Probing the Primordial Universe using Massive Fields

Inflation models are numerous. It is extremely difficult, if possible at all, to identify the actual underlying inflation model of our primordial universe. Thus, for the purpose of proving/falsifying inflation and using inflation to probe new physics, model independent approaches are crucial. Massive fields play a uniquely important role in those missions. This short review is based on a talk by one of the authors (YW) in the 2nd LeCosPA Symposium.
Comment: 7 pages, prepared for the proceeding of the 2nd LeCosPA Symposium "Everything About Gravity"