Single Higgs production in association with a photon at electron-positron colliders in extended Higgs models

We study associated Higgs production with a photon at electron-positron colliders, e(+)e(-) -> h gamma, in various extended Higgs models, such as the inert doublet model, the inert triplet model, and the two Higgs doublet model. The cross section in the standard model (SM) is maximal around root s = 250 GeV, and we present how and how much the new physics can enhance or reduce the production rate. We also discuss the correlation with the h -> gamma gamma and h -> Z gamma decay rates. We find that, with a sizable coupling to a SM-like Higgs boson, charged scalars can give considerable contributions to both the production and the decay if their masses are around 100 GeV. Under the theoretical constraints from vacuum stability and perturbative unitarity as well as the current constraints from the Higgs measurements at the LHC, the production rate can be enhanced from the SM prediction at most by a factor of 2 in the inert doublet model. In the inert triplet model, in addition, we find a particular parameter region where the h gamma production significantly increases by a factor of about 6 to 8, but the h -> gamma gamma decay still remains as in the SM. In the two Higgs doublet model, possible deviations from the SM prediction are minor in the viable parameter space.