Lepton Flavor Equilibration and Leptogenesis

TL;DR

This paper investigates how lepton flavor equilibration affects leptogenesis, especially in supersymmetric models, and derives simplified Boltzmann equations considering flavor and spectator effects at low scales.

Contribution

It demonstrates that for certain soft breaking masses and energy scales, leptogenesis can be accurately described by a one-flavor approximation, and provides a simplified Boltzmann equation including flavor and spectator effects.

Findings

Flavor effects are negligible if soft masses are above 1 GeV and leptogenesis occurs below 100 TeV.

Spectator effects significantly influence low-scale leptogenesis dynamics.

Derived a simplified Boltzmann equation incorporating flavor and spectator effects.

Abstract

We study the role played in leptogenesis by the equilibration of lepton flavors, as could be induced in supersymmetric models by off diagonal soft breaking masses for the scalar lepton doublets $\tilde m_{\alpha\beta}$, or more generically by new sources of lepton flavor violation. We show that if $\tilde m_{\alpha\beta}\gsim 1 $GeV and leptogenesis occurs below $\sim 100 $TeV, dynamical flavor effects are irrelevant and leptogenesis is correctly described by a one-flavor Boltzmann equation. We also discuss spectator effects in low scale leptogenesis by taking into account various chemical equilibrium conditions enforced by the reactions that are in thermal equilibrium. We write down the Boltzmann equation for low scale supersymmetric leptogenesis that includes flavor and spectator effects in the presence of lepton flavor equilibration, and we show how it reduces to a particularly simple form.