Metastability in a continuous mean-field model at low temperature and strong interaction

Abstract

We consider a system of $ N \in \mathbb{N} $ mean-field interacting stochastic differential equations that are driven by a single-site potential of double-well form and by Brownian noise. The strength of the noise is measured by a small parameter $ \varepsilon >0$ (which we interpret as the \emph{temperature}), and we suppose that the strength of the interaction is given by $ J>0 $. Choosing the \emph{empirical mean} ($ P:\mathbb{R}^N \rightarrow \mathbb{R} $, $ Px =1/N \sum_i x_i $) as the macroscopic order parameter for the system, we show that the resulting macroscopic Hamiltonian has two global minima, one at $ -m^\star_\varepsilon <0 $ and one at $ m^\star_\varepsilon>0 $. Following this observation, we are interested in the average transition time of the system to $ P^{-1}(m^\star_\varepsilon) $, when the initial configuration is drawn according to a probability measure (the so-called \emph{last-exit distribution}), which is supported around the hyperplane $ P^{-1}(-m^\star_\varepsilon) $. Under the assumption of strong interaction, $ J>1 $, the main result is a formula for this transition time, which is reminiscent of the celebrated Eyring-Kramers formula up to a multiplicative error term that tends to $ 1 $ as $ N \rightarrow \infty $ and $ \varepsilon \rightarrow 0 $. The proof is based on the \emph{potential-theoretic approach to metastability.} In the last chapter we add some estimates on the metastable transition time in the high temperature regime, where $ \varepsilon =1 $, and for a large class of single-site potentials.