eV Hubble Scale Inflation with Radiative Plateau: Very light Inflaton, Reheating & Dark Matter in B-L Extensions

Abstract

We study radiative plateau-like inflation \& Z${}_{BL}$-portal freeze-in fermionic dark matter (DM) in a minimal B-L extended model. The U(1)${}_{B-L}$ Higgs, responsible for heavy neutrino masses, also drives inflation in the early universe, thanks to radiative corrections from the heavy neutrinos \& the Z${}_{BL}$ gauge boson. In our benchmark choice for the U(1)${}_{B-L}$ gauge coupling $g_{B-L}\sim 10^{-4}$, a light Z${}_{BL}$ boson can be explored by current and future lifetime frontier experiments, such as FASER and FASER 2 at the LHC, SHiP, Belle II and LHCb. For the benchmark, the Hubble scale of inflation (${\mathcal{H}}_{inf}$) is very low (${\mathcal{H}}_{inf}=\mathcal{O}(100)$ eV) \& the inflaton turns out to be very light with mass of $\mathcal{O}(1)$ eV, and consequently the decay width of inflaton is extremely small. We investigate a 2-field system with the inflaton/B-L Higgs and the Standard Model (SM) Higgs, and find that the reheating with a suffuciently high temperature occurs when the water-fall direction to the SM Higgs direction opens up in the trajectory of the scalar field evolution.

Comments: 19 pages, 5 figures, This version is accepted in PRD