BELOW-UNITARITY-THRESHOLD BRANCH CUT IN THE ((Q)OVER-BAR-Q) COEFFICIENT OF THE AXIAL-VECTOR 2-CURRENT CORRELATION-FUNCTION

The dimension-3 quark-condensate component of the flavour-diagonal axial-vector two-current correlation function is evaluated to all orders in the quark mass m(qk) through use of the quark-condensate component of the nonperturbative fermion propagator. The result obtained is analytic in p2 except for a branch cut for 0 < p2 < (2m(qk))2, corresponding to a branch cut occurring below the qqBAR kinematic threshold. The deep Euclidean region of the longitudinal component of this correlation function is utilized to obtain leading and subleading contributions to the QCD sum-rule relating m(qk) to [qqBAR]. These same sum-rule results are obtained by means of an alternative derivation involving integration over the discontinuity in the correlation function along the branch cut, demonstrating the consistency of the physical-momentum-region branch cut with results obtained via standard means in the deep Euclidean region.