On the strong coupling problem in cosmologies with "strong gravity in the past"

TL;DR

This paper investigates the strong coupling issue in bouncing cosmologies with strong gravity in the past, demonstrating that apparent strong coupling problems in the Jordan frame are resolved when viewed from the Einstein frame, through explicit calculations.

Contribution

The paper clarifies the strong coupling problem in bouncing cosmologies by showing frame-dependent cancellations, resolving apparent issues in the Jordan frame with explicit calculations.

Findings

Naive dimensional analysis suggests low strong coupling scale in Jordan frame.

Explicit calculations reveal cancellations that prevent strong coupling issues.

The Einstein frame perspective confirms the absence of problematic strong coupling at early times.

Abstract

We examine the potential strong coupling problem at early times in a bouncing cosmological model with "strong gravity in the past" (Jordan frame), which is conformally related to inflation (Einstein frame). From naive dimensional analysis in the Jordan frame one would conclude that the quantum strong coupling energy scale can be lower than the classical energy scale. However, from the Einstein frame prospective this should not be the case. We illustrate this point by calculation in the Jordan frame which shows cancellations of the dangerous contributions in the tree level amplitude.