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1. Atomic dark matter, interacting dark radiation, and the Hubble tension

   https://doi.org/10.1007/JHEP07(2025)084  

   Buen-Abad, Manuel A; Chacko, Zackaria; Flood, Ina; Kilic, Can; Marques-Tavares, Gustavo; Youn, Taewook (July 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> We present a new class of interacting dark sector models that can address the Hubble tension. Interacting dark radiation (DR) has previously been put forward as a solution to the problem, but this proposal is disfavored by the high-ℓcosmic microwave background (CMB) data. We modify this basic framework by introducing a subcomponent of dark matter (DM) that interacts strongly with the DR, so that together they constitute a tightly coupled fluid at early times. We show that if this subcomponent decouples from the interacting DR during the CMB epoch, theℓmodes of the CMB that entered the horizon before decoupling are impacted differently from those that entered after, allowing a solution to the problem. We present a model that realizes this framework, which we dub “New Atomic Dark Matter”, or nuADaM, in which the interacting dark matter (iDM) subcomponent is composed of dark atoms, and dark “neutrinos” with long-range interactions contribute to the DR, hence the name of the model. This iDM subcomponent is acoustic at early times but decouples from the DR following dark recombination. In contrast to conventional atomic dark matter (ADM) models, the dark photon is part of a richer DR sector, which ensures that it continues to be self-interacting even after recombination. We show that this model admits a significantly larger value ofH₀than ΛCDM when fit to CMB and BAO data, while maintaining a comparable goodness of fit. Once the SHOES data set is included, it provides a significantly better fit than ΛCDM. 

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2. CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations: IV. Testing warm dark matter cosmologies with galaxy scaling relations: A joint simulation–observation study using DREAMS simulations

   https://doi.org/10.1051/0004-6361/202556698  

   Silvestrini, M; Tortora, C; Busillo, V; Brooks, Alyson M; Farahi, A; Garcia, A M; Kallivayalil, N; Napolitano, N R; Rose, J C; Torrey, P; et al (February 2026, Astronomy & Astrophysics)

   Small-scale discrepancies in the standard Lamda cold dark matter paradigm have motivated the exploration of alternative dark matter (DM) models, such as warm dark matter (WDM). In our work, we investigate the constraining power of galaxy scaling relations on cosmological, astrophysical, and WDM parameters using a joint analysis of multiresolution hydrodynamic simulations and observational data. Our study is based on the DREAMS project and combines large-volume uniform-box simulations with high-resolution Milky Way (MW) zoom-in runs exploring a ΛWDM cosmology. To ensure consistency between the different simulation sets, we applied calibrations to account for resolution effects, which allowed us to better exploit the complementary strengths of the two suites. We compared the simulated relations, such as stellar size, DM mass, and fraction, within the stellar half-mass radius and the total-to-stellar mass ratio with two complementary galaxy samples: the Spitzer Photometry and Accurate Rotation Curves catalog, providing resolved kinematics for nearby spirals, and the Local Volume Database catalog, which includes structural and dynamical measurements for dwarf galaxies in the Local Volume. By applying a bootstrap-based fitting procedure, we show that key cosmological parameters (Ω_m,σ₈) and supernova feedback strength can be recovered with good accuracy, particularly from the uniform-box simulations. Although the WDM particle mass remains unconstrained, the MW zoom-in simulations reveal subtle WDM-induced trends, especially at low stellar masses, in the scaling relations of both the DM mass and the total-to-stellar mass ratio within the stellar half-mass radius. Additionally, we find that the galaxy abundance as a function of total stellar mass shows a measurable dependence on WDM particle mass, with a suppression at log₁₀M_*/M_⊙≲ 8 that appears separable from the impact of feedback, suggesting this observable is a valuable complementary probe. Our results highlight the importance of combining simulations at multiple resolutions with diverse observational catalogs to jointly constrain baryonic processes and DM properties. In particular, future low-mass galaxy surveys such as Euclid will play a crucial role in tightening the constraints on alternative DM scenarios through joint structural and statistical analyses. At the same time, higher-resolution simulations will be essential to fully capturing the small-scale features and improving the discriminatory power of such analyses, especially in the context of WDM. 

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3. Dark matter-radiation scattering enhances CMB phase shift through dark matter-loading

   https://doi.org/10.1088/1475-7516/2025/01/058  

   Ghosh, Subhajit; Ho, Daven_Wei Ren; Tsai, Yuhsin (January 2025, Journal of Cosmology and Astroparticle Physics)

   Abstract A phase shift in the acoustic oscillations of cosmic microwave background (CMB) spectra is a characteristic signature for the presence of non-photon radiation propagating differently from photons, even when the radiation couples to the Standard Model particles solely gravitationally. It is well-established that compared to the presence of free-streaming radiation, CMB spectra shift to higherℓ-modes in the presence of self-interacting non-photon radiation such as neutrinos and dark radiation. In this study, we further demonstrate that the scattering of non-photon radiation with dark matter can further amplify this phase shift. We show that when the energy density of the interacting radiation surpasses that of interacting dark matter around matter-radiation equality, the phase shift enhancement is proportional to the interacting dark matter abundance and remains insensitive to the radiation energy density. Given the presence of dark matter-radiation interaction, this additional phase shift emerges as a generic signature of models featuring an interacting dark sector or neutrino-dark matter scattering. Using neutrino-dark matter scattering as an example, we numerically calculate the amplified phase shift and offer an analytical interpretation of the result by modeling photon and neutrino perturbations with coupled harmonic oscillators. This framework also explains the phase shift contrast between self-interacting and free-streaming neutrinos. Fitting models with neutrino-dark matter or dark radiation-dark matter interactions to CMB and large-scale structure data, we validate the presence of the enhanced phase shift, affirmed by the linear dependence observed between the preferred regions of the sound horizon angleθ_sand interacting dark matter abundance. An increasedθ_sand a suppressed matter power spectrum is therefore a generic feature of models containing dark matter scattering with abundant dark radiation. 

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4. Forecasts for Galaxy Formation and Dark Matter Constraints from Dwarf Galaxy Surveys

   https://doi.org/10.3847/1538-4357/ad3bb1  

   Nadler, Ethan O; Gluscevic, Vera; Driskell, Trey; Wechsler, Risa H; Moustakas, Leonidas A; Benson, Andrew; Mao, Yao-Yuan (May 2024, The Astrophysical Journal)

   Abstract The abundance of faint dwarf galaxies is determined by the underlying population of low-mass dark matter (DM) halos and the efficiency of galaxy formation in these systems. Here, we quantify potential galaxy formation and DM constraints from future dwarf satellite galaxy surveys. We generate satellite populations using a suite of Milky Way (MW)–mass cosmological zoom-in simulations and an empirical galaxy–halo connection model, and assess sensitivity to galaxy formation and DM signals when marginalizing over galaxy–halo connection uncertainties. We find that a survey of all satellites around one MW-mass host can constrain a galaxy formation cutoff at peak virial masses of ${\mathcal{M}}_{50}={10}^8{M}_{\odot }$at the 1σlevel; however, a tail toward low ${\mathcal{M}}_{50}$prevents a 2σmeasurement. In this scenario, combining hosts with differing bright satellite abundances significantly reduces uncertainties on ${\mathcal{M}}_{50}$at the 1σlevel, but the 2σtail toward low ${\mathcal{M}}_{50}$persists. We project that observations of one (two) complete satellite populations can constrain warm DM models withm_WDM≈ 10 keV (20 keV). Subhalo mass function (SHMF) suppression can be constrained to ≈70%, 60%, and 50% that in cold dark matter (CDM) at peak virial masses of 10⁸, 10⁹, and 10¹⁰M_⊙, respectively; SHMF enhancement constraints are weaker (≈20, 4, and 2 times that in CDM, respectively) due to galaxy–halo connection degeneracies. These results motivate searches for faint dwarf galaxies beyond the MW and indicate that ongoing missions like Euclid and upcoming facilities including the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope will probe new galaxy formation and DM physics. 

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5. Cosmological constraints from the eBOSS Lyman-α forest using the PRIYA simulations

   https://doi.org/10.1088/1475-7516/2024/07/029  

   Fernandez, MA; Bird, Simeon; Ho, Ming-Feng (July 2024, Journal of Cosmology and Astroparticle Physics)

   Abstract We present new cosmological parameter constraints from the eBOSS Lyman-α forest survey. We use a new theoretical model and likelihood based on the PRIYA simulation suite. PRIYA is the first suite to resolve the Lyman-αforest in a (120 Mpc/h)³volume, using a multi-fidelity emulation technique. We use PRIYA to predict Lyman-αforest observables with ≲ 1% interpolation error over an 11 dimensional (9 simulated, 2 in post-processing) parameter space. We identify an internal tension within the flux power spectrum data. Once the discrepant data is removed, we find the primeval scalar spectral index measured at a pivot scale ofk₀= 0.78 Mpc^-1to ben_P= 1.009^+0.027_-0.018at 68% confidence. This measurement from the Lyman-αforest flux power spectrum alone is in reasonable agreement with Planck, and in tension with earlier eBOSS analyses. The amplitude of matter fluctuations isσ₈= 0.733^+0.026_-0.029at 68% confidence, in agreement with Dark Energy Survey weak lensing measurements and other small-scale structure probes and in tension with CMB measurements from Planck and ACT. The effective optical depth to Lyman-α  photons from our pipeline is in good agreement with earlier high resolution measurements. We find a linear power atz= 3 andk= 0.009 s/km of Δ²_L= 0.302^+0.024_-0.027with a slopen_eff= -2.264^+0.026_-0.018. Our flux power spectrum only chains prefer a low level of heating during helium reionization. When we add IGM temperature data we findn_P= 0.983 ± 0.020 andσ₈= 0.703^+0.023_-0.027. Our chains prefer an early and long helium reionization event, as suggested by measurements from the helium Lyman-αforest. In the near future we will use our pipeline to infer cosmological parameters from the DESI Lyman-α data. 

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