Implications of the S8 tension for decaying dark matter with warm decay products
Abstract
Recent weak lensing surveys have revealed that the direct measurement of the parameter combination S8σ8(m/0.3)0.5 -- where σ8 is a measure of the amplitude of matter fluctuations on 8 h-1Mpc scales -- is 3σ discrepant with the value reconstructed from cosmic microwave background (CMB) data assuming the model. In this article, we show that it is possible to resolve the tension if dark matter (DM) decays with a lifetime of -1 55 \ Gyrs into one massless and one massive product, and transfers a fraction 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 σ8 value as compared to that inferred from the standard 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 z1 can further test this scenario.