Einstein-Aether Theory

TL;DR

Einstein-æther theory introduces a dynamical unit timelike vector field to gravity, yielding a generally covariant framework with a locally preferred frame and Lorentz violation. The paper develops the action, analyzes linearized wave modes, Newtonian and PPN limits, energy content, and astrophysical/cosmological implications, and delineates theoretical and observational constraints on the theory’s parameters $c_i$. Key results include stability and positivity conditions for linearized modes, a renormalized cosmological gravitational constant, and potential observational handles from binary pulsars and nucleosynthesis, while outlining open questions about non-linear energy positivity and black-hole solutions. Overall, the work maps viable regions in parameter space and identifies concrete tests to distinguish Einstein-æther theory from general relativity.

Abstract

We review the status of "Einstein-Aether theory", a generally covariant theory of gravity coupled to a dynamical, unit timelike vector field that breaks local Lorentz symmetry. Aspects of waves, stars, black holes, and cosmology are discussed, together with theoretical and observational constraints. Open questions are stressed.