Nf dependence of the quark condensate from a chiral sum rule
I.P.N., Groupe de Physique Théorique,
Université Paris-Sud, 91406 Orsay Cédex, France
Received: 3 September / Published online: 6 April 2000 - © Springer-Verlag 2000
How fast does the quark condensate in QCD-like theories vary as a function of Nfis inferred from real QCD using chiral perturbation theory at order one loop. A sum rule is derived for the single relevant chiral coupling constant, L6. A model independent lower bound is obtained. The spectral function satisfies a Weinberg-type superconvergence relation. It is discussed how this, together with chiral constraints, allows a solid evaluation of L6, based on experimental - S-wave T-matrix input. The resulting value of L6 is compatible with a strong Nf dependence possibly suggestive of the proximity of a chiral phase transition.
Copyright Società Italiana di Fisica, Springer-Verlag 2000