Entanglement entropy of cosmological perturbations for S-brane Ekpyrosis
  We calculate the entanglement entropy of scalar perturbations due to
gravitational non-linearities present in any model of canonically-coupled,
single-field ekpyrosis. Specifically, we focus on a recent model of improved
ekpyrosis which is able to generate a scale-invariant power spectrum of
curvature perturbations and gravitational waves as well as have a non-singular
bounce due to an S-brane at the end of ekpyrotic contraction. By requiring that
the entanglement entropy remians subdominant to the thermal entropy produced
during reheating, we get an upper bound on the energy scale of the bounce.
