On the universality of the fluctuation-dissipation ratio in non-equilibrium critical dynamics

TL;DR

This paper investigates the universality of the fluctuation-dissipation ratio in non-equilibrium critical dynamics of 1D kinetic spin systems, revealing dependence on initial states and symmetry properties, with implications for different classes of models.

Contribution

It demonstrates that the fluctuation-dissipation ratio's universality depends on initial conditions and symmetry, identifying two distinct universality classes in 1D kinetic spin systems.

Findings

X_infinity depends on initial domain wall count

Two universality classes identified based on initial states

C-symmetry invariance determines universality class

Abstract

The two-time nonequilibrium correlation and response functions in 1D kinetic classical spin systems with non-conserved dynamics and quenched to their zero-temperature critical point are studied. The exact solution of the kinetic Ising model with Glauber dynamics for a wide class of initial states allows for an explicit test of the universality of the non-equilibrium limit fluctuation-dissipation ratio X_{\infty}. It is shown that the value of X_{\infty} depends on whether the initial state has finitely many domain walls or not and thus two distinct dynamic universality classes can be identified in this model. Generic 1D kinetic spin systems with non-conserved dynamics fall into the same universality classes as the kinetic Glauber-Ising model provided the dynamics is invariant under the C-symmetry of simultaneous spin and magnetic-field reversal. While C-symmetry is satisfied for magnetic systems, it need not be for lattice gases which may therefore display hitherto unexplored types of non-universal kinetics.