On the stability of the electroweak vacuum in the presence of low-scale seesaw models

TL;DR

This paper investigates how low-scale seesaw models with sizable Yukawa couplings influence the stability of the electroweak vacuum, establishing bounds that impact observable lepton flavor violation and neutrinoless double beta decay.

Contribution

It demonstrates that large Yukawa couplings in low-scale seesaw models can destabilize the electroweak vacuum, providing bounds that constrain model parameters and related observables.

Findings

Yukawa couplings with Tr(Y_ν†Y_ν) ≥ 0.4 are excluded.

Bounds on Yukawa couplings affect predictions for μ→eγ.

Constraints impact neutrinoless double beta decay observables.

Abstract

The scale of neutrino masses and the Planck scale are separated by more than twenty-seven order of magnitudes. However, they can be linked by imposing the stability of the electroweak (EW) vacuum. The crucial ingredient is provided by the generation of neutrino masses via a seesaw mechanism triggered by Yukawa interactions between the standard model (SM) Higgs and lepton doublets and additional heavy right-handed neutrinos. These neutrinos participate to the renormalization group (RG) running of the dimensionless SM couplings, affecting their high-energy behavior. The Higgs quartic coupling is dragged towards negative values, thus altering the stability of the EW vacuum. In the usual type-I seesaw model, this effect is too small to be a threat since, in order to comply with low-energy neutrino data, one is forced to consider either too small Yukawa couplings or too heavy right-handed neutrinos. In this paper we explore this general idea in the context of low-scale seesaw models. These models are characterized by sizable Yukawa couplings and right-handed neutrinos with mass of the order of the EW scale, thus maximizing their impact on the RG flow. As a general result, we find that Yukawa couplings such that ${\rm Tr}(Y_{\nu}^{\dag}Y_{\nu}) \gtrsim 0.4$ are excluded. We discuss the impact of this bound on several observables, with a special focus on the lepton flavor violating process $\mu\to e\gamma$ and the neutrino-less double beta decay.