WIMP Dark Matter and Unitarity-Conserving Inflation via a Gauge Singlet
  Scalar
  A gauge singlet scalar with non-minimal coupling to gravity can drive
inflation and later freeze out to become cold dark matter. We explore this idea
by revisiting inflation in the singlet direction (S-inflation) and Higgs Portal
Dark Matter in light of the Higgs discovery, limits from LUX and observations
by Planck. We show that large regions of parameter space remain viable, so that
successful inflation is possible and the dark matter relic abundance can be
reproduced. Moreover, the scalar singlet can stabilise the electroweak vacuum
and at the same time overcome the problem of unitarity-violation during
inflation encountered by Higgs Inflation, provided the singlet is a real
scalar. The 2-$\sigma$ Planck upper bound on $n_s$ imposes that the singlet
mass is below 2 TeV, so that almost the entire allowed parameter range can be
probed by XENON1T.
