Cosmic bubble and domain wall instabilities III: The role of oscillons
  in three-dimensional bubble collisions
  We study collisions between pairs of bubbles nucleated in an ambient false
vacuum. For the first time, we include the effects of small initial (quantum)
fluctuations around the instanton profiles describing the most likely initial
bubble profile. Past studies of this problem neglect these fluctuations and
work under the assumption that the collisions posess an exact SO(2,1) symmetry.
We use three-dimensional lattice simulations to demonstrate that for
double-well potentials, small initial perturbations to this symmetry can be
amplified as the system evolves. Initially the amplification is well-described
by linear perturbation theory around the SO(2,1) background, but the onset of
strong nonlinearities amongst the fluctuations quickly leads to a drastic
breaking of the original SO(2,1) symmetry and the production of oscillons in
the collision region. We explore several single-field models, and we find it is
hard to both realize inflation inside of a bubble and produce oscillons in a
collision. Finally, we extend our results to a simple two-field model. The
additional freedom allowed by the second field allows us to construct viable
inflationary models that allow oscillon production in collisions. The breaking
of the SO(2,1) symmetry allows for a new class of observational signatures from
bubble collisions that do not posess azimuthal symmetry, including the
production of gravitational waves which cannot be supported by an SO(2,1)
spacetime.
