Beginning of Universe through large field hybrid inflation

Understand

Recent detection of $B$-mode polarization induced from tensor perturbations by the BICEP2 experiment implies so-called large field inflation, where an inflaton field takes super-Planckian expectation value during inflation, at a high energy scale.

• We show however, if another inflation follows hybrid inflation, the hybrid inflation can generate a large tensor perturbation with not super-Plankian but Planckian field value.
• This scenario would relax the tension between BICEP2 and Planck concerning the tensor-to-scalar ratio, because a negative large running can also be obtained for a certain number of e-fold of the hybrid inflation.
• A natural interpretation of a large gravitational wave mode with or without the scalar spectral running might be multiple inflation in the early Universe.