Critical behaviour of integrable mixed-spin chains

We construct a mixed spin 1/2 and $S$ integrable model and investigate its finite size properties. For a certain conformal invariant mixed spin system the central charge can be decomposed in terms of the conformal anomaly of two single integrable models of spin 1/2 and spin $(S-1/2)$. We also compute the ground state energy and the sound velocity in the thermodynamic limit.