Inflaton Regeneration via Scalar Couplings: Generic Models and the Higgs Portal

TL;DR

This paper shows that in certain inflationary models, the inflaton can be regenerated after reheating through scalar couplings, impacting dark matter and cosmological constraints.

Contribution

It introduces a generic mechanism for inflaton regeneration via scalar couplings, especially through the Higgs portal, affecting reheating and dark matter scenarios.

Findings

Inflaton mass vanishes asymptotically, enabling regeneration after reheating.

Regenration occurs via 1-to-2 decays and 2-to-2 scatterings of bath particles.

Constraints on couplings can be derived from overproduction, BBN, CMB, and collider data.

Abstract

The standard cosmological paradigm assumes that the inflaton field becomes dynamically negligible during the post-reheating evolution of the Universe. We demonstrate that this assumption fails for a broad class of inflationary models where the potential behaves as a monomial form $V(\phi) \propto \phi^k$ (with $k \ge 4$) around the minimum. In such scenarios, the effective inflaton mass depends on the field amplitude and vanishes asymptotically as the Universe expands. This vanishing-mass mechanism renders the inflaton kinematically accessible to the thermal plasma long after reheating, facilitating the regeneration of inflaton quanta through 1-to-2 decays and 2-to-2 scatterings of bath particles. This mechanism is quite generic and the coupling responsible for reheating can be constrained if the inflaton is overproduced, while the inflaton quanta can constitute dark matter in specific scenarios. Furthermore, if reheating occurs via the Standard Model Higgs portal, the process can be further constrained by big bang nucleosynthesis, cosmic microwave background, and colliders such as the LHC. This mechanism provides a new framework for probing post-inflationary reheating.