Eternal Higgs inflation and cosmological constant problem
  We investigate the Higgs potential beyond the Planck scale in the superstring
theory, under the assumption that the supersymmetry is broken at the string
scale. We identify the Higgs field as a massless state of the string, which is
indicated by the fact that the bare Higgs mass can be zero around the string
scale. We find that, in the large field region, the Higgs potential is
connected to a runaway vacuum with vanishing energy, which corresponds to
opening up an extra dimension. We verify that such universal behavior indeed
follows from the toroidal compactification of the non-supersymmetric
$SO(16)\times SO(16)$ heterotic string theory. We show that this behavior fits
in the picture that the Higgs field is the source of the eternal inflation. The
observed small value of the cosmological constant of our universe may be
understood as the degeneracy with this runaway vacuum, which has vanishing
energy, as is suggested by the multiple point criticality principle.
