Speaker
Description
Pulsar timing arrays reported strong evidence for a stochastic gravitational-wave background whose peak frequency corresponds to the Hubble scale at a temperature of O(100) MeV in the early Universe, redshifted to the present. Such a signal had already been predicted in the QCD-induced little inflation scenario proposed by Boeckel and Schaffner-Bielich in 2009. In this talk, I revisit this scenario and argue that the amount of supercooling required to dilute the baryon number density is inconsistent with our current understanding of the critical endpoint of the QCD phase diagram. I then introduce the chiral density wave (CDW) phase, a hypothetical phase at high baryon density, and show that it can provide sufficient dilution. The reheating temperature after the transition from the CDW phase to the hadronic phase, however, is expected to be far below the BBN temperature, and we therefore conclude that the PTA signal cannot be explained by Standard Model QCD even in the presence of a large baryon density.