27 research outputs found
On higher spin interactions with matter
Cubic couplings between a complex scalar field and a tower of symmetric
tensor gauge fields of all ranks are investigated. A symmetric conserved
current, bilinear in the scalar field and containing r derivatives, is provided
for any rank r>0 and is related to the corresponding rigid symmetry of
Klein-Gordon's Lagrangian. Following Noether's method, the tensor gauge fields
interact with the scalar field via minimal coupling to the conserved currents.
The corresponding cubic vertex is written in a compact form by making use of
Weyl's symbols. This enables the explicit computation of the non-Abelian gauge
symmetry group, the current-current interaction between scalar particles
mediated by any gauge field and the corresponding four-scalar elastic
scattering tree amplitude. The exact summation of these amplitudes for an
infinite tower of gauge fields is possible and several examples for a definite
choice of the coupling constants are provided where the total amplitude
exhibits fast (e.g. exponential) fall-off in the high-energy limit.
Nevertheless, the long range interaction potential is dominated by the exchange
of low-spin particles in the low-energy limit.Comment: 32 pages, v2: typos corrected and comments added; accepted for
publication in JHE
Measuring the Efficiency of Public Schools using Data Envelopment Analysis – An Exploratory Study
We explore measuring and comparing the efficiency of selected Abu Dhabi secondary public schools using data envelopment analysis. For better identification and specification, certain scenarios were developed using different combinations of inputs and outputs. Sensitivity analysis was carried out to identify expected reductions (in inputs) or increases (in outputs) needed for inefficient schools to become efficient. The inputs with greatest impact were cost per teacher and cost per students. The outputs with greatest impact were two student tests conducted at the national level. Analysis of variance showed that location and type of school had a significant impact on school efficiencies. Keywords: School efficiency, Data Envelopment Analysis, Abu Dhab
QFT with Twisted Poincar\'e Invariance and the Moyal Product
We study the consequences of twisting the Poincare invariance in a quantum
field theory. First, we construct a Fock space compatible with the twisting and
the corresponding creation and annihilation operators. Then, we show that a
covariant field linear in creation and annihilation operators does not exist.
Relaxing the linearity condition, a covariant field can be determined. We show
that it is related to the untwisted field by a unitary transformation and the
resulting n-point functions coincide with the untwisted ones. We also show that
invariance under the twisted symmetry can be realized using the covariant field
with the usual product or by a non-covariant field with a Moyal product. The
resulting S-matrix elements are shown to coincide with the untwisted ones up to
a momenta dependent phase.Comment: 11 pages, references adde
Group theoretical approach to quantum fields in de Sitter space I. The principal series
Using unitary irreducible representations of the de Sitter group, we
construct the Fock space of a massive free scalar field.
In this approach, the vacuum is the unique dS invariant state. The quantum
field is a posteriori defined by an operator subject to covariant
transformations under the dS isometry group. This insures that it obeys
canonical commutation relations, up to an overall factor which should not
vanish as it fixes the value of hbar. However, contrary to what is obtained for
the Poincare group, the covariance condition leaves an arbitrariness in the
definition of the field. This arbitrariness allows to recover the amplitudes
governing spontaneous pair creation processes, as well as the class of alpha
vacua obtained in the usual field theoretical approach. The two approaches can
be formally related by introducing a squeezing operator which acts on the state
in the field theoretical description and on the operator in the present
treatment. The choice of the different dS invariant schemes (different alpha
vacua) is here posed in very simple terms: it is related to a first order
differential equation which is singular on the horizon and whose general
solution is therefore characterized by the amplitude on either side of the
horizon. Our algebraic approach offers a new method to define quantum field
theory on some deformations of dS space.Comment: 35 pages, 2 figures ; Corrected typo, Changed referenc
Orientifolds of String Theory Melvin backgrounds
We study the dynamics of type I strings on Melvin backgrounds, with a single
or multiple twisted two-planes. We construct two inequivalent types of
orientifold models that correspond to (non-compact) irrational versions of
Scherk-Schwarz type breaking of supersymmetry. In the first class of vacua,
D-branes and O-planes are no longer localized in space-time but are smeared
along the compact Melvin coordinate with a characteristic profile. On the other
hand, the second class of orientifolds involves O-planes and D-branes that are
both rotated by an angle proportional to the twist. In case of ``multiple
Melvin spaces'', some amount of supersymmetry is recovered if the planes are
twisted appropriately and part of the original O-planes are transmuted into new
ones. The corresponding boundary and crosscap states are determined.Comment: 34 pages, LaTe
Effective action in a higher-spin background
We consider a free massless scalar field coupled to an infinite tower of
background higher-spin gauge fields via minimal coupling to the traceless
conserved currents. The set of Abelian gauge transformations is deformed to the
non-Abelian group of unitary operators acting on the scalar field. The gauge
invariant effective action is computed perturbatively in the external fields.
The structure of the various (divergent or finite) terms is determined. In
particular, the quadratic part of the logarithmically divergent (or of the
finite) term is expressed in terms of curvatures and related to conformal
higher-spin gravity. The generalized higher-spin Weyl anomalies are also
determined. The relation with the theory of interacting higher-spin gauge
fields on anti de Sitter spacetime via the holographic correspondence is
discussed.Comment: 40 pages, Some errors and typos corrected, Version published in JHE
Boundary action of free AdS higher-spin gauge fields and the holographic correspondence
Déformations de la symétrie de Poincaré et ses conséquences sur la théorie quantique de champs scalaires
PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF