700 research outputs found
Berry phase for spin--1/2 particles moving in a spacetime with torsion
Berry phase for a spin--1/2 particle moving in a flat spacetime with torsion
is investigated in the context of the Einstein-Cartan-Dirac model. It is shown
that if the torsion is due to a dense polarized background, then there is a
Berry phase only if the fermion is massless and its momentum is perpendicular
to the direction of the background polarization. The order of magnitude of this
Berry phase is discussed in other theoretical frameworks.Comment: 9 pages. Some typos corrected, a discussion on propagating torsion is
added, accepted for publication in Eur. Phys. J. C (2001
The universal R-matrix for the Jordanian deformation of sl(2), and the contracted forms of so(4)
We introduce a universal R matrix for the Jordanian deformation of \U{
\sl(2)}. Using \Uh{\so(4)}=\Uh{\sl(2)} \oplus {\rm U}_{-h}(\sl(2)), we
obtain the universal R matrix for \Uh{\so(4)}. Applying the graded
contractions on the universal R matrix of \Uh{\so(4)}, we show that there
exist three distinct R matrices for all of the contracted algebras. It is shown
that \Uh{\sl(2)}, \Uh{\so(4)}, and all of these contracted algebras are
triangular.Comment: LaTeX, 8 page
Quantum reflection of massless neutrinos from a torsion-induced potential
In the context of the Einstein-Cartan-Dirac model, where the torsion of the
space-time couples to the axial currents of the fermions, we study the effects
of this quantum-gravitational interaction on a massless neutrino beam crossing
through a medium with high number density of fermions at rest. We calculate the
reflection amplitude and show that a specific fraction of the incident
neutrinos reflects from this potential if the polarization of the medium is
different from zero. We also discuss the order of magnitude of the fermionic
number density in which this phenomenon is observable, in other theoretical
contexts, for example the strong-gravity regime and the effective field theory
approach.Comment: 8 pages, LaTe
A Triangular Deformation of the two Dimensional Poincare Algebra
Contracting the -deformation of \SL(2,\Real), we construct a new
deformation of two dimensional Poincar\'e algebra, the algebra of functions on
its group and its differential structure. It is also shown that the Hopf
algebra is triangular, and its universal R matrix is also constructed
explicitly. Then, we find a deformation map for the universal enveloping
algebra, and at the end, give the deformed mass shells and Lorentz
transformation.Comment: 11 pages, LaTeX, Two figures upon reques
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