  The effective potential for the Standard Model Higgs field allows two
quasi-degenerate vacua; one is our vacuum at the electroweak scale, while the
other is at a much higher scale. The latter minimum may be at a scale much
smaller than the Planck scale, if the potential is lifted by new physics. This
gives rise to a possibility of domain wall formation after inflation. If the
high-scale minimum is a local minimum, domain walls are unstable and disappear
through violent annihilation processes, producing a significant amount of
gravitational waves. We estimate the amount of gravitational waves produced
from unstable domain walls in the Higgs potential and discuss detectability
with future experiments.
