Gravitational waves from low-scale cosmic strings without scaling

TL;DR

This paper investigates how particle decay processes affect the gravitational wave spectrum from low-scale cosmic strings in non-scaling scenarios, providing analytical conditions for spectral cutoffs and comparing with numerical results.

Contribution

It introduces analytical conditions for the cutoff frequency in GW spectra from cosmic strings in nonscaling regimes, extending previous scaling model analyses.

Findings

Analytical expressions for cutoff frequency in nonscaling models

Conditions for the existence of a spectral cutoff

Comparison of analytical estimates with numerical spectra

Abstract

Cosmic strings are predicted in many extensions of the Standard Model and constitute a plausible source of gravitational waves (GWs) from the early Universe. In a previous article arXiv:2405.10937v2, we pointed out that the GW spectrum from a population of string loops in the scaling regime can exhibit a sharp cutoff frequency associated with the fundamental oscillation mode of string loops. In this paper, we study the effect of particle decay due to kink-kink collisions and cusps on the GW spectrum in the nonscaling scenario introduced in Ref. arXiv:1911.12066. We find analytical conditions for the existence of a cutoff frequency in the fundamental spectrum and provide expressions for this frequency. In large regions of parameter space, our results in the nonscaling model turn out to be identical to those in the scaling model. Finally, we demonstrate how the spectrum changes when transitioning from the regime with a cutoff frequency to the regime without a cutoff frequency. Our analytical estimates are validated at qualitatively different benchmark points by comparing them with numerical spectra.