1/R Correction to Gravity in the Early Universe
  To explain the accelerated expansion of late universe, the 1/R correction to
Einstein gravity is usually considered, where R is the Ricci scalar. This
correction term is generally believed to be negligible in the early universe.
However, if the 1/R term is inflaton-dependent, it will dramatically change the
story of inflation. The entropy perturbation will naturally appear and drive
the evolution of curvature perturbation outside the Hubble horizon. In a large
class of models, the entropy perturbation can be made nearly scale-invariant.
In Einstein gravity the single-field inflation with a quartic potential has
been ruled out by recent observations, but it revives when the 1/R term is
turned on. The evolution of non-Gaussianities on large scale are also studied
and applied to inflation with 1/R correction. In some specific models, a large
non-Gaussianity can be naturally generated outside the horizon.
