Constraining Viscous Dark Matter in light of CMB Spectral Distortion

TL;DR

This paper investigates how viscous dark matter interactions could cause spectral distortions in the CMB, using observational limits to constrain the properties of such dark matter.

Contribution

It introduces a novel approach to constrain viscous dark matter properties through CMB spectral distortion analysis, considering non-standard baryon-dark matter interactions.

Findings

PIXIE bounds significantly limit viscous dark matter parameters.

Viscous dark matter can induce measurable CMB spectral distortions.

Constraints improve understanding of dark matter-baryon interactions.

Abstract

We calculate the $\mu$- and \textit{y}-type spectral distortions of Cosmic Microwave Background (CMB), taking a non-standard interaction between baryons and viscous dark matter. Using the CMB spectral distortion observations, we can constrain any exotic mechanism that may change the energy of the CMB photon, leading to a CMB spectrum distortion. Depending on the viscosity of dark matter, the energy transfer between dark matter and baryons may modify, leading to a modification in CMB distortion. The existing Cosmic Background Explorer (COBE)/FIRAS and the Primordial Inflation Explorer (PIXIE) set limits on \textit{y} and $\mu$ types of distortions to $y = 1.5\times10^{-5}$, $\mu = 9.0\times10^{-5}$ and $y = 10^{-8}$, $\mu = 5.0\times10^{-8}$, respectively. In this paper, we discuss the pre-recombination contributions to $\mu$ and \textit{y}-type distortions by viscous dark matter and constrain the parameter space using PIXIE bounds on spectral distortion.