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arXiv 2102.13014math.AP
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含导数的非线性薛定谔方程的简并孤子的不稳定性

Instability of degenerate solitons for nonlinear Schrödinger equations with derivative

Noriyoshi Fukaya, Masayuki Hayashi

摘要:

我们考虑下列带导数的非线性薛定谔方程:\begin{equation} iu_t =-u_{xx} -i |u|^{2}u_x -b|u|^4u , \quad (t,x) \in \mathbb{R}\times\mathbb{R}, \ b \in\mathbb{R}. \end{equation}如果是$b=0$,则此方程是著名的导数非线性薛定谔(DNLS)方程的规范等价形式。DNLS的孤子剖面满足一定的双幂次椭圆型方程,具有五阶非线性。我们方程中的五次非线性只影响椭圆型方程中五次项前的系数,所以在这个意义上,附加的非线性作为DNLS的保孤子轮廓扰动是自然的。当满足$b\ge 0$时,方程中存在动量和能量均为零的简并孤子;当满足$b=0$时,方程中存在代数孤子。受$L^2$ -临界广义KdV方程不稳定性理论研究的启发,我们对退化孤子的不稳定性进行了定性研究,当$b>0$时,我们得到了产生不稳定性的大量初始数据.除了我们证明$b=0$情形中的一个步骤外,其他的论证都是以完全相同的方式进行的,这是理解DNLS方程代数孤子动力学的一小步。

英文摘要:

We consider the following nonlinear Schrödinger equation with derivative: \begin{equation} iu_t =-u_{xx} -i |u|^{2}u_x -b|u|^4u , \quad (t,x) \in \mathbb{R}\times\mathbb{R}, \ b \in\mathbb{R}. \end{equation} If $b=0$, this equation is a gauge equivalent form of the well-known derivative nonlinear Schrödinger (DNLS) equation. The soliton profile of DNLS satisfies a certain double power elliptic equation with cubic-quintic nonlinearities. The quintic nonlinearity in our equation only affects the coefficient in front of the quintic term in the elliptic equation, so in this sense the additional nonlinearity is natural as a perturbation preserving soliton profiles of DNLS. When $b\ge 0$, the equation has degenerate solitons whose momentum and energy are zero, and if $b=0$, they are algebraic solitons. Inspired from the works on instability theory of the $L^2$-critical generalized KdV equation, we study the instability of degenerate solitons in a qualitative way, and when $b>0$, we obtain a large set of initial data yielding the instability. The arguments except one step in our proof work for the case $b=0$ in exactly the same way, which is a small step towards understanding the dynamics around algebraic solitons of the DNLS equation.

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