Hamiltonian analysis of nonprojectable Ho\v{r}ava-Lifshitz gravity with $U(1)$ symmetry

TL;DR

This paper performs a Hamiltonian analysis of nonprojectable U(1) extended Hořava-Lifshitz gravity to determine conditions for the absence of the scalar graviton, revealing it generally persists due to quantum corrections.

Contribution

It identifies the specific conditions under which the scalar graviton is absent at the nonlinear level in the theory.

Findings

Scalar graviton absent if and only if two coupling constants are zero

These coupling constants are marginal and generated by quantum corrections

In general, the scalar graviton persists in the theory

Abstract

We study the nature of constraints and count the number of degrees of freedom in the nonprojectable version of the $U(1)$ extension of Ho\v{r}ava-Lifshitz gravity, using the standard method of Hamiltonian analysis in the classical field theory. This makes it possible for us to investigate the condition under which the scalar graviton is absent at a fully nonlinear level. We show that the scalar graviton does not exist at the classical level if and only if two specific coupling constants are exactly zero. The operators corresponding to these two coupling constants are marginal for any values of the dynamical critical exponent of the Lifshitz scaling and thus should be generated by quantum corrections even if they are eliminated from the bare action. We thus conclude that the theory in general contains the scalar graviton.