Interpretation of Nanohertz Gravitational Waves via Cosmic Strings in Post-BBN Matter and Kination Domination
Abstract
Recent pulsar timing array (PTA) observations have reported evidence for a common low frequency signal consistent with a stochastic gravitational wave background. In this work, we investigate the cosmic string interpretation of this signal in a non-standard cosmological history between big bang nucleosynthesis and recombination, featuring an early matter-dominated era followed by a kination phase. Previous studies have shown that kination can significantly modify the cosmic-string-induced gravitational wave spectrum, generating characteristic features in the nanohertz range and producing a shape consistent with current PTA data. Building on this, we perform separate Bayesian analyses of the NANOGrav 15-year and EPTA DR2 New+ datasets to quantify the extent to which such a cosmological history is favored by the data. We find substantial evidence for a transient period of matter and kination domination over the standard cosmological history within a cosmic-string interpretation of the gravitational-wave signal, with a Bayes factor 3.63+0.22−0.21 from the NANOGrav 15-year dataset, while leaving the inferred cosmic-string tension nearly unchanged. This cosmic-string-dominated scenario is particularly relevant if the contribution from supermassive black hole binaries (SMBHBs) is small, as hinted at by astrophysical population simulations. Compared with a scenario where gravitational waves are produced purely by SMBHBs, cosmic-string interpretations with and without an additional contribution from SMBHBs, across both expansion histories and datasets, reveal no significant preference.
Related
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BibTeX
@misc{co2026interpretation,
title = {{Interpretation of Nanohertz Gravitational Waves via Cosmic Strings in Post-BBN Matter and Kination Domination}},
author = {Raymond T. Co and Siu Cheung Lam and Taegyu Lee},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.10674},
eprint = {2610.10674},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.10674},
}
RIS
TY - UNPB
TI - Interpretation of Nanohertz Gravitational Waves via Cosmic Strings in Post-BBN Matter and Kination Domination
AU - Raymond T. Co
AU - Siu Cheung Lam
AU - Taegyu Lee
PY - 2026
DA - 2026/10/07
PB - arXiv
DO - 10.48550/arxiv.2610.10674
UR - https://arxiv.org/abs/2610.10674
AB - Recent pulsar timing array (PTA) observations have reported evidence for a common low frequency signal consistent with a stochastic gravitational wave background. In this work, we investigate the cosmic string interpretation of this signal in a non-standard cosmological history between big bang nucleosynthesis and recombination, featuring an early matter-dominated era followed by a kination phase. Previous studies have shown that kination can significantly modify the cosmic-string-induced gravitational wave spectrum, generating characteristic features in the nanohertz range and producing a shape consistent with current PTA data. Building on this, we perform separate Bayesian analyses of the NANOGrav 15-year and EPTA DR2 New+ datasets to quantify the extent to which such a cosmological history is favored by the data. We find substantial evidence for a transient period of matter and kination domination over the standard cosmological history within a cosmic-string interpretation of the gravitational-wave signal, with a Bayes factor 3.63^+0.22_−0.21 from the NANOGrav 15-year dataset, while leaving the inferred cosmic-string tension nearly unchanged. This cosmic-string-dominated scenario is particularly relevant if the contribution from supermassive black hole binaries (SMBHBs) is small, as hinted at by astrophysical population simulations. Compared with a scenario where gravitational waves are produced purely by SMBHBs, cosmic-string interpretations with and without an additional contribution from SMBHBs, across both expansion histories and datasets, reveal no significant preference.
ER -