Primordial perturbations from ultra-slow-roll single-field inflation with quantum loop effects

TL;DR

This paper investigates how quantum loop effects influence primordial perturbations during ultra-slow-roll inflation, clarifying their impact on primordial black hole formation and observational constraints.

Contribution

It derives constraints on growing modes during transition phases in inflation considering loop corrections, addressing recent debates on black hole formation viability.

Findings

Loop corrections affect large-scale curvature perturbations.

Constraints limit the growth of modes during phase transition.

Results clarify the viability of primordial black hole formation.

Abstract

It is known that the single-field inflation with a transient ultra-slow-roll phase can produce a large curvature perturbation at small scales for the formation of primordial black holes. In our previous work, we have considered quantum loop corrections to the curvature perturbation and found that the growth of these small-scale modes would affect the curvature perturbation at large scales probed by cosmic microwave background observation. In this work, we will further derive the constraints on the growing modes in the transition between the slow-roll and the ultra-slow-roll phases under the effect of the loop corrections. Our results would help clarify the recent controversy on whether or not the primordial-black-hole formation from the single-field inflation is ruled out at one-loop level.