Non-perturbative improvement of the axial current for dynamical Wilson fermions

A non-perturbative determination of the axial current improvement coefficient cA is performed with two flavors of dynamical improved Wilson fermions and plaquette gauge action. The improvement condition is formulated with Schroedinger functional boundary conditions and enforced at constant physical volume. Large sensitivity is obtained by using two different pseudo-scalar states in the PCAC relation. We estimate the resulting correction to F_PS at beta=5.2 to be around 10%.