Reducible gauge symmetry versus unfree gauge symmetry in Hamiltonian formalism

TL;DR

This paper explores the differences between reducible and unfree gauge symmetries in Hamiltonian formalism, showing their relationship, implications for conserved quantities like the cosmological constant, and the impact on BRST cohomology.

Contribution

It demonstrates the existence of an alternative higher order gauge symmetry for unfree gauge theories and analyzes their relationship within the Hamiltonian BFV-BRST formalism.

Findings

Unfree gauge symmetry leads to global conserved quantities defined by asymptotics.

An equivalent higher order reducible gauge symmetry exists for unfree gauge theories.

The local map between unfree and reducible gauge algebras is established, but the inverse is non-local.

Abstract

The unfree gauge symmetry implies that gauge variation of the action functional vanishes provided for the gauge parameters are restricted by the differential equations. The unfree gauge symmetry is shown to lead to the global conserved quantities whose on shell values are defined by the asymptotics of the fields or data on the lower dimension surface, or even at the point of the space-time, rather than Cauchy hyper-surface. The most known example of such quantity is the cosmological constant of unimodular gravity. More examples are provided in the article for the higher spin gravity analogues of the cosmological constant. Any action enjoying the unfree gauge symmetry is demonstrated to admit the alternative form of gauge symmetry with the higher order derivatives of unrestricted gauge parameters. The higher order gauge symmetry is reducible in general, even if the unfree symmetry is not. The relationship is detailed between these two forms of gauge symmetry in the constrained Hamiltonian formalism. The local map is shown to exist from the unfree gauge algebra to the reducible higher order one, while the inverse map is non-local, in general. The Hamiltonian BFV-BRST formalism is studied for both forms of the gauge symmetry. These two Hamiltonian formalisms are shown connected by canonical transformation involving the ghosts. The generating function is local for the transformation, though the transformation as such is not local, in general. Hence, these two local BRST complexes are not quasi-isomorphic in the sense that their local BRST-cohomology groups can be different. This difference in particular concerns the global conserved quantities. From the standpoint of the BRST complex for unfree gauge symmetry, these quantities are BRST-exact, while for the alternative complex, these quantities are the non-trivial co-cycles.