Marco Zannetti

Off-equilibrium generalization of the fluctuation dissipation theorem for Ising spins and measurement of the linear response function.

We derive for Ising spins an off-equilibrium generalization of the fluctuation dissipation theorem, which is formally identical to the one previously obtained for soft spins with Langevin dynamics [L.F. Cugliandolo, J. Kurchan, and G. Parisi, J. Phys. I 4, 1641 (1994)]. The result is quite general and holds both for dynamics with conserved and nonconserved order parameters. On the basis of this fluctuation dissipation relation, we construct an efficient numerical algorithm for the computation of the linear response function without imposing the perturbing field, which is alternative to those of Chatelain [J. Phys. A 36, 10 739 (2003)] and Ricci-Tersenghi [Phys. Rev. E 68, 065104(R) (2003)]. As applications of the new algorithm, we present very accurate data for the linear response function of the Ising chain, with conserved and nonconserved order parameter dynamics, finding that in both cases the structure is the same with a very simple physical interpretation. We also compute the integrated response function of the two-dimensional Ising model, confirming that it obeys scaling chi (t, t(w)) approximately equal to t(-a)(w) f (t/t(w)) , with a =0.26+/-0.01 , as previously found with a different method.

Fluctuation dissipation ratio in the one-dimensional kinetic ising model

The exact relation between the response function

Fluctuation dissipation relations far from equilibrium

R(t,t^{\prime})

Nonlinear response and fluctuation-dissipation relations

and the two time correlation function

Scaling behavior of response functions in the coarsening dynamics of disordered ferromagnets

C(t,t^{\prime})

Slow relaxation in the large-N model for phase ordering.

is derived analytically in the one dimensional kinetic Ising model subjected to a temperature quench. The fluctuation dissipation ratio

The effective temperature in the quenching of coarsening systems to and to below TC

X(t,t^{\prime})

Interface fluctuations, bulk fluctuations, and dimensionality in the off-equilibrium response of coarsening systems.

is found to depend on time through

Crossover in growth law and violation of superuniversality in the random-field Ising model.

C(t,t^{\prime})

Nonlinear susceptibilities and the measurement of a cooperative length

in the time region where scaling