Geometric formulation of the Covariant Phase Space methods with boundaries

TL;DR

This paper develops a geometric framework for covariant phase space methods in field theories with boundaries, introducing the relative bicomplex framework to handle boundary and corner contributions, and clarifies boundary terms' roles.

Contribution

It introduces the relative bicomplex framework combining boundary and variational bicomplexes, providing a systematic way to analyze boundary effects in covariant phase space methods.

Findings

Established formal equivalence between boundary and non-boundary theories.

Constructed a canonical (pre)symplectic structure including boundary contributions.

Provided the CPS-algorithm for practical construction of the (pre)symplectic structure.

Abstract

We analyze in full-detail the geometric structure of the covariant phase space (CPS) of any local field theory defined over a space-time with boundary. To this end, we introduce a new frame: the "relative bicomplex framework". It is the result of merging an extended version of the "relative framework" (initially developed in the context of algebraic topology by R.~Bott and L.W.~Tu in the 1980s to deal with boundaries) and the variational bicomplex framework (the differential geometric arena for the variational calculus). The relative bicomplex framework is the natural one to deal with field theories with boundary contributions, including corner contributions. In fact, we prove a formal equivalence between the relative version of a theory with boundary and the non-relative version of the same theory with no boundary. With these tools at hand, we endow the space of solutions of the theory with a (pre)symplectic structure canonically associated with the action and which, in general, has boundary contributions. We also study the symmetries of the theory and construct, for a large group of them, their Noether currents, and charges. Moreover, we completely characterize the arbitrariness (or lack thereof for fiber bundles with contractible fibers) of these constructions. This clarifies many misconceptions about the role of the boundary terms in the CPS description of a field theory. Finally, we provide what we call the CPS-algorithm to construct the aforementioned (pre)symplectic structure and apply it to some relevant examples.