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Stability of Two Soliton Collision for Nonintegrable gKdV Equations
Authors:Yvan Martel and Frank Merle
Institution:(1) Université de Versailles Saint-Quentin-en-Yvelines, Mathématiques, UMR 8100, 45, av. des Etats-Unis, 78035 Versailles cedex, France;(2) Université de Cergy-Pontoise, IHES and CNRS, Mathématiques, 2, av. Adolphe Chauvin, 95302 Cergy-Pontoise cedex, France
Abstract:We continue our study of the collision of two solitons for the subcritical generalized KdV equations
$$\label{kdvabs}\partial_{t}u\,{+}\,\partial_{x}(\partial_{x}^{2}u\,{+}\,f(u)) = 0.\quad \quad (0.1)$$
Solitons are solutions of the type $${u(t, x) = Q_{c_{0}}(x - x_{0} - c_{0}t)}$$ where c 0  >  0. In 21], mainly devoted to the case f (u)  =  u 4, we have introduced a new framework to understand the collision of two solitons $${Q_{c_{1}}}$$ , $${Q_{c_{2}}}$$ for (0.1) in the case $${c_{2} \ll c_{1}}$$ (or equivalently, $${\|Q_{c_{2}}\|_{H^{1}}\ll \|Q_{c_{1}}\|_{H^{1}}}$$). In this paper, we consider the case of a general nonlinearity f (u) for which $${Q_{c_{1}}}$$ , $${Q_{c_{2}}}$$ are nonlinearly stable. In particular, since f is general and c 1 can be large, the results are not perturbations of the ones for the power case in 21]. First, we prove that the two solitons survive the collision up to a shift in their trajectory and up to a small perturbation term whose size is explicitly controlled from above: after the collision, $${u(t) \sim Q_{c_{1}^{+}}+Q_{c_{2}^{+}}}$$ , where $${c_{j}^{+}}$$ is close to c j (j  =  1, 2). Then, we exhibit new exceptional solutions similar to multi-soliton solutions: for all $${c_{1}, c_{2} > 0, c_{2} \ll c_{1}}$$ , there exists a solution $${\varphi(t)}$$ such that
$$ \begin{aligned} \varphi(t,x)\,&=\,Q_{c_{1}}(x-\rho_{1}(t)) + Q_{c_{2}}(x-\rho_{2}(t)) + \eta(t,x), {\rm for}\, t\ll -1,\\ \varphi(t,x)\,&=\,Q_{c_{1}}(x-\rho_{1}(t)) + Q_{c_{2}}(x-\rho_{2}(t)) + \eta(t,x), {\rm for}\, t\gg 1, \end{aligned}$$
where $${\rho_{j}(t) \to c_{j}}$$ (j  =  1, 2) and $${\eta(t)}$$ converges to 0 in a neighborhood of the solitons as $${t \to \pm \infty}$$ . The analysis is split in two distinct parts. For the interaction region, we extend the algebraic tools developed in 21] for the power case, by expanding f (u) as a sum of powers plus a perturbation term. To study the solutions in large time, we rely on previous tools on asymptotic stability in 17,22] and 18], refined in 19,20]. This research was supported in part by the Agence Nationale de la Recherche (ANR ONDENONLIN).
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