Time asymmetric extensions of general relativity

TL;DR

This paper introduces a class of modified gravity theories that break time reversal symmetry and locality, potentially affecting cosmological evolution while preserving key physical properties, inspired by shape dynamics.

Contribution

It proposes a novel Hamiltonian framework for time asymmetric extensions of general relativity that maintain the algebra of constraints and linearized equations.

Findings

Observable effects on cosmological scales.

Preservation of local degrees of freedom.

Compatibility with linearized equations of motion.

Abstract

We describe a class of modified gravity theories that deform general relativity in a way that breaks time reversal invariance and, very mildly, locality. The algebra of constraints, local physical degrees of freedom, and their linearized equations of motion, are unchanged, yet observable effects may be present on cosmological scales, which have implications for the early history of the universe. This is achieved in the Hamiltonian framework, in a way that requires the constant mean curvature gauge conditions and is, hence, inspired by shape dynamics.