Assessing perturbativity and vacuum stability in high-scale leptogenesis

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 Tr[YN†YN] ≲ 0.66 on the neutrino Yukawa matrix. We also investigate this scenario in the presence of a large number NF of coloured Majorana octet fermions in order to make quantum chromodynamics asymptotically safe in the ultraviolet.