The Camassa-Holm hierarchy, related N-dimensional integrable systems,   and algebro-geometric solution on a symplectic submanifold
  This paper shows that the Camassa-Holm (CH) spectral problem yields two different integrable hierarchies of nonlinear evolution equations (NLEEs), one is of negative order CH hierachy while the other one is of positive order CH hierarchy. The two CH hierarchies possess the zero curvature representations through solving a key matrix equation. We find that the well-known CH equation is included in the negative order CH hierarchy while a Dym type equation is included in the positive order CH hierarchy. Furthermore, under two constraint conditions between the eigenfunctions and the potentials, the CH spectral problem is cast in: (enumerate) a new Neumann-like N-dimensional system when it is restricted into a symplectic submanifold of $\R^{2N}$ which is proven to be integrable by using the Dirac-Poisson bracket and the r-matrix process; and a new Bargmann-like N-dimensional system when it is considered in the whole $\R^{2N}$ which is proven to be integrable by using the standard Poisson bracket and the r-matrix process. (enumerate) In the paper, we present two $4\times4$ instead of $N\times N$ r-matrix structures. One is for the Neumann-like CH system (not the peaked CH system), while the other one is for the Bargmann-like CH system. The whole CH hierarchy (both positive and negative order) is shown to have the parametric solution which obey the constraint relation. In particular, the CH equation constrained to some symplectic submanifold, and the Dym type equation have the parametric solutions. Moreover, we see that the kind of parametric solution of the CH equation is not gauge equivalent to the peakons. Solving the parametric representation of solution on the symplectic submanifold gives a class of new algebro-geometric solution of the CH equation. 
Darryl D. Holm, Zhijun Qiao