Exploring the Self Interacting Dark Matter Properties From Low Redshift Observations

TL;DR

This paper investigates the properties of self-interacting dark matter (SIDM) using kinetic theory, deriving new constraints on its cross section and mass, and explores how SIDM viscosity influences cosmic evolution at low redshift.

Contribution

It introduces a novel approach to constrain SIDM properties using the KSS bound and studies the impact of SIDM viscosity on late-time cosmic observations.

Findings

KSS bound constrains SIDM particle mass to be sub-GeV.

SIDM viscosity increases at low redshift, affecting cosmic dissipation.

Viscous SIDM aligns with low redshift observations and standard cosmology.

Abstract

The small scale observations indicate that the dark matter may be self-interacting. In this paper, we calculate the shear ($\eta$) and bulk viscosity ($\zeta$) of Self Interacting Dark Matter (SIDM) fluid, in kinetic theory formalism. Further, using the KSS bound on $\eta/\mathfrak{s}$, we derive a new upper limit on the ratio of dark matter self interaction cross section to its mass, $ \sigma/m $. Then, using the $ \sigma/m $ constraint, we show that KSS bound allows only sub-GeV mass of SIDM particle. Further, with the assumption of a power-law form of $\eta$ and $\zeta$, we study its evolution in the light of low redshift observations. We find that at the large redshift, the SIDM viscosity is small but at the small redshift it becomes sufficiently large and contributes significantly in cosmic dissipation. As a consequence, viscous SIDM can explain the low redshift observations and also consistent with the standard cosmological prediction.