41,834 research outputs found
Primordial torsion fields as an explanation of the anisotropy in cosmological electromagnetic propagation
In this note we provide a simple explanation of the recent finding of
anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston
(astro-ph/9704196). We consider, as a possible origin of such effect, the
effective coupling between EM fields and some tiny background torsion field.
The coupling is obtained after integrating out charged fermions, it is gauge
invariant and does not require the introduction of any new physics.Comment: 8 pages, LaTeX, one figure, enlarged version with minor correction
Faddeev-Jackiw approach to gauge theories and ineffective constraints
The general conditions for the applicability of the Faddeev-Jackiw approach
to gauge theories are studied. When the constraints are effective a new proof
in the Lagrangian framework of the equivalence between this method and the
Dirac approach is given. We find, however, that the two methods may give
different descriptions for the reduced phase space when ineffective constraints
are present. In some cases the Faddeev-Jackiw approach may lose some
constraints or some equations of motion. We believe that this inequivalence can
be related to the failure of the Dirac conjecture (that says that the Dirac
Hamiltonian can be enlarged to an Extended Hamiltonian including all first
class constraints, without changes in the dynamics) and we suggest that when
the Dirac conjecture fails the Faddeev-Jackiw approach fails to give the
correct dynamics. Finally we present some examples that illustrate this
inequivalence.Comment: 21 pages, Latex. To be published in Int. J. Mod. Phys.
Jordan weak amenability and orthogonal forms on JB*-algebras
We prove the existence of a linear isometric correspondence between the
Banach space of all symmetric orthogonal forms on a JB-algebra
and the Banach space of all purely Jordan generalized derivations
from into . We also establish the existence of a
similar linear isometric correspondence between the Banach spaces of all
anti-symmetric orthogonal forms on , and of all Lie Jordan
derivations from into
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