Modulus of continuity for polymer fluctuations and weight profiles in Poissonian last passage percolation

TL;DR

This paper investigates the regularity and fluctuation properties of polymers and weight profiles in Poissonian last passage percolation, revealing sharp bounds involving power laws and logarithmic corrections within the KPZ universality class.

Contribution

It establishes sharp modulus of continuity bounds for polymers and weight profiles, identifying specific exponent pairs for fluctuations and weight variations in the KPZ class.

Findings

Polymer fluctuations have modulus of continuity at most $t^{2/3}(ig( ext{log } t^{-1}ig)^{1/3}$.

Maximum transversal fluctuation among polymers scales as $t^{2/3}( ext{log } t^{-1})^{1/3}.

Weight profile variations have sharp modulus of continuity of order $t^{1/3}( ext{log } t^{-1})^{2/3}.

Abstract

In last passage percolation models, the energy of a path is maximized over all directed paths with given endpoints in a random environment, and the maximizing paths are called geodesics. The geodesics and their energy can be scaled so that transformed geodesics cross unit distance and have fluctuations and scaled energy of unit order. Here we consider Poissonian last passage percolation, a model lying in the KPZ universality class, and refer to scaled geodesics as polymers and their scaled energies as weights. Polymers may be viewed as random functions of the vertical coordinate and, when they are, we show that they have modulus of continuity whose order is at most $t^{2/3}\big(\log t^{-1}\big)^{1/3}$. The power of one-third in the logarithm may be expected to be sharp and in a related problem we show that it is: among polymers in the unit box whose endpoints have vertical separation $t$ (and a horizontal separation of the same order), the maximum transversal fluctuation has order $t^{2/3}\big(\log t^{-1}\big)^{1/3}$. Regarding the orthogonal direction, in which growth occurs, we show that, when one endpoint of the polymer is fixed at $(0,0)$ and the other is varied vertically over $(0,z)$, $z\in [1,2]$, the resulting random weight profile has sharp modulus of continuity of order $t^{1/3}\big(\log t^{-1}\big)^{2/3}$. In this way, we identify exponent pairs of $(2/3,1/3)$ and $(1/3,2/3)$ in power law and polylogarithmic correction, respectively for polymer fluctuation, and polymer weight under vertical endpoint perturbation. The two exponent pairs describe [10,11,9] the fluctuation of the boundary separating two phases in subcritical planar random cluster models.