Violation of causality in f(R) gravity

TL;DR

This paper investigates whether f(R) gravity theories allow for solutions that violate causality, demonstrating that such solutions exist in both metric and Palatini formalisms with physically reasonable matter content.

Contribution

The study shows that f(R) gravity theories can admit causality-violating solutions, highlighting potential issues with these theories in describing physically realistic spacetimes.

Findings

f(R) gravity admits causality-violating solutions

Violations occur in both metric and Palatini formalisms

Solutions are compatible with physically reasonable matter

Abstract

We examine the question as to whether the f(R) gravity theories, in both metric and in Palatini formalisms, permit space-times in which the causality is violated. We show that the field equations of these f(R) gravity theories admit solutions with violation of causality for a physically well-motivated perfect-fluid matter content.