Approximation Method for the Relaxed Covariant Form of the Gravitational   Field Equations for Particles
  We present a study of the so called relaxed field equations of general relativity in terms of a decomposition of the metric; which is designed to deal with the notion of particles. Several known results are generalized to a coordinate free covariant discussion. We apply our techniques to the study of a particle up to second order. 
Emanuel Gallo and O. M. Moreschi
gr-qc