Suppression of large-scale perturbations by stiff solid

TL;DR

This paper investigates how a stiff solid component in the early universe can suppress large-scale scalar perturbations, emphasizing the importance of radiation dominance before recombination to match observed CMB spectra.

Contribution

It introduces the effect of stiff solid dominance on large-scale perturbations and quantifies the suppression, highlighting conditions to avoid overly steep CMB spectra.

Findings

Large-scale perturbations can be suppressed by several orders of magnitude.

Radiation dominance before recombination is necessary to match CMB observations.

Stiff solid presence affects the evolution of scalar perturbations.

Abstract

Evolution of large-scale scalar perturbations in the presence of stiff solid (solid with pressure to energy density ratio > 1/3) is studied. If the solid dominated the dynamics of the universe long enough, the perturbations could end up suppressed by as much as several orders of magnitude. To avoid too steep large-angle power spectrum of CMB, radiation must have prevailed over the solid long enough before recombination.