Leptogenesis in fast expanding Universe

TL;DR

This paper explores how a fast expanding early Universe, driven by an additional scalar field, significantly alters leptogenesis outcomes, impacting the resulting lepton asymmetry in non-standard cosmological models.

Contribution

It introduces a modified Hubble expansion rate due to a scalar field, demonstrating its effect on leptogenesis from type-I seesaw with heavy neutrinos in non-standard cosmology.

Findings

Scalar field can dominate early Universe energy density

Lepton asymmetry can deviate significantly from standard predictions

Results are applicable to various leptogenesis frameworks

Abstract

With the consideration of a fast expanding Universe in effect due to an additional scalar field, we present a study of leptogenesis in non-standard cosmology. The Hubble expansion rate is modified by the new added scalar field $\varphi$, which can change the abundance of lepton asymmetry resulted by the leptogenesis mechanism. We report a significant deviation from the standard unflavored leptogenesis scenario can be achieved in presence of the scalar field $\varphi$ that dominates the energy budget of the early Universe. We present our results for leptogenesis from type-I seesaw with heavy right-handed Majorana neutrinos. The results are based on Boltzmann equations and effects of the scalar field are similar for other kinds of leptogenesis framework.