Unitarity-violation in Generalized Higgs Inflation Models
  Unitarity-violation presents a challenge for non-minimally coupled models of
inflation based on weak-scale particle physics. We examine the energy scale of
tree-level unitarity-violation in scattering processes for generalized models
with multiple scalar fields where the inflaton is either a singlet scalar or
the Higgs. In the limit that the non-minimal couplings are all equal (e.g. in
the case of Higgs or other complex inflaton), the scale of tree-level
unitarity-violation matches the existing result. However if the inflaton is a
singlet, and if it has a larger non-minimal coupling than other scalars in the
model, then this hierarchy increases the scale of tree-level
unitarity-violation. A sufficiently strong hierarchy pushes the scale of
tree-level unitarity-violation above the Planck scale. We also discuss models
which attempt to resolve the issue of unitarity-violation in Higgs Inflation.
