The KPZ equation in a half space with flat initial condition and the unbinding of a directed polymer from an attractive wall

TL;DR

This paper provides an exact solution for the KPZ equation in a half space with flat initial conditions, revealing a binding transition of a directed polymer from an attractive wall and connections to random matrix theory.

Contribution

It introduces an exact solution for the KPZ height distribution in a half space with flat initial condition and characterizes the binding transition and related statistical identities.

Findings

Exact height distribution for KPZ in half space at any time

Identification of a binding transition at a critical wall attractiveness

Distributional identities between half-space and full-space partition functions

Abstract

We present an exact solution for the height distribution of the KPZ equation at any time $t$ in a half space with flat initial condition. This is equivalent to obtaining the free energy distribution of a polymer of length $t$ pinned at a wall at a single point. In the large $t$ limit a binding transition takes place upon increasing the attractiveness of the wall. Around the critical point we find the same statistics as in the Baik-Ben--Arous-P\'ech\'e transition for outlier eigenvalues in random matrix theory. In the bound phase, we obtain the exact measure for the endpoint and the midpoint of the polymer at large time. We also unveil curious identities in distribution between partition functions in half-space and certain partition functions in full space for Brownian type initial condition.