Vacuum stability and naturalness in type-II seesaw

TL;DR

This paper investigates the stability, naturalness, and experimental constraints of the minimal type-II seesaw model, focusing on Higgs mass corrections, decay deviations, and testability at the LHC.

Contribution

It provides new constraints on the model parameters from vacuum stability, naturalness, and Higgs decay measurements, highlighting the limited observable deviations at the LHC.

Findings

Heavy Higgs masses should be below 350 GeV for naturalness.

Higgs decay to gamma gamma is slightly enhanced, with R_{γγ} ≤ 1.1.

Large parameter regions are excluded by current LHC data.

Abstract

We study the vacuum stability and perturbativity conditions in the minimal type-II seesaw model. These conditions give characteristic constraints to model parameters. In the model, there is a $SU(2)_L$ triplet scalar field, which could cause a large Higgs mass correction. From the naturalness point of view, heavy Higgs masses should be lower than $350\,{\rm GeV}$, which can be testable by the LHC Run-II results. Due to effects of the triplet scalar field, branching ratios of the Higgs decay ($h\to \gamma \gamma, Z\gamma$) deviate from the standard model, and large parameter region is excluded by the recent ATLAS and CMS combined analysis of $h\to \gamma \gamma$. Our result of the signal strength for $h\to \gamma \gamma$ is $R_{\gamma \gamma} \lesssim 1.1$, but its deviation is too small to observe at the LHC experiment.