On power-counting renormalizability of Ho\v{r}ava gravity with detailed balance

TL;DR

This paper analyzes the power-counting renormalizability of Hořava gravity with detailed balance, finding that only by fine-tuning couplings can the spin-0 graviton be renormalizable, raising doubts about the detailed balance approach.

Contribution

It demonstrates that achieving power-counting renormalizability for the spin-0 graviton in Hořava gravity with detailed balance requires setting a specific coupling to zero, questioning the viability of the detailed balance condition.

Findings

Spin-2 graviton is always power-counting renormalizable.

Spin-0 graviton requires fine-tuning of couplings for renormalizability.

Detailed balance condition may not be suitable for consistent Hořava gravity.

Abstract

We consider the version of Ho\v{r}ava gravity where "detailed balance" is consistently implemented, so as to limit the huge proliferation of couplings in the full theory and obtain healthy dynamics at low energy. Since a superpotential which is third-order in spatial derivatives is not sufficient to guarantee the power-counting renormalizability of the spin-0 graviton, one needs to go an order beyond in derivatives, building a superpotential up to fourth-order spatial derivatives. Here we perturb the action to quadratic order around flat space and show that the power-counting renormalizability of the spin-0 graviton is achieved only by setting to zero a specific coupling of the theory, while the spin-2 graviton is always power-counting renormalizable for any choice of the couplings. This result raises serious doubts about the use of detailed balance.