Vacuum decay in quadratic gravity

TL;DR

This paper investigates how quadratic Ricci scalar terms in modified gravity theories influence vacuum decay, demonstrating that such terms universally prevent decay regardless of the scalar potential.

Contribution

It introduces a new analytic method to analyze bounce solutions and proves that quadratic Ricci scalar terms universally inhibit vacuum decay in these theories.

Findings

Quadratic Ricci scalar prevents vacuum decay in modified gravity theories.

Scalar field on the bounce exhibits universal behavior at large Euclidean radii.

The new analytic method effectively analyzes bounce solutions in complex theories.

Abstract

Metastable states decay at zero temperature through quantum tunneling at an exponentially small rate, which depends on the Coleman-de Luccia instanton, also known as bounce. In some theories, the bounce may not exist or its on-shell action may be ill-defined or infinite, thus hindering the vacuum decay process. In this paper, we test this possibility in modified theories of gravity interacting with a real scalar field. We consider an Einstein-Hilbert term with a non-minimally coupled scalar field and a quadratic Ricci scalar contribution. To tackle the problem we use a new analytic method, with which we prove that the scalar field on the bounce has a universal behaviour at large Euclidean radii, almost independently of the potential. Our main result is that the quadratic Ricci scalar prevents the decay, regardless of the other terms in the action.