Evolution of gravitational waves through the cosmological QCD transition

TL;DR

This paper investigates how the spectrum of inflation-produced gravitational waves is altered during the QCD transition, considering both first-order and crossover scenarios, and calculates the transfer function for these effects.

Contribution

It provides the first detailed calculation of the transfer function for gravitational wave spectra during the QCD transition, including both first-order and crossover cases.

Findings

QCD transition causes steps in the gravitational wave spectrum

Transfer function depends on the nature of the transition

Results applicable to future gravitational wave observations

Abstract

The spectrum of gravitational waves that have been produced in inflation is modified during cosmological transitions. Large drops in the number of relativistic particles, like during the QCD transition or at $e^+e^-$ annihilation, lead to steps in the spectrum of gravitational waves. We calculate the transfer function for the differential energy density of gravitational waves for a first-order and for a crossover QCD transition.