Abstract
It is argued that it is valid to use QCD sum rules to determine the
scalar and pseudoscalar two-point functions at zero momentum, which in
turn determine the ratio of the strange to non-strange quark
condensates Rsu = ⟨
s⟩/⟨
q⟩ with
(q = u, d). This is done in the framework of a new set of QCD Finite
Energy Sum Rules (FESR) that involve as integration kernel a second
degree polynomial, tuned to reduce considerably the systematic
uncertainties in the hadronic spectral functions. As a result, the
parameters limiting the precision of this determination are
ΛQCD, and to a major extent the strange quark mass. From
the positivity of Rsu there follows an upper bound on the latter:
(2 GeV) ⩽ 121 (105) MeV, for ΛQCD = 330 (420) MeV.
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