Paramagnetic effect of light quark loops on chiral symmetry breaking

We argue that light quark loops produce a paramagnetic suppression of infrared-sensitive order parameters such as , as the number Nf of light fermions increases. The possibly strong dependence of on Nf is related to the observed Zweig rule violation in the scalar channel. Presuming the existence of a chiral phase transition for not too large Nf, we discuss the phenomenological possibilities of separately determining the two-flavour and three-flavour condensates and the quark mass ratio r=2 ms/ (mu + md). The issue is closely related to the interpretation of new forthcoming precise pi-pi data at low energy. (author)