816 research outputs found
Spontaneous Lorentz symmetry breaking in nonlinear electrodynamics
We review some of the basic features and predictions of a gauge invariant
spontaneous Lorentz symmetry breaking model arising from the nonzero vacuum
expectation value of the electromagnetic tensor and leading to a nonlinear
electrodynamics. The model is stable in the small Lorentz invariance violation
approximation. The speed of light is independent of the frequency and one of
the propagating modes is highly anisotropic. The bound (Delta c)/c < 10^{-32}
is obtained for such anisotropy measured in perpendicular directions.Comment: 5 pages, no figures, Invited talk to the Fifth Meeting on CPT and
Lorentz Symmetry, Bloomington, Indiana, June 28-July 2, 201
The algebra of supertraces for 2+1 super de Sitter gravity
The algebra of the observables for 2+1 super de Sitter gravity, for one genus of the spatial surface is calculated. The algebra turns out to be an infinite Lie algebra subject to non-linear constraints. The constraints are solved explicitly in terms of five independent complex supertraces. These variables are the true degrees of freedom of the system and their quantized algebra generates a new structure which is referred to as a 'central extension' of the quantum algebra SU(2)q
Orthogonality Relations and Supercharacter Formulas of U(m|n) Representations
In this paper we obtain the orthogonality relations for the supergroup
U(m|n), which are remarkably different from the ones for the U(N) case. We
extend our results for ordinary representations, obtained some time ago, to the
case of complex conjugated and mixed representations. Our results are expressed
in terms of the Young tableaux notation for irreducible representations. We use
the supersymmetric Harish-Chandra-Itzykson-Zuber integral and the character
expansion technique as mathematical tools for deriving these relations. As a
byproduct we also obtain closed expressions for the supercharacters and
dimensions of some particular irreducible U(m|n) representations. A new way of
labeling the U(m|n) irreducible representations in terms of m + n numbers is
proposed. Finally, as a corollary of our results, new identities among the
dimensions of the irreducible representations of the unitary group U(N) are
presented.Comment: 56 pages, LaTeX, changes only in the writing of the titl
Green's function approach to Chern-Simons extended electrodynamics: an effective theory describing topological insulators
Boundary effects produced by a Chern-Simons (CS) extension to electrodynamics
are analyzed exploiting the Green's function (GF) method. We consider the
electromagnetic field coupled to a -term in a way that has been
proposed to provide the correct low energy effective action for topological
insulators (TI). We take the -term to be piecewise constant in
different regions of space separated by a common interface , to be
called the -boundary. Features arising due to the presence of the
boundary, such as magnetoelectric effects, are already known in CS extended
electrodynamics and solutions for some experimental setups have been found with
specific configuration of sources. In this work we illustrate a method to
construct the GF that allows to solve the CS modified field equations for a
given -boundary with otherwise arbitrary configuration of sources. The
method is illustrated by solving the case of a planar -boundary but can
also be applied for cylindrical and spherical geometries for which the
-boundary can be characterized by a surface where a given coordinate
remains constant. The static fields of a point-like charge interacting with a
planar TI, as described by a planar discontinuity in , are calculated
and successfully compared with previously reported results. We also compute the
force between the charge and the -boundary by two different methods,
using the energy momentum tensor approach and the interaction energy calculated
via the GF. The infinitely straight current-carrying wire is also analyzed
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