Gel'fand-Zakharevich Systems and Algebraic Integrability: the Volterra Lattice Revisited

In this paper we will discuss some features of the bihamiltonian method for solving the Hamilton-Jacobi (H-J) equations by Separation of Variables, and make contact with the theory of Algebraic Complete Integrability and, specifically, with the Veselov--Novikov notion of algebro-geometric (AG) Poisson brackets. The "bihamiltonian" method for separating the Hamilton-Jacobi equations is based on the notion of pencil of Poisson brackets and on the Gel'fand-Zakharevich (GZ) approach to integrable systems. We will herewith show how, quite naturally, GZ systems may give rise to AG Poisson brackets, together with specific recipes to solve the H-J equations. We will then show how this setting works by framing results by Veselov and Penskoi about the algebraic integrability of the Volterra lattice within the bihamiltonian setting for Separation of Variables.