Assessing Perturbativity and Vacuum Stability in High-Scale Leptogenesis

TL;DR

This paper explores the parameter space of high-scale leptogenesis models, ensuring perturbativity and vacuum stability up to the Planck scale, and examines the impact of additional fermions on QCD safety.

Contribution

It identifies conditions on neutrino Yukawa couplings for stability and perturbativity, and investigates the role of colored fermions in achieving asymptotic safety.

Findings

Large parameter space satisfies stability and perturbativity.

Neutrino Yukawa trace constrained to less than 0.66.

Introduction of colored fermions can make QCD asymptotically safe.

Abstract

We consider the requirements that all coupling constants remain perturbative and the electroweak vacuum metastable up to the Planck scale in high-scale thermal leptogenesis, in the context of a type-I seesaw mechanism. We find a large region of the model parameter space that satisfies these conditions in combination with producing the baryon asymmetry of the Universe. We demonstrate these conditions require ${\rm Tr}[Y_N^\dagger Y_N] \lesssim 0.66$ on the neutrino Yukawa matrix. We also investigate this scenario in the presence of a large number $N_F$ of coloured Majorana octet fermions in order to make quantum chromodynamics asymptotically safe in the ultraviolet.