English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We argue that there is nothing puzzling in the fact that the Hamiltonianformulation of a covariant theory, General Relativity, after a non-covariantchange of field variables is not canonically related to the formulation basedon the original variable, the metric tensor. Were such a puzzle to be "solved"it would lead to the conclusion that a covariant theory can be converted into anon-covariant one in many different ways and without consequence. Thenon-canonicity of transformations from covariant to non-covariant variablesshows the need to work in the original variables so as to be able to restorethe covariant gauge transformations in the Hamiltonian approach. Anymodification of Dirac's procedure for the constrained Hamiltonian with the aimto prove the legitimacy of non-covariant changes of field variables, orrejection of Dirac's procedure as "not fundamental and undoubted" because itdoes not allow such changes (as recently suggested by Shestakova [CGQ, 28(2011) 055009]), is equivalent to the rejection of the covariance of GeneralRelativity, and to surrender to such temptation is truly puzzling.

Lagrangian symmetries of the ADM action. Do we need a solution to the "non-canonicity puzzle"?