Mean-field spin glass models from the cavity-ROSt perspective

Abstract

The Sherrington-Kirkpatrick spin glass model has been studied as a source of insight into the statistical mechanics of systems with hi ghly diversified collections of competing low energy states. The goal of this summary is to present some of the ideas which have emerged in the mathematical study of its free energy. In particular, we high- light the perspective of the cavity dynamics, and the relate d variational principle. These are expressed in terms of Random Overlap Structures (ROSt), which are used to describe the possible states of the reservoir in the cavity step. The P arisi solution is presented as reflecting the ansatz that it suffices to restrict the variati on to hierarchal structures which are discussed here in some detail. While the Parisi solution was proven to be correct, through recent works of F. Guerra and M. Talagrand, the reasons for the effectiveness of the Parisi ansatz still remain to be elucidated. We question whether this could be related to the quasi-stationarity of the special subclass of ROSts giv en by Ruelle's hierarchal 'random probability cascades' (also known as GREM).