title: Fluctuation-dissipation relation in an Ising model without detailed balance.
abstract: We consider the modified Ising model introduced by de Oliveira, Mendes, and Santos [J. Phys. A 26, 2317 (1993)], where the temperature depends locally on the spin configuration and detailed balance and local equilibrium are not obeyed. We derive a relation between the linear response function and correlation functions that generalizes the fluctuation-dissipation theorem. In the stationary states of the model, which are the counterparts of the Ising equilibrium states, the fluctuation-dissipation theorem breaks down due to the lack of time reversal invariance. In the nonstationary phase-ordering kinetics, the parametric plot of the integrated response function chi(t,t(w)) vs the autocorrelation function is different from that of the kinetic Ising model. However, splitting chi(t,t(w)) into a stationary and an aging term chi(t,t(w)) = chi(st)(t-t(w)) + chi(ag)(t,t(w)), we find chi(ag)(t,t(w)) approximately t(w)(-a(chi)) f(t/t(w)), and a numerical value of a(chi) consistent with a(chi)= 1/4, as in the kinetic Ising model.
authors.affiliation: Istituto Nazionale di Fisica della Materia, Unità di Salerno and Dipartimento di Fisica E.R.Caianiello, Università di Salerno, 84081 Baronissi (Salerno), Italy. andrenacci@sa.infn.it
authors.forename: Natascia
authors.initials: N
authors.lastname: Andrenacci
authors.forename: Federico
authors.initials: F
authors.lastname: Corberi
authors.forename: Eugenio
authors.initials: E
authors.lastname: Lippiello