Some Remarks on the Operators' Formalism for Nonlocal Poisson Brackets

TL;DR

This paper explicitly defines functional spaces for nonlocal Poisson brackets, proving classical results and applying the framework to validate a theorem by Ferapontov, thereby advancing the operatorial theory of nonlocal brackets.

Contribution

It introduces and studies functional spaces for weakly nonlocal Poisson brackets, providing a rigorous foundation and translating classical results into this new framework.

Findings

Defined spaces for local and nonlocal functionals

Characterized variational derivatives of nonlocal functionals

Validated a theorem by Ferapontov using the new framework

Abstract

A common approach to the theory of nonlocal Poisson brackets, seen from the operatorial point of view, has been to keep implicit the sets on which these brackets act. In this paper we aim to explicitly define appropriate functional spaces underlying to the theory of 1 codimensional weakly nonlocal Poisson brackets, motivating the definitions, and to prove the validity in this context of some classical results in the field. We start by introducing the spaces for the local case, which will serve as building tools for those in the nonlocal one. The definition and the study of these nonlocal functionals are the core of this work; in particular we work out a characterization of the variational derivative of such objects. We then translate everything to the level of manifolds, defining a global version of the functionals, and introduce the notion nonlocal Poisson brackets in this context. We conclude by applying all the machinery to prove a theorem due to Ferapontov. This last application is the natural conclusion of our discussion and shows that the spaces we introduce are suitable objects to work with when studying topics in this theory.