Gravitational wave pathway to testable leptogenesis

We analyze the classically scale-invariant B-L model in the context of resonant leptogenesis with the recently proposed mass-gain mechanism. The B-L symmetry breaking in this scenario is associated with a strong first-order phase transition that gives rise to detectable gravitational waves (GWs) via bubble collisions. The same B-L symmetry breaking also gives Majorana mass to right-handed neutrinos inside the bubbles, and their out-of-equilibrium decays can produce the observed baryon asymmetry of the Universe via leptogenesis. We show that the current LIGO-VIRGO limit on stochastic GW background already excludes part of the B-L parameter space, complementary to the collider searches for heavy Z′ resonances. Moreover, future GW experiments like Einstein Telescope and Cosmic Explorer can effectively probe the parameter space of leptogenesis over a wide range of the B-L symmetry-breaking scales and gauge coupling values.