Inflation, (P)reheating and Neutrino Anomalies: Production of Sterile Neutrinos with Secret Interactions

TL;DR

This paper explores how sterile neutrinos with secret interactions can be produced during (p)reheating after inflation, analyzing conditions that make their cosmological effects consistent with observations despite initial abundance concerns.

Contribution

It investigates sterile neutrino production during (p)reheating in large field inflation models, identifying parameter regions that ensure cosmological viability.

Findings

Sterile neutrinos can be produced copiously during (p)reheating.

Certain parameter regimes suppress sterile neutrino overproduction.

The model remains consistent with cosmological constraints under specific conditions.

Abstract

A number of experimental anomalies involving neutrinos hint towards the existence of at least an extra (a very light) sterile neutrino. However, such a species, appreciably mixing with the active neutrinos, is disfavored by different cosmological observations like Big Bang Nucleosynthesis (BBN), Cosmic Microwave Background (CMB) and Large Scale Structure (LSS). Recently, it was shown that the presence of additional interactions in the sterile neutrino sector via light bosonic mediators can make the scenario cosmologically viable by suppressing the production of the sterile neutrinos from active neutrinos via matter-like effect caused by the mediator. This mechanism works assuming the initial population of this sterile sector to be negligible with respect to that of the Standard Model (SM) particles, before the production from active neutrinos. However, there is fair chance that such bosonic mediators may couple to the inflaton and can be copiously produced during (p)reheating epoch. Consequently, they may ruin this assumption of initial small density of the sterile sector. In this article we, starting from inflation, investigate the production of such a sterile sector during (p)reheating in a large field inflationary scenario and identify the parameter region that allows for a viable early Universe cosmology.