Squeezing Cosmological Phase Transitions with International Pulsar Timing Array

Understand

A first-order MeV-scale cosmological phase transition (PT) can generate a peak in the power spectrum of stochastic gravitational wave background around nanohertz frequencies.

• With the recent International Pulsar Timing Array data release two covering nanohertz frequencies, we search for such a phase transition signal.
• For the standard 4-parameter PT model, we obtain the PT temperature $T_\star\in$ [66 MeV, 30 GeV], which indicates that dark or QCD phase transitions occurring below 66 MeV have been ruled out at $2\,\sigma$ confidence level.
• This constraint is much tighter than $T_\star\sim$ [1 MeV, 100 GeV] from NANOGrav.