Graviton production in non-inflationary cosmology

TL;DR

This paper analyzes graviton production during early Universe transitions, showing standard models produce negligible gravitons and deriving formulas to constrain alternative early expansion histories.

Contribution

It provides detailed calculations of graviton generation during radiation to matter transition and introduces a general formula to assess early matter-dominated eras.

Findings

Standard radiation/matter transition produces negligible gravitons

Derived a formula to modify initial graviton spectra due to early matter domination

Constraints on early Universe expansion laws based on graviton production

Abstract

We discuss the creation of massless particles in a Universe, which transits from a radiation-dominated era to any other expansion law. We calculate in detail the generation of gravitons during the transition to a matter dominated era. We show that the resulting gravitons generated in the standard radiation/matter transition are negligible. We use our result to constrain one or more previous matter dominated era, or any other expansion law, which may have taken place in the early Universe. We also derive a general formula for the modification of a generic initial graviton spectrum by an early matter dominated era.