Perturbations with bulk viscosity in modified chaplygin gas cosmology

TL;DR

This paper studies how bulk viscosity in a modified chaplygin gas model affects cosmological perturbations and large-scale structure formation, revealing differences from the standard Lambda-CDM model.

Contribution

It introduces a covariant and gauge-invariant framework for analyzing viscous modified chaplygin gas perturbations and compares their evolution to Lambda-CDM.

Findings

Energy overdensity contrast decays with redshift.

Viscous effects cause significant deviations from Lambda-CDM predictions.

Perturbations differ notably when viscosity is included.

Abstract

In the present work, we investigate cosmological perturbations of viscous modified chaplygin gas model. Using 1 + 3 covariant formalism, we define covariant and gauge invariant gradient variables, which after the application of scalar decomposition and harmonic decomposition techniques together with redshift transformation method, provide the energy overdensity perturbation equations in redshift space, responsible for large scale structure formation. In order to analyse the effect of the viscous modified chaplygin gas model on matter overdensity contrast, we numerically solve the perturbation equations in both long and short wavelength limits. The numerical results show that the energy overdensity contrast decays with redshift. However, the perturbations which include amplitude effects due to the viscous modified chaplygin model do differ remarkably from those in the {\Lambda}CDM. In the absence of viscous modified chaplygin model, the results reduce to those of {\Lambda}CDM.