Renormalisation and off-shell improvement in lattice perturbation theory

We discuss the improvement of flavour non-singlet point and one-link lattic e quark operators, which describe the quark currents and the first moment o f the DIS structure functions respectively. Suitable bases of improved oper ators are given, and the corresponding renormalisation factors and improvem ent coefficients are calculated in one-loop lattice perturbation theory, us ing the Sheikholeslami-Wohlert (clover) action. To this order we achieve of f-shell improvement by eliminating the effect of contact terms. We use mass ive fermions, and our calculations are done keeping all terms up to first o rder in the lattice spacing, for arbitrary m(2)/p(2), in a general covarian t gauge. We also compare clover fermions with fermions satisfying the Ginsp arg-Wilson relation, and show how to remove O (a) effects off-shell in this case too, and how this is in many aspects simpler than for clover fermions . Finally, tadpole improvement is also considered. (C) 2001 Elsevier Scienc e B.V. All rights reserved.