Dynamics of the anisotropic conformal Horava theory versus its kinetic-conformal formulation

TL;DR

This paper compares the dynamics of anisotropic conformal Horava gravity with its kinetic-conformal version, analyzing their constraints, degrees of freedom, and specific solutions, revealing how symmetry breaking affects physical modes.

Contribution

It provides a detailed canonical analysis of both theories, showing how the Weyl symmetry influences constraints and degrees of freedom, and introduces explicit models including the Cotton^2 potential.

Findings

Both theories propagate the same degrees of freedom as General Relativity.

Breaking Weyl symmetry converts a first-class constraint into a second-class constraint.

Explicit conformally flat solutions are found in both theories.

Abstract

We contrast the dynamics of the Horava theory with anisotropic Weyl symmetry with the case when this symmetry is explicitly broken, which is called the kinetic-conformal Horava theory. To do so we perform the canonical formulation of the anisotropic conformal theory at the classical level with a general conformal potential. Both theories have the generator of the anisotropic Weyl transformations as a constraint but it changes from first to second-class when the Weyl symmetry is broken. The FDiff-covariant vector a_i = \partial_i \ln N plays the role of gauge connection for the anisotropic Weyl transformations. A Lagrange multiplier plays also the role of gauge connection, being the time component. The anisotropic conformal theory propagates the same number of degrees of freedom of the kinetic-conformal theory, which in turn are the same of General Relativity. This is due to exchange of a second-class constraint in the kinetic-conformal case by a gauge symmetry in the anisotropic conformal case. An exception occurs if the conformal potential does not depend on the lapse function N, as is the case of the so called Cotton^2 potential, in which case one of the physical modes becomes odd. We develop in detail two explicit anisotropic conformal models. One of them depends on N whereas the other one is the Cotton^2 model. We also study conformally flat solutions in the anisotropic conformal and the kinetic-conformal theories, defining as conformally flat the spatial metric, but leaving for N a form different to the one dictated by the anisotropic Weyl transformations. We find that in both theories these configurations have vanishing canonical momentum and they are critical points of the potential. In the kinetic-conformal theory we find explicitly an exact, nontrivial, conformally flat solution.