Vacuum Stability, Perturbativity, EWPD and Higgs-to-diphoton rate in Type II Seesaw Models

We study constraints from perturbativity and vacuum stability as well as the EWPD in the type II seesaw model. As a result, we can put stringent limits on the Higgs triplet couplings depending on the cut-off scale. The EWPD tightly constrain the Higgs triplet mass splitting to be smaller than 40 GeV. Analyzing the Higgs-to-diphoton rate in the allowed parameter region, we show a possible enhancement by up to 100 % and 50 % for the cut-off scale of 100 TeV and ${10}^{19}$ GeV, respectively, if the doubly charged Higgs boson mass is as low as 100 GeV.