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. Full text in Research Archive Show summary

  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. Full text in Research Archive Show summary

  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. Full text in Research Archive Show summary

  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. Full text in Research Archive Show summary

  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. [Show all 8 contributors for this article] (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. Full text in Research Archive Show summary

  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. Full text in Research Archive Show summary

  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. Full text in Research Archive Show summary

  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. Full text in Research Archive Show summary

  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. Full text in Research Archive Show summary

  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.

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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. Full text in Research Archive Show summary

  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.

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