50 research outputs found

### The Ostrogradsky Method for Local Symmetries. Constrained Theories with Higher Derivatives

In the generalized Hamiltonian formalism by Dirac, the method of constructing
the generator of local-symmetry transformations for systems with first- and
second-class constraints (without restrictions on the algebra of constraints)
is obtained from the requirement for them to map the solutions of the
Hamiltonian equations of motion into the solutions of the same equations. It is
proved that second-class constraints do not contribute to the transformation
law of the local symmetry entirely stipulated by all the first-class
constraints (and only by them). A mechanism of occurrence of higher derivatives
of coordinates and group parameters in the symmetry transformation law in the
Noether second theorem is elucidated. It is shown that the obtained
transformations of symmetry are canonical in the extended (by Ostrogradsky)
phase space. An application of the method in theories with higher derivatives
is demonstrated with an example of the spinor Christ -- Lee model.Comment: 8 pages, LaTex; Talk given at the II International Workshop
``Classical and Quantum Integrable Systems'', Dubna, July 8-12, 1996; the
essentially reduced version of the talk is published in Intern. J. Mod. Phys.
A12, (1997)

### Constrained Dynamical Systems: Separation of Constraints into First and Second Classes

In the Dirac approach to the generalized Hamiltonian formalism, dynamical
systems with first- and second-class constraints are investigated. The
classification and separation of constraints into the first- and second-class
ones are presented with the help of passing to an equivalent canonical set of
constraints. The general structure of second-class constraints is clarified.Comment: 12 pages, LaTex; Preprint of Joint Institute for Nuclear Research
E2-96-227, Dubna, 1996; to be published in Physical Review

### Light-cone sum rules for the $N\gamma\Delta$ transitions for real photons

We examine the radiative $\Delta \to \gamma N$ transition at the real photon
point $Q^2=0$ using the framework of light-cone QCD sum rules. In particular,
the sum rules for the transition form factors $G_M(0)$ and $R_{EM}$ are
determined up to twist 4. The result for $G_M(0)$ agrees with experiment within
10% accuracy. The agreement for $R_{EM}$ is also reasonable. In addition, we
derive new light-cone sum rules for the magnetic moments of nucleons, with a
complete account of twist-4 corrections based on a recent reanalysis of photon
distribution amplitudes.Comment: 34 pages, 9 figures, revised version, published in Phys. Rev. D, one
misplaced reference correcte

### Unconstrained Hamiltonian Formulation of SU(2) Gluodynamics

SU(2) Yang-Mills field theory is considered in the framework of the
generalized Hamiltonian approach and the equivalent unconstrained system is
obtained using the method of Hamiltonian reduction. A canonical transformation
to a set of adapted coordinates is performed in terms of which the
Abelianization of the Gauss law constraints reduces to an algebraic operation
and the pure gauge degrees of freedom drop out from the Hamiltonian after
projection onto the constraint shell. For the remaining gauge invariant fields
two representations are introduced where the three fields which transform as
scalars under spatial rotations are separated from the three rotational fields.
An effective low energy nonlinear sigma model type Lagrangian is derived which
out of the six physical fields involves only one of the three scalar fields and
two rotational fields summarized in a unit vector. Its possible relation to the
effective Lagrangian proposed recently by Faddeev and Niemi is discussed.
Finally the unconstrained analog of the well-known nonnormalizable groundstate
wave functional which solves the Schr\"odinger equation with zero energy is
given and analysed in the strong coupling limit.Comment: 20 pages REVTEX, no figures; final version to appear in Phys. Rev. D;
minor changes, notations simplifie