When Does Leptogenesis Survive Lepton Flavor Violation Constraints? High- and Low-Scale Realizations in the Scotogenic Model

TL;DR

This paper explores how leptogenesis can occur without conflicting with lepton flavor violation constraints in the scotogenic model, identifying parameter regions where both phenomena coexist successfully.

Contribution

It demonstrates that high-scale leptogenesis is naturally compatible with LFV constraints, and finds a narrow resonant window for low-scale leptogenesis with suppressed LFV effects.

Findings

High-scale leptogenesis remains viable due to decoupling from LFV.

Low-scale resonant leptogenesis is constrained but possible within a narrow parameter space.

Benchmark points show quasi-degenerate fermions with resonant CP asymmetry and suppressed LFV.

Abstract

We investigate the interplay between lepton flavor violation (LFV) and leptogenesis in the minimal scotogenic model, comparing high-scale hierarchical leptogenesis and low-scale resonant leptogenesis within a unified Casas--Ibarra framework. Since the same Yukawa couplings simultaneously govern radiative neutrino mass generation, charged LFV processes, and the CP asymmetry required for baryogenesis, strong phenomenological correlations arise. We show that high-scale leptogenesis remains naturally viable due to the effective decoupling between LFV and baryogenesis, while low-scale resonant leptogenesis is strongly constrained by the MEG bound on $\mu \rightarrow e\gamma$. Nevertheless, we identify a narrow but nonvanishing resonant window where successful baryogenesis, controlled washout, and LFV safety coexist simultaneously. In particular, we obtain fully allowed benchmark points characterized by quasi-degenerate heavy fermions, resonantly enhanced CP asymmetry, and suppressed flavor violation through Casas--Ibarra phase alignment.