title: Fluctuation-dissipation relations and field-free algorithms for the computation of response functions.
abstract: We discuss the relation between the fluctuation-dissipation relation derived by Chatelain and Ricci-Tersenghi [C. Chatelain, J. Phys. A 36, 10739 (2003); F. Ricci-Tersenghi, Phys. Rev. E 68, 065104(R) (2003)] and that by Lippiello-Corberi-Zannetti [E. Lippiello, F. Corberi, and M. Zannetti, Phys. Rev. E 71, 036104 (2005)]. In order to do that, we rederive the fluctuation-dissipation relation for systems of discrete variables evolving in discrete time via a stochastic nonequilibrium Markov process. The calculation is carried out in a general formalism comprising the Chatelain, Ricci-Tersenghi, result and that by Lippiello-Corberi-Zannetti as special cases. The applicability, generality, and experimental feasibility of the two approaches are thoroughly discussed. Extending the analytical calculation to the variance of the response function, we show the advantage of field-free numerical methods with respect to the standard method, where the perturbation is applied. We also show that the signal-to-noise ratio is better (by a factor square root of 2) in the algorithm of Lippiello-Corberi-Zannetti with respect to that of Chatelain-Ricci Tersenghi.
authors.affiliation: Dipartimento di Matematica ed Informatica and INFN, Gruppo Collegato di Salerno and CNISM, Unitá di Salerno, Università di Salerno, Via Ponte don Melillo, Fisciano (SA), Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Corberi
authors.forename: Eugenio
authors.initials: E
authors.lastname: Lippiello
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sarracino
authors.forename: Marco
authors.initials: M
authors.lastname: Zannetti