Torsten Bringmann

Fullstendig liste: ​​

• Balazs, Csaba; Bringmann, Torsten; Kahlhoefer, Felix & White, Martin (2026). A primer on dark matter. I Howlett, Cullan (Red.), Encyclopedia of Astrophysics. Elsevier. ISSN 9780443214400. s. 32–32. doi: 10.1016/b978-0-443-21439-4.00070-5. Fulltekst i vitenarkiv
• Bringmann, Torsten; Croon, Djuna & Muñoz, Sergio Sevillano (2026). Updated Constraints on the Primordial Power Spectrum at Sub-Mpc Scales. Physical Review Letters. ISSN 0031-9007. 137(6). doi: 10.1103/2jhb-n2rk. Fulltekst i vitenarkiv
• Balan, Sowmiya; Bringmann, Torsten; Kahlhoefer, Felix; Matuszak, Jonas & Tasillo, Carlo (2025). Sub-GeV dark matter and nano-Hertz gravitational waves from a classically conformal dark sector. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(08), s. 062–062. doi: 10.1088/1475-7516/2025/08/062. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Strong first-order phase transitions in a dark sector offer a compelling explanation for the stochastic gravitational wave background in the nano-Hertz range recently detected by pulsar timing arrays (PTAs). We explore the possibility that such a phase transition at the same time gives mass to a stable fermion that accounts for the observed dark matter abundance and leads to testable effects in laboratory experiments. Concretely, we consider a classically conformal dark sector with a hidden U(1)^' gauge symmetry that couples to the Standard Model via kinetic mixing. Since the PTA signal requires a phase transition in the MeV temperature range, spontaneous symmetry breaking gives rise to a sub-GeV dark matter candidate that couples to the Standard Model via a dark photon mediator and obtains its relic abundance via annihilations into electrons and dark Higgs bosons. Such a scenario is tightly constrained by laboratory searches for dark photons and cosmological constraints on the decays of dark Higgs bosons after the phase transition. We show that viable parameter regions can be found both for the case that the dark Higgs bosons remain in equilibrium with the Standard Model and that they decouple and only decay much later. In the latter case, the parameter regions preferred by the PTA signal and the dark matter relic abundance can be fully explored by future beam-dump experiments searching for missing energy.

• Abe, K.; Abe, S.; Abhir, J.; Abhishek, A.; Acero, F. & Acharyya, A. [Vis alle 494 forfattere av denne artikkelen] (2025). Prospects for dark matter observations in dwarf spheroidal galaxies with the Cherenkov Telescope Array Observatory. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 544(3), s. 2946–2986. doi: 10.1093/mnras/staf1798. Fulltekst i vitenarkiv
• Balan, Sowmiya; Balazs, Csaba; Bringmann, Torsten; Cappiello, Christopher; Catena, Riccardo & Emken, Timon [Vis alle 12 forfattere av denne artikkelen] (2025). Resonant or asymmetric: the status of sub-GeV dark matter. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(1). doi: 10.1088/1475-7516/2025/01/053. Fulltekst i vitenarkiv Vis sammendrag

  Sub-GeV dark matter (DM) particles produced via thermal freeze-out evade many of the strong constraints on heavier DM candidates but at the same time face a multitude of new constraints from laboratory experiments, astrophysical observations and cosmological data. In this work we combine all of these constraints in order to perform frequentist and Bayesian global analyses of fermionic and scalar sub-GeV DM coupled to a dark photon with kinetic mixing. For fermionic DM, we find viable parameter regions close to the dark photon resonance, which expand significantly when including a particle-antiparticle asymmetry. For scalar DM, the velocity-dependent annihilation cross section evades the strongest constraints even in the symmetric case. Using Bayesian model comparison, we show that both asymmetric fermionic DM and symmetric scalar DM are preferred over symmetric fermionic DM due to the reduced fine-tuning penalty. Finally, we explore the discovery prospects of near-future experiments both in the full parameter space and for specific benchmark points. We find that the most commonly used benchmark scenarios are already in tension with existing constraints and propose a new benchmark point that can be targeted with future searches.

• 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.

• Abe, S.; Abhir, J.; Abhishek, A.; Acero, F.; Acharyya, A. & Adam, R. [Vis alle 565 forfattere av denne artikkelen] (2024). Dark matter line searches with the Cherenkov Telescope Array. Journal of Cosmology and Astroparticle Physics (JCAP). 2024(7). doi: 10.1088/1475-7516/2024/07/047. Fulltekst i vitenarkiv Vis sammendrag

  Monochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from astrophysical or instrumental backgrounds. We provide an updated assessment of the sensitivity of the Cherenkov Telescope Array (CTA) to such signals, based on observations of the Galactic centre region as well as of selected dwarf spheroidal galaxies. We find that current limits and detection prospects for dark matter masses above 300 GeV will be significantly improved, by up to an order of magnitude in the multi-TeV range. This demonstrates that CTA will set a new standard for gamma-ray astronomy also in this respect, as the world's largest and most sensitive high-energy gamma-ray observatory, in particular due to its exquisite energy resolution at TeV energies and the adopted observational strategy focussing on regions with large dark matter densities. Throughout our analysis, we use up-to-date instrument response functions, and we thoroughly model the effect of instrumental systematic uncertainties in our statistical treatment. We further present results for other potential signatures with sharp spectral features, e.g. box-shaped spectra, that would likewise very clearly point to a particle dark matter origin.

• Bringmann, Torsten; Gonzalo, Tomás E.; Kahlhoefer, Felix; Matuszak, Jonas & Tasillo, Carlo (2024). Hunting WIMPs with LISA: correlating dark matter and gravitational wave signals. Journal of Cosmology and Astroparticle Physics (JCAP). 2024(5). doi: 10.1088/1475-7516/2024/05/065. Fulltekst i vitenarkiv Vis sammendrag

  The thermal freeze-out mechanism in its classical form is tightly connected to physics beyond the Standard Model around the electroweak scale, which has been the target of enormous experimental efforts. In this work we study a dark matter model in which freeze-out is triggered by a strong first-order phase transition in a dark sector, and show that this phase transition must also happen close to the electroweak scale, i.e. in the temperature range relevant for gravitational wave searches with the LISA mission. Specifically, we consider the spontaneous breaking of a U(1)' gauge symmetry through the vacuum expectation value of a scalar field, which generates the mass of a fermionic dark matter candidate that subsequently annihilates into dark Higgs and gauge bosons. In this set-up the peak frequency of the gravitational wave background is tightly correlated with the dark matter relic abundance, and imposing the observed value for the latter implies that the former must lie in the milli-Hertz range. A peculiar feature of our set-up is that the dark sector is not necessarily in thermal equilibrium with the Standard Model during the phase transition, and hence the temperatures of the two sectors evolve independently. Nevertheless, the requirement that the universe does not enter an extended period of matter domination after the phase transition, which would strongly dilute any gravitational wave signal, places a lower bound on the portal coupling that governs the entropy transfer between the two sectors. As a result, the predictions for the peak frequency of gravitational waves in the LISA band are robust, while the amplitude can change depending on the initial dark sector temperature.

• Bringmann, Torsten; Depta, Paul Frederik; Hufnagel, Marco; Kersten, Jörn; Ruderman, Joshua T. & Schmidt-Hoberg, Kai (2023). Minimal sterile neutrino dark matter. Physical Review D. ISSN 2470-0010. 107(7). doi: 10.1103/PhysRevD.107.L071702. Fulltekst i vitenarkiv Vis sammendrag

  We propose a novel mechanism to generate sterile neutrinos νs in the early Universe, by converting ordinary neutrinos να in scattering processes νsνα→νsνs. After initial production by oscillations, this leads to an exponential growth in the νs abundance. We show that such a production regime naturally occurs for self-interacting νs, and that this opens up significant new parameter space where νs make up all of the observed dark matter. Our results provide strong motivation to further push the sensitivity of X-ray line searches, and to improve on constraints from structure formation.

• Bringmann, Torsten; Depta, Paul Frederik; Konstandin, Thomas; Schmidt-Hoberg, Kai & Tasillo, Carlo (2023). Does NANOGrav observe a dark sector phase transition? Journal of Cosmology and Astroparticle Physics (JCAP). 2023(11). doi: 10.1088/1475-7516/2023/11/053. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Gravitational waves from a first-order cosmological phase transition, at temperatures at the MeV-scale, would arguably be the most exciting explanation of the common red spectrum reported by the NANOGrav collaboration, not the least because this would be direct evidence of physics beyond the standard model. Here we perform a detailed analysis of whether such an interpretation is consistent with constraints on the released energy deriving from big bang nucleosynthesis and the cosmic microwave background. We find that a phase transition in a completely secluded dark sector with sub-horizon sized bubbles is strongly disfavoured with respect to the more conventional astrophysical explanation of the putative gravitational wave signal in terms of supermassive black hole binaries. On the other hand, a phase transition in a dark sector that subsequently decays, before the time of neutrino decoupling, remains an intriguing possibility to explain the data. From the model-building perspective, such an option is easily satisfied for couplings with the visible sector that are small enough to evade current collider and astrophysical constraints. The first indication that could eventually corroborate such an interpretation, once the observed common red spectrum is confirmed as a nHz gravitational wave background, could be the spectral tilt of the signal. In fact, the current data already show a very slight preference for a spectrum that is softer than what is expected from the leading astrophysical explanation.

• Bringmann, Torsten; Domcke, Valerie; Fuchs, Elina & Kopp, Joachim (2023). High-frequency gravitational wave detection via optical frequency modulation. Physical Review D. ISSN 2470-0010. 108(6). doi: 10.1103/PhysRevD.108.L061303. Fulltekst i vitenarkiv Vis sammendrag

  High frequency gravitational waves can be detected by observing the frequency modulation they impart on photons. We discuss fundamental limitations to this method related to the fact that it is impossible to construct a perfectly rigid detector. We then propose several novel methods to search for O(MHz − GHz)gravitational waves based on the frequency modulation induced in the spectrum of an intense laser beam, by applying optical frequency demodulation techniques, or by using optical atomic clock technology. We find promising sensitivities across a broad frequency range.

• Alvey, James; Bringmann, Torsten & Kolesova, Helena (2023). No room to hide: implications of cosmic-ray upscattering for GeV-scale dark matter. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2023:123, s. 1–43. doi: 10.1007/JHEP01(2023)123. Fulltekst i vitenarkiv Vis sammendrag

  The irreducible upscattering of cold dark matter by cosmic rays opens up the intriguing possibility of detecting even light dark matter in conventional direct detection experiments or underground neutrino detectors. The mechanism also significantly enhances sensitivity to models with very large nuclear scattering rates, where the atmosphere and rock overburden efficiently stop standard non-relativistic dark matter particles before they could reach the detector. In this article, we demonstrate that cosmic-ray upscattering essentially closes the window for strongly interacting dark matter in the (sub-)GeV mass range. Arriving at this conclusion crucially requires a detailed treatment of both nuclear form factors and inelastic dark matter-nucleus scattering, as well as including the full momentum-transfer dependence of scattering amplitudes. We illustrate the latter point by considering three generic situations where such a momentum-dependence is particularly relevant, namely for interactions dominated by the exchange of light vector or scalar mediators, respectively, and for dark matter particles of finite size. As a final concrete example, we apply our analysis to a putative hexaquark state, which has been suggested as a viable baryonic dark matter candidate. Once again, we find that the updated constraints derived in this work close a significant part of otherwise unconstrained parameter space.

• Bringmann, Torsten; Heeba, Saniya; Kahlhoefer, Felix & Vangsnes, Kristian Gjestad (2022). Freezing-in a hot bath: resonances, medium effects and phase transitions. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2022(2). doi: 10.1007/JHEP02(2022)110. Fulltekst i vitenarkiv Vis sammendrag

  A bstract Relic density calculations of dark matter freezing out from the primordial plasma have reached a high level of sophistication, with several numerical tools readily available that match the observationally required accuracy. Dark matter production via the freeze-in mechanism, on the other hand, is sensitive to much higher temperatures than in the freeze-out case, implying both technical and computational difficulties when aiming for the same level of precision. We revisit the formulation of freeze-in production in a way that facilitates the inclusion of in-medium corrections like plasma effects and the spin statistics of relativistic quantum gases, as well as the temperature dependence of dark matter production rates induced by the electroweak and strong phase transitions, and we discuss in detail the additional complications arising in the presence of s -channel resonances. We illustrate our approach in the context of Higgs portal models, and provide the most accurate calculation to date of the freeze-in abundance of Scalar Singlet dark matter. We explore in particular the case of small reheating temperatures, for which the couplings implied by the freeze-in mechanism may be testable at the LHC. Together with this article we present a major update 6.3 of DarkSUSY with the added capability of performing general freeze-in calculations, including all complications mentioned above.

• Abdussalam, Shehu S.; Agocs, Fruzsina J.; Allanach, Benjamin C.; Athron, Peter; Balázs, Csaba & Bagnaschi, Emanuele [Vis alle 75 forfattere av denne artikkelen] (2022). Simple and statistically sound recommendations for analysing physical theories. Reports on progress in physics (Print). ISSN 0034-4885. 85(5). doi: 10.1088/1361-6633/ac60ac. Fulltekst i vitenarkiv
• Acharyya, A.; Adam, R.; Adams, C.; Agudo, I.; Aguirre-Santaella, A. & Alfaro, R. [Vis alle 450 forfattere av denne artikkelen] (2021). Sensitivity of the Cherenkov Telescope Array to a dark matter signal from the Galactic centre. Journal of Cosmology and Astroparticle Physics (JCAP). 2021(1). doi: 10.1088/1475-7516/2021/01/057. Fulltekst i vitenarkiv Vis sammendrag

  We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA's unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale diffuse emission in high-energy gamma rays, constituting a background for dark matter searches for which we adopt state-of-the-art models based on current data. Throughout our analysis, we use up-to-date event reconstruction Monte Carlo tools developed by the CTA consortium, and pay special attention to quantifying the level of instrumental systematic uncertainties, as well as background template systematic errors, required to probe thermally produced dark matter at these energies.

• Athron, Peter; Kozar, Neal Avis; Balázs, Csaba; Beniwal, Ankit; Bloor, Sanjay & Bringmann, Torsten [Vis alle 26 forfattere av denne artikkelen] (2021). Thermal WIMPs and the scale of new physics: global fits of Dirac dark matter effective field theories. European Physical Journal C. ISSN 1434-6044. 81(11). doi: 10.1140/epjc/s10052-021-09712-6. Fulltekst i vitenarkiv Vis sammendrag

  Abstract We assess the status of a wide class of WIMP dark matter (DM) models in light of the latest experimental results using the global fitting framework . We perform a global analysis of effective field theory (EFT) operators describing the interactions between a gauge-singlet Dirac fermion and the Standard Model quarks, the gluons and the photon. In this bottom-up approach, we simultaneously vary the coefficients of 14 such operators up to dimension 7, along with the DM mass, the scale of new physics and several nuisance parameters. Our likelihood functions include the latest data from Planck , direct and indirect detection experiments, and the LHC. For DM masses below 100 GeV, we find that it is impossible to satisfy all constraints simultaneously while maintaining EFT validity at LHC energies. For new physics scales around 1 TeV, our results are influenced by several small excesses in the LHC data and depend on the prescription that we adopt to ensure EFT validity. Furthermore, we find large regions of viable parameter space where the EFT is valid and the relic density can be reproduced, implying that WIMPs can still account for the DM of the universe while being consistent with the latest data.

• Bringmann, Torsten; Depta, Paul Frederik; Hufnagel, Marco; Ruderman, Joshua T. & Schmidt-Hoberg, Kai (2021). Dark Matter from Exponential Growth. Physical Review Letters. ISSN 0031-9007. 127(19). doi: 10.1103/PhysRevLett.127.191802. Fulltekst i vitenarkiv Vis sammendrag

  We propose a novel mechanism for the production of dark matter (DM) from a thermal bath based on the idea that DM particles χ can transform heat bath particles ψ: χψ→χχ. For a small initial abundance of χ, this leads to an exponential growth of the DM number density in close analogy to other familiar exponential growth processes in nature. We demonstrate that this mechanism complements freeze-in and freeze-out production in a generic way, opening new parameter space to explain the observed DM abundance, and we discuss observational prospects for such scenarios.

• Binder, Tobias; Bringmann, Torsten; Gustafsson, Michael & Hryczuk, Andrzej (2021). Dark matter relic abundance beyond kinetic equilibrium. European Physical Journal C. ISSN 1434-6044. 81(7). doi: 10.1140/epjc/s10052-021-09357-5. Fulltekst i vitenarkiv Vis sammendrag

  Abstract We introduce , a numerical precision tool for predicting the dark matter relic abundance also in situations where the standard assumption of kinetic equilibrium during the freeze-out process may not be satisfied. comes with a set of three dedicated Boltzmann equation solvers that implement, respectively, the traditionally adopted equation for the dark matter number density, fluid-like equations that couple the evolution of number density and velocity dispersion, and a full numerical evolution of the phase-space distribution. We review the general motivation for these approaches and, for illustration, highlight three concrete classes of models where kinetic and chemical decoupling are intertwined in a way that quantitatively impacts the relic density: (i) dark matter annihilation via a narrow resonance, (ii) Sommerfeld-enhanced annihilation and (iii) ‘forbidden’ annihilation to final states that are kinematically inaccessible at threshold. We discuss all these cases in some detail, demonstrating that the commonly adopted, traditional treatment can result in an estimate of the relic density that is wrong by up to an order of magnitude. The public release of , along with several examples of how to calculate the relic density in concrete models, is provided at drake.hepforge.org

• Bringmann, Torsten; Depta, Paul Frederik; Hufnagel, Marco & Schmidt-Hoberg, Kai (2021). Precise dark matter relic abundance in decoupled sectors. Physics Letters B. ISSN 0370-2693. 817. doi: 10.1016/j.physletb.2021.136341. Fulltekst i vitenarkiv Vis sammendrag

  Dark matter (DM) as a thermal relic of the primordial plasma is increasingly pressured by direct and indirect searches, while the same production mechanism in a decoupled sector is much less constrained. We extend the standard treatment of the freeze-out process to such scenarios and perform precision calculations of the annihilation cross-section required to match the observed DM abundance. We demonstrate that the difference to the canonical value of this ‘thermal cross-section’ is generally sizeable, and can reach orders of magnitude. Our results directly impact the interpretation of DM searches in hidden sector scenarios.

• Stöcker, Patrick; Balázs, Csaba; Bloor, Sanjay; Bringmann, Torsten; Gonzalo, Tomás E. & Handley, Will J. [Vis alle 13 forfattere av denne artikkelen] (2021). Strengthening the bound on the mass of the lightest neutrino with terrestrial and cosmological experiments. Physical Review D. ISSN 2470-0010. 103(12), s. 123508-1–123508-9. doi: 10.1103/PhysRevD.103.123508. Fulltekst i vitenarkiv Vis sammendrag

  We determine the upper limit on the mass of the lightest neutrino from the most robust recent cosmological and terrestrial data. Marginalizing over possible effective relativistic degrees of freedom at early times (Neff) and assuming normal mass ordering, the mass of the lightest neutrino is less than 0.037 eV at 95% confidence; with inverted ordering, the bound is 0.042 eV. These results improve upon the strength and robustness of other recent limits and constrain the mass of the lightest neutrino to be barely larger than the largest mass splitting. We show the impacts of realistic mass models and different sources of Neff.

• Renk, Janina J.; Stöcker, Patrick; Bloor, Sanjay; Hotinli, Selim; Balázs, Csaba & Bringmann, Torsten [Vis alle 14 forfattere av denne artikkelen] (2021). CosmoBit: A GAMBIT module for computing cosmological observables and likelihoods. Journal of Cosmology and Astroparticle Physics (JCAP). 2021(2). doi: 10.1088/1475-7516/2021/02/022. Fulltekst i vitenarkiv
• Bondarenko, Kyrylo; Boyarsky, Alexey; Bringmann, Torsten; Hufnagel, Marco; Schmidt-Hoberg, Kai & Sokolenko, Anastasia (2020). Direct detection and complementary constraints for sub-GeV dark matter. Journal of High Energy Physics (JHEP). ISSN 1126-6708. doi: 10.1007/JHEP03(2020)118. Fulltekst i vitenarkiv
• Bohr, Sebastian; Zavala, Jesús; Cyr-Racine, Francis-Yan; Vogelsberger, Mark; Bringmann, Torsten & Pfrommer, Christoph (2020). ETHOS – an effective parametrization and classification for structure formation: the non-linear regime at z ≳ 5. Monthly Notices of the Royal Astronomical Society: Letters (MNRAS Letters). ISSN 1745-3925. 498(3), s. 3403–3419. doi: 10.1093/mnras/staa2579. Fulltekst i vitenarkiv
• Plestid, Ryan; Takhistov, Volodomyr; Tsai, Yu-Dai; Bringmann, Torsten; Kusenko, Alexander & Pospelov, Maxim (2020). New Constraints on Millicharged Particles from Cosmic-ray Production. Physical Review D. ISSN 2470-0010. 102(11), s. 1–13. doi: 10.1103/PhysRevD.102.115032. Fulltekst i vitenarkiv Vis sammendrag

  We study cosmic-ray-atmosphere collisions as a permanent production source of exotic millicharged particles (MCPs) for all terrestrial experiments. [MCPs are also known as charged massive particles (CHAMPs).] Based on data from Super-K, this allows us to derive new limits on MCPs that are competitive with, or improve, the currently leading bounds from accelerator-based searches for masses up to 1.5 GeV. In models where a subdominant component of dark matter (DM) is fractionally charged, these constraints probe parts of the parameter space that is inaccessible for conventional direct-detection DM experiments, independently of assumptions about the DM abundance.

• Bringmann, Torsten; Cline, James M & Cornell, Jonathan M. (2019). Baryogenesis from neutron-dark matter oscillations. Physical Review D. ISSN 2470-0010. 99(3). doi: 10.1103/PhysRevD.99.035024. Fulltekst i vitenarkiv Vis sammendrag

  It was recently suggested that dark matter consists of ∼ GeV particles that carry baryon number and mix with the neutron. We demonstrate that this could allow for resonant dark matter–neutron oscillations in the early Universe, at finite temperature, leading to low-scale baryogenesis starting from a primordial dark matter asymmetry. In this scenario, the asymmetry transfer happens around 30 MeV, just before big bang nucleosynthesis. We illustrate the idea using a model with a dark U(1)′ gauge interaction, which has recently been suggested as a way of addressing the neutron lifetime anomaly. The asymmetric dark matter component of this model is both strongly self-interacting and leads to a suppression of matter density perturbations at small scales, allowing it to mitigate the small-scale problems of cold dark matter cosmology. Future cosmic microwave background experiments will be able to consistently probe, or firmly exclude, this scenario.

• Bringmann, Torsten; Depta, Paul Frederik; Domcke, Valerie & Schmidt-Hoberg, Kai (2019). Towards closing the window of primordial black holes as dark matter: The case of large clustering. Physical Review D. ISSN 2470-0010. 99(6). doi: 10.1103/PhysRevD.99.063532. Fulltekst i vitenarkiv Vis sammendrag

  The idea of dark matter in the form of primordial black holes has seen a recent revival triggered by the LIGO detection of gravitational waves from binary black hole mergers. In this context, it has been argued that a large initial clustering of primordial black holes can help alleviate the strong constraints on this scenario. In this work, we show that, on the contrary, with large initial clustering the problem is exacerbated and constraints on primordial black hole dark matter become overwhelmingly strong.

• Bringmann, Torsten & Pospelov, Maxim (2019). Novel Direct Detection Constraints on Light Dark Matter. Physical Review Letters. ISSN 0031-9007. 122(17), s. 1–6. doi: 10.1103/PhysRevLett.122.171801. Fulltekst i vitenarkiv Vis sammendrag

  All attempts to directly detect particle dark matter (DM) scattering on nuclei suffer from the partial or total loss of sensitivity for DM masses in the GeV range or below. We derive novel constraints from the inevitable existence of a subdominant, but highly energetic, component of DM generated through collisions with cosmic rays. Subsequent scattering inside conventional DM detectors, as well as neutrino detectors sensitive to nuclear recoils, limits the DM-nucleon scattering cross section to be below 10 − 31     cm 2 for both spin-independent and spin-dependent scattering of light DM.

• Bose, Sownak; Vogelsberger, Mark; Zavala, Jesús; Pfrommer, Christoph; Cyr-Racine, Francis-Yan & Bohr, Sebastian [Vis alle 7 forfattere av denne artikkelen] (2019). ETHOS – an Effective Theory of Structure Formation: detecting dark matter interactions through the Lyman-α forest. Monthly Notices of the Royal Astronomical Society: Letters (MNRAS Letters). ISSN 1745-3925. 487(1), s. 522–536. doi: 10.1093/mnras/stz1276. Fulltekst i vitenarkiv Vis sammendrag

  We perform a series of cosmological hydrodynamic simulations to investigate the effects of non-gravitational dark matter (DM) interactions on the intergalactic medium (IGM). In particular, we use the ETHOS framework to compare statistics of the Lyman-α forest in cold dark matter (CDM) with an alternative model in which the DM couples strongly with a relativistic species in the early universe. These models are characterized by a cut-off in the linear power spectrum, followed by a series of ‘dark acoustic oscillations’ (DAOs) on sub-dwarf scales. While the primordial cut-off delays the formation of the first galaxies, structure builds up more rapidly in the interacting DM model compared to CDM. We show that although DAOs are quickly washed away in the non-linear clustering of DM at z ≲ 10, their signature can be imprinted prominently in the Lyman-α flux power spectrum at z > 5. On scales larger than the cut-off (k ∼ 0.08 s km−1 for the specific model considered here), the relative difference to CDM is reminiscent of a warm dark matter (WDM) model with a similar initial cut-off; however, the redshift evolution on smaller scales is distinctly different. The appearance and disappearance of DAOs in the Lyman-α flux spectrum provides a powerful way to distinguish interacting DM models from WDM and, indeed, variations in the thermal history of the IGM that may also induce a small-scale cut-off.

• Bringmann, Torsten; Kahlhoefer, Felix; Schmidt-Hoberg, Kai & Walia, Parampreet Singh (2018). Converting nonrelativistic dark matter to radiation. Physical Review D. ISSN 2470-0010. 98(2), s. 1–22. doi: 10.1103/PhysRevD.98.023543. Fulltekst i vitenarkiv Vis sammendrag

  Dark matter in the cosmological concordance model is parametrized by a single number, describing the covariantly conserved energy density of a nonrelativistic fluid. Here we test this assumption in a model-independent and conservative way by considering the possibility that, at any point during the cosmological evolution, dark matter may be converted into a noninteracting form of radiation. This scenario encompasses, but is more general than, the cases where dark matter decays or annihilates into these states. We show that observations of the cosmic microwave background allow us to strongly constrain this scenario for any conversion time after big bang nucleosynthesis. We discuss in detail, both from a Bayesian and frequentist point of view, in which sense adding large-scale structure observations may even provide a certain preference for a conversion of dark matter to radiation at late times. Finally we apply our general results to a specific particle physics realization of such a scenario, featuring late kinetic decoupling and Sommerfeld-enhanced dark matter annihilation. We identify a small part of parameter space that both mitigates the tension between cosmic microwave and large-scale structure data and allows for velocity-dependent dark matter self-interactions strong enough to address the small-scale problems of structure formation.

• Bondarenko, Kyrylo; Boyarsky, Alexey; Bringmann, Torsten & Sokolenko, Anastasia (2018). Constraining self-interacting dark matter with scaling laws of observed halo surface densities. Journal of Cosmology and Astroparticle Physics (JCAP). 2018(4), s. 1–27. doi: 10.1088/1475-7516/2018/04/049. Fulltekst i vitenarkiv Vis sammendrag

  The observed surface densities of dark matter halos are known to follow a simple scaling law, ranging from dwarf galaxies to galaxy clusters, with a weak dependence on their virial mass. Here we point out that this can not only be used to provide a method to determine the standard relation between halo mass and concentration, but also to use large samples of objects in order to place constraints on dark matter self-interactions that can be more robust than constraints derived from individual objects. We demonstrate our method by considering a sample of about 50 objects distributed across the whole halo mass range, and by modelling the effect of self-interactions in a way similar to what has been previously done in the literature. Using additional input from simulations then results in a constraint on the self-interaction cross section per unit dark matter mass of about σ/mχlesssim 0.3 cm2/g. We expect that these constraints can be significantly improved in the future, and made more robust, by i) an improved modelling of the effect of self-interactions, both theoretical and by comparison with simulations, ii) taking into account a larger sample of objects and iii) by reducing the currently still relatively large uncertainties that we conservatively assign to the surface densities of individual objects. The latter can be achieved in particular by using kinematic observations to directly constrain the average halo mass inside a given radius, rather than fitting the data to a pre-selected profile and then reconstruct the mass. For a velocity-independent cross-section, our current result is formally already somewhat smaller than the range 0.5−5 cm2/g that has been invoked to explain potential inconsistencies between small-scale observations and expectations in the standard collisionless cold dark matter paradigm.

• Sokolenko, Anastasia; Bondarenko, Kyrylo; Brinckmann, Thejs; Zavala, Jesús; Vogelsberger, Mark & Bringmann, Torsten [Vis alle 7 forfattere av denne artikkelen] (2018). Towards an improved model of self-interacting dark matter haloes. Journal of Cosmology and Astroparticle Physics (JCAP). 2018:039(12), s. 1–32. doi: 10.1088/1475-7516/2018/12/038. Fulltekst i vitenarkiv Vis sammendrag

  We discuss the relation between the strength of the self-interaction ofdark matter particles and the predicted properties of the inner density distributionsof dark matter haloes. We present the results ofN-body simulations for 28 galaxycluster sized haloes performed with the same initial conditions for cold dark matterand for self-interacting dark matter with cross-sections ranging from 0.1 to 10 cm2/g.We provide a simple phenomenological description of these results and compare themto the semi-analytical model typically used in the literature. We find that some of theassumptions made in this model are not satisfied in the simulations. We identify thereasons for this disagreement and improve the semi-analytical model correspondingly.We discuss how simulation results can be properly compared with observations and inparticular how quantities like the core radius and the inner dark matter surface densitydepend on the self-interaction cross-section.

• Angelis, Alessandro De; Tatischeff, Vincent; Grenier, Isabelle A.; McEnery, Julie E.; Mallamaci, Manuela & Tavani, Marco [Vis alle 51 forfattere av denne artikkelen] (2018). Science with e-ASTROGAM: A space mission for MeV–GeV gamma-ray astrophysics. Journal of High Energy Astrophysics. ISSN 2214-4048. 19, s. 1–106. doi: 10.1016/j.jheap.2018.07.001. Fulltekst i vitenarkiv
• Bringmann, Torsten; Edsjo, Torsten; Gondolo, Paolo; Ullio, Piero & Bergström, Lars (2018). DarkSUSY 6: An advanced tool to compute dark matter properties numerically. Journal of Cosmology and Astroparticle Physics (JCAP). 2018(7), s. 1–55. doi: 10.1088/1475-7516/2018/07/033. Fulltekst i vitenarkiv Vis sammendrag

  The nature of dark matter remains one of the key science questions. Weakly Interacting Massive Particles (WIMPs) are among the best motivated particle physics candidates, allowing to explain the measured dark matter density by employing standard big-bang thermodynamics. Examples include the lightest supersymmetric particle, though many alternative particles have been suggested as a solution to the dark matter puzzle. We introduce here a radically new version of the widely used DarkSUSY package, which allows to compute the properties of such dark matter particles numerically. With DarkSUSY 6 one can accurately predict a large variety of astrophysical signals from dark matter, such as direct detection rates in low-background counting experiments and indirect detection signals through antiprotons, antideuterons, gamma rays and positrons from the Galactic halo, or high-energy neutrinos from the center of the Earth or of the Sun. For thermally produced dark matter like WIMPs, high-precision tools are provided for the computation of the relic density in the Universe today, as well as for the size of the smallest dark matter protohalos. Furthermore, the code allows to calculate dark matter self-interaction rates, which may affect the distribution of dark matter at small cosmological scales. Compared to earlier versions, DarkSUSY 6 introduces many significant physics improvements and extensions. The most fundamental new feature of this release, however, is that the code has been completely re-organized and brought into a highly modular and flexible shape. Switching between different pre-implemented dark matter candidates has thus become straight-forward, just as adding new—WIMP or non-WIMP—particle models or replacing any given functionality in a fully user-specified way. In this article, we describe the physics behind the computer package, along with the main structure and philosophy of this major revision of DarkSUSY. A detailed manual is provided together with the public release at www.darksusy.org.

• Bringmann, Torsten; Kahlhoefer, Felix; Schmidt-Hoberg, Kai & Walia, Parampreet Singh (2017). Strong Constraints on Self-Interacting Dark Matter with Light Mediators. Physical Review Letters. ISSN 0031-9007. 118(14). doi: 10.1103/PhysRevLett.118.141802. Fulltekst i vitenarkiv
• Athron, Peter; Balázs, Csaba; Bringmann, Torsten; Buckley, Andy; Chrząszcz, Martin & Conrad, Jan [Vis alle 31 forfattere av denne artikkelen] (2017). GAMBIT: The Global and Modular Beyond-the-Standard-Model Inference Tool. European Physical Journal C. ISSN 1434-6044. 77(11), s. 784–784. doi: 10.1140/epjc/s10052-017-5321-8. Fulltekst i vitenarkiv Vis sammendrag

  We describe the open-source global fitting package GAMBIT: the Global And Modular Beyond-the-Standard-Model Inference Tool. GAMBIT combines extensive calculations of observables and likelihoods in particle and astroparticle physics with a hierarchical model database, advanced tools for automatically building analyses of essentially any model, a flexible and powerful system for interfacing to external codes, a suite of different statistical methods and parameter scanning algorithms, and a host of other utilities designed to make scans faster, safer and more easily-extendible than in the past. Here we give a detailed description of the framework, its design and motivation, and the current models and other specific components presently implemented in GAMBIT. Accompanying papers deal with individual modules and present first GAMBIT results. GAMBIT can be downloaded from gambit.hepforge.org

• Athron, Peter; Balázs, Csaba; Bringmann, Torsten; Buckley, Andy; Chrząszcz, Marcin & Conrad, Jan [Vis alle 26 forfattere av denne artikkelen] (2017). Status of the scalar singlet dark matter model. European Physical Journal C. ISSN 1434-6044. 77(8), s. 568–568. doi: 10.1140/epjc/s10052-017-5113-1. Fulltekst i vitenarkiv Vis sammendrag

  One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a Z2 symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above ∼ 1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.

• Athron, Peter; Balázs, Csaba; Bringmann, Torsten; Buckley, Andy; Chrząszcz, Marcin & Conrad, Jan [Vis alle 24 forfattere av denne artikkelen] (2017). A global fit of the MSSM with GAMBIT. European Physical Journal C. ISSN 1434-6044. 77(12), s. 879–879. doi: 10.1140/epjc/s10052-017-5196-8. Fulltekst i vitenarkiv Vis sammendrag

  We study the seven-dimensional Minimal Supersymmetric Standard Model (MSSM7) with the new GAMBIT software framework, with all parameters defined at the weak scale. Our analysis significantly extends previous weak-scale, phenomenological MSSM fits, by adding more and newer experimental analyses, improving the accuracy and detail of theoretical predictions, including dominant uncertainties from the Standard Model, the Galactic dark matter halo and the quark content of the nucleon, and employing novel and highly-efficient statistical sampling methods to scan the parameter space. We find regions of the MSSM7 that exhibit co-annihilation of neutralinos with charginos, stops and sbottoms, as well as models that undergo resonant annihilation via both light and heavy Higgs funnels. We find high-likelihood models with light charginos, stops and sbottoms that have the potential to be within the future reach of the LHC. Large parts of our preferred parameter regions will also be accessible to the next generation of direct and indirect dark matter searches, making prospects for discovery in the near future rather good.

• Bringmann, Torsten; Conrad, Jan; Cornell, Jonathan M.; Dal, Lars Andreas; Edsjö, Joakim & Farmer, Ben [Vis alle 14 forfattere av denne artikkelen] (2017). DarkBit: A GAMBIT module for computing dark matter observables and likelihoods. European Physical Journal C. ISSN 1434-6044. 77(12), s. 831–831. doi: 10.1140/epjc/s10052-017-5155-4. Fulltekst i vitenarkiv Vis sammendrag

  We introduce DarkBit, an advanced software code for computing dark matter constraints on various extensions to the Standard Model of particle physics, comprising both new native code and interfaces to external packages. This release includes a dedicated signal yield calculator for gamma-ray observations, which significantly extends current tools by implementing a cascade-decay Monte Carlo, as well as a dedicated likelihood calculator for current and future experiments (gamLike). This provides a general solution for studying complex particle physics models that predict dark matter annihilation to a multitude of final states. We also supply a direct detection package that models a large range of direct detection experiments (DDCalc), and that provides the corresponding likelihoods for arbitrary combinations of spin-independent and spin-dependent scattering processes. Finally, we provide custom relic density routines along with interfaces to DarkSUSY, micrOMEGAs, and the neutrino telescope likelihood package nulike. DarkBit is written in the framework of the Global And Modular Beyond the Standard Model Inference Tool (GAMBIT), providing seamless integration into a comprehensive statistical fitting framework that allows users to explore new models with both particle and astrophysics constraints, and a consistent treatment of systematic uncertainties. In this paper we describe its main functionality, provide a guide to getting started quickly, and show illustrative examples for results obtained with DarkBit (both as a stand-alone tool and as a GAMBIT module). This includes a quantitative comparison between two of the main dark matter codes (DarkSUSY and micrOMEGAs), and application of DarkBit ’s advanced direct and indirect detection routines to a simple effective dark matter model.

• Bringmann, Torsten; Calore, Francesca; Galea, Ahmad & Garny, Mathias (2017). Electroweak and Higgs boson internal bremsstrahlung. General considerations for Majorana dark matter annihilation and application to MSSM neutralinos. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2017(9). doi: 10.1007/JHEP09(2017)041. Fulltekst i vitenarkiv
• Athron, Peter; Balázs, Csaba; Bringmann, Torsten; Buckley, Andy; Chrząszcz, Marcin & Conrad, Jan [Vis alle 25 forfattere av denne artikkelen] (2017). Global fits of GUT-scale SUSY models with GAMBIT. European Physical Journal C. ISSN 1434-6044. 77(12), s. 824–824. doi: 10.1140/epjc/s10052-017-5167-0. Fulltekst i vitenarkiv Vis sammendrag

  We present the most comprehensive global fits to date of three supersymmetric models motivated by grand unification: the constrained minimal supersymmetric standard model (CMSSM), and its Non-Universal Higgs Mass generalisations NUHM1 and NUHM2. We include likelihoods from a number of direct and indirect dark matter searches, a large collection of electroweak precision and flavour observables, direct searches for supersymmetry at LEP and Runs I and II of the LHC, and constraints from Higgs observables. Our analysis improves on existing results not only in terms of the number of included observables, but also in the level of detail with which we treat them, our sampling techniques for scanning the parameter space, and our treatment of nuisance parameters. We show that stau co-annihilation is now ruled out in the CMSSM at more than 95% confidence. Stop co-annihilation turns out to be one of the most promising mechanisms for achieving an appropriate relic density of dark matter in all three models, whilst avoiding all other constraints. We find high-likelihood regions of parameter space featuring light stops and charginos, making them potentially detectable in the near future at the LHC. We also show that tonne-scale direct detection will play a largely complementary role, probing large parts of the remaining viable parameter space, including essentially all models with multi-TeV neutralinos.

• Binder, Tobias; Bringmann, Torsten; Gustafsson, Michael & Hryczuk, Andrzej Jan (2017). Early kinetic decoupling of dark matter: when the standard way of calculating the thermal relic density fails. Physical Review D. ISSN 2470-0010. 96(11), s. 1–15. doi: 10.1103/PhysRevD.96.115010. Fulltekst i vitenarkiv
• Bringmann, Torsten; Galea, Ahmad; Hryczuk, Andrzej Jan & Weniger, Christoph (2017). Novel Spectral Features in MeV Gamma Rays from Dark Matter. Physical Review D. ISSN 2470-0010. 95(4). doi: 10.1103/PhysRevD.95.043002. Fulltekst i vitenarkiv
• Vogelsberger, Mark; Zavala, Jesús; Cyr-Racine, Francis-Yan; Pfrommer, Christoph; Bringmann, Torsten & Sigurdson, Kris (2016). ETHOS - an effective theory of structure formation: Dark matter physics as a possible explanation of the small-scale CDM problems. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 460(2), s. 1399–1416. doi: 10.1093/mnras/stw1076. Fulltekst i vitenarkiv
• Bringmann, Torsten; Ihle, Håvard Tveit; Kersten, Jörn Andreas & Walia, Parampreet Singh (2016). Suppressing structure formation at dwarf galaxy scales and below: Late kinetic decoupling as a compelling alternative to warm dark matter. Physical Review D. ISSN 1550-7998. 94(10). doi: 10.1103/PhysRevD.94.103529. Fulltekst i vitenarkiv
• Bringmann, Torsten; Galea, Ahmad & Walia, Parampreet Singh (2016). Leading QCD corrections for indirect dark matter searches: A fresh look. Physical Review D. ISSN 1550-7998. 93(4). doi: 10.1103/PhysRevD.93.043529. Fulltekst i vitenarkiv
• Carr, John; Balasz, Csaba; Bringmann, Torsten; Buanes, Trygve; Daniel, M & Doro, M [Vis alle 23 forfattere av denne artikkelen] (2016). Prospects for Indirect Dark Matter Searches with the Cherenkov Telescope Array (CTA). Proceedings of Science (PoS). ICRC2015. doi: 10.22323/1.236.1203. Fulltekst i vitenarkiv
• Aslanyan, Grigor; Price, Layne C; Adams, Jenni; Bringmann, Torsten; Clark, Hamish A & Easther, Richard [Vis alle 8 forfattere av denne artikkelen] (2016). Ultracompact Minihalos as Probes of Inflationary Cosmology. Physical Review Letters. ISSN 0031-9007. 117(14). doi: 10.1103/PhysRevLett.117.141102. Fulltekst i vitenarkiv
• Cyr-Racine, Francis-Yan; Sigurdson, Kris; Zavala, Jesús; Bringmann, Torsten; Vogelsberger, Mark & Pfrommer, Christoph (2016). ETHOS - An effective theory of structure formation: From dark particle physics to the matter distribution of the Universe. Physical Review D. ISSN 1550-7998. 93:123527(12). doi: 10.1103/PhysRevD.93.123527. Fulltekst i vitenarkiv
• Carr, John; Balázs, Csaba; Bringmann, Torsten; Buanes, Trygve; Daniel, Michael K. & Doro, Michelle [Vis alle 23 forfattere av denne artikkelen] (2015). Prospects for indirect dark matter searches with the cherenkov telescope array (CTA). Proceedings of Science (PoS). 30-July-2015. Fulltekst i vitenarkiv
• Bringmann, Torsten; Vollmann, Martin & Weniger, Christoph (2014). Updated cosmic-ray and radio constraints on light dark matter: Implications for the GeV gamma-ray excess at the Galactic Center. Physical Review D. ISSN 1550-7998. 90(12). doi: 10.1103/PhysRevD.90.123001. Fulltekst i vitenarkiv
• Bringmann, Torsten; Hasenkamp, Jasper & Kersten, Jörn (2014). Tight bonds between sterile neutrinos and dark matter. Journal of Cosmology and Astroparticle Physics (JCAP). 2014(7). doi: 10.1088/1475-7516/2014/07/042. Fulltekst i vitenarkiv
• Bringmann, Torsten; Calore, Francesca; Mauro, Mattia Di & Donato, Fiorenza (2014). Constraining dark matter annihilation with the isotropic γ -ray background: Updated limits and future potential. Physical Review D. ISSN 1550-7998. 89(2). doi: 10.1103/PhysRevD.89.023012. Fulltekst i vitenarkiv
• Bringmann, Torsten & Calore, Francesca (2014). Significant enhancement of neutralino dark matter annihilation from electroweak bremsstrahlung. Physical Review Letters. ISSN 0031-9007. 112(7). doi: 10.1103/PhysRevLett.112.071301. Fulltekst i vitenarkiv
• Arina, Chiara; Bringmann, Torsten; Silk, Joseph & Vollmann, Martin (2014). Enhanced line signals from annihilating Kaluza-Klein dark matter. Physical Review D. ISSN 1550-7998. 90(8). doi: 10.1103/PhysRevD.90.083506. Fulltekst i vitenarkiv

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• Krichevskiy, Daniil; Kolesova, Helena; Melkild, Halvor; Bringmann, Torsten & Pomper, Joachim (2026). Beyond 3→2: Towards Realistic SIMP Dark Matter. Fulltekst i vitenarkiv Vis sammendrag

  Strongly interacting dark sectors with pseudo–Nambu–Goldstone bosons provide a versatile framework for sub-GeV dark matter. While the original SIMP paradigm emphasises number-changing 3 to 2 processes as the origin of the relic abundance, the phenomenology of pionic dark matter is considerably richer. Depending on the spectrum and couplings, the relic density can instead be controlled by 2 to 2 annihilations (WIMP-like regime), semi-annihilation channels involving vector mesons and further processes like \pi\pi\pi to \pi\rho. A consistent treatment therefore requires a framework that simultaneously captures pion dynamics, vector mesons, anomalous interactions, and portal effects. We consider QCD-like dark sectors in which the dark matter candidates are pions stabilized by unbroken dark flavor symmetries. The effective theory is formulated using the Hidden Local Symmetry (HLS) approach. The HLS Lagrangian, supplemented by the gauged Wess–Zumino–Witten term, is constructed in a representation-independent manner and is applicable to complex, real, and pseudo-real fermion theories. As a minimal benchmark, we focus on the pseudo-real symmetry-breaking pattern SU(2N_f)/Sp(2N_f) with Nf=2. We incorporate lattice results for Sp(N_c=4) to obtain realistic relations between m_\pi/f_\pi and m_\rho/m_\pi. A dark photon portal is included to maintain thermal equilibrium with the visible sector and to assess its impact on relic abundance and dark matter stability within the HLS framework.

• Melkild, Halvor; Bringmann, Torsten & Brekke, Anton Andreas (2026). Charged Sterile Neutrinos as Dark Matter. doi: https:/indico2.uis.no/event/64/contributions/2002/. Fulltekst i vitenarkiv
• Melkild, Halvor; Bringmann, Torsten & Brekke, Anton Andreas (2026). Charged Sterile Neutrinos as Dark Matter. Fulltekst i vitenarkiv
• Melkild, Halvor; Krichevskiy, Daniil; Kolesova, Helena & Bringmann, Torsten (2026). Beyond 3→2: Towards Realistic SIMP Dark Matter. Fulltekst i vitenarkiv
• Melkild, Halvor; Krichevskiy, Daniil; Kolesova, Helena & Bringmann, Torsten (2026). Beyond 3→2: Towards Realistic SIMP Dark Matter. Fulltekst i vitenarkiv
• Bringmann, Torsten (2026). Dark matter and gravitational wave signals from a phase transition in the early universe. Fulltekst i vitenarkiv Vis sammendrag

  A strong first-order phase transition offers the intriguing possibility of explaining the stochastic gravitational wave background at nHz frequencies. In order to avoid cosmological constraints, such a phase transition must have occurred in a dark sector with non-negligible couplings to the standard model - opening promising avenues of connecting the gravitational wave signal to the cosmological dark matter abundance. In order to illustrate this, I will consider a classically conformal dark sector with a U(1) gauge symmetry. The spontaneous breaking of this symmetry generates both gravitational waves and sources the mass of a fermionic sub-GeV dark matter candidate. Contact with the standard model is established through kinetic mixing of the U(1) gauge bosons with ordinary photons, a possibility that is actively being searched for at various collider experiments. I will discuss the rich phenomenology of such a scenario, demonstrating that it can successfully generate both the observed nHz gravitational wave background and the cosmological dark matter abundance, while at the same time avoiding all current constraints.

• Bringmann, Torsten (2026). New directions in secluded dark matter searches. Fulltekst i vitenarkiv Vis sammendrag

  Less than 20% of the total matter content of the universe consists of known forms of matter. After decades of experimental efforts, the leading hypothesis for the missing part - namely a new type of weakly interacting massive particle - is starting to become seriously pressured. As a result, the true nature of dark matter is more elusive now than ever. I will start with a pedagogic reminder of the most convincing pieces of evidence that we have for the existence of dark matter. I will then highlight new model building avenues that may explain why traditional searches have, so far, failed to see any signals. In fact, I will argue that it might well be generally impossible to directly detect or produce any dark matter particles in the laboratory - but that cosmological and astrophysical observations still have the potential to conclusively pinpoint some of their microscopic properties.

• Bringmann, Torsten (2026). Dark matter and gravitational wave signals from a phase transition in the early universe. Fulltekst i vitenarkiv Vis sammendrag

  A strong first-order phase transition offers the intriguing possibility of explaining the stochastic gravitational wave background at nHz frequencies. In order to avoid cosmological constraints, such a phase transition must have occurred in a dark sector with non-negligible couplings to the standard model -- opening promising avenues of connecting the gravitational wave signal to the cosmological dark matter abundance. In order to illustrate this, I will consider a classically conformal dark sector with a U(1) gauge symmetry. The spontaneous breaking of this symmetry generates both gravitational waves and sources the mass of a fermionic sub-GeV dark matter candidate. Contact with the standard model is established through kinetic mixing of the U(1) gauge bosons with ordinary photons, a possibility that is actively being searched for at various collider experiments. I will discuss the rich phenomenology of such a scenario, demonstrating that it can successfully generate both the observed nHz gravitational wave background and the cosmological dark matter abundance, while at the same time avoiding all current constraints. If time allows, I will further contemplate about what a future gravitational wave signal observed by LISA may tell us about dark matter production in the early universe.

• Bringmann, Torsten (2025). First-order phase transitions and stochastic gravitational wave background. Fulltekst i vitenarkiv
• Bringmann, Torsten (2025). The (un)reasonable elusiveness of dark matter. Fulltekst i vitenarkiv Vis sammendrag

  Only about 15% of the total matter content of the universe consists of known forms of matter. After decades of experimental efforts, the leading hypothesis for the missing part - namely a new type of weakly interacting massive particle - is starting to become seriously pressured. As a result, the true nature of dark matter is more elusive now than ever. In this talk, I will start with a pedagogic review of some of the most convincing pieces of evidence that we currently have for the existence of dark matter. I will then highlight new model building avenues that may explain why traditional searches have, so far, failed to see any signals. In fact, I will argue that it might well be generally impossible to directly detect or produce any dark matter particles in the laboratory - but that cosmological observations still have the potential to conclusively pinpoint some of their properties.

• Melkild, Halvor; Bringmann, Torsten; Krichevskiy, Daniil; Kolesova, Helena & Pomper, Joachim (2025). Towards realistic SIMP dark matter. Fulltekst i vitenarkiv Vis sammendrag

  The so-called "strongly interacting massive particles" (SIMPs) refer to a class of dark matter candidates with the relic abundance set by the 3\to2 interactions which allows for dark matter with sub-GeV masses, not yet strongly constrained by direct detection experiments. Interestingly, SIMP dark matter features relatively strong self-interactions that may explain the small-scale structure puzzles. We investigate the realisation of SIMP models where dark pions form dark matter, protected from decay by dark flavour symmetries. We observe that the relic abundance of the dark pions depends sensitively on the masses of heavier states present in dark QCD-like scenarios such as dark vector mesons. We improve on existing results by using recent lattice simulations connecting the masses of dark pions and vector mesons. Furthermore, a portal between dark and visible sectors is usually assumed to maintain thermal equilibrium. To obtain fully realistic results, we explicitly add the dark photon portal and study its effect on dark matter relic abundance and stability.

• Tranberg, Anders; Bringmann, Torsten & Ravanis, Julia (2024). Wonderful World: Dark Matter (moderator). Fulltekst i vitenarkiv
• Bringmann, Torsten & Hofmann, Stefan (2016). Thermal decoupling of WIMPs from first principles. Journal of Cosmology and Astroparticle Physics (JCAP). 1603. doi: 10.1088/1475-7516/2016/03/E02. Fulltekst i vitenarkiv
• Bringmann, Torsten & Pfrommer, Christoph (2013). Bringmann and Pfrommer Reply. Physical Review Letters. ISSN 0031-9007. 111(19). doi: 10.1103/PhysRevLett.111.199002. Fulltekst i vitenarkiv

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