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Implications of the $S_8$ tension for decaying dark matter with warm decay products
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abstract
Recent weak lensing surveys have revealed that the direct measurement of the parameter combination $S_8\equiv\sigma_8(\Omega_m/0.3)^{0.5}$ -- where $\sigma_8$ is a measure of the amplitude of matter fluctuations on 8 $h^{-1}$Mpc scales -- is $\sim3\sigma$ discrepant with the value reconstructed from cosmic microwave background (CMB) data assuming the $\Lambda$CDM model. In this article, we show that it is possible to resolve the tension if dark matter (DM) decays with a lifetime of $\Gamma^{-1} \simeq 55 \ \text{Gyrs}$ into one massless and one massive product, and transfers a fraction $\varepsilon\simeq 0.7 \ \%$ of its rest mass energy to the massless component. The velocity-kick received by the massive daughter leads to a suppression of gravitational clustering below its free-streaming length, thereby reducing the $\sigma_8$ value as compared to that inferred from the standard $\Lambda$CDM model, in a similar fashion to massive neutrino and standard warm DM. Contrarily to the latter scenarios, the time-dependence of the power suppression and the free-streaming scale allows the 2-body decaying DM scenario to accommodate CMB, baryon acoustic oscillation, growth factor and un-calibrated supernova Ia data. We briefly discuss implications for DM model building, galactic small-scale structure problems and the recent Xenon-1T excess. Future experiments measuring the growth factor to high accuracy at $0\lesssim z\lesssim1$ can further test this scenario.
Forward citations
Cited by 7 Pith papers
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Cosmological evolution with decaying dark matter: an integral-equation approach
CLASSIER-DDM evaluates generic two-body decaying dark matter perturbations via iterative integral equations at O(0.1%) accuracy and O(1 min) cost without a Boltzmann hierarchy or fluid approximation.
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Decaying Dark Matter Halo Abundance from a Revised Spherical Collapse Model
A mass-dependent collapse threshold from a revised spherical collapse model predicts the decaying-dark-matter halo mass function, matching N-body simulations at z≈1 and for mild kicks at z=0.
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Neutrino mass limits and decaying dark matter: background evolution versus perturbations
Decaying dark matter can hide neutrino mass from expansion-history data, but CMB lensing unmasks it and restores ∑mν ≲ 0.079 eV.
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Interpreting the Hubble tension with a cascade decaying dark matter sector
A cascade decaying dark matter model combining early and late effects still cannot reduce the Hubble tension below about 3 sigma, and is statistically disfavored relative to Lambda CDM.
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CLASSIER computes cosmological perturbation spectra with non-cold relics using iterated integral equations and non-uniform fast Fourier transforms, matching a converged Boltzmann hierarchy to <0.01% in the matter powe...
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A frequentist view on the two-body decaying dark matter model
A frequentist reanalysis of Planck and KiDS-1000 data shows that a two-body decaying dark matter model can produce S8 values consistent with weak lensing surveys, and that prior choices dominated earlier Bayesian exclusions.
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Sign Switching in Dark Sector Coupling Interactions as a Candidate for Resolving Cosmological Tensions
A sign-switching dark-sector coupling, fitted to CMB, DESI BAO, and supernova data, can simultaneously raise H0 and lower S8, but the preference over LambdaCDM depends on using SH0ES-calibrated supernovae.
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