Spinodal Backreaction During Inflation and Initial Conditions
  We investigate how long wavelength inflationary fluctuations can cause the
background field to deviate from classical dynamics. For generic potentials, we
show that, in the Hartree approximation, the long wavelength dynamics can be
encapsulated by a two-field model operating in an effective potential. The
latter is given by a simple Gaussian integral transformation of the original
inflationary potential. We use this new expression to study backreaction
effects in quadratic, hilltop, flattened, and axion monodromy potentials. We
find that the net result of the altered dynamics is to slightly modify the
spectral tilt, drastically decrease the tensor-to-scalar ratio, and to
effectively smooth over any features of the potential, with the size of these
deviations set by the initial value of power in large scale modes and the shape
of the potential during the entire evolution.
