Unconventional Cosmology

TL;DR

This paper reviews two alternative cosmological models, the matter bounce and emergent scenarios, comparing them to inflation and showing they can produce similar scale-invariant perturbation spectra.

Contribution

It introduces and compares two non-inflationary cosmological paradigms, highlighting their potential to generate scale-invariant spectra.

Findings

Both models produce approximately scale-invariant perturbation spectra

They offer viable alternatives to inflationary cosmology

Comparison shows similarities and differences with inflation

Abstract

I review two cosmological paradigms which are alternative to the current inflationary scenario. The first alternative is the "matter bounce", a non-singular bouncing cosmology with a matter-dominated phase of contraction. The second is an "emergent" scenario, which can be implemented in the context of "string gas cosmology". I will compare these scenarios with the inflationary one and demonstrate that all three lead to an approximately scale-invariant spectrum of cosmological perturbations.