Degenerate Fermi gas perturbations at standard background cosmology

TL;DR

This paper investigates how a tiny fraction of the universe modeled as a degenerate Fermi gas influences cosmological perturbations across different background regimes, providing analytical tools for early universe structure formation.

Contribution

It introduces analytical expressions for perturbations of a degenerate Fermi gas in various cosmological backgrounds, extending previous models to include matter and dark energy dominated eras.

Findings

Derived explicit formulas for density fluctuations, velocity divergence, and shear stress.

Analyzed perturbation evolution in radiation, matter, and $ mf extLambda$CDM backgrounds.

Provided insights into large structure formation involving degenerate Fermi gas.

Abstract

The hypothesis of a tiny fraction of the cosmic inventory evolving cosmologically as a degenerate Fermi gas test fluid at some dominant cosmological background is investigated. Our analytical results allow for performing preliminary computations to the evolution of perturbations for relativistic and non-relativistic test fluids. The density fluctuation, $\delta$, the fluid velocity divergence, $\theta$, and an explicit expression for the dynamics of the shear stress, $\sigma$, are obtained for a degenerate Fermi gas in the background regime of radiation. Extensions to the dominance of matter and to the $\Lambda$CDM cosmological background are also investigated and lessons concerning the formation of large structures of degenerate Fermi gas are depicted.