On universality in aging ferromagnets

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This work is a contribution to the study of universality in out-of-equilibrium lattice models undergoing a second-order phase transition at equilibrium. The experimental protocol that we have chosen is the following: the system is prepared in its high-temperature phase and then quenched at the critical temperature Tc. We investigated by mean of Monte Carlo simulations two quantities that are believed to take universal values: the exponent λ/z obtained from the decay of autocorrelation functions and the asymptotic value X∞ of the fluctuation-dissipation ratio X(t,s). This protocol was applied to the Ising model, the 3-state clock model and the 4-state Potts model on square, triangular and honeycomb lattices and to the Ashkin-Teller model at the point belonging at equilibrium to the 3-state Potts model universality class and to a multispin Ising model and the Baxter-Wu model both belonging to the 4-state Potts model universality class at equilibrium.