The good, the bad and the ugly .... of Horava gravity

TL;DR

This paper reviews the strengths and weaknesses of non-projectable Horava gravity, discussing its construction, issues like strong coupling, and potential phenomenological problems such as violations of the Equivalence Principle.

Contribution

It provides a critical analysis of non-projectable Horava gravity, highlighting challenges related to strong coupling and phenomenological viability, and discusses implications for the theory's consistency.

Findings

Strong coupling occurs in non-projectable Horava gravity

Potential violations of the Equivalence Principle are possible

Challenges to renormalisability and phenomenology are identified

Abstract

I review the good, the bad and the ugly of the non-projectable versions of Horava gravity. I explain how this non-relativistic theory was constructed and why it was touted with such excitement as a quantum theory of gravity. I then review some of the issues facing the theory, explaining how strong coupling occurs and why this is such a problem for both phenomenology and the question of renormalisability. Finally I comment on possible violations of Equivalence Principle, and explain why these could be an issue for Blas et al's "healthy extension". This paper was presented as a talk at PASCOS 2010 in Valencia.