What is the temperature of a granular medium?

Abstract

In this paper we discuss whether thermodynamical concepts and in particular\nthe notion of temperature could be relevant for the dynamics of granular\nsystems. We briefly review how a temperature-like quantity can be defined and\nmeasured in granular media in very different regimes, namely the glassy-like,\nthe liquid-like and the granular gas. The common denominator will be given by\nthe Fluctuation-Dissipation Theorem, whose validity is explored by means of\nboth numerical and experimental techniques. It turns out that, although a\ndefinition of a temperature is possible in all cases, its interpretation is far\nfrom being obvious. We discuss the possible perspectives both from the\ntheoretical and, more importantly, from the experimental point of view.\n