Gravitational Waves from Current-Carrying Cosmic Strings

TL;DR

This paper models the gravitational wave spectrum emitted by current-carrying cosmic strings using an extended VOS model, revealing an enhanced GW signal due to string currents, with implications for future GW detection efforts.

Contribution

It introduces a generalized VOS model that accounts for internal currents in cosmic strings, providing more realistic GW predictions compared to minimal models.

Findings

Enhanced GW signal across a broad frequency range due to string currents

Temporary growth in cosmic-string energy density affects GW spectrum

Implications for GW experiments in Hz to MHz band

Abstract

Cosmic strings are predicted by many Standard Model extensions involving the cosmological breaking of a symmetry with nontrivial first homotopy group and represent a potential source of primordial gravitational waves (GWs). Present efforts to model the GW signal from cosmic strings are often based on minimal models, such as, eg, the Nambu--Goto action that describes cosmic strings as exactly one-dimensional objects without any internal structure. In order to arrive at more realistic predictions, it is therefore necessary to consider nonminimal models that make an attempt at accounting for the microscopic properties of cosmic strings. With this goal in mind, we derive in this paper the GW spectrum emitted by current-carrying cosmic strings (CCCSs), which may form in a variety of cosmological scenarios. Our analysis is based on a generalized version of the velocity-dependent one-scale (VOS) model, which, in addition to the mean velocity and correlation length of the string network, also describes the evolution of a chiral (light-like) current. As we are able to show, the solutions of the VOS equations imply a temporarily growing fractional cosmic-string energy density, $\Omega_{\rm cs}$. This results in an enhanced GW signal across a broad frequency interval, whose boundaries are determined by the times of generation and decay of cosmic-string currents. Our findings have important implications for GW experiments in the Hz to MHz band and motivate the construction of realistic particle physics models that give rise to large currents on cosmic strings.