Alternatives to Cosmological Inflation

TL;DR

This paper reviews two alternative early universe cosmology models, string gas cosmology and the matter bounce, discussing their successes and challenges as potential replacements for inflation.

Contribution

It provides a comparative review of two alternative models to inflation, highlighting their conceptual advantages and issues.

Findings

String gas cosmology offers a string theory-based early universe scenario.

The matter bounce model presents an alternative to inflation with distinct predictions.

Both models face specific conceptual and observational challenges.

Abstract

The inflationary paradigm, although very successful phenomenologically, suffers from several conceptual problems which motivate the search for alternative scenarios of early universe cosmology. Here, two possible alternatives will be reviewed. - "string gas cosmology" and the "matter bounce". Their successes and problems will be pointed out.