Status of Horava gravity: A personal perspective

TL;DR

This paper reviews the current status of Horava gravity, a quantum gravity theory that breaks Lorentz invariance at high energies, discussing its developments, challenges, and the role of the scalar graviton.

Contribution

It provides a comprehensive overview of Horava gravity, highlighting recent progress and the issues related to the scalar graviton within the framework.

Findings

Horava gravity introduces Lorentz invariance breaking at high energies.

The scalar graviton plays a significant role and poses challenges for the theory.

Maintaining small Lorentz symmetry breaking is crucial for experimental viability.

Abstract

Horava gravity is a relatively recent (Jan 2009) idea in theoretical physics for trying to develop a quantum field theory of gravity. It is not a string theory, nor loop quantum gravity, but is instead a traditional quantum field theory that breaks Lorentz invariance at ultra-high (presumably trans-Planckian) energies, while retaining approximate Lorentz invariance at low and medium (sub-Planckian) energies. The challenge is to keep the Lorentz symmetry breaking controlled and small - small enough to be compatible with experiment. I will give a very general overview of what is going on in this field, paying particular attention to the disturbing role of the scalar graviton.