Decaying dark matter and the tension in $\sigma_8$

TL;DR

This paper investigates whether decaying dark matter can resolve discrepancies between CMB and weak lensing measurements of matter fluctuations, using simulations and data analysis to explore its viability.

Contribution

It develops an accurate non-linear matter power spectrum fitting formula for DDM and compares cosmological parameter overlaps, providing new constraints on dark matter decay rates.

Findings

Increased overlap of parameter posteriors with DDM model

Lower bound on dark matter lifetime: ≥97 Gyr at 95% C.L.

Current data insufficient to confirm non-zero decay rate

Abstract

We consider decaying dark matter (DDM) as a resolution to the possible tension between cosmic microwave background (CMB) and weak lensing (WL) based determinations of the amplitude of matter fluctuations, $\sigma_8$. We perform N-body simulations in a model where dark matter decays into dark radiation and develop an accurate fitting formula for the non-linear matter power spectrum, which enables us to test the DDM model by the combined measurements of CMB, WL and the baryon acoustic oscillation (BAO). We employ a Markov chain Monte Carlo analysis to examine the overlap of posterior distributions of the cosmological parameters, comparing CMB alone with WL+BAO. We find an overlap that is significantly larger in the DDM model than in the standard CDM model. This may be hinting at DDM, although current data is not constraining enough to unambiguously favour a non-zero dark matter decay rate $\Gamma$. From the combined CMB+WL data, we obtain a lower bound $\Gamma^{-1}\ge 97$ Gyr at 95 % C.L, which is less tight than the constraint from CMB alone.