Can Cold Phase Transitions Explain Gravitational Wave Signals?
Info:
| Author | Chih-Ting Lu Associate Professor |
|---|---|
| Affiliation | Nanjing Normal University |
| Time | 2024-09-12 14:00 |
| Location | Purple Mountain Observatory 2-411 Meeting Room |
| Presentation materials | Can_Cold_Phase_Transitions_Explain_Gravitational_Wave_Signals.pdf |
Abstract:
Recent reports from several pulsar timing array collaborations have provided evidence for a stochastic gravitational wave background (SGWB) at nanohertz frequencies. While the SGWB may originate from the mergers of supermassive black holes, it could also be indicative of new physics near the 100 MeV energy scale. A first-order phase transition (FOPT) that ends around the 100 MeV scale is an intriguing explanation, as it could link nanohertz signals with new physics associated with the electroweak scale or higher. However, our research indicates that generating nanohertz signals from cold phase transitions is not straightforward due to two critical issues that may rule out many proposed explanations.
Firstly, we demonstrate that FOPT cannot complete at the required transition temperature near 100 MeV. This overcooling implies a prolonged period dominated by a false vacuum state, which hinders bubble nucleation and the completion of the phase transition. Secondly, we show that even without needing to complete or bypass this constraint, the universe generally reheats to any scale that drives FOPT. The hierarchical structure between the transition temperature and the reheating temperature complicates the calculation of the SGWB spectrum.