Cosmic viscosity as a remedy for tension between PLANCK and LSS data

TL;DR

Introducing viscosity into cold dark matter models can reconcile discrepancies between Planck CMB data and large scale structure observations regarding key cosmological parameters.

Contribution

This paper demonstrates that small but non-zero viscosity in cold dark matter can simultaneously resolve tensions in $\sigma_8$, $H_0$, and $\Omega_m$ between different cosmological data sets.

Findings

Viscosity in cold dark matter can reconcile Planck and LSS data.

Small non-zero viscosity is preferred by observational data.

Viscosity helps resolve multiple cosmological parameter tensions.

Abstract

Measurements of $\sigma_8$ from large scale structure observations show a discordance with the extrapolated $\sigma_8$ from Planck CMB parameters using $\Lambda$CDM cosmology. Similar discordance is found in the value of $H_0$ and $\Omega_m$. In this paper, we show that the presence of viscosity in cold dark matter, shear or bulk or combination of both, can remove the above mentioned conflicts simultaneously. This indicates that the data from Planck CMB observation and different LSS observations prefer small but non-zero amount of viscosity in cold dark matter fluid.