Double inflation via non-minimally coupled spectator
  We argue that double inflation may occur when a spectator field is
non-minimally coupled to gravity. As a concrete example, we study a two-field
inflationary model where the initial spectator field is non-minimally coupled
to gravity while the initial inflaton field is minimally coupled. The
non-minimal coupling results in the growth of the spectator field which, in
turn, drives the second stage of inflation in a significant region of parameter
space. The isocurvature fluctuations originating from the spectator field
source adiabatic ones, and hence the spectator non-minimal coupling can modify
the inflationary predictions for the spectral index and the tensor-to-scalar
ratio even though the initial inflaton field is minimally coupled to gravity.
We explicitly show that quadratic chaotic inflation can become viable by the
introduction of the spectator non-minimal coupling.
