Gaussian Fluctuations for the Stochastic Landau-Lifshitz Navier-Stokes Equation in Dimension $D\geq2$

TL;DR

This paper analyzes Gaussian fluctuations of the stochastic Landau-Lifshitz Navier-Stokes equation in dimensions two and higher, establishing convergence to a renormalized stochastic heat equation and correcting previous conjectures.

Contribution

It introduces a case-by-case analysis and novel techniques to prove convergence and asymptotic expansion of the effective coefficient, correcting prior conjectures in the field.

Findings

Convergence of regularized LLNS to a stochastic heat equation with renormalized coefficient

Asymptotic expansion of the effective coefficient in dimensions ≥ 3

Refutation of a previous conjecture regarding the coefficient's behavior

Abstract

We revisit the large-scale Gaussian fluctuations for the stochastic Landau-Lifshitz Navier-Stokes equation (LLNS) at and above criticality, using the method in \cite{CGT24}. With the classical diffusive scaling in $d\geq 3$ and weak coupling scaling in $d=2$, we obtain the convergence of the regularised LLNS to a stochastic heat equation with a non-trivially renormalized coefficient. Moreover, we obtain an asymptotic expansion of the effective coefficient when $d\geq3$, and show that the one in \cite[Conjecture 6.5]{JP24} is incorrect. The new ingredient in our proof is a case-by-case analysis to track the evolution of the vector under the action of the Leray projection, combined with the use of the anti-symmetric part of the generator and a rotational change of coordinates to derive the desired decoupled stochastic heat equation from the original coupled system.