A nonperturbative determination of cA
  We describe a non-perturbative determination of $c_A$ using correlators containing the axial-vector and pseudoscalar currents at zero and non-zero momentum. We apply the method of Bhattacharya et al to extract $c_A$ from the requirement that the ratio of appropriate correlators for the PCAC relation becomes independent of time in the excited state region. We find that the result depends strongly on the order of the derivatives used in the PCAC relation. We also find that, using the lowest order derivatives, we cannot get a consistent value of $c_A$ between zero and non-zero momentum cases. The $c_A$ values that we obtain as we improve the derivatives are consistent and decrease in magnitude heading towards the perturbative result. 
S. Collins and C.T.H. Davies