Structure formation with causal bulk viscosity

TL;DR

This paper investigates how causal bulk viscosity in dark matter influences large-scale structure formation, showing it can either suppress or enhance clustering depending on parameters, using a Newtonian approximation and Israel-Stewart theory.

Contribution

It introduces a third order evolution equation for dark matter density perturbations with causal bulk viscosity, expanding understanding of dissipative effects in structure formation.

Findings

Bulk viscosity can suppress density contrast compared to ΛCDM.

Under certain parameters, bulk viscosity enhances clustering.

The model employs Israel-Stewart theory for causal dissipative processes.

Abstract

Dissipative features of dark matter affect its clustering properties and could lead to observable consequences for the evolution of large--scale structure. We analyse the evolution of cold dark matter density perturbations allowing for the possibility of bulk viscous pressure in a causal dissipative theory. Our analysis employs a Newtonian approximation for cosmological dynamics and the transport properties of bulk viscosity are described by the Israel--Stewart theory. We obtain a third order evolution equation for density perturbations. For some parameter values the density contrast can be suppressed compared to results obtained in the $\Lambda$CDM scenario. For other values causal bulk viscous dark matter can exhibit an enhancement of clustering.