Poincaré invariance and asymptotic flatness in 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 space-time, 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 nontrivial solution of shape dynamics, consisting of a flat static Universe with a pointlike mass at the center. We calculate its energy through the new formula and rederive the usual Schwarzschild mass.