Experimental tests of curvature couplings of Fermions in General   Relativity
  Spin 1/2 particles in geodesic trajectories experience no gravitational potential but they still have non-zero couplings to the curvature tensor. The effect of space time curvature on fermions can be parameterized by a vector and a pseudo-vector potential. These apparent CPT violating terms can be measured with satellite based spin-polarized torsion balance and clock comparison experiments. The Earth's curvature effect is of the order of 10^{-37} Gev which is not far from the present bounds of ~10^{-29} Gev on such CPT violating couplings. 
S. Mohanty, B. Mukhopadhyay and A. R. Prasanna