A family of completely integrable multi-Hamiltonian systems explicitly related to some celebrated equations

By introducing a spectral problem with an arbitrary parameter, we derive a Kaup-Newell-type hierarchy of nonlinear evolution equations, which is expli citly related to many important equations such as the Kundu equation, the K aup-Newell (KN) equation, the Chen-Lee-Liu (CLL) equation, the Gerdjikov-Iv anov (GI) equation, the Burgers equation, the modified Korteweg-deVries (MK dV) equation and the Sharma-Tasso-Olver equation. It is shown that the hier archy is integrable in Liouville's sense and possesses multi-Hamiltonian st ructure. Under the Bargann constraint between the potentials and the eigenf unctions, the spectral problem is nonlinearized as a finite-dimensional com pletely integrable Hamiltonian system. The involutive representation of the solutions for the Kaup-Newell-type hierarchy is also presented. In additio n, an N-fold Darboux transformation of the Kundu equation is constructed wi th the help of its Lax pairs and a reduction technique. According to the Da rboux transformation, the solutions of the Kundu equation is reduced to sol ving a linear algebraic system and two first-order ordinary differential eq uations. It is found that the KN, CLL, and GI equations can be described by a Kundu-type derivative nonlinear Schrodinger equation involving a paramet er. And then, we can construct the Hamiltonian formulations, Lax pairs and N-fold Darboux transformations for the Kundu, KN, CLL, and GI equations in explicit and unified ways. (C) 2001 American Institute of Physics.