Martin Boundary and the Nonlinear Multiplicative Stochastic Heat Equation in Weak Disorder

TL;DR

This paper explores the structure of invariant random fields for nonlinear stochastic heat equations in weak disorder, linking them to Martin boundary theory and harmonic functions across various geometric settings.

Contribution

It establishes a correspondence between invariant fields and harmonic functions, extending Martin boundary concepts to stochastic heat equations in complex spaces.

Findings

Invariant fields correspond to bounded harmonic functions.

Stochastic evolution converges to invariant fields under certain conditions.

Results apply to negatively curved manifolds and trees.

Abstract

We study invariant random fields of nonlinear multiplicative stochastic heat equations in the weak disorder regime. Under a natural second-moment condition, we show that positive invariant fields are in one-to-one correspondence with bounded positive harmonic functions of the underlying space. This implies that the space of invariant fields inherits the structure of the Martin boundary. We also show that whenever the deterministic heat flow converges to a bounded harmonic function, the stochastic evolution converges to the corresponding invariant field. The results apply to many settings with nontrivial Martin boundary, such as negatively curved manifolds and trees.