The Quark Condensate fromKe4Decays

We show that, independently of the size of the quark condensate, chiral symmetry correlates the two $S$-wave $\pi \pi$ scattering lengths. In view of this constraint, the new precision data on $K_{e_4}$ decay allow a remarkably accurate determination of these quantities. The result confirms the hypothesis that the quark condensate is the leading order parameter.