Converting entropy to curvature perturbations after a cosmic bounce

Understand

We study two-field bouncing cosmologies in which primordial perturbations are created in either an ekpyrotic or a matter-dominated contraction phase.

• We use a non-singular ghost condensate bounce model to follow the perturbations through the bounce into the expanding phase of the universe.
• In contrast to the adiabatic perturbations, which on large scales are conserved across the bounce, entropy perturbations can grow significantly during the bounce phase.
• If they are converted into adiabatic/curvature perturbations after the bounce, they typically form the dominant contribution to the observed temperature fluctuations in the microwave background, which can have several beneficial implications.