Gravitational Waves from Current-Carrying Cosmic Strings

Article
Report number	arXiv:2207.03510 ; CERN-TH-2022-116 ; FERMILAB-PUB-22-508-T ; MS-TP-22-19 ; NUHEP-TH/22-07
Title	Gravitational Waves from Current-Carrying Cosmic Strings
Author(s)	Auclair, Pierre (Louvain U.) ; Blasi, Simone (Brussels U., IIHE) ; Brdar, Vedran (Fermilab ; Northwestern U.) ; Schmitz, Kai (Munster U. ; CERN)
Publication	2023-04-06
Imprint	2022-07-07
Number of pages	18
Note	18 pages, 7 figures, 2 tables, matches published version
In:	JCAP 2304 (2023) pp.009
DOI	10.1088/1475-7516/2023/04/009 (publication)
Subject category	hep-ph ; Particle Physics - Phenomenology ; astro-ph.CO ; Astrophysics and Astronomy
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.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2023-2024 IOP Publishing Ltd and Sissa Medialab

$Benchmark GW spectra emitted by current-carrying cosmic strings. For spectra (A), (C), (E), we assume a cosmic-string tension of $G\mu=0.5\times 10^{-10}$, while for spectra (B) and (E), we assume $G\mu=0.5\times 10^{-17}$. In scenarios (A) and (B), the current flowing on cosmic strings decays around the time of the QCD crossover, while in scenarios (C) and (D), it decays around the time of the electroweak crossover. In scenario (E), the current decays at even earlier times (see text for details). For each scenario, the lower and upper edges of the predicted spectrum respectively correspond to $k=1$ and $k=10^6$ harmonic string modes accounted for in the computation of the GW spectrum. We also show standard (\ie, no current) spectra for string networks with $G\mu=0.5\times 10^{-10}$ and $G\mu=0.5\times 10^{-17}$ (black lines), together with existing constraints and future sensitivities of present and planned GW experiments~\cite{Schmitz:2020syl}. All spectra for $G\mu=0.5\times 10^{-10}$ can explain the PTA signal at nHz frequencies.$ $Streamlines derived from the autonomous system of ordinary differential equations \eqref{eq:autonomous-alpha}, \eqref{eq:autonomous-v} and \eqref{eq:autonomous-y} for $\tilde{c}=0.23$ and $\nu=1/2$. All the trajectories start from the plane $\alpha = 0.27$ and eventually fall into one of the two different attractors, one at $Y=0$ and another one at $Y\sim 1$.$ $Two-dimensional slices of \cref{fig:streamtube} around the $Y\sim 1$ attractor.$ Show more plots

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Záznam vytvorený 2022-07-12, zmenený 2023-11-24

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