Non-Singular Bouncing Cosmology: Consistency of the Effective Description

Understand

We explicitly confirm that spatially flat non-singular bouncing cosmologies make sense as effective theories.

• The presence of a non-singular bounce in a spatially flat universe implies a temporary violation of the null energy condition, which can be achieved through a phase of ghost condensation.
• We calculate the scale of strong coupling and demonstrate that the ghost-condensate bounce remains trustworthy throughout, and that all perturbation modes within the regime of validity of the effective description remain under control.
• For this purpose we require the perturbed action up to third order in perturbations, which we calculate in both flat and co-moving gauge -- since these two gauges allow us to highlight different physical aspects.