Rescuing leptogenesis parameter space of inverse seesaw

TL;DR

This paper explores two novel methods to enhance leptogenesis in inverse seesaw models, addressing previous challenges by considering non-standard cosmology and quasi-degenerate neutrino masses, with testable predictions for upcoming experiments.

Contribution

It introduces two new approaches—non-standard cosmological expansion and quasi-degenerate neutrino spectrum—to successfully generate the observed baryon asymmetry in inverse seesaw models.

Findings

Faster universe expansion reduces washout effects.

Quasi-degenerate neutrino masses increase surviving lepton asymmetry.

Parameter space testable at MEG and MEG II experiments.

Abstract

In a pure inverse seesaw framework, achieving a substantial lepton asymmetry that can be converted into the observed baryon asymmetry of the Universe is extremely challenging. The difficulty arises primarily due to two reasons, (i) partial cancellation of the lepton asymmetries associated with the components of a pseudo-Dirac pair, and (ii) strong wash out caused by the inverse decays. In this work we offer two possible resolutions to overcome the above mentioned challenges considering a (3,3) ISS framework. Our first proposal is based on the assumption of a non-standard cosmological era in the pre-BBN epoch, that triggers a faster expansion of the Universe, thereby reducing the washout by several orders of magnitude. The second proposition is an alternative of first which considers a quasi-degenerate mass spectrum for the singlet heavy neutrinos, resulting into a larger order of lepton asymmetry that survives the impact of strong washout to account for the observed BAU. The viable parameters space, as obtained can be tested at present and future Lepton Flavour Violation experiments {\it e.g.} MEG and MEG II.}