750 GeV Diphoton Excess and Running Couplings

Recently, ATLAS and CMS collaborations at the LHC have reported an excess of diphoton signal around 750 GeV invariant mass. A simple way to explain this excess is to introduce singlet scalar particle which couples to vectror-like fermions charged under the standard model gauge group. The new charged fermions, however, modify the running of gauge coupling constants and such modifications give rise to difficulties in model building. In this talk, I will discuss the diphoton excess and constraints from running gauge couplings.