564 research outputs found

    Study of Bose-Einstein Correlations in e+e- -> W+W- events at LEP

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    Bose-Einstein correlation between like-sign charged-particle pairs in e+e- -> W+W- events recorded with the OPAL detector at LEP at centre-of-mass energies between 183 GeV and 209 GeV are studied. Recently proposed methods which allow direct searches for correlations in the data via distributions of test variables are used to investigate the presence of correlations between hadrons originating from different W bosons in W+W- -> qqqq events. Within the statistics of the data sample no evidence for inter-WW Bose-Einstein correlations is obtained. The data are also compared with predictions of a recent implementation of Bose-Einstein correlation effects in the Monte Carlo model PYTHIA.Comment: 29 pages, 10 figures, Submitted to Eur. Phys. J.

    Lorentz Violating Supersymmetric Quantum Electrodynamics

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    Theory of Supersymmetric Quantum Electrodynamics is extended by interactions with external vector and tensor backgrounds, that are assumed to be generated by some Lorentz-violating (LV) dynamics at an ultraviolet scale perhaps related to the Planck scale. Exact supersymmetry requires that such interactions correspond to LV operators of dimension five or higher, providing a solution to the naturalness problem in the LV sector. We classify all dimension five and six LV operators, analyze their properties at the quantum level and describe observational consequences of LV in this theory. We show that LV operators do not induce destabilizing D-terms, gauge anomaly and the Chern-Simons term for photons. We calculate the renormalization group evolution of dimension five LV operators and their mixing with dimension three LV operators, controlled by the scale of the soft-breaking masses. Dimension five LV operators are constrained by the low-energy precision measurements at 10^{-10}-10^{-5} level in units of the inverse Planck scale, while the Planck-scale suppressed dimension six LV operators are allowed by observational data.Comment: 37 pages LaTeX, minor revisions, and typos correcte

    Global-String and Vortex Superfluids in a Supersymmetric Scenario

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    The main goal of this work is to investigate the possibility of finding the supersymmetric version of the U(1)-global string model which behaves as a vortex-superfluid. To describe the superfluid phase, we introduce a Lorentz-symmetry breaking background that, in an approach based on supersymmetry, leads to a discussion on the relation between the violation of Lorentz symmetry and explicit soft supersymmetry breakings. We also study the relation between the string configuration and the vortex-superfluid phase. In the framework we settle down in terms of superspace and superfields, we actually establish a duality between the vortex degrees of freedom and the component fields of the Kalb-Ramond superfield. We make also considerations about the fermionic excitations that may appear in connection with the vortex formation.Comment: 9 pages. This version presented the relation between Lorentz symmetry violation by the background and the appearance of terms that explicitly break SUS

    Chaos and Universality in a Four-Dimensional Spin Glass

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    We present a finite size scaling analysis of Monte Carlo simulation results on a four dimensional Ising spin glass. We study chaos with both coupling and temperature perturbations, and find the same chaos exponent in each case. Chaos is investigated both at the critical temperature and below where it seems to be more efficient (larger exponent). Dimension four seems to be above the critical dimension where chaos with temperature is no more present in the critical region. Our results are consistent with the Gaussian and bimodal coupling distributions being in the same universality class.Comment: 11 pages, including 6 postscript figures. Latex with revtex macro

    Concentration Kinetics of Serum MMP-9 and TIMP-1 after Blunt Multiple Injuries in the Early Posttraumatic Period

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    Metalloproteinases are secreted in response to a variety of inflammatory mediators and inhibited by tissue inhibitors of matrixmetalloproteinases (TIMPs). Two members of these families, MMP-9 and TIMP-1, were differentially expressed depending on clinical parameters in a previous genomewide mRNA analysis. The aim of this paper was now to evaluate the posttraumatic serum levels and the time course of both proteins depending on distinct clinical parameters. 60 multiple traumatized patients (ISS > 16) were included. Blood samples were drawn on admission and 6 h, 12 h, 24 h, 48 h, and 72 h after trauma. Serum levels were quantified by ELISA. MMP-9 levels significantly decreased in the early posttraumatic period (P < 0.05) whereas TIMP-1 levels significantly increased in all patients (P < 0.05). MMP-9 and TIMP-1 serum concentration kinetics became manifest in an inversely proportional balance. Furthermore, MMP-9 presented a stronger decrease in patients with severe trauma and non-survivors in contrast to minor traumatized patients (ISS ≤ 33) and survivors, initially after trauma

    Numerical Study of Order in a Gauge Glass Model

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    The XY model with quenched random phase shifts is studied by a T=0 finite size defect energy scaling method in 2d and 3d. The defect energy is defined by a change in the boundary conditions from those compatible with the true ground state configuration for a given realization of disorder. A numerical technique, which is exact in principle, is used to evaluate this energy and to estimate the stiffness exponent θ\theta. This method gives θ=0.36±0.013\theta = -0.36\pm0.013 in 2d and θ=+0.31±0.015\theta = +0.31\pm 0.015 in 3d, which are considerably larger than previous estimates, strongly suggesting that the lower critical dimension is less than three. Some arguments in favor of these new estimates are given.Comment: 4 pages, 2 figures, revtex. Submitted to Phys. Rev. Let

    Realism about the Wave Function

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    A century after the discovery of quantum mechanics, the meaning of quantum mechanics still remains elusive. This is largely due to the puzzling nature of the wave function, the central object in quantum mechanics. If we are realists about quantum mechanics, how should we understand the wave function? What does it represent? What is its physical meaning? Answering these questions would improve our understanding of what it means to be a realist about quantum mechanics. In this survey article, I review and compare several realist interpretations of the wave function. They fall into three categories: ontological interpretations, nomological interpretations, and the \emph{sui generis} interpretation. For simplicity, I will focus on non-relativistic quantum mechanics.Comment: Penultimate version for Philosophy Compas

    Robust isothermal electric switching of interface magnetization: A route to voltage-controlled spintronics

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    Roughness-insensitive and electrically controllable magnetization at the (0001) surface of antiferromagnetic chromia is observed using magnetometry and spin-resolved photoemission measurements and explained by the interplay of surface termination and magnetic ordering. Further, this surface in placed in proximity with a ferromagnetic Co/Pd multilayer film. Exchange coupling across the interface between chromia and Co/Pd induces an electrically controllable exchange bias in the Co/Pd film, which enables a reversible isothermal (at room temperature) shift of the global magnetic hysteresis loop of the Co/Pd film along the magnetic field axis between negative and positive values. These results reveal the potential of magnetoelectric chromia for spintronic applications requiring non-volatile electric control of magnetization.Comment: Single PDF file: 27 pages, 6 figures; version of 12/30/09; submitted to Nature Material

    Ferromagnetic transition metal implanted ZnO: a diluted magnetic semiconductor?

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    Recently theoretical works predict that some semiconductors (e.g. ZnO) doped with magnetic ions are diluted magnetic semiconductors (DMS). In DMS magnetic ions substitute cation sites of the host semiconductor and are coupled by free carriers resulting in ferromagnetism. One of the main obstacles in creating DMS materials is the formation of secondary phases because of the solid-solubility limit of magnetic ions in semiconductor host. In our study transition metal ions were implanted into ZnO single crystals with the peak concentrations of 0.5-10 at.%. We established a correlation between structural and magnetic properties. By synchrotron radiation X-ray diffraction (XRD) secondary phases (Fe, Ni, Co and ferrite nanocrystals) were observed and have been identified as the source for ferromagnetism. Due to their different crystallographic orientation with respect to the host crystal these nanocrystals in some cases are very difficult to be detected by a simple Bragg-Brentano scan. This results in the pitfall of using XRD to exclude secondary phase formation in DMS materials. For comparison, the solubility of Co diluted in ZnO films ranges between 10 and 40 at.% using different growth conditions pulsed laser deposition. Such diluted, Co-doped ZnO films show paramagnetic behaviour. However, only the magnetoresistance of Co-doped ZnO films reveals possible s-d exchange interaction as compared to Co-implanted ZnO single crystals.Comment: 27 pages, 8 figure
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