Poincar\'e invariance and asymptotic flatness in Shape Dynamics

TL;DR

This paper demonstrates that Shape Dynamics, a gravity theory with spatial Weyl invariance, exhibits Poincaré symmetry in Minkowski spacetime and formulates it for asymptotically flat manifolds, introducing a new invariant energy definition.

Contribution

It explicitly derives equations of motion for Shape Dynamics, formulates the theory for open asymptotically flat manifolds, and introduces a new invariant total energy measure.

Findings

Shape Dynamics has Poincaré symmetry in Minkowski spacetime.

A new invariant total energy definition is proposed.

Reproduction of Schwarzschild mass within Shape Dynamics.

Abstract

Shape Dynamics is a theory of gravity that waives refoliation invariance in favor of spatial Weyl invariance. It is a canonical theory, constructed from a Hamiltonian, 3+1 perspective. One of the main deficits of Shape Dynamics is that its Hamiltonian is only implicitly constructed as a functional of the phase space variables. In this paper, I write down the equations of motion for Shape Dynamics to show that over a curve in phase space representing a Minkowski spacetime, Shape Dynamics possesses Poincar\'e symmetry for appropriate boundary conditions. The proper treatment of such boundary conditions leads us to completely formulate Shape Dynamics for open manifolds in the asymptotically flat case. We study the charges arising in this case and find a new definition of total energy, which is completely invariant under spatial Weyl transformations close to the boundary. We then use the equations of motion once again to find a non-trivial solution of Shape Dynamics, consisting of a flat static Universe with a point-like mass at the center. We calculate its energy through the new formula and rederive the usual Schwarzschild mass.