mu+md 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 satisfied in the isovector vector channel. The sum rule constraints are sufficiently strong to allow a determination of both m(u) + m(d) and the excited resonance decay constants. The corresponding Borel transformed sum rules are also very well satisfied, providing a non-trivial consistency check on the treatment of direct instanton contributions. We obtain [m(u) + m(d)](2 GeV) = 7.8 +/- 1.1 MeV (in the MS scheme), only marginally compatible with the most recent sum rule determinations, but in good agreement with recent unquenched lattice extractions. (C) 2001 Elsevier Science B.V. All rights reserved.