Scaling and universality in the aging kinetics of the two-dimensional   clock model
  We study numerically the aging dynamics of the two-dimensional p-state clock model after a quench from an infinite temperature to the ferromagnetic phase or to the Kosterlitz-Thouless phase. The system exhibits the general scaling behavior characteristic of non-disordered coarsening systems. For quenches to the ferromagnetic phase, the value of the dynamical exponents, suggests that the model belongs to the Ising-type universality class. Specifically, for the integrated response function $\chi (t,s)\simeq s^{-a_\chi}f(t/s)$, we find $a_\chi $ consistent with the value $a_\chi =0.28$ found in the two-dimensional Ising model. 
Federico Corberi, Eugenio Lippiello and Marco Zannetti