Stochastic Laplacian growth

TL;DR

This paper develops a probabilistic framework for Laplacian growth, linking growth probabilities to electrostatic energies and entropy, and connects it with integrable systems and quantum string theories.

Contribution

It introduces a novel approach to Laplacian growth using action and entropy concepts, linking growth probabilities to Gibbs-Boltzmann statistics and integrable hierarchies.

Findings

Growth probability relates to electrostatic energy layers.

Classical scenario reproduces Laplacian growth equation.

Non-classical scenarios involve Kullback-Leibler entropy.

Abstract

A point source on a plane constantly emits particles which rapidly diffuse and then stick to a growing cluster. The growth probability of a cluster is presented as a sum over all possible scenarios leading to the same final shape. The classical point for the action, defined as a minus logarithm of the growth probability, describes the most probable scenario and reproduces the Laplacian growth equation, which embraces numerous fundamental free boundary dynamics in non-equilibrium physics. For non-classical scenarios we introduce virtual point sources, in which presence the action becomes the Kullback-Leibler entropy. Strikingly, this entropy is shown to be the sum of electrostatic energies of layers grown per elementary time unit. Hence the growth probability of the presented non-equilibrium process obeys the Gibbs-Boltzmann statistics, which, as a rule, is not applied out from equilibrium. Each layer's probability is expressed as a product of simple factors in an auxiliary complex plane after a properly chosen conformal map. The action at this plane is a sum of Robin functions, which solve the Liouville equation. At the end we establish connections of our theory with the tau-function of the integrable Toda hierarchy and with the Liouville theory for non-critical quantum strings.