Causality Constrains Higher Curvature Corrections to Gravity

TL;DR

This paper demonstrates that causality imposes restrictions on the sign of higher curvature terms in gravity theories, impacting the viability of certain quantum gravity models.

Contribution

It establishes causality as a fundamental constraint on the sign of quartic Riemann corrections in gravitational actions.

Findings

Causality restricts the sign of quartic Riemann corrections.

Certain quantum gravity theories are constrained by causality.

The results impact the development of consistent higher curvature gravity models.

Abstract

We show that causality constrains the sign of quartic Riemann corrections to the Einstein-Hilbert action. Our constraint constitutes a restriction on candidate theories of quantum gravity.