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

TL;DR

This paper explores a minimal B-L extended model where the U(1)$_{B-L}$ Higgs drives inflation via radiative corrections, predicts a very light inflaton and Z$_{BL}$ boson, and discusses reheating and dark matter implications.

Contribution

It introduces a radiative plateau inflation model with a very light inflaton and Z$_{BL}$ boson, connecting inflation, reheating, and dark matter in a minimal B-L extension.

Findings

Hubble scale of inflation is very low (~100 eV).

Inflaton mass is around 1 eV with extremely small decay width.

Reheating occurs through a waterfall transition to the SM Higgs direction.

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 $g_{B-L}\sim10^{-4}$, 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.