HIGGS BOSON PAIR PRODUCTION IN NEW PHYSICS MODELS

We study Higgs boson pair production processes at future hadron and lepton colliders includ-ing the photon collision option in several new physics models; i.e., the two-Higgs-doublet model, the scalar leptoquark model, the sequential fourth generation fermion model and the vector-like quark model. Cross sections for these processes can deviate significantly from the standard model predictions due to the one-loop correction to the triple Higgs boson coupling constant. For the one-loop induced processes such as gg → hh and γγ → hh, where h is the (lightest) Higgs boson and g and γ respectively represent a gluon and a photon, the cross sections can also be affected by new physics particles via additional one-loop diagrams. In the two-Higgs-doublet model and scalar leptoquark models, cross sections of e+e − → hhZ and γγ → hh can be enhanced due to the non-decoupling effect in the one-loop corrections to the triple Higgs boson coupling constant. In the sequential fourth generation fermion model, the cross section for gg → hh becomes very large because of the loop effect of the fermions. In the vector-lik