If general relativity is an emergent phenomenon, there may be small violations of diffeomorphism invariance. We propose a phenomenology of perturbatively small violations of general relativity by the inclusion of terms which break general covariance. These can be tested by matching to the parameterized post-Newtonian formalism. The most sensitive tests involve pulsar timing and provide an extremely strong bound, with a dimensionless constraint of order ${10}^{-20}$ relative to gravitational strength.

• Received 22 December 2009

DOI:https://doi.org/10.1103/PhysRevD.81.084059