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arXiv 1111.6135nlin.PS
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具有任意非线性项的强迫非线性Schroedinger方程

Forced Nonlinear Schroedinger Equation with Arbitrary Nonlinearity

Fred Cooper, Avinash Khare, Niurka R. Quintero, Franz G. Mertens, Avadh Saxena

摘要:

考虑具有标量-标量自相互作用$\frac{g^2}{κ+1} (ψ^\star ψ)^{κ+1}$的1+1维非线性薛定谔方程(NLSE),其中存在形式为$r e^{-i(kx + θ)} -δψ$的外力项.我们发现这个问题的新的精确解,并表明孤立波动量守恒的移动框架中,$v_k=2 k$。这些新的精确解减少到恒定相位解的非强迫问题时,$r \rightarrow 0.$-特别是我们研究的行为孤波解的存在下,这些外力在变分近似,允许这些波的位置,动量,宽度和相位随时间变化。我们发现,固定的解决方案的变分方程包括一个解决方案接近的确切的,我们研究小振荡周围的所有固定的解决方案。我们假定不稳定性的动力学条件是$ dp(t)/d \dot{q} (t) < 0$,其中$p(t)$是归一化正则动量$p(t) = \frac{1}{M(t)} \frac {\partial L}{\partial {\dot q}}$,$\dot{q}(t)$是孤立波速度。这里是$M(t) = \int dx ψ^\star(x,t) ψ(x,t)$。稳定性也研究了使用“相图”的孤立子,其动态表示的二维投影的轨迹在四维空间的集体坐标。孤立子稳定性的判据是其轨迹是一条封闭的单曲线,且该曲线绕一个固定点有正向旋转。我们调查我们的变分近似的准确性和这些标准使用数值模拟的NLSE。

英文摘要:

We consider the nonlinear Schr{ö}dinger equation (NLSE) in 1+1 dimension with scalar-scalar self interaction $\frac{g^2}{κ+1} (ψ^\star ψ)^{κ+1}$ in the presence of the external forcing terms of the form $r e^{-i(kx + θ)} -δψ$. We find new exact solutions for this problem and show that the solitary wave momentum is conserved in a moving frame where $v_k=2 k$. These new exact solutions reduce to the constant phase solutions of the unforced problem when $r \rightarrow 0.$ In particular we study the behavior of solitary wave solutions in the presence of these external forces in a variational approximation which allows the position, momentum, width and phase of these waves to vary in time. We show that the stationary solutions of the variational equations include a solution close to the exact one and we study small oscillations around all the stationary solutions. We postulate that the dynamical condition for instability is that $ dp(t)/d \dot{q} (t) < 0$, where $p(t)$ is the normalized canonical momentum $p(t) = \frac{1}{M(t)} \frac {\partial L}{\partial {\dot q}}$, and $\dot{q}(t)$ is the solitary wave velocity. Here $M(t) = \int dx ψ^\star(x,t) ψ(x,t)$. Stability is also studied using a "phase portrait" of the soliton, where its dynamics is represented by two-dimensional projections of its trajectory in the four-dimensional space of collective coordinates. The criterion for stability of a soliton is that its trajectory is a closed single curve with a positive sense of rotation around a fixed point. We investigate the accuracy of our variational approximation and these criteria using numerical simulations of the NLSE.

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