Misc,

Young diagrams and N-soliton solutions of the KP equation

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(2004)cite arxiv:nlin/0406033Comment: 22 pages, 5 figures, some minor corrections and added one section on the KdV N-soliton solutions.

Abstract

We consider $N$-soliton solutions of the KP equation, (-4u_t+u_xxx+6uu_x)_x+3u_yy=0 . An $N$-soliton solution is a solution $u(x,y,t)$ which has the same set of $N$ line soliton solutions in both asymptotics $y\toınfty$ and $y-ınfty$. The $N$-soliton solutions include all possible resonant interactions among those line solitons. We then classify those $N$-soliton solutions by defining a pair of $N$-numbers $(n^+,\bf n^-)$ with $n^\pm=(n_1^\pm,...,n_N^\pm), n_j^\pmın\1,...,2N\$, which labels $N$ line solitons in the solution. The classification is related to the Schubert decomposition of the Grassmann manifolds Gr$(N,2N)$, where the solution of the KP equation is defined as a torus orbit. Then the interaction pattern of $N$-soliton solution can be described by the pair of Young diagrams associated with $(n^+,\bf n^-)$. We also show that $N$-soliton solutions of the KdV equation obtained by the constraint $u/y=0$ cannot have resonant interaction.

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