Perturbations of Kantowski-Sachs models

TL;DR

This paper analyzes how small disturbances evolve in Kantowski-Sachs cosmological models with a positive cosmological constant using gauge-invariant covariant methods, covering scalar, vector, and tensor modes.

Contribution

It introduces a harmonic decomposition framework for perturbations in Kantowski-Sachs models, extending previous work to include multiple mode types in a gauge-invariant setting.

Findings

Derived six evolution equations for harmonic coefficients.

Handled scalar, vector, and tensor perturbations without vorticity.

Provided a comprehensive covariant approach for anisotropic cosmologies.

Abstract

Perturbations of Kantowski-Sachs models with a positive cosmological constant are considered in a harmonic decomposition, in the framework of gauge invariant 1+3 and 1+1+2 covariant splits of spacetime. Scalar, vector and tensor modes are allowed, however they remain vorticity-free and of perfect fluid type. The dynamics is encompassed in six evolution equations for six harmonic coefficients.