Higgs-photon resonances

We study models that produce a Higgs boson plus photon (h⁰γ) resonance at the LHC. When the resonance is a Z^' boson, decays to h⁰γ occur at one loop. If the Z^' boson couples at tree level to quarks, then the h⁰γ branching fraction is typically of order 10^-5 or smaller. Nevertheless, there are models that would allow the observation of Z^' → h⁰γ at √(s) = 13 TeV with a cross section times branching fraction larger than 1 fb for a Z^' mass in the 200-450 GeV range, and larger than 0.1 fb for a mass up to 800 GeV. The one-loop decay of the Z^' into lepton pairs competes with h⁰γ, even if the Z^' couplings to leptons vanish at tree level. We also present a model in which a Z^' boson decays into a Higgs boson and a pair of collimated photons, mimicking an h⁰γ resonance. In this model, the h⁰γ resonance search would be the discovery mode for a Z^' as heavy as 2 TeV. When the resonance is a scalar, although decay to h⁰γ is forbidden by angular momentum conservation, the h⁰ plus collimated photons channel is allowed. We comment on prospects of observing an h⁰γ resonance through different Higgs decays, on constraints from related searches, and on models where h⁰ is replaced by a nonstandard Higgs boson. (orig.)