Towards Testable Type-III Leptogenesis in Non-Standard Early Universe Scenarios

TL;DR

This paper explores how non-standard early universe scenarios can enable testable triplet leptogenesis at lower energy scales than traditionally predicted.

Contribution

It demonstrates that faster expansion or scalar tensor gravity allows successful leptogenesis with triplet fermions at TeV to hundreds of TeV scales.

Findings

Successful leptogenesis at TeV scales in non-standard cosmologies

Faster expansion or scalar tensor gravity relaxes mass constraints

Potential for experimental signatures at accessible energies

Abstract

Leptogenesis is an elegant way to explain the baryon asymmetry of the Universe in connection to the neutrino mass and mixing. Although leptogenesis from the decay of a heavy Majorana neutrino has been the minimal set up, it is also motivating to look for leptogenesis from the decay of triplet fermion as it can have detectable signatures in the experiments. However, due to strong gauge annihilations and constraints from neutrino sector, the triplet fermions have to be as heavy as $10^{10}$ GeV or more to generate the observed baryon asymmetry. While this prediction is based on the standard radiation dominated history of the early Universe, it is also possible to have a non-standard expansion history of the Universe prior to the big-bang nucleosynthesis. In this work we study triplet leptogenesis in two non-standard cosmological scenarios, where the Universe expands faster than radiation and a scalar tensor theory of gravity. We show that it is possible to have successful leptogenesis with a few TeV triplet fermion for fast expanding Universe and a few hundered TeV for a scalar tensor gravity theory.