String Gas Cosmology and Structure Formation - A Brief Review

TL;DR

String gas cosmology proposes that thermal fluctuations of a string gas can produce a scale-invariant spectrum of cosmological perturbations without inflation, with distinctive predictions for gravitational wave spectra.

Contribution

This review highlights how string gas cosmology can generate scale-invariant fluctuations and discusses specific cosmological backgrounds where this mechanism applies.

Findings

Thermal fluctuations of string gas can produce scale-invariant spectra.

The model predicts a small red tilt for density perturbations.

It predicts a small blue tilt for gravitational waves.

Abstract

For suitable cosmological backgrounds, thermal fluctuations of a gas of strings can generate a scale-invariant spectrum of cosmological fluctuations without requiring a phase of inflationary expansion. We highlight the key points of this mechanism, and discuss cosmological backgrounds in which this scenario can be realized. The spectrum of cosmological perturbations has a small red tilt (like in scalar field-driven inflation) but (unlike in inflation) there is a small blue tilt of the spectrum of gravitational waves.