Paramagnetic effect of light quark loops on chiral symmetry breaking

We argue that light quark loops produce a paramagnetic suppression of infra red-sensitive order parameters such as <(q) over bar >q, as the number N-f of light fermions increases. The possibly strong dependence of <(q) over ba r >q on N-f is related to the observed Zweig rule violation in the scalar c hannel. Presuming the existence of a chiral phase transition for not too la rge Nf, we discuss the phenomenological possibilities of separately determi ning the two-flavour and three-flavour condensates and the quark mass ratio r = 2m(s)=(m(u)+m(d)). The issue is closely related to the interpretation of new forthcoming precise pi pi data at low energy.