ar X iv : h ep - t h / 99 01 07 4 v 2 2 1 Ju n 19 99 Chiral Lagrangians and the QCD String

We propose a method to derive the low-energy efective action of QCD assuming that the long-distance properties of strong interactions can be described by a string theory. We bypass the usual problems related to the existence of the tachyon and absence of the adequate Adler zero by using a sigma model approach where excitations above the correct (chirally non-invariant) QCD vacuum are included. Two-dimensional conformal invariance then implies the vanishing of the O(p 4) effective lagrangian coefficients. We interpret this result and discuss ways to go beyond this limit.