Thermal Metastable Strings in One-Scale Models and Gravitational Waves
Abstract
Metastable cosmic strings provide a cosmological interpretation of the nanohertz stochastic gravitational wave background reported by Pulsar Timing Array (PTA) experiments. We revisit this scenario in a minimal dark-sector gauge theory, in which a complex Higgs doublet breaks SU(2)×U(1)→U(1)IR at a single symmetry-breaking scale. This one-scale setup predicts metastable Z-strings whose endpoints are monopole-like defects, and whose zero-temperature decay rate is controlled by the gauge couplings and mass ratios. We show that, once the string-forming transition occurs in a thermal plasma, the dominant decay channel is not the zero-temperature monopole nucleation but thermally induced nucleation on the string worldsheet. We determine the nucleation temperature Tnuc, which we \rev{adopt as the reference string-formation scale}, from the one-loop finite-temperature effective potential with daisy resummation, and use it to evaluate the worldsheet bounce action throughout the model parameter space. \rev{Requiring a PTA-compatible gravitational wave} signal selects a narrow region in the model parameter space, in the (sin2θw,√β) plane, where θw is the dark-sector weak mixing angle and β≡ MΦ2/MZ2 is the squared Higgs-to-Z mass ratio. Thermal effects modify the zero-temperature picture significantly, shifting the PTA-compatible region towards lower values of the dark fine-structure constant α' and larger values of the monopole-to-string-tension ratio κ.
Related
- Gravitational Wave Background from Metastable Current-Carrying Cosmic Strings
- Gravitational Waves and Nambu-Goldstone Bosons from Infrared-Finite Cosmic Strings
- Enhancing Gravitational Waves from Global Strings via a First-Order Phase Transition
- Interpretation of Nanohertz Gravitational Waves via Cosmic Strings in Post-BBN Matter and Kination Domination
- Primordial Black Hole Abundances and Scalar Induced Gravitational Waves from Finite-Width Power Spectra in a Stiff Thermal History
BibTeX
@misc{giorgi2026thermal,
title = {{Thermal Metastable Strings in One-Scale Models and Gravitational Waves}},
author = {Arturo de Giorgi and James Ingoldby and Valentin V. Khoze and Jessica Turner},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.02689},
eprint = {2606.02689},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.02689},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Thermal Metastable Strings in One-Scale Models and Gravitational Waves
AU - Arturo de Giorgi
AU - James Ingoldby
AU - Valentin V. Khoze
AU - Jessica Turner
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2606.02689
UR - https://arxiv.org/abs/2606.02689
AB - Metastable cosmic strings provide a cosmological interpretation of the nanohertz stochastic gravitational wave background reported by Pulsar Timing Array (PTA) experiments. We revisit this scenario in a minimal dark-sector gauge theory, in which a complex Higgs doublet breaks SU(2)×U(1)→U(1)_IR at a single symmetry-breaking scale. This one-scale setup predicts metastable Z-strings whose endpoints are monopole-like defects, and whose zero-temperature decay rate is controlled by the gauge couplings and mass ratios. We show that, once the string-forming transition occurs in a thermal plasma, the dominant decay channel is not the zero-temperature monopole nucleation but thermally induced nucleation on the string worldsheet. We determine the nucleation temperature T_nuc, which we \rev{adopt as the reference string-formation scale}, from the one-loop finite-temperature effective potential with daisy resummation, and use it to evaluate the worldsheet bounce action throughout the model parameter space. \rev{Requiring a PTA-compatible gravitational wave} signal selects a narrow region in the model parameter space, in the (sin^2θ_w,√β) plane, where θ_w is the dark-sector weak mixing angle and β≡ M_Φ^2/M_Z^2 is the squared Higgs-to-Z mass ratio. Thermal effects modify the zero-temperature picture significantly, shifting the PTA-compatible region towards lower values of the dark fine-structure constant α' and larger values of the monopole-to-string-tension ratio κ.
ER -