Out-of-equilibrium dynamics in a Gaussian trap model

Abstract

The violations of the fluctuation–dissipation theorem are analysed for a trap model with aGaussian density of states. In this model, the system reaches thermal equilibrium for longtimes after a quench to any finite temperature and therefore all ageing effectare of a transient nature. For not too long times after the quench it is foundthat the so-called fluctuation–dissipation ratio tends to a non-trivial limit, thusindicating the possibility for the definition of a timescale-dependent effectivetemperature. However, different definitions of the effective temperature yielddistinct results. In particular, plots of the integrated response versus the correlationfunction strongly depend on the way they are constructed. Also the definitionof effective temperatures in the frequency domain is not unique for the modelconsidered. This may have some implications for the interpretation of results fromcomputer simulations and experimental determinations of effective temperatures.