Non-Thermal Leptogenesis in the BLSM with Inverse Seesaw Mechanism

Abstract

We investigate the viability of non-thermal leptogenesis in the gauged $U(1)_{B-L}$ extension of the Standard Model (BLSM) with an inverse seesaw (ISS) mechanism for neutrino mass generation. In this framework, right-handed neutrinos typically have $\mathcal{O}(1)$ Yukawa couplings, which induce strong washout effects and render conventional thermal leptogenesis ineffective. We demonstrate that a successful baryogenesis scenario can nevertheless be realized through non-thermal leptogenesis, where right-handed neutrinos are produced from the decay of the heavy $B\!-\!L$ Higgs boson $\chi$. We explicitly analyze the interplay between the dilution factor $T_R/M_\chi$ and the washout parameter characteristic of the ISS, highlighting the tension between suppressing washout effects and maintaining sufficient reheating. We show that a viable lepton asymmetry can be generated provided the scalar mass spectrum is appropriately tuned --- a condition that requires a fine-tuning of order one part in $10^5$ against one-loop radiative corrections --- allowing for a reduced reheating temperature while keeping washout under control. The resulting lepton asymmetry is efficiently converted into the observed baryon asymmetry of the Universe via sphaleron processes. Our results establish that the inverse-seesaw $B\!-\!L$ model remains a predictive and robust framework for non-thermal leptogenesis and baryogenesis.