Non-adiabatic perturbations in multi-component perfect fluids

TL;DR

This paper investigates the evolution of non-adiabatic perturbations in multi-component perfect fluids with energy transfer, introducing symmetric quantities to better understand their dynamics and gauge-invariant equations.

Contribution

It introduces a new set of symmetric quantities to analyze non-adiabatic perturbations and derives gauge-invariant equations for models with energy transfer.

Findings

Derived gauge-invariant equations for non-adiabatic pressure perturbations.

Analyzed the evolution of these perturbations in specific models.

Provided insights into the dynamics of multi-component fluid perturbations.

Abstract

The evolution of non-adiabatic perturbations in models with multiple coupled perfect fluids with non-adiabatic sound speed is considered. Instead of splitting the entropy perturbation into relative and intrinsic parts, we introduce a set of symmetric quantities, which also govern the non-adiabatic pressure perturbation in models with energy transfer. We write the gauge invariant equations for the variables that determine on a large scale the non-adiabatic pressure perturbation and the rate of changes of the comoving curvature perturbation. The analysis of evolution of the non-adiabatic pressure perturbation has been made for several particular models.