1,325 research outputs found
Superstrings and WZNW Models
We give a brief review of our approach to the quantization of superstrings.
New is a covariant derivation of the measure at tree level and a path integral
formula for this measure.Comment: 12 pp, LaTeX, Contribution to the QTS3 Conference Proceeding
Do the Herschel cold clouds in the Galactic halo embody its dark matter?
Recent Herschel/SPIRE maps of the Small and Large Magellanic Clouds (SMC,
LMC) exhibit in each thousands of clouds. Observed at 250 microns, they must be
cold, T ~ 15 K, hence the name "Herschel cold clouds" (HCCs). From the observed
rotational velocity profile and the assumption of spherical symmetry, the
Galactic mass density is modeled in a form close to that of an isothermal
sphere. If the HCCs constitute a certain fraction of it, their angular size
distribution has a specified shape. A fit to the data deduced from the SMC/LMC
maps supports this and yields for their radius 2.5 pc, with a small change when
allowing for a spread in HCC radii. There are so many HCCs that they will make
up all the missing Halo mass density if there is spherical symmetry and their
average mass is of order 15,000 Mo. This compares well with the Jeans mass of
circa 40,000 Mo and puts forward that the HCCs are in fact Jeans clusters,
constituting all the Galactic dark matter and much of its missing baryons, a
conclusion deduced before from a different field of the sky (Nieuwenhuizen,
Schild and Gibson 2011). A preliminary analysis of the intensities yields that
the Jeans clusters themselves may consist of some billion MACHOs of a few dozen
Earth masses. With a size of dozens of solar radii, they would mostly obscure
stars in the LMC, SMC and towards the Galactic center, and may thus have been
overlooked in microlensing.Comment: Revised and corrected version, matches published version. Conclusions
unchange
The Large N Limit of the (2,0) Superconformal Field Theory
We discuss the large N limit of the (2,0) field theory in six dimensions. We
do this by assuming the validity of Maldacena's conjecture of the
correspondence between large N gauge theories and supergravity backgrounds,
here . We review the spectrum of the supergravity theory and
compute the spectrum of primary operators of the conformal algebra of arbitrary
spin.Comment: Minor changes, version to appear in Physics Letters
Self-Dual Conformal Supergravity and the Hamiltonian Formulation
In terms of Dirac matrices the self-dual and anti-self-dual decomposition of
a conformal supergravity is given and a self-dual conformal supergravity theory
is developed as a connection dynamic theory in which the basic dynamic variabes
include the self-dual spin connection i.e. the Ashtekar connection rather than
the triad. The Hamiltonian formulation and the constraints are obtained by
using the Dirac-Bergmann algorithm.
PACS numbers: 04.20.Cv, 04.20.Fy,04.65.+
Ehrenfest relations at the glass transition: solution to an old paradox
In order to find out whether there exists a thermodynamic description of the
glass phase, the Ehrenfest relations along the glass transition line are
reconsidered. It is explained that the one involving the compressibility is
always satisfied, and that the one involving the specific heat is principally
incorrect.
Thermodynamical relations are presented for non-ergodic systems with a
one-level tree in phase space. They are derived for a spin glass model, checked
for other models, and expected to apply, e.g., to glass forming liquids. The
second Ehrenfest relation gets a contribution from the configurational entropy.Comment: 4 pages revtex, to appear in Phys. Rev. Let
"Optical conductance fluctuations: diagrammatic analysis in Landauer approach and non-universal effects"
The optical conductance of a multiple scattering medium is the total
transmitted light of a diffuse incoming beam. This quantity, very analogous to
the electronic conductance, exhibits universal conductance fluctuations. We
perform a detailed diagrammatic analysis of these fluctuations. With a
Kadanoff-Baym technique all the leading diagrams are systematically generated.
A cancellation of the short distance divergencies occurs, that yields a well
behaved theory. The analytical form of the fluctuations is calculated and
applied to optical systems. Absorption and internal reflections reduce the
fluctuations significantly.Comment: 25 pages Revtex 3.0, 18 seperate postscript figure
Dilaton and Second-Rank Tensor Fields as Supersymmetric Compensators
We formulate a supersymmetric theory in which both a dilaton and a
second-rank tensor play roles of compensators. The basic off-shell multiplets
are a linear multiplet (B_{\mu\nu}, \chi, \phi) and a vector multiplet (A_\mu,
\l; C_{\mu\nu\rho}), where \phi and B_{\m\n} are respectively a dilaton and a
second-rank tensor. The third-rank tensor C_{\mu\nu\rho} in the vector
multiplet is 'dual' to the conventional D-field with 0 on-shell or 1 off-shell
degree of freedom. The dilaton \phi is absorbed into one longitudinal component
of A_\mu, making it massive. Initially, B_{\mu\nu} has 1 on-shell or 3
off-shell degrees of freedom, but it is absorbed into the longitudinal
components of C_{\mu\nu\rho}. Eventually, C_{\mu\nu\rho} with 0 on-shell or 1
off-shell degree of freedom acquires in total 1 on-shell or 4 off-shell degrees
of freedom, turning into a propagating massive field. These basic multiplets
are also coupled to chiral multiplets and a supersymmetric Dirac-Born-Infeld
action. Some of these results are also reformulated in superspace. The proposed
mechanism may well provide a solution to the long-standing puzzle of massless
dilatons and second-rank tensors in supersymmetric models inspired by string
theory.Comment: 15 pages, no figure
Four dimensional R^4 superinvariants through gauge completion
We fully compute the N=1 supersymmetrization of the fourth power of the Weyl
tensor in d=4 x-space with the auxiliary fields. In a previous paper, we showed
that their elimination requires an infinite number of terms; we explicitely
compute those terms to order \kappa^4 (three loop). We also write, in
superspace notation, all the possible N=1 actions, in four dimensions, that
contain pure R^4 terms (with coupling constants). We explicitely write these
actions in terms of the \theta components of the chiral density \epsilon and
the supergravity superfields R, G_m, W_{ABC}. Using the method of gauge
completion, we compute the necessary \theta components which allow us to write
these actions in x-space. We discuss under which circumstances can these extra
R^4 correction terms be reabsorbed in the pure supergravity action, and their
relevance to the quantum supergravity/string theory effective actions.Comment: 20 pages, no figures. Sec. 3 clarified; typos correcte
Role of Visual Dysfunction in Postural Control in Children With Cerebral Palsy
Introduction: Deficient postural control is one of the key problems in cerebral palsy (CP). Little, however, is known about the specific nature of postural problems of children with CP, nor of the relation between abnormal posture and dysfunction of the visual system. Aim of the study: To provide additional information on the association of abnormalities in postural control and visual dysfunction of the anterior or posterior part of the visual system. Methods: Data resulting from ophthalmologic, orthoptic, neurological, neuro-radiological, and ethological investigations of more than 313 neurologically impaired children were retrospectively analyzed. Results: Abnormal postural control related to ocular and ocular motor disorders consisted of anomalous head control and subsequent abnormal head posture and torticollis. The abnormal postural control related to retrochiasmatical damage of the visual system consisted of a torticollis combined with adjustment of the upper part of the body, as if at the same time adapting to a combination of defects and optimizing residual visual functions. Conclusion: Visual dysfunctions play a distinct role in the postural control of children with CP
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