Self-organization, detailed balance, and stress-structure correlations in 2D granular dynamics

We argue that a suite of recent experimental and numerical observations are signatures of cooperative stress-structure self-organisation (SO) in granular dynamics. These observations include: a) detail-insensitive collapses of certain quantities; b) correlations between stress and structure and evidence of entropy-stability competition in settled packings, which cast doubt on most linear stress theories of granular materials; c) detailed balanced steady states, which seem contradictory to the common belief that only systems in thermal equilibrium satisfy detailed balance, but are not, as we explain. We then propose a new statistical mechanical formulation that takes into account the cooperative SO.