Multi-field inflation and cosmological perturbations
  We provide a concise review on multi-field inflation and cosmological perturbations. We discuss convenient and physically meaningful bases in terms of which perturbations can be systematically studied. We give formal accounts on the gauge fixing conditions and present the perturbation action in two gauges. We also briefly review non-linear perturbations. 
Jinn-Ouk Gong
gr-qc astro-ph.CO hep-ph hep-th