Chiral Lagrangians and the QCD string

We propose a method to derive the low-energy effective action of QCD assumi ng that the long-distance properties of strong interactions can be describe d 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 mod el approach where excitations above the correct (chirally non-invariant) QC D vacuum are included. Two-dimensional conformal invariance then implies th e vanishing of the O(p(4)) effective lagrangian coefficients. We interpret this result and discuss ways to go beyond this limit. (C) 1999 Published by Elsevier Science B.V. All rights reserved.