Gravitational wave complementarity and impact of NANOGrav data on gravitational leptogenesis: cosmic strings

Abstract

In seesaw mechanism, if right handed (RH) neutrino masses are generated dynamically by a gauged $U(1)$ symmetry breaking, a stochastic gravitational wave background (SGWB) sourced by a cosmic string network could be a potential probe of leptogenesis. We show that the leptogenesis mechanism that facilitates the dominant production of lepton asymmetry via the quantum effects of right-handed neutrinos in gravitational background, can be probed by GW detectors as well as next-generation neutrinoless double beta decay ($0\nu \beta \beta$) experiments in a complementary way. We infer that for a successful leptogenesis, an exclusion limit on $f-{\Omega }_{\mathrm{GW}}{h}^2$ plane would correspond to an exclusion on the $|m_{\beta \beta }|-m_1$ plane as well. We consider a normal light neutrino mass ordering and discuss how recent NANOGrav pulsar timing data (if interpreted as GW signal) e.g., at 95$\%$ CL, would correlate with the potential discovery or null signal in $0\nu \beta \beta$ decay experiments.

Comments: 16 pages, 4 figures, discussion on flavour couplings added. Explanation on the trace anomaly added. matches with the JHEP version