Abstract
We study asymptotic expansions of spin-spin correlation functions for the XXZHeisenberg chain in the critical regime. We use the fact that the long-distanceeffects can be described by the Gaussian conformal field theory. Comparingexact results for form factors in the XYZ and sine-Gordon models, we determinecorrelation amplitudes for the leading and main sub-leading terms in theasymptotic expansions of spin-spin correlation functions. We also study theisotropic (XXX) limit of these expansions.