Odd-dimensional gravitational waves from a binary system on a three-brane

Abstract

We consider gravitational radiation in the presence of non-compact extra dimensions. If their number is odd, all spacetime becomes odd-dimensional and formation of gravitational radiation becomes non-trivial because of violation of the Huygens principle. Gravitational waves travel with the speed of light, while the full retarded gravitational field of a localized source propagates with all velocities lower or equal to the speed of light, so special care is needed to extract radiation. Here we consider a simplified model consisting of two point masses moving on a three-brane embedded in five-dimensional bulk. Particles are assumed to interact through a massless scalar field living on the same brane, while gravitational radiation is emitted into the full five-dimensional space. We use the Rohrlich-Teitelboim approach to radiation, extracting the radiative component of the retarded gravitational field via splitting of the energy-momentum tensor. The source term consists of the local contribution from the particles and the non-local contribution from the scalar field stresses. The latter is computed using the DIRE approach to the post-Newtonian expansions. In the non-relativistic limit, we find an analog of the quadrupole formula containing the integral over the full history of motion, preceding the retarded moment of time. We compute gravitational radiation and study the orbit evolution of the non-relativistic circular binary system on the brane.