Metric gravity in the Hamiltonian form. Canonical transformations. Dirac's modifications of the Hamilton method and integral invariants of the metric gravity

TL;DR

This paper compares two Hamiltonian formulations of metric gravity in arbitrary dimensions, emphasizing canonical transformations, Dirac's modifications, and integral invariants, to improve the consistency and development of gravitational theories.

Contribution

It introduces conditions for canonical transformations in constrained Hamiltonian systems of metric gravity, highlighting Dirac's modifications as advantageous for theoretical consistency.

Findings

Dirac's modifications enhance Hamiltonian formulations of gravity.

Conditions for canonicity include preservation of Poisson brackets and constraints.

Integral invariants theory reveals peculiarities in constrained Hamiltonian systems.

Abstract

Two different Hamiltonian formulations of the metric gravity are discussed and applied to describe a free gravitational field in the $d$ dimensional Riemann space-time. Theory of canonical transformations, which relate equivalent Hamiltonian formulations of the metric gravity, is investigated in details. In particular, we have formulated the conditions of canonicity for transformation between the two sets of dynamical variables used in our Hamiltonian formulations of the metric gravity. Such conditions include the ordinary condition of canonicity known in classical Hamilton mechanics, i.e., the exact coincidence of the Poisson (or Laplace) brackets which are determined for the both new and old dynamical Hamiltonian variables. However, in addition to this any true canonical transformations defined in the metric gravity, which is a constrained dynamical system, must also guarantee the exact conservation of the total Hamiltonians $H_t$ (in the both formulations) and preservation of the algebra of first-class constraints. We show that Dirac's modifications of the classical Hamilton method contain a number of crucial advantages, which provide an obvious superiority of this method in order to develop various non-contradictory Hamiltonian theories of many physical fields, when a number of gauge conditions are also important. Theory of integral invariants and its applications to the Hamiltonian metric gravity are also discussed. For Hamiltonian dynamical systems with first-class constraints this theory leads to a number of peculiarities some of which have been investigated.