Neutrino mass, Dark Matter and Baryon Asymmetry via TeV-Scale Physics without Fine-Tuning

We propose an extended version of the standard model, in which neutrino oscillation, dark matter, and baryon asymmetry of the Universe can be simultaneously explained by the TeV-scale physics without assuming unnatural hierarchy among the mass scales. Tiny neutrino masses are generated at the three loop level due to the exact $Z_2$ symmetry, by which stability of the dark matter candidate is guaranteed. The extra Higgs doublet is required not only for the tiny neutrino masses but also for successful electroweak baryogenesis. The model provides discriminative predictions especially in Higgs phenomenology, so that it is testable at current and future collider experiments.

Higgs boson pair production at a photon-photon collision in the two Higgs doublet model

We calculate the cross section of Higgs boson pair production at a photon collider in the two Higgs doublet model. We focus on the scenario in which the lightest CP even Higgs boson ($h$) has the standard model like couplings to the gauge bosons. We take into account the one-loop correction to the $hhh$ coupling as well as additional one-loop diagrams due to charged Higgs bosons to the $gammagammato hh$ helicity amplitudes. It is found that the full cross section can be enhanced by both these effects to a considerable level. We discuss the impact of these corrections on the $hhh$ coupling measurement at the photon collider.