About a (standard model) universe dominated by the right matter

TL;DR

This paper explores how a prolonged matter-dominated epoch caused by a long-lived heavy particle, such as a right-handed neutrino, can relax inflation constraints and generate baryon asymmetry through its decay.

Contribution

It introduces a scenario where a long-lived heavy particle induces matter domination, affecting inflationary requirements and baryogenesis, with a focus on right-handed neutrinos.

Findings

Long-lived particles can produce significant entropy, diluting unwanted relics.

A prolonged matter era reduces the needed e-foldings after horizon crossing.

Decays of right-handed neutrinos can generate the observed baryon asymmetry.

Abstract

We analyze the phenomenology of a prolonged early epoch of matter domination by an unstable but very long-lived massive particle. This new matter domination era can help to relax some of the requirements on the primordial inflation. Its main effect is the huge entropy production produced by the decays of such particle that can dilute any possible unwanted relic, as the gravitino in supersymmetric models, and thus relax the constraints on the inflationary reheating temperature. Furthermore, a long period of matter domination reduces the number of $e$-foldings after the horizon crossing by observable perturbations and therefore the requirements on flatness of the inflationary potential. A natural candidate for such heavy, long-lived particle already present in the Standard Model of the electroweak interactions would be a heavy right-handed neutrino. In this case, we show that its decays can also generate the observed baryon asymmetry with right-handed neutrino masses well above the bound from gravitino overproduction.