Enhancement of H -> gamma gamma in SU(5) model with 45_H plet

TL;DR

This paper explores an SU(5) grand unified model with a 45-plet Higgs that can explain the enhanced diphoton decay rate of a 125 GeV Higgs, involving new scalar particles and their effects on Higgs decay and production.

Contribution

It introduces a low energy effective SU(5) model with additional Higgs and scalar doublets, showing how these can enhance Higgs diphoton decay and affect gluon fusion production.

Findings

Charged octet scalars can be light and unconstrained by flavor physics.

Neutral octet scalar mass should exceed 400 GeV for certain parameter choices.

Suppression or flipping of top-Higgs coupling enhances diphoton decay width.

Abstract

We show that the low energy effective model derived from SU(5) with 45-plet Higgs can account for the recently reported enhanced diphoton decay rate of the Standard Model (SM)-like Higgs with mass about 125 GeV. This model extends the SM by an extra Higgs doublet and color-octet scalar doublet. We show that the charged octet scalars are not severely constrained by flavor changing neutral current and can be light. However, the K^0-\bar{K}^0 mixing implies that the neutral octet-scalar mass should be larger than 400 GeV for \tan\beta ~ O(1). The role of charged octet scalar in the loop of Higgs decay into diphoton is investigated . We point out that the most significant impact of this model on the diphoton decay width comes from the suppression of top-quark coupling with SM-like Higgs or even flipping its sign that leads to important enhancement in \Gamma(h -> gamma gamma). We also study the implications of the neutral octet-scalar contributions to the gluon fusion Higgs production cross section in alleviating the apparent tension between enhancement of diphoton decay rate and suppression of \sigma(gg -> h).