Continuous spin models on annealed generalized random graphs

TL;DR

This paper analyzes Gibbs distributions of spins on annealed generalized random graphs, deriving a variational formula for pressure, studying phase transitions, and classifying critical exponents, especially in heavy-tailed weight distributions.

Contribution

It provides a variational formula for annealed pressure, criteria for phase transition absence, and classifies critical exponents for models with second order phase transitions.

Findings

Derived a variational formula for annealed pressure.

Identified conditions for absence of phase transitions.

Classified critical exponents and their dependence on tail behavior.

Abstract

We study Gibbs distributions of spins taking values in a general compact Polish space, interacting via a pair potential along the edges of a generalized random graph with a given asymptotic weight distribution $P$, obtained by annealing over the random graph distribution. First we prove a variational formula for the corresponding annealed pressure and provide criteria for absence of phase transitions in the general case. We furthermore study classes of models with second order phase transitions which include rotation-invariant models on spheres and models on intervals, and classify their critical exponents. We find critical exponents which are modified relative to the corresponding mean-field values when $P$ becomes too heavy-tailed, in which case they move continuously with the tail-exponent of $P$. For large classes of models they are the same as for the Ising model treated in \cite{DomGiaGibHofPri16}. On the other hand, we provide conditions under which the model is in a different universality class, and construct an explicit example of such a model on the interval.