Wick's theorem for nonsymmetric normal ordered products and contractions

We consider arbitrary splits of field operators into two parts; psi = psi() - psi(-), and use the corresponding definition of normal ordering introdu ced earlier [T. S. Evans and D. A. Steer, Nucl. Phys. B 474, 481 (1996)]. I n this case the normal ordered products and contractions have none of the s pecial symmetry properties assumed in existing proofs of Wick's theorem. De spite this, we prove that Wick's theorem still holds in its usual form as l ong as the contraction is a c-number. Wick's theorem is thus shown to be mu ch more general than existing derivations suggest, and we discuss possible simplifying applications of this result. (C) 1998 American Institute of Phy sics. [S0022-2488(98)01911-2].