CURRENT CORRELATORS TO ALL ORDERS IN THE QUARK MASSES

The contributions to the coefficient functions of the quark and the mi xed quark-gluon condensate to mesonic correlators are calculated for t he first time to all orders in the quark masses, and to lowest order i n the strong coupling constant. Existing results on the coefficient fu nctions of the unit operator and the gluon condensate are reviewed. Th e proper factorization of short- and long-distance contributions in th e operator product expansion is discussed in detail. It is found that to accomplish this task rigorously the operator product expansion has to be performed in terms of non-normal-ordered condensates. The result ing coefficient functions are improved with the help of the renormaliz ation group. The scale invariant combination of dimension 5 operators, including mixing with the mass operator, which is needed for the reno rmalization group improvement, is calculated in the leading order.