Ultra-high frequency gravitational waves from cosmic strings with friction

TL;DR

This paper investigates how frictional forces between cosmic strings and background plasma influence the ultra-high frequency gravitational wave spectrum, revealing a potential secondary peak that encodes early universe physics.

Contribution

It introduces the effect of friction into gravitational wave calculations from cosmic strings, predicting a distinctive secondary peak in the spectrum.

Findings

Friction causes partial suppression of gravitational wave emission.

Intense loop production in the early Kibble regime enhances the friction signature.

A secondary peak in the ultra-high frequency spectrum indicates friction effects.

Abstract

We include the effect of the frictional force caused by interactions between cosmic strings and the particles of the background plasma in the computation of the stochastic gravitational wave background generated by cosmic string loops. Although our results show that friction leads to a partial suppression of the emission of gravitational radiation by cosmic string loops, we also find that loop production is very intense in the early stages of the Kibble regime. We show that, in many instances, this leads to a prominent signature of friction in the ultra-high frequency range of the spectrum, in the form of a secondary peak. The signature of friction is not only sensitive to cosmic string properties, but also to the initial conditions of the network and its surroundings. A detection of this signature would then allow us to extract information about the physics of the early universe that cannot be uncovered when probing the rest of the stochastic gravitational wave background spectrum.