  In a recently proposed Higgs-Seesaw model the observed scale of dark energy
results from a metastable false vacuum energy associated with mixing of the
standard model Higgs particle and a scalar associated with new physics at the
GUT or Planck scale. Here we address the issue of how to ensure metastability
of this state over cosmological time. We consider new tree-level operators, the
presence of a thermal bath of hidden sector particles, and quantum corrections
to the effective potential. We find that in the thermal scenario many
additional light degrees of freedom are typically required unless coupling
constants are somewhat fine-tuned. However quantum corrections arising from as
few as one additional light scalar field can provide the requisite support. We
also briefly consider implications of late-time vacuum decay for the perdurance
of observed structures in the universe in this model.
