  We study the enhancement of the di-Higgs production cross section resulting
from the resonant decay of a heavy Higgs boson at hadron colliders in a model
with a Higgs singlet. This enhancement of the double Higgs production rate is
crucial in understanding the structure of the scalar potential and we determine
the maximum allowed enhancement such that the electroweak minimum is a global
minimum. The di-Higgs production enhancement can be as large as a factor of ~
18 (13) for the mass of the heavy Higgs around 270 (420) GeV relative to the
Standard Model rate at 14 TeV for parameters corresponding to a global
electroweak minimum.
