Uniqueness of Gibbs measures for continuous hardcore models
Name
1708.04263.pdf
Description
Submitted version
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667.74 KB
Format
Adobe PDF
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b4ce834b263ff821110fc5dd487145e4
Author(s)
Gamarnik, David
Ramanan, Kavita
Date Issued
2019
Journal
The Annals of Probability
Publisher
Institute of Mathematical Statistics
Version
Original manuscript
Abstract
© 2019, Institute of Mathematical Statistics. We formulate a continuous version of the well-known discrete hardcore (or independent set) model on a locally finite graph, parameterized by the so-called activity parameter λ > 0. In this version the state or "spin value" xu of any node u of the graph lies in the interval [0, 1], the hardcore constraint xu + xv ≤ 1 is satisfied for every edge (u, v) of the graph, and the space of feasible configurations is given by a convex polytope. When the graph is a regular tree, we show that there is a unique Gibbs measure associated to each activity parameter λ > 0. Our result shows that, in contrast to the standard discrete hardcore model, the continuous hardcore model does not exhibit a phase transition on the infinite regular tree. We also consider a family of continuous models that interpolate between the discrete and continuous hardcore models on a regular tree when λ = 1 and show that each member of the family has a unique Gibbs measure, even when the discrete model does not. In each case the proof entails the analysis of an associated Hamiltonian dynamical system that describes a certain limit of the marginal distribution at a node. Furthermore, given any sequence of regular graphs with fixed degree and girth diverging to infinity, we apply our results to compute the asymptotic limit of suitably normalized volumes of the corresponding sequence of convex polytopes of feasible configurations. In particular this yields an approximation for the partition function of the continuous hard core model on a regular graph with large girth in the case λ = 1.
MIT Department
Sloan School of Management
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DOI of Published Version
https://doi.org/10.1214/18-AOP1298
