LETTER TO THE EDITOR: Discrete symmetries and <B> S</B>-matrix of the <B> XXZ</B> 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 0305-4470/31/37/001/img1 states in the critical regime, and we give a direct computation of the S-matrix.