On Coupling NEC-Violating Matter to Gravity

TL;DR

This paper demonstrates that matter theories violating the null energy condition cannot be minimally coupled to Einstein gravity without inconsistency, but may still be compatible with non-minimal coupling or higher-curvature gravity theories.

Contribution

It establishes the incompatibility of NEC-violating matter with minimal Einstein gravity and explores alternative coupling possibilities.

Findings

NEC-violating matter cannot be minimally coupled to Einstein gravity.

Such matter theories are inconsistent with string theory and black hole thermodynamics.

Non-minimal or higher-curvature couplings may still be viable.

Abstract

We show that effective theories of matter that classically violate the null energy condition cannot be minimally coupled to Einstein gravity without being inconsistent with both string theory and black hole thermodynamics. We argue however that they could still be either non-minimally coupled or coupled to higher-curvature theories of gravity.