Enhancement of H→γγ in SU(5) model with 45H-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 K0-K¯0 mixing implies that the neutral octet-scalar mass should be larger than 400 GeV for tanβ∼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 Γ(h→γγ). 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 σ(gg→h).