Cosmological Perturbations Through a Non-Singular
  Ghost-Condensate/Galileon Bounce
  We study the propagation of super-horizon cosmological perturbations in a
non-singular bounce spacetime. The model we consider combines a ghost
condensate with a Galileon term in order to induce a ghost-free bounce. Our
calculation is performed in harmonic gauge, which ensures that the linearized
equations of motion remain well-defined and non-singular throughout. We find
that, despite the fact that near the bounce the speed of sound becomes
imaginary, super-horizon curvature perturbations remain essentially constant
across the bounce. In fact, we show that there is a time close to the bounce
where curvature perturbations of all wavelengths are required to be momentarily
exactly constant. We relate our calculations to those performed in other
gauges, and comment on the relation to previous results in the literature.
