m_u+m_d From Isovector Pseudoscalar Sum Rules

Abstract

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\pm 1.1 MeV (in the MS bar scheme), only marginally compatible with the most recent sum rule determinations, but in good agreement with recent unquenched lattice extractions.

15 pages, 6 figures