m(u)+m(d) from isovector pseudoscalar sum rules

We revisit the isovector pseudoscalar sum rule determination of m(u) + m(d) , using families of finite energy sum rules known to be very accurately sat isfied in the isovector vector channel. The sum rule constraints are suffic iently strong to allow a determination of both m(u) + m(d) and the excited resonance decay constants. The corresponding Borel transformed sum rules ar e also very well satisfied, providing a non-trivial consistency check on th e treatment of direct instanton contributions. We obtain [m(u) + m(d)](2 Ge V) = 7.8 +/- 1.1 MeV (in the MS scheme), only marginally compatible with th e most recent sum rule determinations, but in good agreement with recent un quenched lattice extractions. (C) 2001 Elsevier Science B.V. All rights res erved.