Singlet scalars as Higgs boson imposters at the Large Hadron Collider

An electroweak singlet scalar can couple to pairs of vector bosons through loop-induced dimension five operators. Compared to a standard model Higgs boson, the singlet decay widths in the diphotons and Z gamma channels are generically enhanced, while decays into massive final states like WW and ZZ are kinematically disfavored. The overall event rates into gamma gamma and Z gamma can exceed the standard model expectations by orders of magnitude. Such a singlet may appear as a resonant signal in the gamma gamma and Z gamma channels, even with a mass above the WW kinematic threshold.