Sharp well-posedness and ill-posedness of the Cauchy problem for the higher-order KdV

TL;DR

This paper establishes the precise regularity thresholds for well-posedness and ill-posedness of the higher-order KdV equation on periodic domains, using new estimates and function spaces.

Contribution

It improves existing results by determining the exact Sobolev space regularity for well-posedness and ill-posedness of the higher-order KdV equation.

Findings

Well-posedness for s ≥ -j + 1/2 in H^s(𝕋).

Ill-posedness for s < -j + 1/2 in H^s(𝕋) with solution map not smooth.

Introduction of new Strichartz estimates and function spaces.

Abstract

In this paper, we investigate the Cauchy problem for the higher-order KdV-type equation \begin{eqnarray*} u_{t}+(-1)^{j+1}\partial_{x}^{2j+1}u + \frac{1}{2}\partial_{x}(u^{2}) = 0,j\in N^{+},x\in\mathbf{T}= [0,2\pi \lambda) \end{eqnarray*} with low regularity data and $\lambda\geq 1$. Firstly, we show that the Cauchy problem for the periodic higher-order KdV equation is locally well-posed in $H^{s}(\mathbf{T})$ with $s\geq -j+\frac{1}{2},j\geq2.$ By using some new Strichartz estimate and some new function spaces, we also show that the Cauchy problem for the periodic higher-order KdV equation is ill-posed in $H^{s}(\mathbf{T})$ with $s<-j+\frac{1}{2},j\geq2$ in the sense that the solution map is $C^{3}.$ The result of this paper improves the result of \cite{H} with $j\geq2$.