9,319 research outputs found
Maximal supersymmetry and exceptional groups
The article is a tribute to my old mentor, collaborator and friend Murray
Gell-Mann. In it I describe work by Pierre Ramond, Sung-Soo Kim and myself
where we describe the N = 8 Supergravity in the light-cone formalism. We show
how the Cremmer-Julia E7(7) non-linear symmetry is implemented and how the full
supermultiplet is a representation of the E7(7) symmetry. I also show how the
E7(7) symmetry is a key to understand the higher order couplings in the theory
and is very useful when we discuss possible counterterms for this theory.Comment: Proceedings of Conference in Honour of Murray Gell-Mann's 80th
Birthda
Orbital-Peierls State in NaTiSi2O6
Does the quasi one-dimensional titanium pyroxene NaTiSi2O6 exhibit the novel
{\it orbital-Peierls} state? We calculate its groundstate properties by three
methods: Monte Carlo simulations, a spin-orbital decoupling scheme and a
mapping onto a classical model. The results show univocally that for the spin
and orbital ordering to occur at the same temperature --an experimental
observation-- the crystal field needs to be small and the orbitals are active.
We also find that quantum fluctuations in the spin-orbital sector drive the
transition, explaining why canonical bandstructure methods fail to find it. The
conclusion that NaTiSi2O6 shows an orbital-Peierls transition is therefore
inevitable.Comment: 4 pages, 3 figure
Comparative postcranial osteomorphology and osteometry of springbok, Antidorcas marsupialis (Zimmerman, 1780) and grey rhebok, Pelea capreolus (Forster, 1790) (Mammalia: Bovidae)
Oxidizing SuperYang-Mills from (N=4,d=4) to (N=1,d=10)
We introduce superspace generalizations of the transverse derivatives to
rewrite the four-dimensional N=4 Yang-Mills theory into the fully
ten-dimensional N=1 Yang-Mills in light-cone form. The explicit SuperPoincare
algebra is constructed and invariance of the ten-dimensional action is proved.Comment: 15 page
Absence of magnetic monopoles in Maxwellian magnetoelectrics
The electromagnetic response of topological insulators is governed by axion
electrodynamics, which features a topological magnetoelectric term in the
Maxwell equations. As a consequence magnetic fields become the source of
electric fields and vice-versa, a phenomenon that is general for any material
exhibiting a linear magnetoelectric effect. Axion electrodynamics has been
associated with the possibility to create magnetic monopoles, in particular by
a electrical charge that is screened above the surface of a magnetoelectric
material. Here we present the exact solution for the electromagnetic fields in
this geometry and show that while vortex-like magnetic screening fields are
generated by the electrical charge their divergence is identically zero at
every point in space which implies a strict absence of magnetic monopoles.
Although magnetic image charges can be made explicit in the problem, no bound
state with electric charges yielding a dyon arises. A dyon-like angular
momentum follows from our analysis, but is quantized in a universal way,
because of its dependence on the dielectric constant. This is consistent with a
general argument that precludes magnetic monopoles to be generated in Maxwell
magnetoelectrics.Comment: v2: 9 pages, 3 figures; improved presentation and more detailed
appendices; added calculation of angular momentum; appendix is made more
pedagogical and now includes the detailed solution for a point charge in the
presence of a topological dielectric sphere; several references are adde
The BLG Theory in Light-Cone Superspace
The light-cone superspace version of the d=3, N=8 superconformal theory of
Bagger, Lambert and Gustavsson (BLG) is obtained as a solution to constraints
imposed by OSp(2,2|8) superalgebra. The Hamiltonian of the theory is shown to
be a quadratic form of the dynamical supersymmetry transformation.Comment: 45 pages, v2: reference added, minor typos corrected, published
versio
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