Implications of the S8 tension for decaying dark matter with warm decay products

Abellán, Guillermo F.;Murgia, Riccardo;Poulin, Vivian;Lavalle, Julien

2022-01-01

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Abstract

Recent weak-lensing surveys have revealed that the direct measurement of the parameter combination S-8 equivalent to 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 similar to 3 sigma discrepant with the value reconstructed from cosmic microwave background (CMB) data assuming the Lambda-cold dark matter (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) similar or equal to 55 Gyrs into one massless and one massive product, and transfers a fraction epsilon similar or equal to 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 uncalibrated 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 less than or similar to z less than or similar to 1 can further test this scenario.