Significance of the non-2-spinon part of $S(q,\omega)$ in the   one-dimensional $S=1/2$ Heisenberg antiferromagnet at zero temperature
  The impact of the non-2-spinon excitations of the one-dimensional $S=1/2$ Heisenberg antiferromagnet on the integrated intensity, the susceptibility, the frequency moments, and the Euclidian time representation of the $T=0$ dynamic spin structure factor $S(q,\omega)$ is studied on the basis of finite-size data for chains with up to $N=28$ sites. 
A Fledderjohann, K H M\"utter, M Karbach, G M\"uller