Title: Primordial Black Holes from Null Energy Condition Violation in Inflation

Abstract: We propose a novel approach to generate Primordial Black Holes (PBHs) in inflationary cosmology via an intermediate stage which violates the Null Energy Condition (NEC). The formation of PBHs in the early universe is vastly studied due to its relevance to astrophysical and cosmological phenomena such as dark matters and supermassive black holes. The production of abundant amount of PBHs relies on the amplification of primordial curvature power spectrum P_ζ∝H^2/ϵ on small scales, which is conventionally achieved by an intermediate stage where the slow-roll parameter ϵ is suppressed. In our work, we present a new approach by enhancing the curvature perturbations through the growth of Hubble parameter H in an intermediate stage in inflation. The growth of H implies the violation of NEC, and by making use of the recent development in modified gravity theory, we successfully construct pathology-free models where NEC violation takes place in inflationary cosmology. We successfully generate sizable PBHs of astrophysical interests. Additionally, our scenario simultaneously predicts a peaked scalar-induced gravitational wave signal and a nearly scale-invariant primordial gravitational waves in different frequency band, admitting our model to be falsified by joint observations of gravitational waves in near future.

Title: TBA

Abstract: TBA