Discrete Symmetries and S Matrix of the XXZ Chain
  We formulate the notion of parity for the periodic XXZ spin chain within the Quantum Inverse Scattering Method. We also propose an expression for the eigenvalues of the charge conjugation operator. We use these discrete symmetries to help classify low-lying S^z=0 states in the critical regime, and we give a direct computation of the S matrix. 
Anastasia Doikou and Rafael I. Nepomechie