Localization of directed polymers in continuous space

TL;DR

This paper introduces a new way to measure the space of probability measures and applies it to study localization phenomena of directed polymers in Euclidean spaces, revealing phase transitions between high and low temperature regimes.

Contribution

It provides a new metrization of the Mukherjee--Varadhan topology and extends localization results for directed polymers to general Euclidean random walks.

Findings

Distribution concentrated on zero measure is unique in high temperature.

Asymptotic clustering occurs in low temperature.

Endpoint distribution is localized with positive density in low temperature.

Abstract

The first main goal of this article is to give a new metrization of the Mukherjee--Varadhan topology, recently introduced as a translation-invariant compactification of the space of probability measures on Euclidean spaces. This new metrization allows us to achieve our second goal which is to extend the recent program of Bates and Chatterjee on localization for the endpoint distribution of discrete directed polymers to polymers based on general random walks in Euclidean spaces. Following their strategy, we study the asymptotic behavior of the endpoint distribution update map and study the set of its distributional fixed points satisfying a variational principle. We show that the distributdion concentrated on the zero measure is a unique element in this set if and only if the system is in the high temperature regime. This enables us to prove that the asymptotic clustering (a natural continuous analogue of the asymptotic pure atomicity property) holds in the low temperature regime and that the endpoint distribution is geometrically localized with positive density if and only if the system is in the low temperature regime.