Mirror QCD phase transition as the origin of the nanohertz Stochastic Gravitational-Wave Background.

• DOI: 10.48550/arxiv.2306.16769
• Publication Date: 2024-03-01
• Authors: Zu, Lei; Zhang, Chi; Li, Yao-Yu; Gu, Yu-Chao; Tsai, Yue-Lin Sming; Fan, Yi-Zhong
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology; Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); FOS: Physical sciences; Astrophysics - High Energy Astrophysical Phenomena; Astrophysics - Cosmology and Nongalactic Astrophysics

7 pages, 4 figures<br/>Several Pulsar Timing Array (PTA) collaborations have recently provided strong evidence for a nHz Stochastic Gravitational-Wave Background (SGWB). Here we investigate the implications of a first-order phase transition occurring within the early universe's dark quantum chromodynamics (dQCD) epoch, specifically within the framework of the mirror twin Higgs dark sector model. Our analysis indicates a distinguishable SGWB signal originating from this phase transition, which can explain the measurements obtained by PTAs. Remarkably, a significant portion of the parameter space for the SGWB signal also effectively resolves the existing tensions in both the $H_0$ and $S_8$ measurements in Cosmology. This intriguing correlation suggests a possible common origin of these three phenomena for $0.2 < ΔN_{\rm eff} < 0.5$, where the mirror dark matter component constitutes about $30\%$ of the total dark matter abundance. Next generation CMB experiment such as CMB-S4 is able to test this parameter region.<br/>