistic dark energy-baryon cross-sections. As a caveat, our results hold to linear order in perturbation theory.

• Yang, Weiqiang; Pan, Supriya; Nunes, Rafael C. & Mota, David (2020). Dark calling dark: interaction in the dark sector in presence of neutrino properties after Planck CMB final release. Journal of Cosmology and Astroparticle Physics (JCAP). 2020(04). doi: 10.1088/1475-7516/2020/04/008. Fulltekst i vitenarkiv Vis sammendrag

  We investigate a well known scenario of interaction in the dark sector where the vacuum energy is interacting with cold dark matter throughout the cosmic evolution in light of the cosmic microwave background (CMB) data from final Planck 2018 release. In addition to this minimal scenario, we generalize the model baseline by including the properties of neutrinos, such as the neutrino mass scale (Mν) and the effective number of neutrino species (Neff) as free parameters, in order to verify the possible effects that such parameters might generate on the coupling parameter, and vice versa. As already known, we again confirm that in light of the Planck 2018 data, such dark coupling can successfully solve the H0 tension (with and without the presence of neutrinos). Concerning the properties of neutrinos, we find that Mν may be wider than expected within the ΛCDM model and Neff is fully compatible with three neutrino species (similar to ΛCDM prevision). The parameters characterizing the properties of neutrinos do not correlate with the coupling parameter of the interaction model. When considering the joint analysis of CMB from Planck 2018 and an estimate of H0 from Hubble Space Telescope 2019 data, we find an evidence for a non-null value of the coupling parameter at more than 3σ confidence-level. We also discuss the possible effects on the interacting scenario due to the inclusion of baryon acoustic oscillations data with Planck 2018. Our main results updating the dark sectors' interaction and neutrino properties in the model baseline, represent a new perspective in this direction. Clearly, a possible new physics in light of some dark interaction between dark energy and dark matter can serve as an alternative to ΛCDM scenario to explain the observable Universe, mainly in light of the current tension on H0.

• Allahyari, Alireza; Khodali, Mohsen; Vagnozzi, Sunny & Mota, David (2020). Magnetically charged black holes from non-linear electrodynamics and the Event Horizon Telescope. Journal of Cosmology and Astroparticle Physics (JCAP). 2020(2). doi: 10.1088/1475-7516/2020/02/003. Fulltekst i vitenarkiv Vis sammendrag

  Non-linear electrodynamics (NLED) theories are well-motivated extensions of QED in the strong field regime, and have long been studied in the search for regular black hole (BH) solutions. We consider two well-studied and well-motivated NLED models coupled to General Relativity: the Euler-Heisenberg model and the Bronnikov model. After carefully accounting for the effective geometry induced by the NLED corrections, we determine the shadows of BHs within these two models. We then compare these to the shadow of the supermassive BH M87* recently imaged by the Event Horizon Telescope collaboration. In doing so, we are able to extract upper limits on the black hole magnetic charge, thus providing novel constraints on fundamental physics from this new extraordinary probe.

• Popolo, Antonino Del; Chan, Man Ho & Mota, David (2020). Turnaround radius in ΛCDM and dark matter cosmologies with shear and vorticity. Physical Review D. ISSN 2470-0010. 101(8). doi: 10.1103/PhysRevD.101.083505. Fulltekst i vitenarkiv Vis sammendrag

  We determine the relationship between the turnaround radius, Rt, and mass, Mt, in Λ CDM , and in dark energy scenarios, using an extended spherical collapse model taking into account the effects of shear and vorticity. We find a more general formula than that usually described in literature, showing a dependence of Rt from shear, and vorticity. The Rt− M t relation differs from that obtained not taking into account shear, and rotation, especially at galactic scales, differing ≃ 30 % from the result given in literature. This has effects on the constraint of the w parameter of the equation of state. We compare the Rt− M t relationship obtained for the Λ CDM , and different dark energy models to that obtained in the f(R) modified gravity (MG) scenario. The Rt− M t relationship in Λ CDM , and dark energy scenarios are tantamount to the prediction of the f(R) theories. Then, the Rt− M t relationship is not a good probe to test gravity theories beyond Einstein’s general relativity.

• Sahlu, Shambel; Ntahompagaze, Joseph; Abebe, Amare & Mota, David (2020). Inflationary constraints in teleparallel gravity theory. International Journal of Geometric Methods in Modern Physics (IJGMMP). ISSN 0219-8878. 18(02). doi: 10.1142/S0219887821500274. Fulltekst i vitenarkiv
• Hagala, Robert; Llinares, Claudio & Mota, David (2019). The slingshot effect as a probe of transverse motions of galaxies. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 628. doi: 10.1051/0004-6361/201935261. Fulltekst i vitenarkiv Vis sammendrag

  Context: There are currently no reliable methods to measure the transverse velocities of galaxies. This is an important piece of information that is lacking in galaxy catalogues, and it could allow us to probe the physics of structure formation and to test the underlying theory of gravity. The slingshot effect (a special case of the integrated Sachs–Wolfe effect) is expected to create dipole signals in the temperature fluctuations of the cosmic microwave background (CMB) radiation. This effect creates a hot spot behind and a cold spot in front of moving massive objects. The dipole signal created by the slingshot effect can be used to measure transverse velocities, but because the signal is expected to be weak, the effect has not been measured yet. Aims: Our aim is to show that the slingshot effect can be measured by stacking the signals of galaxies falling into a collapsing cluster. Furthermore, we evaluate whether the effect can probe modified gravity. Methods: We used data from a simulated galaxy catalogue (MultiDark Planck 2) to mimic observations. We identified a 1015 M⊙ cluster, and made maps of the slingshot effect for photons passing near 8438 infalling galaxies. To emulate instrument noise, we added uncorrelated Gaussian noise to each map. We assumed that the average velocity is directed towards the centre of the cluster. The maps were rotated according to the expected direction of motion. This assures that the dipole signal adds up constructively when stacking the maps. We compared the stacked maps to a dipole stencil to determine the quality of the signal. We also evaluated the probability of fitting the stencil in the absence of the slingshot signal. Results: Each galaxy gives a signal of around ΔT/T ≈ 10−9, while the current precision of CMB experiments is ΔT/T ≈ 4 × 10−6. By stacking around 10 000 galaxies and performing a stencil fit, the slingshot signal can be over the detectable threshold with today’s experiments. However, due to the difficulty of distinguishing an actual signal from false positives, future CMB experiments must be used to be certain of the strength of the observed signal.

• Yang, Weiqiang; Vagnozzi, Sunny; Valentino, Eleonora Di; Nunes, Rafael C.; Pan, Supriya & Mota, David (2019). Listening to the sound of dark sector interactions with gravitational wave standard sirens. Journal of Cosmology and Astroparticle Physics (JCAP). 2019(7), s. 1–27. doi: 10.1088/1475-7516/2019/07/037. Fulltekst i vitenarkiv Vis sammendrag

  We consider two stable Interacting Dark Matter-Dark Energy models and confront them against current Cosmic Microwave Background data from the Planck satellite. We then generate luminosity distance measurements from Script O(103) mock Gravitational Wave events matching the expected sensitivity of the proposed Einstein Telescope. We use these to forecast how the addition of Gravitational Wave standard sirens data can improve current limits on the Dark Matter-Dark Energy coupling strength (ξ). We find that the addition of Gravitational Waves data can reduce the current uncertainty by a factor of 5. Moreover, if the underlying cosmological model truly features Dark Matter-Dark Energy interactions with a value of ξ within the currently allowed 1σ upper limit, the addition of Gravitational Wave data would help disentangle such an interaction from the standard case of no interaction at a significance of more than 3σ.

• Du, Minghui; Yang, Weiqiang; Xu, Lixin; Pan, Supriya & Mota, David (2019). Future constraints on dynamical dark-energy using gravitational-wave standard sirens. Physical Review D. ISSN 2470-0010. 100. doi: 10.1103/PhysRevD.100.043535. Fulltekst i vitenarkiv Vis sammendrag

  The detection of gravitational waves (GW) by the LIGO and Virgo collaborations offers a whole new range of possible tests and opens up a new window that may shed light on the nature of dark energy and dark matter. In the present work we investigate how future gravitational-wave data could help to constrain different dynamical dark energy models. In particular, we perform cosmological forecastings of a class of well-known and most used dynamical dark energy models using the third-generation gravitational wave detector, the Einstein Telescope. We have considered 1000 simulated GW events in order to constrain the parameter space of the dynamical dark energy models. Our analyses show that the inclusion of the GW data from the Einstein Telescope significantly improves the parameter space of the dynamical dark energy models compared to their constraints extracted from the standard cosmological probes, namely, the cosmic microwave observations, baryon acoustic oscillations distance measurements, supernove type Ia, and the Hubble parameter measurements.

• Popolo, Antonino Del; Pace, Francesco & Mota, David (2019). Mass-temperature relation in ΛCDM and modified gravity. Physical Review D. ISSN 2470-0010. 100. doi: 10.1103/PhysRevD.100.024013. Fulltekst i vitenarkiv Vis sammendrag

  We derive the mass-temperature relation using an improved top-hat model and a continuous formation model which takes into account the effects of the ordered angular momentum acquired through tidal-torque interaction between clusters, random angular momentum, dynamical friction, and modifications of the virial theorem to include an external pressure term usually neglected. We show that the mass-temperature relation differs from the classical self-similar behavior, M∝T3/2, and shows a break at 3–4 keV and a steepening with a decreasing cluster temperature. We then compare our mass-temperature relation with those obtained in the literature with N-body simulations for f(R) and symmetron models. We find that the mass-temperature relation is not a good probe to test gravity theories beyond Einstein’s general relativity, because the mass-temperature relation of the ΛCDM model is similar to that of the modified gravity theories.

• Hagstotz, Steffen; Gronke, Max Balthasar; Mota, David & Baldi, Marco (2019). Breaking cosmic degeneracies: Disentangling neutrinos and modified gravity with kinematic information. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 629. doi: 10.1051/0004-6361/201935213. Fulltekst i vitenarkiv Vis sammendrag

  Searches for modified gravity in the large-scale structure try to detect the enhanced amplitude of density fluctuations caused by the fifth force present in many of these theories. Neutrinos, on the other hand, suppress structure growth below their free-streaming length. Both effects take place on comparable scales, and uncertainty in the neutrino mass leads to a degeneracy with modified gravity parameters for probes that are measuring the amplitude of the matter power spectrum. We explore the possibility to break the degeneracy between modified gravity and neutrino effects in the growth of structures by considering kinematic information related to either the growth rate on large scales or the virial velocities inside of collapsed structures. In order to study the degeneracy up to fully non-linear scales, we employ a suite of N-body simulations including both f(R) modified gravity and massive neutrinos. Our results indicate that velocity information provides an excellent tool to distinguish massive neutrinos from modified gravity. Models with different values of neutrino masses and modified gravity parameters possessing a comparable matter power spectrum at a given time have different growth rates. This leaves imprints in the velocity divergence, which is therefore better suited than the amplitude of density fluctuations to tell the models apart. In such models with a power spectrum comparable to ΛCDM today, the growth rate is strictly enhanced. We also find the velocity dispersion of virialised clusters to be well suited to constrain deviations from general relativity without being affected by the uncertainty in the sum of neutrino masses.

• Najafi, Sh.; Mirtorabi, M. T.; Ansari, Z. & Mota, David (2019). Red giant evolution in modified gravity. Journal of Cosmology and Astroparticle Physics (JCAP). 2019(2). doi: 10.1088/1475-7516/2019/02/011. Fulltekst i vitenarkiv
• Marttens, Rodrigo F. von; Casarini, Luciano; Mota, David & Zimdahl, Winfried (2019). Cosmological constraints on parametrized interacting dark energy. Physics of the Dark Universe. 23. doi: 10.1016/j.dark.2018.10.007. Fulltekst i vitenarkiv
• Perico, Eder Leonardo Duarte; Voivodic, Rodrigo; Lima, Marcos & Mota, David (2019). Cosmic voids in modified gravity scenarios. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 632. doi: 10.1051/0004-6361/201935949. Fulltekst i vitenarkiv Vis sammendrag

  Modified gravity (MG) theories aim to reproduce the observed acceleration of the Universe by reducing the dark sector while simultaneously recovering General Relativity (GR) within dense environments. Void studies appear to be a suitable scenario to search for imprints of alternative gravity models on cosmological scales. Voids cover an interesting range of density scales where screening mechanisms fade out, which reaches from a density contrast δ ≈ −1 close to their centers to δ ≈ 0 close to their boundaries. We present an analysis of the level of distinction between GR and two modified gravity theories, the Hu–Sawicki f) and the symmetron theory. This study relies on the abundance, linear bias, and density profile of voids detected in N-body cosmological simulations. We define voids as connected regions made up of the union of spheres with a mean density given by ρ = 0.2 ρ, but disconnected from any other voids. We find that the height of void walls is considerably affected by the gravitational theory, such that it increases for stronger gravity modifications. Finally, we show that at the level of dark matter N-body simulations, our constraints allow us to distinguish between GR and MG models with |f| &gt; 10−6 and z &gt;  1. Differences of best-fit values for MG parameters that are derived independently from multiple void probes may indicate an incorrect MG model. This serves as an important consistency check.

• Asghari, Mahnaz; Jimenez, Jose Beltran; Khosravi, Shahram & Mota, David (2019). On structure formation from a small-scales-interacting dark sector. Journal of Cosmology and Astroparticle Physics (JCAP). 2019(4). doi: 10.1088/1475-7516/2019/04/042. Fulltekst i vitenarkiv Vis sammendrag

  We consider a cosmological model with an interaction between dark matter and dark energy which leaves the background cosmology unaffected and only affects the evolution of the perturbations. This is achieved by introducing a coupling given in terms of the relative velocities of dark matter and dark energy. This interaction has the distinctive feature of appearing predominantly on small scales, where peculiar velocities can become important. We confront the predictions of the model to cosmological observations and find a potential alleviation of the known tension in the amplitude of density perturbations as measured by low redshift galaxy surveys and the Planck data. The model also predicts a shift in the turnover of the matter power spectrum which does not depend on the horizon at equality (fixed by the background cosmology and, thus, unaffected by the perturbations) and is entirely due to the interaction between dark matter and dark energy. A bias in the peculiar velocity between baryons and dark matter is also shown to be a unique feature of this type of interactions in the dark sector.

• Yang, Weiqiang; Pan, Supriya; Xu, Lixin & Mota, David (2019). Effects of anisotropic stress in interacting dark matter – dark energy scenarios. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 482(2), s. 1858–1871. doi: 10.1093/mnras/sty2789. Fulltekst i vitenarkiv Vis sammendrag

  We study a novel interacting dark energy − dark matter scenario where the anisotropic stress of the large-scale inhomogeneities is considered. The dark energy has a constant equation of state and the interaction model produces stable perturbations. The resulting picture is constrained using different astronomical data aiming to measure the impact of the anisotropic stress on the cosmological parameters. Our analyses show that a non-zero interaction in the dark sector is allowed, while a non-interaction scenario is recovered within 68 per cent CL. The anisotropic stress is also constrained to be small, and its zero value is permitted within 68 per cent CL. The dark energy equation of state, wx, is also found to be close to ‘−1’ boundary. However, from the ratio of the CMB TT spectra, we see that the model has a mild deviation from the CDM cosmology, while such deviation is almost forbidden from the CMB TT spectra alone. Although the deviation is not much significant, but from this data, we cannot exclude such deviation. Overall, at the background level, the model is close to the CDM cosmology, while at the level of perturbations, a non-zero but a very small interaction in the dark sector is permitted. Perhaps, a more accurate conclusion can be made with the next generation of surveys. We also found that the region, wx < −1, is found to be effective to release the tension on H0. Finally, from the Bayesian analysis, we find that CDM remains still preferred over the interacting scenarios.

• Yang, Weiqiang; Pan, Supriya; Vagnozzi, Sunny; Valentino, Eleonora Di; Mota, David & Capozziello, Salvatore (2019). Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal. Journal of Cosmology and Astroparticle Physics (JCAP). 2019(11). doi: 10.1088/1475-7516/2019/11/044. Fulltekst i vitenarkiv Vis sammendrag

  While the origin and composition of dark matter and dark energy remains unknown, it is possible that they might represent two manifestations of a single entity, as occurring in unified dark sector models. On the other hand, advances in our understanding of the dark sector of the Universe might arise from Cosmic Dawn, the epoch when the first stars formed. In particular, the first detection of the global 21-cm absorption signal at Cosmic Dawn from the EDGES experiment opens up a new arena wherein to test models of dark matter and dark energy. Here, we consider generalized and modified Chaplygin gas models as candidate unified dark sector models. We first constrain these models against Cosmic Microwave Background data from the Planck satellite, before exploring how the inclusion of the global 21-cm signal measured by EDGES can improve limits on the model parameters, finding that the uncertainties on the parameters of the Chaplygin gas models can be reduced by a factor between 1.5 and 10. We also find that within the generalized Chaplygin gas model, the tension between the CMB and local determinations of the Hubble constant H0 is reduced from ≈ 4σ to ≈ 1.3σ. In conclusion, we find that the global 21-cm signal at Cosmic Dawn can provide an extraordinary window onto the physics of unified dark sectors.

• Pace, Francesco; Schimd, Carlo; Mota, David & Popolo, Antonino Del (2019). Halo collapse: virialization by shear and rotation in dynamical dark-energy models. Effects on weak-lensing peaks. Journal of Cosmology and Astroparticle Physics (JCAP). 2019(9), s. 1–27. doi: 10.1088/1475-7516/2019/09/060. Fulltekst i vitenarkiv Vis sammendrag

  The evolution of the virial overdensity Δvir for ΛCDM and seven dynamical dark-energy models is investigated in the extended spherical collapse model (SCM). Here the virialization process is naturally achieved by introducing shear and rotation instead of using the virial theorem. We generalise two approaches proposed in the literature and show that, regardless of the dark-energy model, the new virialization term can be calibrated on the peculiar velocity of the shell as measured from Einstein-de Sitter simulations. The two virialization recipes qualitatively reproduce the features of the ordinary SCM, i.e., a constant Δvir for the EdS model and time-variation for dark-energy models, but without any mass dependence. Depending on the actual description of virialization and on the dark-energy model, the value of Δvir varies between 10 and 40 percent. We use the new recipes to predict the surface-mass-density profile of dark matter haloes and the number of convergence density peaks for LSST- and Euclid-like weak lensing surveys.

• Barack, Leor; Cardoso, Vitor; Nissanke, Samaya; Sotiriou, Thomas P.; Askar, Abbas & Belczynski, Chris [Vis alle 208 forfattere av denne artikkelen] (2019). Black holes, gravitational waves and fundamental physics: A roadmap. Classical and Quantum Gravity. ISSN 0264-9381. 36(14). doi: 10.1088/1361-6382/ab0587. Fulltekst i vitenarkiv
• Aviles, Alejandro; Cervantes-Cota, Jorge L & Mota, David (2019). Screenings in modified gravity: a perturbative approach. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 622. doi: 10.1051/0004-6361/201834383. Fulltekst i vitenarkiv Vis sammendrag

  We present a formalism to study screening mechanisms in modified theories of gravity through perturbative methods in different cosmological scenarios. We consider Einstein-frame posed theories that are recast as Jordan-frame theories, where a known formalism is employed, although the resulting nonlinearities of the Klein–Gordon equation acquire an explicit coupling between matter and the scalar field, which is absent in Jordan-frame theories. The obtained growth functions are then separated into screening and non-screened contributions to facilitate their analysis. This allows us to compare several theoretical models and to recognize patterns that can be used to distinguish models and their screening mechanisms. In particular, we find anti-screening features in the symmetron model. In contrast, chameleon-type theories in both the Jordan and Einstein frames always present a screening behaviour. Up to third order in perturbation, we find no anti-screening behaviour in theories with a Vainshtein mechanism, such as the Dvali Gabadadze Porrati braneworld model and the cubic Galileon. © ESO 2019

• Sapa, Stharporn; Karwan, Khamphee & Mota, David (2018). Spherical collapse and cluster number counts in dark energy models disformally coupled to dark matter. Physical Review D. ISSN 2470-0010. 98(2). doi: 10.1103/PhysRevD.98.023528. Fulltekst i vitenarkiv Vis sammendrag

  We investigate the effects of a disformal coupling between dark energy and dark matter in the predictions of the spherical collapse and its signatures in galaxy cluster number counts. We find that the disformal coupling has no significant effects on spherical collapse at high redshifts, and in particular during matter domination epoch. However, at lower redshifts, the extrapolated linear density contrast at collapse close to redshift z ≲ 1 and overdensity at virialization can be strongly suppressed by a disformal coupling between dark energy and dark matter. We also find that disformal coupling can have different imprints on cluster number counts compared with conformal coupling, such that the disformal coupling can strongly suppress the predicted number of clusters per redshift interval at z > 0.1 while enhance the number of cluster at z < 0.05. Using the specifications of eROSITA survey, we find that the disformal coupling between dark energy and dark matter can be tightly constrained by cluster number counts. © 2018 American Physical Society

• Mota, David (2018). Probing screened modified gravity with nonlinear structure formation. International Journal of Modern Physics D. ISSN 0218-2718. 27(4). doi: 10.1142/S0218271818300033. Fulltekst i vitenarkiv
• Ho, Alex; Gronke, Max Balthasar; Falck, Bridget Lynn & Mota, David (2018). Probing modified gravity in cosmic filaments. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 619. doi: 10.1051/0004-6361/201833899. Fulltekst i vitenarkiv Vis sammendrag

  Multiple modifications of general relativity (GR) have been proposed in the literature in order to understand the nature of the accelerated expansion of the Universe. However, thus far all the predictions of GR have been confirmed with constantly increasing accuracy. In this work, we study the imprints of a particular class of models – “screened” modified gravity theories – on cosmic filaments. We have utilized the N-body code ISIS/RAMSES to simulate the symmetron model and the Hu–Sawicky f(R) model, and we post-process the output with DisPerSE to identify the filaments of the cosmic web. We investigated how the global properties of the filaments – such as their lengths, masses, and thicknesses – as well as their radial density and speed profiles change under different gravity theories. We find that filaments are, on average, shorter and denser in modified gravity models compared to in ΛCDM. We also find that the speed profiles of the filaments are enhanced, consistent with theoretical expectations. Overall, our results suggest that cosmic filaments can be an effective complementary probe of screened modified gravity theories on Mpc scales.

• Ellewsen, Thor Andreas Seiff; Falck, Bridget Lynn & Mota, David (2018). Degeneracies between modified gravity and baryonic physics. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 615. doi: 10.1051/0004-6361/201731938. Fulltekst i vitenarkiv Vis sammendrag

  In order to determine the observable signatures of modified gravity theories, it is important to consider the effect of baryonic physics. We used a modified version of the ISIS code to run cosmological hydrodynamic simulations in order to study degeneracies between modified gravity and radiative hydrodynamic processes. One of the simulations was the standard Λ cold dark matter model and four were variations of the Symmetron model. For each model we ran three variations of baryonic processes: nonradiative hydrodynamics; cooling and star formation; and cooling, star formation, and supernova feedback. We constructed stacked gas density, temperature, and dark matter density profiles of the halos in the simulations, and studied the differences between them. We find that both radiative variations of the models show degeneracies between their processes and at least two of the three parameters defining the Symmetron model.

• santos, Marcelo Vargas dos; Alcaniz, Jailson S; Mota, David & Capozziello, Salvatore (2018). Screening mechanisms in hybrid metric-Palatini gravity. Physical Review D. ISSN 2470-0010. 97(10). doi: 10.1103/PhysRevD.97.104010. Fulltekst i vitenarkiv Vis sammendrag

  We investigate the efficiency of screening mechanisms in the hybrid metric-Palatini gravity. The value of the field is computed around spherical bodies embedded in a background of constant density. We find a thin shell condition for the field depending on the background field value. To quantify how the thin shell effect is relevant, we analyze how it behaves in the neighborhood of different astrophysical objects (planets, moons, or stars). We find that the condition is very well satisfied except only for some peculiar objects. Furthermore we establish bounds on the model using data from Solar System experiments such as the spectral deviation measured by the Cassini mission and the stability of the Earth-Moon system, which gives the best constraint to date on f(R) theories. These bounds contribute to fix the range of viable hybrid gravity models. © 2018 American Physical Society

• Amendola, Luca; Appleby, Stephen; Avgoustidis, Anastasios; Bacon, David; Baker, Tessa & Baldi, Marco [Vis alle 71 forfattere av denne artikkelen] (2018). Cosmology and fundamental physics with the Euclid satellite. Living Reviews in Relativity. 21. doi: 10.1007/s41114-017-0010-3. Fulltekst i vitenarkiv Vis sammendrag

  Euclid is a European Space Agency medium-class mission selected for launch in 2020 within the cosmic vision 2015–2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the universe. Euclid will explore the expansion history of the universe and the evolution of cosmic structures by measuring shapes and red-shifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid’s Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

• Yang, Weiqiang; Pan, Supriya; Valentino, Eleonora Di; Nunes, Rafael C.; Vagnozzi, Sunny & Mota, David (2018). Tale of stable interacting dark energy, observational signatures, and the H_0 tension. Journal of Cosmology and Astroparticle Physics (JCAP). 2018(9). doi: 10.1088/1475-7516/2018/09/019. Fulltekst i vitenarkiv

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• Mylius-Kroken, Johan; Wally, Youssef; Mota, David & Wickstrøm, Kristoffer (2026). Hyperbolic Representation Learning for Astrophysical Photometric Survey Data. doi: https:/openreview.net/forum?id=hGV1cIU2N1&referrer=%5BAuthor%20Console%5D%28%2Fgroup%3Fid%3Dthecvf.com%2FECCV%2F2026%2FWorkshop%2FBEW%2FAuthors%23your-submissions%29. Fulltekst i vitenarkiv Vis sammendrag

  We compare unsupervised representation learning on the miniJPAS narrow-band photometric survey using three architecturally identical autoencoders whose latent spaces differ only in geometry: Euclidean $\mathbb{R}^{32}$ and two variants on the Lorentz hyperboloid $\mathbb{H}^{32}$. The hyperbolic choice is motivated by Gromov $\delta$-hyperbolicity analysis, which confirms that the miniJPAS feature space has intrinsically tree-like geometry. Training on a reconstruction objective without label supervision, the Lorentzian models produce qualitatively different embeddings: stars concentrate in compact regions near the Poincar\'{e} disc boundary, and an emergent photometric redshift gradient is visible across all three latent spaces, though the embedding does not yet exhibit the radial, tree-like organisation that hyperbolic geometry in principle affords. Classification accuracy is comparable across all three models ($\approx$78\%), confirming that these structural differences emerge at no discriminative cost. These results motivate a more systematic investigation of geometry-aware training objectives for astrophysical survey data.

• Christiansen, Øyvind; Mota, David & Winther, Hans Arnold (2024). Cosmological Simulations of Phase Transitions in Screened Scalar-Tensor Gravity: Cosmic acceleration, topological defects, gravitational waves and relativistic observables. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Christiansen presents cosmological simulations of the (a)symmetron, a scalar-tensor theory of gravity undergoing a phase transition in the late-time universe. He demonstrates novel signatures in gravitational waves and other relativistic observables, and explores in detail the formation of domain walls and their imprint on cosmic structure formation, including dark matter halos and the cosmic web. Christiansen uncovers an interesting part of the parameter space where phase transitions occur inside the nonlinear underdensities, and proposes an application of the nonlinear and dynamical theory to explain late-time cosmology as well as to unify the dark sector.

• Hartman, Stian Thomas Heimdal; Mota, David & Winther, Hans Arnold (2022). Cosmology of Scalar Field Dark Matter with Self-Interactions. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  In the standard model of the universe, the presence of a cold and dark form of matter is essential for explaining a wide range of observables, from the very largest scales such as the microwave background radiation, to galaxies and sub-galactic scales. However, despite this dark matter being about five times more abundant than all of the visible matter in our universe, its true identity is a complete mystery. Unveiling the fundamental nature of dark matter would contribute to a deeper understanding of our universe and the physical laws that govern it, and is therefore one of the Holy Grails of modern physics. In this thesis I have explored how dark matter behaves (in sometimes surprising ways) in models where the hypothetical dark matter particle is very light and self-interacting, using both theoretical tools and numerical simulations. This effort has contributed to an improved understanding of these models in certain scenarios, as well as provided additional constraints on the free parameters of these models by investigating their effect on observables.

• Christiansen, Øyvind & Mota, David (2020). Charged Black Hole Mergers: Emissions, Orbital Evolution, Gravitational Waveform and Observer Bias. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Gravitational waveforms from mergers or close-encounters of astrophysical compact bodies provide a new and separate window into high energy physics and dark objects. Although there is a zoo of theoretical compact objects that the current detectors of this channel might be sensitive to, we still have not found anything we did not already expect, apart from slightly surprising high stellar mass black hole merger rates and small final spins, both of which are at slight tension with common binary system formation mechanisms. The reason why no such object has appeared in our data might be because we are not looking for them, detections typically being done using matched filtering -- a statistical method requiring a highly precise theoretical prediction of the signal to dig it out of the noise. In this work we extend some of the analysis already done at lowest order to compact objects carrying some U(1) charge. We consider how the extra interaction and emission modifies the dynamics in the slow-inspiral regime and evolve the orbit until its merger phase. The circularisation is shown to be slightly weaker for orbits where the gauge-field dominates the back-reaction, though both here and in the standard gravitationally dominated emission do we expect to have mergers circularise by the time they enter detector sensitivity, given a large enough initial separation. We find the first correction from U(1) emission to the gravitational emission driven orbit, this representing the small charge limit, and find again the orbital evolution, which in turn gives us the gravitational waveform. Having the waveform, we consider how it would be interpreted in gravitational wave detectors where neutral signals are expected, or whether it would be detected at all, using the least squares method and matched filtering. We find, under some assumptions, that the projection onto neutral templates would bias a large mass, without a very large loss of signal. This would, together with previous research done in the field, point towards a possible explanation for both aforementioned curiosities in the detector data so far. Finally we present discussions on how the analysis might be extended to unbound encounters and mergers carrying electric \textit{and} magnetic charges, presenting the $\mathcal{O}(v)$ order orbital dynamics and emissions for the latter.

• Mina, Mattia; Mota, David & Winther, Hans Arnold (2020). Cosmology at small scales: ultra-light dark matter and baryon cycles in galaxies. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The standard model of cosmology has been quite successful in describing how baryonic matter and dark matter cluster by means of gravity, forming the structures we can see today while looking at the sky, and it can reproduce many of the general properties of the observed Universe. However, on the scales of individual galaxies, this model has several complications due to the fact that the true nature of dark matter is still unknown and physical processes involving ordinary matter withing galaxies are not fully understood. By means of computer simulations, I first studied a specific class of dark matter models, called Ultra-Light Dark Matter. I showed that these models better describe some of the properties of dark matter halos, and they develop distinct features which can be tested against astronomical observations. Then, I studied how stars can affect the life cycle of galaxies and dark matter halos. I showed that using a realistic model for supernova explosions can potentially solve the discrepancies between the theoretical predictions of the standard model of cosmology and astronomical observations, reproducing dwarf galaxies and dark matter halos that closely resemble observed ones.

• Hagala, Robert; Mota, David & Llinares, Claudio (2019). Astrophysical Simulations for Uncovering Signatures of Gravity. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Einstein's theory of general relativity is currently our best model for how gravity works. It can be used to predict motions of planets, the speed-up of clocks on GPS satellites, and gravitational waves. General relativity has been used to model the history and expansion of the Universe as a whole, but on these vast scales, problems start appearing. To make the theory match our observations, we have to add two components we don't know much about, and that we have never observed: dark matter and dark energy. To explain the shortcomings of general relativity, it is important to explore alternative theories of gravity. In my work, I have used special designed computer simulations to better understand specific theories of modified gravity, and to investigate the simplifying assumptions that are often applied by researchers studying these theories. I have also studied possible new observational signatures that can be used to distinguish between different gravitational theories. My work explores new phenomena in one specific modified gravity theory, called disformal quintessence. Furthermore, it is showed that in some cases one cannot ignore commonly neglected terms in the equations.

• Valberg, Pål; Elgarøy, Øystein & Mota, David (2018). On the theory of dark matter superfluidity. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The ''theory of dark matter superfluidity'' \cite{berezhiani2015theory} is reproduced in SI units with the inclusion of intermediate, and precise, steps in the calculations. By use of another measure of the mean interparticle separation, the bound on dark matter particle mass is less stringent than in \cite{berezhiani2015theory}, though the sub-eV mass range is still found. Using the conjectured superfluid phonon effective field theory, the equation of state is found to be polytropic $P \propto \rho^3$. Due to the increased precision in calculations, the resulting condensate halo radius is found to be less than in \cite{berezhiani2015theory}. The proper acceleration needed is derived in higher precision than in \cite{berezhiani2015theory}, though, when compared to standard gravitational acceleration, is not dominant on large scales $(\sim 100\,\text{kpc})$. Superfluid phonons are generated in galaxies, and breakdown of coherence within the fluid occurs closer to the source than in \cite{berezhiani2015theory}, though dark matter is still found to exist in its normal phase within the Solar System. A relativistic theory that produces proper dynamics in the non-relativistic, weak-field limit is considered, and a starting point for the inclusion of coupling to baryonic matter is suggested. Cosmological dark matter is found in the superfluid state, and the theory is altered to account for this in order to obtain ''cold dark matter'' on these scales. In addition to this, the evolution of the condensate mass density is found to reveal a finite (non-zero) scale factor for which it diverges. Finally, consequences to this theory, mostly considering Bose-Einstein condensate theory, is discussed in short, as well as the same points regarding astrophysics discussed in \cite{berezhiani2015theory}.

• Ho, Alex; Mota, David & Falck, Bridget Lynn (2018). Probing Modified Gravity in Cosmic Filaments. Universitetet i Oslo. Fulltekst i vitenarkiv

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