Triplet Higgs assisted leptogenesis from axion oscillation after inflation

Abstract

Leptogenesis via axion oscillation after inflation is an alternate mechanism of thermal leptogenesis. In this mechanism, the requirement of the existence of a lepton number ($L$) violating process in equilibrium to drive the lepton number requires the temperature of leptogenesis at $\sim 10^{13}$ GeV. Triplet scalars, due to their interaction with gauge bosons, make a suitable candidate to prevail in the thermal bath via gauge scattering at such high energy. Also, owing to its interaction with Standard Model (SM) leptons and the Higgs scalar, it can mediate $\Delta L =2$ process. Moreover, just one triplet is enough to serve the purpose as opposed to thermal leptogenesis, where at least one more triplet scalar/right-handed neutrino is required to generate a sizable $CP$ violation. In this work, we study a model where the SM gauge group is extended with $U(1)_{\rm PQ}$, with the addition of one Higgs doublet, one scalar triplet, and one complex scalar singlet. The presence of a complex scalar singlet decouples the PQ symmetry breaking from the electroweak scale. It also provides a common source of an axion-like particle and seesaw scale. The scalar triplet offers a common link between leptogenesis via axion oscillation and neutrino mass. Further, with the presence of one triplet scalar, the lepton flavor violation process is directly determined from low-energy neutrino oscillation data.