Testing Gravity Theories In The Radiative Regime Using Pulsar Timing   Arrays
  General relativity has predicted the existence of gravitational waves (GW), which are waves of the distortions of space-time with two degrees of polarization and the propagation speed of light. Alternative theories predict more polarizations, up to a maximum of six, and possible deviation of propagation speed from the light speed. The present paper reviews recent proposals to test the gravity theories in the radiation regime by observing GWs using pulsar timing arrays. 
K.J.Lee
astro-ph.HE gr-qc