Bouncing Cosmologies: Progress and Problems
  We review the status of bouncing cosmologies as alternatives to cosmological inflation for providing a description of the very early universe, and a source for the cosmological perturbations which are observed today. We focus on the motivation for considering bouncing cosmologies, the origin of fluctuations in these models, and the challenges which various implementations face. 
Robert Brandenberger and Patrick Peter
hep-th astro-ph.CO gr-qc hep-ph