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Delayed Charged Lepton Yukawa Equilibration and Thermal Leptogenesis

Rishav Roshan, Sudipta Show

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.

Delayed Charged Lepton Yukawa Equilibration and Thermal Leptogenesis

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.

Paper Structure

This paper contains 1 section, 11 equations, 3 figures.

Table of Contents

  1. Acknowledgment

Figures (3)

  • Figure 1: Evolution of the various energy densities as a function of the relative scale factor, $a/a_{\text{RH}}$.
  • Figure 2: Variation of $\langle \Gamma_\alpha \rangle/\mathcal{H}$ vs. $T$ for standard (solid lines) and modified (dot-dashed and dashed) scenarios.
  • Figure 3: Evolution of the baryon asymmetry with the expansion of the universe for a fixed value of parameters: $M_3=10^{14}~\rm{GeV},~M_1=10^{11}~\rm{GeV},~r=10,~a=0.6,~b=-0.8$ for three different values of $m_{\ell}$.