QCD SUM-RULE CONSISTENCY OF LOWEST-LYING Q(Q)OVER-BAR SCALAR RESONANCES

We investigate lowest-lying scalar meson properties predicted from QCD Laplace sum rules based upon isovector and isoscalar non-strange (q) over bar q currents. The hadronic content of these sum rules incorpora tes deviations from the narrow resonance approximation anticipated fro m physical resonance widths. The field theoretical content of these su m rules incorporates purely perturbative QCD contributions to three-lo op order, the direct single-instanton contribution in the instanton li quid model, and leading contributions from QCD-vacuum condensates. In the isovector channel, the results we obtain are compatible with a(0)( 1450) being the lowest-lying q (q) over bar resonance, and are indicat ive of a non-q (q) over bar interpretation for a(0)(980). In the isosc alar channel, the results we obtain are compatible with the lowest lyi ng q (q) over bar resonance being f(0)(980) or a state somewhat lighte r than f(0)(980) whose width is less than half of its mass. A linear s igma-model interpretation of the lowest-lying resonance's coupling, wh en compared to the coupling predicted by sum rules, is indicative of a renormalization-group invariant light-quark mass between 4 and 6 MeV. (C) 1998 Elsevier Science B.V.