Magnetization of fluid phonons and large-scale curvature perturbations

TL;DR

This paper derives a gauge-invariant framework for analyzing fluid phonons and curvature perturbations in magnetized cosmological backgrounds, revealing how initial conditions influence large-scale structure during radiation domination.

Contribution

It introduces a coupled differential equation system for magnetized fluid perturbations and provides a general solution depending on five initial parameters.

Findings

The gauge-invariant description captures anisotropic stress and entropic fluctuations.

Large-scale curvature perturbations depend on five initial data points.

The framework applies to the radiation-dominated era of the universe.

Abstract

The quasinormal mode of a gravitating and magnetized fluid in a spatially flat, isotropic and homogeneous cosmological background is derived in the presence of the fluid sources of anisotropic stress and of the entropic fluctuations of the plasma. The obtained gauge-invariant description involves a system of two coupled differential equations whose physical content is analyzed in all the most relevant situations. The Cauchy problem of large-scale curvature perturbations during the radiation dominated stage of expansion can be neatly formulated and its general solution is shown to depend on five initial data assigned when the relevant physical wavelengths are larger than the particle horizon. The consequences of this approach are explored.