Fluctuation-dissipation relation and the Edwards entropy for a glassy granular compaction model

TL;DR

This paper analytically investigates a one-dimensional glassy granular compaction model, revealing a non-equilibrium fluctuation-dissipation relation and confirming Edwards entropy's consistency with dynamical fluctuations.

Contribution

It provides the first analytical confirmation of Edwards entropy matching dynamical fluctuations in a non-mean-field glassy model.

Findings

Correlation and response functions are exactly calculated in the dense, low tapping strength limit.

A non-equilibrium fluctuation-dissipation theorem relates response and correlation functions.

Edwards entropy matches the fluctuations observed in the dynamical analysis.

Abstract

We analytically study a one dimensional compaction model in the glassy regime. Both correlation and response functions are calculated exactly in the evolving dense and low tapping strength limit, where the density relaxes in a $1/\ln t$ fashion. The response and correlation functions turn out to be connected through a non-equilibrium generalisation of the fluctuation-dissipation theorem. The initial response in the average density to an increase in the tapping strength is shown to be negative, while on longer timescales it is shown to be positive. On short time scales the fluctuation-dissipation theorem governs the relation between correlation and response, and we show that such a relationship also exists for the slow degrees of freedom, albeit with a different temperature. The model is further studied within the statistical theory proposed by Edwards and co-workers, and the Edwards entropy is calculated in the large system limit. The fluctuations described by this approach turn out to match the fluctuations as calculated through the dynamical consideration. We believe this to be the first time these ideas have been analytically confirmed in a non-mean-field model.