447 research outputs found
Extended Loop Quantum Gravity
We discuss constraint structure of extended theories of gravitation (also
known as f(R) theories) in the vacuum selfdual formulation introduced in ref.
[1].Comment: 7 pages, few typos correcte
Once again about quantum deformations of D=4 Lorentz algebra: twistings of q-deformation
This paper together with the previous one (arXiv:hep-th/0604146) presents the
detailed description of all quantum deformations of D=4 Lorentz algebra as Hopf
algebra in terms of complex and real generators. We describe here in detail two
quantum deformations of the D=4 Lorentz algebra o(3,1) obtained by twisting of
the standard q-deformation U_{q}(o(3,1)). For the first twisted q-deformation
an Abelian twist depending on Cartan generators of o(3,1) is used. The second
example of twisting provides a quantum deformation of Cremmer-Gervais type for
the Lorentz algebra. For completeness we describe also twisting of the Lorentz
algebra by standard Jordanian twist. By twist quantization techniques we obtain
for these deformations new explicit formulae for the deformed coproducts and
antipodes of the o(3,1)-generators.Comment: 17 page
Constraints on the quantum gravity scale from kappa - Minkowski spacetime
We compare two versions of deformed dispersion relations (energy vs momenta
and momenta vs energy) and the corresponding time delay up to the second order
accuracy in the quantum gravity scale (deformation parameter). A general
framework describing modified dispersion relations and time delay with respect
to different noncommutative kappa -Minkowski spacetime realizations is firstly
proposed here and it covers all the cases introduced in the literature. It is
shown that some of the realizations provide certain bounds on quadratic
corrections, i.e. on quantum gravity scale, but it is not excluded in our
framework that quantum gravity scale is the Planck scale. We also show how the
coefficients in the dispersion relations can be obtained through a
multiparameter fit of the gamma ray burst (GRB) data.Comment: 9 pages, final published version, revised abstract, introduction and
conclusion, to make it clear to general reade
Noether's second theorem in a general setting. Reducible gauge theories
We prove Noether's direct and inverse second theorems for Lagrangian systems
on fiber bundles in the case of gauge symmetries depending on derivatives of
dynamic variables of an arbitrary order. The appropriate notions of reducible
gauge symmetries and Noether's identities are formulated, and their equivalence
by means of certain intertwining operator is proved.Comment: 20 pages, to be published in J. Phys. A (2005
The LHC Beam Pipe Waveguide Mode Reflectometer
The waveguide-mode reflectometer for obstacle detection in the LHC beam pipe has been intensively used for more than 18 months. The âワAssemblyâ version is based on the synthetic pulse method using a modern vector network analyzer. It has mode selective excitation couplers for the first TE and TM mode and uses a specially developed waveguide mode dispersion compensation algorithm with external software. In addition there is a similar âワIn Situâ version of the reflectometer which uses permanently installed microwave couplers at the end of each of the nearly 3 km long LHC arcs. During installation a considerable number of unexpected objects have been found in the beam pipes and subsequently removed. Operational statistics and lessons learned are presented and the overall performance is discussed
Unbraiding the braided tensor product
We show that the braided tensor product algebra
of two module algebras of a quasitriangular Hopf algebra is
equal to the ordinary tensor product algebra of with a subalgebra of
isomorphic to , provided there exists a
realization of within . In other words, under this assumption we
construct a transformation of generators which `decouples' (i.e.
makes them commuting). We apply the theorem to the braided tensor product
algebras of two or more quantum group covariant quantum spaces, deformed
Heisenberg algebras and q-deformed fuzzy spheres.Comment: LaTex file, 29 page
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