Global existence for perturbations of the 2D stochastic Navier-Stokes equations with space-time white noise

TL;DR

This paper establishes global well-posedness for perturbed 2D stochastic Navier-Stokes equations driven by space-time white noise, using energy estimates and paracontrolled calculus, without relying on invariant measures.

Contribution

It introduces a novel approach to prove global existence for the 2D stochastic Navier-Stokes equations with white noise, accommodating anticipative initial data and perturbations outside the invariant measure's Cameron-Martin space.

Findings

Proves global well-posedness for the perturbed stochastic Navier-Stokes equations.

Develops an energy estimate based on high-low frequency decomposition and paracontrolled calculus.

Allows initial data in the critical space $L^2$ and perturbations outside the invariant measure.

Abstract

We prove global in time well-posedness for perturbations of the 2D stochastic Navier-Stokes equations \begin{equation*} \partial_t u + u \cdot \nabla u = \Delta u - \nabla p + \zeta + \xi \;, \quad u (0, \cdot) = u_{0}(\cdot) \;, \quad \mathrm{div} (u) = 0 \;, \end{equation*} driven by additive space-time white noise $ \xi $, with perturbation $ \zeta $ in the H\"older-Besov space $\mathcal{C}^{-2 + 3\kappa} $, periodic boundary conditions and initial condition $ u_{0} \in \mathcal{C}^{-1 + \kappa} $ for any $ \kappa >0 $. The proof relies on an energy estimate which in turn builds on a dynamic high-low frequency decomposition and tools from paracontrolled calculus. Our argument uses that the solution to the linear equation is a $ \log$-correlated field, yielding a double exponential growth bound on the solution. Notably, our method does not rely on any explicit knowledge of the invariant measure to the SPDE, hence the perturbation $ \zeta $ is not restricted to the Cameron-Martin space of the noise, and the initial condition may be anticipative. Finally, we introduce a notion of weak solution that leads to well-posedness for all initial data $u_{0}$ in $ L^{2} $, the critical space of initial conditions.