  We study Higgs boson pair production processes at future hadron and lepton
colliders including 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 $gg \to hh$ and
$\gamma\gamma\to hh$, where $h$ is the (lightest) Higgs boson and $g$ and
$\gamma$ 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
$e^+e^-\to hhZ$ and $\gamma\gamma\to hh$ 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 $gg\to hh$ becomes very large because of the loop effect of the
fermions. In the vector-like quark model, effects are small because the theory
has decoupling property. Measurements of the Higgs boson pair production
processes can be useful to explore new physics through the determination of the
Higgs potential.
