Perturbative calculation of improvement coefficients to O(g²a) for bilinear quark operators in lattice QCD

We calculate the O(g^2 a) mixing coefficients of bilinear quark operators in lattice QCD using a standard perturbative evaluation of on-shell Green's functions. Our results for the plaquette gluon action are in agreement with those previously obtained with the Schr\"odinger functional method. The coefficients are also calculated for a class of improved gluon actions having six-link terms.