High Order Asymptotic Expansion at Infinity for Strong Solutions to Incompressible Navier-Stokes Equations
We discuss an interesting distinction between the incompressible Navier-Stokes equations (the velocity equations) and its vorticity form in whole space. We show that if the initial vorticity has a Gaussian bound then the bound is inherited up to the maximal lifespan of the strong solution. However, it turns out that the velocity equations don not share the same property. In fact, $L^p$-strong solutions to the velocity equations arising from ``well-localized" initial value generally behave at infinity like derivatives (of order $\geq3$) of the fundamental solution of Laplacian. To show this, a clean expansion up to maximal lifespan is derived : \begin{align} u(x,t)=-\nabla\sum_{|\alpha|=0}^{d-1}\frac{(-1)^{|\alpha|}}{\alpha !}\partial^\alpha\partial_{i,j}^2\Gamma(x)\int_0^t{\rm M}_{\alpha}^{i,j}(s){\rm d}s+O\big(|x|^{-2d-1}\big)\nonumber \end{align} where ${\rm M}_{\alpha}^{i,j}(t):=\int_{\mathbb R^d}y^\alpha u^i(y,t)u^j(y,t){\rm d}y$ and $\Gamma$ is the fundamental solution of Laplacian. This improves the first order expansion given by L. Brandolese and F. Vigneron \cite{BV07}.