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Constraining Dark Matter -- Dark Radiation interactions with CMB, BAO, and Lyman-$\alpha$
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abstract
Several interesting Dark Matter (DM) models invoke a dark sector leading to two types of relic particles, possibly interacting with each other: non-relativistic DM, and relativistic Dark Radiation (DR). These models have interesting consequences for cosmological observables, and could in principle solve problems like the small-scale cold DM crisis, Hubble tension, and/or low $\sigma_8$ value. Their cosmological behaviour is captured by the ETHOS parametrisation, which includes a DR-DM scattering rate scaling like a power-law of the temperature, $T^n$. Scenarios with $n=0$, $2$, or $4$ can easily be realised in concrete dark sector set-ups. Here we update constraints on these three scenarios using recent CMB, BAO, and high-resolution Lyman-$\alpha$ data. We introduce a new Lyman-$\alpha$ likelihood that is applicable to a wide range of cosmological models with a suppression of the matter power spectrum on small scales. For $n=2$ and $4$, we find that Lyman-$\alpha$ data strengthen the CMB+BAO bounds on the DM-DR interaction rate by many orders of magnitude. However, models offering a possible solution to the missing satellite problem are still compatible with our new bounds. For $n=0$, high-resolution Lyman-$\alpha$ data bring no stronger constraints on the interaction rate than CMB+BAO data, except for extremely small values of the DR density. Using CMB+BAO data and a theory-motivated prior on the minimal density of DR, we find that the $n=0$ model can reduce the Hubble tension from $4.1\sigma$ to $2.7\sigma$, while simultaneously accommodating smaller values of the $\sigma_8$ and $S_8$ parameters hinted by cosmic shear data.
Forward citations
Cited by 7 Pith papers
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The $H_0$ world cup. II. A comprehensive competition between proposed Hubble tension solutions
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21 cm Cosmology Sensitivity to Small-Scale Structure: Warm vs Neutrino-Interacting Dark Matter
21 cm forecasts show HERA can detect νDM interactions down to ~3×10⁻³⁵ cm² (assuming zero modelling error) but cannot distinguish νDM from warm dark matter.
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Interacting Dark Sector (ETHOS $n=0$): Cosmological Constraints from SPT Cluster Abundance with DES and HST Weak Lensing Data
Cluster abundance with weak-lensing masses sets the dark matter-dark radiation temperature ratio to ξ_DR < 0.098 at 95% credibility when combined with CMB and BAO data.
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Running of the spectral index: Reconciling the CMB with the Lyman-$\alpha$ Forest
Combining Planck, ACT, SPT-3G and eBOSS data, the authors report a ~2σ preference for a nonzero second derivative of the primordial spectral index and show that featureful inflationary potentials fit the data better t...
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Simulation-based inference on warm dark matter from HERA forecasts
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