Robustness of Inflation to Inhomogeneous Initial Conditions
  We consider the effects of inhomogeneous initial conditions in both the
scalar field profile and the extrinsic curvature on different inflationary
models. In particular, we compare the robustness of small field inflation to
that of large field inflation, using numerical simulations with Einstein
gravity in 3+1 dimensions. We find that small field inflation can fail in the
presence of subdominant gradient energies, suggesting that it is much less
robust to inhomogeneities than large field inflation, which withstands dominant
gradient energies. However, we also show that small field inflation can be
successful even if some regions of spacetime start out in the region of the
potential that does not support inflation. In the large field case, we confirm
previous results that inflation is robust if the inflaton occupies the
inflationary part of the potential. Furthermore, we show that increasing
initial scalar gradients will not form sufficiently massive inflation-ending
black holes if the initial hypersurface is approximately flat. Finally, we
consider the large field case with a varying extrinsic curvature K, such that
some regions are initially collapsing. We find that this may again lead to
local black holes, but overall the spacetime remains inflationary if the
spacetime is open, which confirms previous theoretical studies.
