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arXiv · 2603.07739

Impact of chirality imbalance and nonlocal interactions on the QCD biased axionic domainwall interpretation of NANOGrav 15 year data

Ruotong Zhao·Zhao Zhang
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Abstract

We investigate the influence of the chirality imbalance with local CP-breaking in hot QCD on the generation of a stochastic gravitational wave background (SGWB) sourced by the axion-like particle (ALP) domain-wall annihilation, induced by the QCD bias. Such a bias is quantified by the QCD topological susceptibility $χ_t$, and its dependence on the $θ$ angle and the chiral chemical potential $μ_5$ is investigated at temperatures near the QCD scale within a nonlocal Nambu-Jona-Lasinio (NJL) model. We find that, besides the small-$θ$ range, the axionic domain-wall interpretation of NANOGrav 15-year data on the nHz gravitational waves is still possible for a certain large-$θ$ range if $μ_5$ is large enough. We confirm that the peak of $|χ_t|$ at the critical temperature $T_c$ for the CP restoration at $θ=π$ exhibits a pronounced width compared to the local NJL result. Thus, for $θ$ at and around $π$, the QCD bias near $T_c$ can also produce a GW signal strength compatible with the NANOGrav 15-year data.

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Ruotong Zhao, Zhao Zhang. 2026-03-08. Impact of chirality imbalance and nonlocal interactions on the QCD biased axionic domainwall interpretation of NANOGrav 15 year data. https://arxiv.org/abs/2603.07739

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