Delayed Charged Lepton Yukawa Equilibration and Thermal Leptogenesis

TL;DR

This paper investigates how the heaviest right-handed neutrino, often neglected, can influence early universe lepton flavor dynamics and leptogenesis, with implications for cosmology and experimental detection.

Contribution

It demonstrates the significant cosmological impact of the decoupled heavy neutrino on charged lepton Yukawa equilibration and flavor effects in thermal leptogenesis.

Findings

Heavy neutrino alters Yukawa equilibration temperature

Reassessment of lepton flavor regimes needed

Potential experimental probes identified

Abstract

While most studies of the minimal type-I seesaw neglect the heaviest decoupled right-handed neutrino, assuming negligible contributions to neutrino masses and leptogenesis, we demonstrate that its cosmological role can be significant. When long-lived, the presence of this particle can substantially modify the charged lepton Yukawa equilibration temperature in the early universe, necessitating reassessment of lepton flavor effects in thermal leptogenesis and potentially shifting flavor regime boundaries. Additionally, we identify experimental probes, including neutrino oscillation measurements and gravitational wave observations to investigate this scenario.