125 GeV Higgs Boson and the Type-II Seesaw Model

TL;DR

This paper investigates the stability, unitarity, and decay predictions of the type-II seesaw model with a 125 GeV Higgs, identifying parameter space constraints and experimental prospects for charged Higgs bosons at the LHC.

Contribution

It provides a comprehensive analysis of the parameter space of the type-II seesaw model compatible with a 125 GeV Higgs, including decay predictions and experimental bounds.

Findings

Large parameter space exists for a 125 GeV Higgs satisfying stability and unitarity.

Correlation between Higgs diphoton and Z+photon decay rates.

Upper bound on seesaw scale (~450 GeV) for >10% diphoton enhancement.

Abstract

We study the vacuum stability and unitarity conditions for a 125 GeV Standard Model (SM)-like Higgs boson mass in the type-II seesaw model. We find that, as long as the seesaw scale is introduced below the SM vacuum instability bound, there exists a large parameter space predicting a 125 GeV Higgs mass, irrespective of the exact value of the seesaw scale, satisfying both stability and unitarity conditions up to the Planck scale. We also study the model predictions for the Higgs partial decay widths in the diphoton and Z+photon channels with respect to their SM expectations and find that the decay rates for these two processes are correlated. We further show that for any given enhancement in the Higgs-to-diphoton rate over its SM expectation, there exists an upper bound on the type-II seesaw scale, and hence, on the masses of the associated doubly- and singly-charged Higgs bosons in the allowed parameter space. For instance, if more than 10% enhancement persists in the Higgs-to-diphoton channel, the upper limit on the type-II seesaw scale is about 450 GeV which is completely within the reach of the 14 TeV LHC. We believe this to be an encouraging result for the experimental searches of the singly- and doubly-charged Higgs bosons which, in combination with improved sensitivity in the Higgs-to-diphoton and Higgs-to-Z+photon signal strengths, could probe the entire allowed parameter space of the minimal type-II seesaw model, and establish/eliminate it as a single viable extension of the SM.