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Sep 24, 2013
09/13

by
A. Armoni; M. Shifman; G. Veneziano

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We outline a full non-perturbative proof of planar (large-N) equivalence between bosonic correlators in a theory with Majorana fermions in the adjoint representation and one with Dirac fermions in the two-index (anti)symmetric representation. In a particular case (one flavor), this reduces to our previous result - planar equivalence between super-Yang--Mills theory and a non-supersymmetric ``orientifold field theory.'' The latter theory becomes one-flavor massless QCD at N=3.

Source: http://arxiv.org/abs/hep-th/0412203v3

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Sep 18, 2013
09/13

by
A. E. Shabad

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The Dirac equation for an electron in the central Coulomb field of a point-like nucleus with the charge greater than 137 is considered. This singular problem, to which the fall-down onto the centre is inherent, is addressed using a new approach, based on a black-hole concept of the singular centre and capable of producing cut-off-free results. To this end the Dirac equation is presented as a generalized eigenvalue boundary problem of a self-adjoint operator. The eigenfunctions make complete...

Source: http://arxiv.org/abs/hep-th/0502139v1

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Sep 18, 2013
09/13

by
A. H. Zemanian

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The bounds on the statuses of the nodes in a finite graph established by Entringer, Jackson, and Snyder are extended herein so that they apply to the nodes in a transfinite graph of a certain kind.

Source: http://arxiv.org/abs/math/0502310v1

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Sep 21, 2013
09/13

by
A. Le Yaouanc

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Analytical methods in heavy quark physics are shortly reviewed, with emphasis on the problems of dynamical calculations. Then, attention is attracted to the various difficulties raised by a tentative experimental determination of $\tau_{1/2}$

Source: http://arxiv.org/abs/hep-ph/0407310v2

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Sep 18, 2013
09/13

by
A. Martinez-Finkelshtein; K. T. -R. McLaughlin; E. B. Saff

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We provide a representation in terms of certain canonical functions for a sequence of polynomials orthogonal with respect to a weight that is strictly positive and analytic on the unit circle. These formulas yield a complete asymptotic expansion for these polynomials, valid uniformly in the whole complex plane. As a consequence, we obtain some results about the distribution of zeros of these polynomials. The main technique is the steepest descent analysis of Deift and Zhou, based on the matrix...

Source: http://arxiv.org/abs/math/0502300v1

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Sep 18, 2013
09/13

by
A. R. Dzierba; R. Mitchell; A. P. Szczepaniak; M. Swat; S. Teige

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A partial wave analysis (PWA) of the pi-pi-pi+ and pi-pi0pi0 systems produced in the reaction pi- p -> (3pi)-p at 18 GeV/c was carried out using an isobar model assumption. This analysis is based on 3.0M pi-pi0pi0 events and 2.6M pi-pi-pi+ events and shows production of the a2(1320), pi2(1670) and \pi(1800) mesons. An earlier analysis of 250K pi-pi-pi+ events from the same experiment showed possible evidence for a J^{PC}=1^{-+}$ exotic meson with a mass of 1.6 GeV/c^2 decaying into rho pi....

Source: http://arxiv.org/abs/hep-ex/0502022v2

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Sep 23, 2013
09/13

by
A. Retzker; J. I. Cirac; B. Reznik

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We propose and study a method for detecting ground-state entanglement in a chain of trapped ions, which realizes a suggested scheme for detecting vacuum entanglement in quantum field theory. We show that the entanglement between single ions or groups of ions can be swapped to the internal levels of two ions by sending laser pulses that couple the internal and motional degrees of freedom. This allows to entangle two ions without actually doing gates. A proof of principle of the effect can be...

Source: http://arxiv.org/abs/quant-ph/0408059v2

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Sep 18, 2013
09/13

by
A. V. Borisov; I. S. Mamaev

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In this paper we propose a new approach to the study of integrable cases based on intensive computer methods' application. We make a new investigation of Kovalevskaya and Goryachev-Chaplygin cases of Euler-Poisson equations and obtain many new results in rigid body dynamics in absolute space. Also we present the visualization of some special particular solutions.

Source: http://arxiv.org/abs/nlin/0502030v1

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Sep 18, 2013
09/13

by
A. V. Borisov; I. S. Mamaev

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Motion of a cylinder dynamically interacting with n point vortices in a perfect fluid is considered. A nonliniear Poisson structure and two integrals of motion are found. The equations of motion a priori are not Hamiltonian. For n=1, the problem is integrable.

Source: http://arxiv.org/abs/nlin/0502031v1

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Sep 18, 2013
09/13

by
Adam Leroy; Alberto D. Bolatto; Joshua D. Simon; Leo Blitz

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We present a new survey for CO in dwarf galaxies using the Kitt Peak 12m telescope. We observed the central regions of 121 northern dwarfs with IRAS detections and no known CO emission. We detect CO in 28 of these galaxies and marginally detect another 16, increasing by about 50% the number of such galaxies known to have significant CO emission. The galaxies we detect are comparable in mass to the LMC, although somewhat brighter in CO and fainter in the FIR. Within dwarfs, we find that the CO...

Source: http://arxiv.org/abs/astro-ph/0502302v1

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Sep 18, 2013
09/13

by
Ahmad Shariati; Nosratollah Jafari

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We argue that if the velocity of electromagnetic waves in vacuum, \cem, is different from the limiting velocity for massive particles, \cst, then, a proton moving with velocity $\cem < v < \cst$ would radiate Cherenkov radiation. Because we have seen protons with energy $\sim 10^{19}$ eV coming from a distance of order more than 1 Mpc, we can put a constraint on $\Delta := (\cst - \cem)/\cst$: $\Delta < 10^{-27}$.

Source: http://arxiv.org/abs/gr-qc/0502071v1

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Sep 22, 2013
09/13

by
Ahsan Nazir; Brendon Lovett; Sean Barrett; John H. Reina; Andrew Briggs

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We consider two coupled generic quantum dots, each modelled by a simple potential which allows the derivation of an analytical expression for the inter-dot Foerster coupling, in the dipole-dipole approximation. We investigate the energy level behaviour of this coupled two-dot system under the influence of an external applied electric field and predict the presence of anticrossings in the optical spectra due to the Foerster interaction.

Source: http://arxiv.org/abs/quant-ph/0309099v2

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Sep 18, 2013
09/13

by
Alexander Kroeller; Sandor P. Fekete; Carsten Buschmann; Stefan Fischer; Dennis Pfisterer

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Localization is one of the fundamental issues in sensor networks. It is almost always assumed that it must be solved by assigning coordinates to the nodes. This article discusses positioning algorithms from a theoretical, practical and simulative point of view, and identifies difficulties and limitations. Ideas for more abstract means of location awareness are presented and the resulting possible improvements for applications are shown. Nodes with certain topological or environmental properties...

Source: http://arxiv.org/abs/cs/0502069v1

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Sep 18, 2013
09/13

by
Alexis Devulder

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In this paper, we are interested in some questions of Greven and den Hollander about the rate function $I\_{\eta}^q$ of quenched large deviations for random walk in random environment. By studying the hitting times of RWRE, we prove that in the recurrent case, $\lim\_{\theta\to 0^+}(I\_{\eta}^q)''(\theta)=+\infty$, which gives an affirmative answer to a conjecture of Greven and den Hollander. We also establish a comparison result between the rate function of quenched large deviations for a...

Source: http://arxiv.org/abs/math/0502316v1

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Sep 22, 2013
09/13

by
Andrei Khrennikov

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We perform the analysis of probabilistic assumptions of Bell's approach. We emphasize that J. Bell wrote about probability without to specify the concrete axiomatics of probability theory. The careful analysis demonstrated that (surprisingly) J. Bell did not apply the classical probability model (Kolmogorov) to describe ``classical physical framework.'' In fact, he created his own probabilistic model and compared it with the quantum one. The crucial point is that J. Bell did not pay attention...

Source: http://arxiv.org/abs/quant-ph/0308078v4

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Sep 18, 2013
09/13

by
Andrew F. Boden; Guillermo Torres; Christian A. Hummel

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We report on a significantly improved determination of the physical orbit of the double-lined spectroscopic binary system 12 Boo. We have a 12 Boo interferometry dataset spanning six years with the Palomar Testbed Interferometer, a smaller amount of data from the Navy Prototype Optical Interferometer, and a radial velocity dataset spanning 14 years from the Harvard-Smithsonian Center for Astrophysics. We have updated the 12 Boo physical orbit model with our expanded interferometric and radial...

Source: http://arxiv.org/abs/astro-ph/0502250v2

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Sep 18, 2013
09/13

by
Antonio N. Bernal; Miguel Sánchez

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The folk questions in Lorentzian Geometry, which concerns the smoothness of time functions and slicings by Cauchy hypersurfaces, are solved by giving simple proofs of: (a) any globally hyperbolic spacetime $(M,g)$ admits a smooth time function $\tau$ whose levels are spacelike Cauchy hyperfurfaces and, thus, also a smooth global splitting $M= \R \times {\cal S}$, $g= - \beta(\tau,x) d\tau^2 + \bar g_\tau $, (b) if a spacetime $M$ admits a (continuous) time function $t$ (i.e., it is stably...

Source: http://arxiv.org/abs/gr-qc/0401112v3

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Sep 18, 2013
09/13

by
Aurelien Drezet

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In the above paper, it is claimed that with a particular use of the Bell inequality a simple single photon experiment could be performed to show the impossibility of any deterministic hidden variable theory in quantum optics. A careful analysis of the concept of probability for hidden variables and a detailed discussion of the hidden variable model of de Broglie-Bohm show that the reasoning and main conclusion of this paper are not correct.

Source: http://arxiv.org/abs/quant-ph/0502095v1

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Sep 18, 2013
09/13

by
Axel Brandenburg

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Arguments for and against the widely accepted picture of a solar dynamo being seated in the tachocline are reviewed and alternative ideas concerning dynamos operating in the bulk of the convection zone, or perhaps even in the near-surface shear layer, are discussed. Based on the angular velocities of magnetic tracers it is argued that the observations are compatible with a distributed dynamo that may be strongly shaped by the near-surface shear layer. Direct simulations of dynamo action in a...

Source: http://arxiv.org/abs/astro-ph/0502275v1

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Sep 23, 2013
09/13

by
B. E. Carlson; E. Brobeck; C. J. Jillings; M. B. Larson; T. W. Lynn; R. D. McKeown; James E. Hill; B. Falkowski; R. Seki; J. Sepikas; G. B. Yodh

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We present the results of a search for time correlations in high energy cosmic ray data (primary E > 10^{14} eV) collected by the California HIgh school Cosmic ray ObServatory (CHICOS) array. Data from 60 detector sites spread over an area of 400 km^2 were studied for evidence of correlated events separated by more than 1 km with coincidence times ranging from 1 microsec up to 1 second. All searches were consistent with the absence of excess coincidences except for a 2.9 sigma excess...

Source: http://arxiv.org/abs/astro-ph/0411212v2

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Sep 18, 2013
09/13

by
B. K. Gibson; Y. Fenner; A. Kiessling

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Motivated by the inability of Galactic chemical evolution models to reproduce some of the observed solar neighbourhood distribution of elements (and isotopes) with atomic numbers 6 < Z < 15, we have revisited the relevant stellar and Galactic models as part of an ambitious new program aimed at resolving these long-standing discrepancies. Avoiding the use of (traditional) parametric models for low- and intermediate-mass stellar evolution, we have generated a new, physically...

Source: http://arxiv.org/abs/astro-ph/0502280v1

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Jul 20, 2013
07/13

by
B. Melic; B. Nizic; K. Passek

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We briefly review the calculational procedure for the PQCD prediction for hard exclusive quantities and reconsider the problem of the factorization scale dependence.

Source: http://arxiv.org/abs/hep-ph/0107311v5

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Sep 18, 2013
09/13

by
B. Simovic; C. Ellenberger; K. Ensslin; Wegscheider

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We have measured the magneto-resistance of a two-dimensional electron gas (2DEG) under continuous microwave irradiation as a function of electron density and mobility tuned with a metallic top-gate. In the entire range of density and mobility we have investigated, we observe microwave induced oscillations of large amplitude that are B-periodic. These B-periodic oscillations are reminiscent of the ones reported by Kukushkin \textit{et al}[1] and which were attributed to the presence of...

Source: http://arxiv.org/abs/cond-mat/0502350v1

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Sep 18, 2013
09/13

by
Barbara Jagoda-Cwiklik; Lukasz Cwiklik; Marek Frankowicz

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Dynamic Monte Carlo simulations for the open coarse-grained model of MFI type zeolite were used to study the dynamics of adsorption and diffusion of n-butane in silicalite-1. We demonstrated the influence of the confinement of the structure of zeolite channels on both the dynamics of the adsorption process and the maximum loading of adsorbate. We showed that the confinement and channel blocking limit the adsorption and desorption processes. Moreover, they cause the maximum loading in the...

Source: http://arxiv.org/abs/cond-mat/0502368v1

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Sep 23, 2013
09/13

by
Benjamin Dollet; Miguel Aubouy; Francois Graner

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To understand the mechanics of a complex fluid such as a foam we propose a model experiment (a bidimensional flow around an obstacle) for which an external sollicitation is applied, and a local response is measured, simultaneously. We observe that an asymmetric obstacle (cambered airfoil profile) experiences a downards lift, opposite to the lift usually known (in a different context) in aerodynamics. Correlations of velocity, deformations and pressure fields yield a clear explanation of this...

Source: http://arxiv.org/abs/cond-mat/0411632v2

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Sep 18, 2013
09/13

by
Benjamin F. Williams

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A search for variable stars is performed using two epochs of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging data for a 9.28 square arcminute portion of M31. This data set reveals 254 sources that vary by at least 4-sigma between epochs. The positions and 2-epoch B-band (equivalent) photometry of these sources are presented. The photometry suggests that this catalog includes most of the RR Lyrae population of this portion of M31.

Source: http://arxiv.org/abs/astro-ph/0502294v1

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Sep 18, 2013
09/13

by
Bernhard Kroetz; Sundaram Thangavelu; Yuan Xu

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The heat kernel transform H_t for the Heisenberg group is studied in detail. The main result shows that the image of H_t is a direct sum of two weighted Bergman spaces whose associated weighted functions are of oscillatory nature, i.e. attain positive and negative values.

Source: http://arxiv.org/abs/math/0401243v2

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Sep 23, 2013
09/13

by
Bruno Nachtergaele; Shannon Starr

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We prove ferromagnetic ordering of energy levels for XXX Heisenberg chains of any spin and XXZ spin chains with all spins equal to 1/2. Ferromagnetic ordering means that the minimum energies in the invariant subspaces of fixed total spin are monotone decreasing as a function of the total spin. This result provides a ferromagnetic analogue of the well-known theorem by Lieb and Mattis about ordering of energy levels in antiferromagnetic and ferrimagnetic systems on bipartite graphs.

Source: http://arxiv.org/abs/math-ph/0408020v3

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Sep 18, 2013
09/13

by
C. Adiga; T. Kim; M. S. Mahadeva Naika; H. S. Madhusudhan

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We study Ramanujan's cubic continued fraction and explicit evaluations of theta-functions

Source: http://arxiv.org/abs/math/0502323v1

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Sep 18, 2013
09/13

by
C. D. J. Sinclair; J. A. Retter; E. A. Curtis; B. V. Hall; I. Llorente Garcia; S. Eriksson; B. E. Sauer; E. A. Hinds

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We describe an array of microscopic atom traps formed by a pattern of magnetisation on a piece of videotape. We describe the way in which cold atoms are loaded into one of these micro-traps and how the trapped atom cloud is used to explore the properties of the trap. Evaporative cooling in the micro-trap down to a temperature of 1 microkelvin allows us to probe the smoothness of the trapping potential and reveals some inhomogeneity produced by the magnetic film. We discuss future prospects for...

Source: http://arxiv.org/abs/physics/0502073v1

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Sep 24, 2013
09/13

by
C. Forssen; P. Navratil; W. E. Ormand; E. Caurier

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We are presenting the first ab initio structure investigation of the loosely bound 11-Be nucleus, together with a study of the lighter isotope 9-Be. The nuclear structure of these isotopes is particularly interesting due to the appearance of a parity-inverted ground state in 11-Be. Our study is performed in the framework of the ab initio no-core shell model. Results obtained using four different, high-precision two-nucleon interactions, in model spaces up to 9\hbar\Omega, are shown. For both...

Source: http://arxiv.org/abs/nucl-th/0412049v2

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Sep 18, 2013
09/13

by
C. M. Gutierrez; M. Lopez-Corredoira

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We present spectroscopic observations of six optical counterparts of intermediate luminosity X-ray sources (ULXs) around nearby galaxies. The spectra of the six objects show the presence of broad emission features. The identification of these allow us to classify all of the objects as quasars at higher redshift than their assigned parent galaxy. This is one of the first and largest identifications of such objects using unambigous optical spectral features. These results, in conjuction with...

Source: http://arxiv.org/abs/astro-ph/0502290v1

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Sep 18, 2013
09/13

by
C. Schuessler-Langeheine; J. Schlappa; A. Tanaka; Z. Hu; C. F. Chang; E. Schierle; M. Benomar; H. Ott; E. Weschke; G. Kaindl; O. Friedt; G. A. Sawatzky; H. -J. Lin; C. T. Chen; M. Braden; L. H. Tjeng

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Strong resonant enhancements of the charge-order and spin-order superstructure-diffraction intensities in La1.8Sr0.2NiO4 are observed when x-ray energies in the vicinity of the Ni L2,3 absorption edges are used. The pronounced photon-energy and polarization dependences of these diffraction intensities allow for a critical determination of the local symmetry of the ordered spin and charge carriers. We found that not only the antiferromagnetic order but also the charge-order superstructure...

Source: http://arxiv.org/abs/cond-mat/0502357v1

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Sep 18, 2013
09/13

by
Carles Casacuberta; Boris Chorny

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It is known that the existence of localization with respect to an arbitrary (possibly proper) class of maps in the category of simplicial sets is implied by a large-cardinal axiom called Vopenka's principle.In this article we extend the validity of this result to any left proper, combinatorial, simplicial model category $\cat M$ and show that, under additional assumptions on $\cat M$, every homotopy idempotent functor is in fact a localization with respect to some set of maps. These results are...

Source: http://arxiv.org/abs/math/0502329v1

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Sep 18, 2013
09/13

by
Christian G. Boehmer; Piotr Bronowski

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Recent interest in brane world models motivates the investigation of generic first order dilaton gravity actions, with potentials having some non-smoothness. We consider two different types of \delta-like contributions in the action and analyse their effects on the solutions. Furthermore a second source of non-smoothness arises due to the remaining ambiguities in the solutions in the separated smooth patches, after fixing all other constants by matching and asymptotic conditions. If moreover...

Source: http://arxiv.org/abs/gr-qc/0502030v2

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Sep 18, 2013
09/13

by
Claude Cibils; Andrea Solotar

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We consider categories over a field $k$ in order to prove that smash extensions and Galois coverings with respect to a finite group coincide up to Morita equivalence of $k$-categories. For this purpose we describe processes providing Morita equivalences called contraction and expansion. We prove that composition of these processes provides any Morita equivalence, a result which is related with the karoubianisation (or idempotent completion) and additivisation of a $k$-category.

Source: http://arxiv.org/abs/math/0502308v1

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Sep 18, 2013
09/13

by
Claude Ederer; Nicola A. Spaldin

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The dependencies on strain and oxygen vacancies of the ferroelectric polarization and the weak ferromagnetic magnetization in the multiferroic material bismuth ferrite, BiFeO_3, are investigated using first principles density functional theory calculations. The electric polarization is found to be rather independent of strain, in striking contrast to most conventional perovskite ferroelectrics. It is also not significantly affected by oxygen vacancies, or by the combined presence of strain and...

Source: http://arxiv.org/abs/cond-mat/0502364v1

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Sep 18, 2013
09/13

by
Claude Pache

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We find out for which $t$ shells of selfdual lattices and of theirs shadows are spherical $t$-designs. The method uses theta series of lattices, which are modular forms. We analyse fully cubic and Witt lattices, as well as all selfdual lattices of rank at most 24.

Source: http://arxiv.org/abs/math/0502313v1

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Sep 18, 2013
09/13

by
Cristina Oliveira; Jean Dupuis; Pierre Chayer; H. Warren Moos

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We present new measurements of the oxygen gas-phase abundance along four sightlines probing gas inside the Local Bubble, using data obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Hubble Space Telecope (HST). Combining these with seven previously published N(O I) and N(H I) measurements we determine a mean O/H ratio for the Local Bubble, (O/H) = (3.45 +/- 0.19)x10^(-4) (1 sigma in the mean). Our result is virtually identical to O/H = (3.43 +/- 0.15)x10^(-4) derived from...

Source: http://arxiv.org/abs/astro-ph/0502295v1

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Sep 21, 2013
09/13

by
D. Bazeia; F. A. Brito; W. Freire; R. F. Ribeiro

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We investigate confinement from new global defect structures in three spatial dimensions. The global defects arise in models described by a single real scalar field, governed by special scalar potentials. They appear as electrically, magnetically or dyonically charged structures. We show that they induce confinement, when they are solutions of effective QCD-like field theories in which the vacua are regarded as color dielectric media with an anti-screening property. As expected, in three...

Source: http://arxiv.org/abs/hep-th/0311160v2

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Jul 20, 2013
07/13

by
D. Riechers; Y. Balega; T. Driebe; K. -H. Hofmann; A. B. Men'shchikov; G. Weigelt

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We present near-infrared speckle interferometry of the OH/IR star OH 104.9+2.4 in the K' band obtained with the 6m telescope of the Special Astrophysical Observatory (SAO). At a wavelength of lambda = 2.12 micron the diffraction-limited resolution of 74 mas was attained. The reconstructed visibility reveals a spherically symmetric, circumstellar dust shell (CDS) surrounding the central star. The visibility function shows that the stellar contribution to the total flux at lambda = 2.12 micron is...

Source: http://arxiv.org/abs/astro-ph/0406092v2

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Sep 20, 2013
09/13

by
Dan Israel; Costas Kounnas; Domenico Orlando; P. Marios Petropoulos

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We analyze asymmetric marginal deformations of SU(2)_k and SL(2,R)_k WZW models. These appear in heterotic string backgrounds with non-vanishing Neveu--Schwarz three-forms plus electric or magnetic fields, depending on whether the deformation is elliptic, hyperbolic or parabolic. Asymmetric deformations create new families of exact string vacua. The geometries which are generated in this way, deformed S^3 or AdS_3, include in particular geometric cosets such as S^2, AdS_2 or H_2. Hence, the...

Source: http://arxiv.org/abs/hep-th/0405213v2

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Sep 18, 2013
09/13

by
David Seckel; Todor Stanev

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Observations of ultrahigh energy cosmic rays (UHECR) do not uniquely determine both the injection spectrum and the evolution model for UHECR sources - primarily because interactions during propagation obscure the early Universe from direct observation. Detection of neutrinos produced in those same interactions, coupled with UHECR results, would provide a full description of UHECR source properties.

Source: http://arxiv.org/abs/astro-ph/0502244v2

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Sep 18, 2013
09/13

by
E. Novais; F. Guinea; A. H. Castro Neto

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The phase diagram of a dissipative particle in a periodic potential and a magnetic field is studied in the weak barrier limit and in the tight-biding regime. For the case of half flux per plaquette, and for a wide range of values of the dissipation, the physics of the model is determined by a non trivial fixed point. A combination of exact and variational results is used to characterize this fixed point. Finally, it is also argued that there is an intermediate energy scale that separates the...

Source: http://arxiv.org/abs/cond-mat/0502363v1

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Sep 18, 2013
09/13

by
Emmanuel Candes; Terence Tao

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This paper considers the classical error correcting problem which is frequently discussed in coding theory. We wish to recover an input vector $f \in \R^n$ from corrupted measurements $y = A f + e$. Here, $A$ is an $m$ by $n$ (coding) matrix and $e$ is an arbitrary and unknown vector of errors. Is it possible to recover $f$ exactly from the data $y$? We prove that under suitable conditions on the coding matrix $A$, the input $f$ is the unique solution to the $\ell_1$-minimization problem...

Source: http://arxiv.org/abs/math/0502327v1

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Sep 18, 2013
09/13

by
F. Affouard; M. Descamps

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Slow dynamics of difluorotetrachloroethane in both supercooled plastic crystal and supercooled liquid states have been investigated from Molecular Dynamics simulations. The temperature and wave-vector dependence of collective dynamics in both states are probed using coherent dynamical scattering functions $S(Q,t)$. Our results confirm the strong analogy between molecular liquids and plastic crystals for which $\alpha$-relaxation times and non-ergodicity parameters are controlled by the non...

Source: http://arxiv.org/abs/cond-mat/0502352v1

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69

Sep 23, 2013
09/13

by
F. Heidrich-Meisner; A. Honecker; W. Brenig

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We study the heat conduction of the spin-1/2 XXZ chain in finite magnetic fields where magnetothermal effects arise. Due to the integrability of this model, all transport coefficients diverge, signaled by finite Drude weights. Using exact diagonalization and mean-field theory, we analyze the temperature and field dependence of the thermal Drude weight for various exchange anisotropies under the condition of zero magnetization-current flow. First, we find a strong magnetic field dependence of...

Source: http://arxiv.org/abs/cond-mat/0408529v2

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37

Sep 18, 2013
09/13

by
Falk Rohsiepe

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In the context of string dualities, fibration structures of Calabi-Yau manifolds play a prominent role. In particular, elliptic and K3 fibered Calabi-Yau fourfolds are important for dualities between string compactifications with four flat space-time dimensions. A natural framework for studying explicit examples of such fibrations is given by Calabi-Yau hypersurfaces in toric varieties, because this class of varieties is sufficiently large to provide examples with very different features while...

Source: http://arxiv.org/abs/hep-th/0502138v1

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28

Sep 22, 2013
09/13

by
Florian Girelli; Etera R. Livine

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Loop Quantum Gravity defines the quantum states of space geometry as spin networks and describes their evolution in time. We reformulate spin networks in terms of harmonic oscillators and show how the holographic degrees of freedom of the theory are described as matrix models. This allow us to make a link with non-commutative geometry and to look at the issue of the semi-classical limit of LQG from a new perspective. This work is thought as part of a bigger project of describing quantum...

Source: http://arxiv.org/abs/gr-qc/0501075v2

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31

Sep 18, 2013
09/13

by
Frank Wilczek

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Asymptotic freedom was developed as a response to two paradoxes: the weirdness of quarks, and in particular their failure to radiate copiously when struck; and the coexistence of special relativity and quantum theory, despite the apparent singularity of quantum field theory. It resolved these paradoxes, and catalyzed the development of several modern paradigms: the hard reality of quarks and gluons, the origin of mass from energy, the simplicity of the early universe, and the power of symmetry...

Source: http://arxiv.org/abs/hep-ph/0502113v2