Transition rates via Bethe ansatz for the spin-1/2 Heisenberg chain
  We use the exact determinantal representation derived by Kitanine, Maillet, and Terras for matrix elements of local spin operators between Bethe wave functions of the one-dimensional s=1/2 Heisenberg model to calculate and numerically evaluate transition rates pertaining to dynamic spin structure factors. For real solutions z_1,...,z_r of the Bethe ansatz equations, the size of the determinants is of order r x r. We present applications to the zero-temperature spin fluctuations parallel and perpendicular to an external magnetic field. 
Daniel Biegel, Michael Karbach and Gerhard Muller