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

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).