Enhancement of $h \to \gamma \gamma$ by seesaw-motivated exotic scalars

Abstract

We examine the role of seesaw motivated exotic scalars in loop-mediated Higgs decays. We consider a simple TeV-scale seesaw model built upon the fermionic quintuplet mediator in conjunction with the scalar quadruplet, where we examine portions of the model parameter space for which the contributions of charged components of the scalar quadruplet significantly increase the $h \to \gamma \gamma$ decay rate. The most significant change in the diphoton width comes from a doubly charged scalar \Phi^{--} which should be the lightest component in the scalar quadruplet. There is a mild suppression of the $h \to Z \gamma$ decay width by a factor 0.9 -- 0.7 in the part of the parameter space where the $h \to \gamma \gamma$ decay width is enhanced by a factor 1.25 -- 2.