Have pulsar timing arrays detected the hot big bang: Gravitational waves from strong first order phase transitions in the early Universe

The origins of matter and radiation in the universe lie a hot big bang. We present number well-motivated cosmologies which bang occurs through strong first-order phase transition---either at end inflation, after period kination (``kination-induced bang''), or second vacuum domination early Universe (``supercooled bang''); we also propose ``dark bang'' where only dark is created transition much inflation. In all these scenarios, resulting gravitational can explain tentative signals reported by NANOGrav, Parkes, European Pulsar Timing Array experiments if reheating temperature bang, correspondingly energy scale false vacuum, falls range ${T}_{*}\ensuremath{\sim}{\ensuremath{\rho}}_{\mathrm{vac}}^{1/4}=\mathrm{MeV}--100\text{ }\mathrm{GeV}$. All same models higher temperatures will be interest to upcoming ground- space-based interferometer searches for waves larger frequency.