Errico Presutti

Statistical mechanics of systems of unbounded spins

We develop the statistical mechanics of unboundedn-component spin systems on the latticeZv interacting via potentials which are superstable and strongly tempered. We prove the existence and uniqueness of the infinite volume free energy density for a wide class of boundary conditions. The uniqueness of the equilibrium state (whose existence is established in general) is then proven for one component ferromagnetic spins whose free energy is differentiable with respect to the magnetic field.

Heat Flow in an Exactly Solvable Model

A chain of one-dimensional oscillators is considered. They are mechanically uncoupled and interact via a stochastic process which redistributes the energy between nearest neighbors. The total energy is kept constant except for the interactions of the extremal oscillators with reservoirs at different temperatures. The stationary measures are obtained when the chain is finite; the thermodynamic limit is then considered, approach to the Gibbs distribution is proven, and a linear temperature profile is obtained.

Stability of the interface in a model of phase separation.

The paper is concerned with the asymptotic behaviour of the solutions to a nonlocal evolution equation which arises in models of phase separation. As in the Allen–Cahn equations, stationary spatially nonhomogeneous solutions exist, which represent the interface profile between stable phases. Local stability of these interface profiles is proved.

Glauber evolution with Kac potentials. I. Mesoscopic and macroscopic limits, interface dynamics

This is the first of three papers on the Glauber evolution of Ising spin systems with Kac potentials. We begin with the analysis of the mesoscopic limit, where space scales like the diverging range, gamma -1, of the interaction while time is kept finite: we prove that in this limit the magnetization density converges to the solution of a deterministic, nonlinear, nonlocal evolution equation. We also show that the long time behaviour of this equation describes correctly the evolution of the spin system till times which diverge as gamma to 0 but are small in units log gamma -1. In this time regime we can give a very precise description of the evolution and a sharp characterization of the spin trajectories. As an application of the general theory, we then prove that for ferromagnetic interactions, in the absence of external magnetic fields and below the critical temperature, on a suitable macroscopic limit, an interface between two stable phases moves by mean curvature. All the proofs are consequence of sharp estimates on special correlation functions, the v-functions, whose analysis is reminiscent of the cluster expansion in equilibrium statistical mechanics.

Travelling fronts in non-local evolution equations

The existence of travelling fronts and their uniqueness modulo translations are proved in the context of a one-dimensional, non-local, evolution equation derived in [5] from Ising systems with Glauber dynamics and Kac potentials. The front describes the moving interface between the stable and the metastable phases and it is shown to attract all the profiles which at ± ∞ are in the domain of attraction of the stable and, respectively, the metastable states. The results are compared with those of Fife & McLeod [13] for the Allen-Cahn equation.

Surface tension in Ising systems with Kac potentials

We consider an Ising spin system with Kac potentials in a torus of ℤd,d>-2, and fix the temperature below its Lebowitz-Penrose critical value. We prove that when the Kac scaling parameter γ vanishes, the log of the probability of an interface becomes proportional to its area and the surface tension, related to the proportionality constant, converges to the van der Waals surface tension. The results are based on the analysis of the rate functionals for Gibbsian large deviations and on the proof that they Γ-converge to the perimeter functional of geometric measure theory (which extends the notion of area). Our considerations include nonsmooth interfaces, proving that the Gibbsian probability of an interface depends only on its area and not on its regularity.

Existence and uniqueness of DLR measures for unbounded spin systems

SummaryA system of random variables(spins) Sx,x∈ℤ v, taking on values in ℝ is considered. Conditional probabilities for the joint distributions of a finite number of spins are prescribed; a DLR measure is then a process on the random variables which is consistent with the assigned conditional probabilities [1,2]. A case of physical interest both in Statistical Mechanics and in the lattice approximation to Quantum Field Theory is considered for which the spins interact pairwise via a potential JxySxSy, Jxy∈ℝ and via a self-interaction F(Sx), which, as ¦Sx¦→∞, diverges at least quadratically [3].By use of a technique introduced in [2] it is proven that the set

Ultraviolet stability in Euclidean scalar field theories

\mathfrak{E} = \{ v is DLR|\exists c(v), \mathop {sup}\limits_{x \in \mathbb{Z}^v } \int {v(dS_x )} |S_x | < c(v)\}