Smooth vs instant inflationary transitions: steepest growth re-examined and primordial black holes

Understand

Primordial black holes (PBHs) can be produced by a range of mechanisms in the early universe.

• A particular formation channel that connects PBHs with inflationary phenomenology invokes enhanced primordial curvature perturbations at small scales.
• In this paper, we examine how rapidly the background can transition between different values of the parameters of the Hubble hierarchy in the context of single-clock inflation, which must ultimately derive from a consistent derivative expansion for the background inflaton field.
• We discuss artefacts associated with instant or very rapid transitions, and consider the impact on the steepest power spectrum growth and the formation of PBHs.