7,991 research outputs found
A Gauge Field Theory for Continuous Spin Tachyons
We present a gauge field theory for unitary infinite dimensional tachyonic
representations of the Poincar\'e group. It was obtained by a dimensional
reduction from the gauge field theory for continuous spin particles in a
cotangent bundle over Minkowski space-time. We discuss its BRST formulation and
compute the partition function. Some cubic vertices are also presented and
their properties discussed. In the massless limit the gauge theory for
continuous spin tachyons reduces to the gauge theory for continuous spin
particles.Comment: 22 pages, typos correcte
Noncommutative Supersymmetric Field Theories
We discuss some properties of noncommutative supersymmetric field theories
which do not involve gauge fields. We concentrate on the renormalizability
issue of these theories.Comment: 12 pages, updated version of a talk presented at the XXI Brazilian
National Meeting on Particles and Fields, Sao Lorenco, MG, Oct. 23 - 26, 200
Remarks on a Gauge Theory for Continuous Spin Particles
We discuss in a systematic way the gauge theory for a continuous spin
particle proposed by Schuster and Toro. We show that it is naturally formulated
in a cotangent bundle over Minkowski spacetime where the gauge field depends on
the spacetime coordinate and on a covector . We discuss how
fields can be expanded in in different ways and how these expansions
are related to each other. The field equation has a derivative of a Dirac delta
function with support on the -hyperboloid and we show how it
restricts the dynamics of the gauge field to the -hyperboloid. We then
show that on-shell the field carries one single irreducible unitary
representation of the Poincar\'e group for a continuous spin particle. We also
show how the field can be used to build a set of covariant equations found by
Wigner describing the wave function of one-particle states for a continuous
spin particle. Finally we show that it is not possible to couple minimally a
continuous spin particle to a background abelian gauge field, and make some
comments about the coupling to gravity.Comment: 21 pages, typos corrected, improved presentation of section VI, final
versio
Duality in Noncommutative Maxwell-Chern-Simons Theory
Applying a master action technique we obtain the dual of the noncommutative
Maxwell-Chern-Simons theory. The equivalence between the Maxwell-Chern-Simons
theory and the self-dual model in commutative space-time does not survive in
the non-commutative setting. We also point out an ambiguity in the
Seiberg-Witten map.Comment: 10 pages; Fifth International Conference on Mathematical Methods in
Physics, Rio de Janeiro, April 24-28, 2006; PoS documentclas
Non Abelian Fields in Very Special Relativity
We study non-Abelian fields in the context of very special relativity (VSR).
For this we define the covariant derivative and the gauge field gauge
transformations, both of them involving a fixed null vector , related
to the VSR breaking of the Lorentz group to the Hom(2) or Sim(2) subgroups. As
in the Abelian case the gauge field becomes massive. Moreover we show that the
VSR gauge transformations form a closed algebra. We then write actions coupling
the gauge field to various matter fields (bosonic and fermionic). We mention
how we can use the spontaneous symmetry breaking mechanism to give a flavor
dependent VSR mass to the gauge bosons. Finally, we quantize the model using
the BRST formalism to fix the gauge. The model is renormalizable and unitary
and for non abelian groups, asymptotically free.Comment: 11 pages, late
Ferromagnetic and insulating behavior of LaCoO3 films grown on a (001) SrTiO3 substrate. A simple ionic picture explained ab initio
This paper shows that the oxygen vacancies observed experimentally in thin
films of LaCoO3 subject to tensile strain are thermodynamically stable
according to ab initio calculations. By using DFT calculations, we show that
oxygen vacancies on the order of 6 % forming chains perpendicular to the (001)
direction are more stable than the stoichiometric solution. These lead to
magnetic Co2+ ions surrounding the vacancies that couple ferromagnetically. The
remaining Co3+ cations in an octahedral environment are non magnetic. The gap
leading to a ferromagnetic insulating phase occurs naturally and we provide a
simple ionic picture to explain the resulting electronic structure.Comment: 7 pages, 7 figure
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