Structure formation in a $\Lambda$ $viscous$ CDM universe

TL;DR

This paper explores a viscous dark matter model within a $b3$CDM universe, showing that viscosity can address small-scale issues and affect structure formation, with constraints derived from observational data.

Contribution

It introduces a $b3$CDM model with viscous dark matter, analyzing its impact on structure formation and providing bounds on dark matter viscosity.

Findings

Viscous dark matter reduces small-scale structure problems.

The linear power spectrum is altered by viscosity effects.

An upper bound on dark matter viscosity is established.

Abstract

The possibility of dark matter being a dissipative component represents an option for the standard view where cold dark matter (CDM) particles behave on large scales as an ideal fluid. By including a physical mechanism to the dark matter description like viscosity we construct a more realistic model for the universe. Also, the known small scale pathologies of the standard CDM model either disappear or become less severe. We study clustering properties of a $\Lambda$CDM-like model in which dark matter is described as a bulk viscous fluid. The linear power spectrum, the nonlinear spherical "top hat" collapse and the mass functions are presented. We use the analysis with such structure formation tools in order to place an upper bound on the magnitude of the dark matter's viscosity.