On the compatible weakly-nonlocal Poisson brackets of Hydrodynamic Type

Abstract

We consider the pairs of general weakly non-local Poisson brackets of Hydrodynamic Type (Ferapontov brackets) and the corresponding integrable hierarchies. We show that under the requirement of non-degeneracy of the corresponding "first" pseudo-Riemannian metric $g_{(0)}^{νμ}$ and also some non-degeneracy requirement for the nonlocal part it is possible to introduce a "canonical" set of "integrable hierarchies" based on the Casimirs, Momentum functional and some "Canonical Hamiltonian functions". We prove also that all the "Higher" "positive" Hamiltonian operators and the "negative" symplectic forms have the weakly non-local form in this case. The same result is also true for "negative" Hamiltonian operators and "positive" Symplectic structures in the case when both pseudo-Riemannian metrics $g_{(0)}^{νμ}$ and $g_{(1)}^{νμ}$ are non-degenerate.