CONSTRAINT-PRESERVING BOUNDARY CONDITIONS: THE GOWDY WAVES TEST-BED

The Gowdy waves metric is proposed as a strong-field test-bed for constraint-preserving boundary conditions in Numerical Relativity. The 3-torus space topology allows periodic boundary conditions, so that one can test the constraint-related degrees of freedom by themselves, without requiring any further ansatz for the remaining modes. Also, the planar symmetry of the solution allows testing separately the longitudinal and transverse modes, by applying the boundary conditions selectively to one or another face.