Spin Correlation Functions And Decay Of Quasiparticles In Xxz Spin Chain At T > 0

We study a one-dimensional anisotropic XXZ spin-1/2 model with ferromagnetic sign of the coupling and z-z exchange constant J(z) = Delta J, where Delta < 1, and J is the coupling within the XY spin plane. We calculate the damping of low-energy excitations with. omega << T due to their scattering from thermal excitation bath with temperature T << J, taking into account nonzero curvature of the excitation spectrum, epsilon(q) = uq + delta epsilon (q). We calculate also longitudinal spin-spin correlation function < S-z(x, t) S-z(0,0) > at x approximate to ut and find the shape of the spreading "wave packet".