Local limit theorem for directed polymers beyond the $L^2$-phase

TL;DR

This paper establishes a local limit theorem for directed polymers in the weak disorder phase, demonstrating $L^p$-boundedness of the partition function beyond the $L^2$-phase, with implications for understanding polymer measure behavior.

Contribution

It proves the $L^p$-boundedness of the partition function beyond the $L^2$-phase and derives a local limit theorem for the polymer measure.

Findings

Partition function approximated by point-to-plane functions

$L^p$-boundedness holds beyond the $L^2$-critical point

Local limit theorem for the polymer measure

Abstract

We consider the directed polymer model in the weak disorder phase under the assumption that the partition function is $L^p$-bounded for some $p>1+\frac{2}d$. We prove that the point-to-point partition function can be approximated by two point-to-plane partition functions at the startpoint and endpoint, and in particular that it is $L^p$-bounded as well. Some consequences of this result are also discussed, the most important of which is a local limit theorem for the polymer measure. We furthermore show that the required $L^p$-boundedness holds for some range of $\beta$ beyond the $L^2$-critical point, and in the whole interior of the weak disorder phase for environments with finite support.