Higher-Stage Noether Identities and Second Noether Theorems

The direct and inverse second Noether theorems are formulated in a general case of reducible degenerate Grassmann-graded Lagrangian theory of even and odd variables on graded bundles. Such Lagrangian theory is characterized by a hierarchy of nontrivial higher-stage Noether identities which is described in the homology terms. If a certain homology regularity condition holds, one can associate with a reducible degenerate Lagrangian the exact Koszul–Tate chain complex possessing the boundary operator whose nilpotentness is equivalent to all complete nontrivial Noether and higher-stage Noether identities. The second Noether theorems associate with the above-mentioned Koszul–Tate complex a certain cochain sequence whose ascent operator consists of the gauge and higher-order gauge symmetries of a Lagrangian system. If gauge symmetries are algebraically closed, this operator is extended to the nilpotent BRST operator which brings the above-mentioned cochain sequence into the BRST complex and provides a BRST extension of an original Lagrangian.

GRADED LAGRANGIAN FORMALISM

Graded Lagrangian formalism in terms of a Grassmann-graded variational bicomplex on graded manifolds is developed in a very general setting. This formalism provides the comprehensive description of reducible degenerate Lagrangian systems, characterized by hierarchies of non-trivial higher-order Noether identities and gauge symmetries. This is a general case of classical field theory and Lagrangian non-relativistic mechanics.

Inequivalent Lagrangians for the damped harmonic oscillator

A constant of the motion, in addition to what exists in the literature, is presented for the damped harmonic oscillator and its dynamical origin is investigated. These two constants of motion are used to construct expressions for a hierarchy of inequivalent Lagrangians. It is shown that each inequivalent Lagrangian may be related to a higher order degenerate Lagrangian. The hierarchical Lagrangians tend to pose some characteristic problems for discussing the corresponding phase-space structure. PACS Nos.: 47.20.Ky, 42.81.Dp

Canonical structure of the coupled Korteweg–de Vries equations

The inverse problem of variational calculus is solved for the coupled Korteweg–de Vries equations resulting from a complex Lax pair. The system is found to be characterized by a second-order degenerate Lagrangian density having some common feature with the well-known Morse–Feshbach Lagrangian. The Hamiltonian structure is examined using Dirac's theory of constraints. PACS Nos.: 47.20.Ky, 42.81.Dp

POISSON BRACKETS ON PRESYMPLECTIC MANIFOLDS

The problem of defining Poisson brackets for a degenerate Lagrangian without introduction of canonical variables is discussed. More generally, we introduce and give a complete geometrical description of a class of Poisson brackets on a presymplectic manifold. The construction is illustrated by both finite-dimensional and field-theoretic examples.