Glimpsing Physics of Nano-Hz Gravitational Waves in Neutrinos from Core-Collapse Supernovae

Abstract

The growing evidence for nano-hertz gravitational waves, from NANOGrav and other observations, may be pointing to a cosmological first-order phase transition at temperatures of $\mathcal{O}(10-100)\;\mathrm{MeV}$. Such an interpretation requires dynamics beyond the Standard Model in this energy range. If so, it may well be the case that core-collapse supernova explosions would recreate the first-order phase transition leaving a unique imprint on the spectrum of neutrinos emitted in the initial few seconds. This scenario is also suggestive of a low-mass seesaw mechanism to explain neutrino masses. We outline the prospects for future observations of Galactic supernovae to uncover the signals of this scenario, which could get further confirmation with additional pulsar timing array data establishing the primordial origin of the observed nano-hertz gravitational waves.

Figures (2)

• Figure 1: The temperature ($T_\mathrm{BSM}$) after the all six neutrino flavors, two sterile neutrinos at $m_R=100$ MeV, and scalar equilibration as a function of the SM CCSN temperature ($T_\mathrm{SM}$) and chemical potential of electron neutrinos ($\mu_{\nu_e}$). The black star depicts a representative value for the conditions just after the core bounce in SM CCSN core. Note that the final temperature $T_\mathrm{BSM}$ achieved by the equilibration of the massive scalars with neutrinos will be reduced once the scalars undergo the FOPT.
• Figure 2: The expected flux fraction, or flavor ratio, of any of the neutrino signals from the $\phi$ field at the Earth after undergoing the MSW effect. In addition, the $\nu/\bar{\nu}$ ratio should be one. The left panel shows the normal ordering (NO) and the constraint from cosmology Planck:2018vyg in gray, the right panel shows the inverted ordering (IO) which is nominally disfavored by cosmology while oscillation data remain unclear.