Speedy sound and cosmic structure

TL;DR

This paper explores how an increased early Universe sound speed could generate scale-invariant density fluctuations without traditional horizon problem solutions, providing mathematical models and discussing their broader implications.

Contribution

It introduces a novel mechanism for generating density fluctuations via high sound speed, supported by detailed mathematical solutions and various model realizations.

Findings

High early Universe sound speed can produce scale-invariant spectra

Mathematical solutions demonstrate the mechanism's feasibility

Models based on scalar fields and hydrodynamics realize the concept

Abstract

If the speed of sound were vastly larger in the early Universe a near scale-invariant spectrum of density fluctuations could have been produced even if the Universe did not submit to conventional solutions to the horizon problem. We examine how the mechanism works, presenting full mathematical solutions and their heuristics. We then discuss several concrete models based on scalar fields and hydrodynamical matter which realize this mechanism, but stress that the proposed mechanism is more fundamental and general.