Phase Ordering Dynamics in the Continuum q-state Clock Model
  The order parameter correlation function of the nonconserved, continuum $q$-state clock model is evaluated in the asymptotic scaling limit, during the phase ordering process after a temperature quench. The short distance behavior of the order parameter scaling function exhibits explicit crossover from that characteristic of the Ising universality class to that of the $O(2)$ model. 
Fong Liu and Gene F. Mazenko