9,188 research outputs found

    A note on BRST quantization of SU(2) Yang-Mills mechanics

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    The quantization of SU(2) Yang-Mills theory reduced to 0+1 space-time dimensions is performed in the BRST framework. We show that in the unitary gauge A0=0A_0 = 0 the BRST procedure has difficulties which can be solved by introduction of additional singlet ghost variables. In the Lorenz gauge Aňô0=0\dot{A}_0 = 0 one has additional unphysical degrees of freedom, but the BRST quantization is free of the problems in the unitary gauge.Comment: 17 page

    Experimental studies of QCD using flavour tagged jets with DELPHI

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    Identified bb‚Äĺgb\overline{b}g and qq‚Äĺő≥q\overline{q}\gamma events from DELPHI are used to measure the ratio of the mean charged particle multiplicity distribution between gluon and quark jets. The dependence of this ratio with the jet energy is established using about three million Z0^0 decays. Results from all other detectors are discussed and compared. A nice agreement is found among all them. The ratio between the normalized total three-jet cross sections of bb‚Äĺgb\overline{b}g and qq‚Äĺg,q‚Č°u,d,sq\overline{q}g, q \equiv u,d,s events is also determined. The preliminary value obtained indicates that bb quarks are experimentaly seen to radiate less than light quarks due to their higher mass. The suggested experimental error is ‚ąľ\sim300 MeV for the bb mass determination at the MZ_Z scale.Comment: Latex, 5 pages, 3 figures,to appear in the Proceedings of the High Energy Physics International Euroconference on Quantum Chromodynamics (QCD '96), Montpellier, France, 4-12th July 1996. Ed. S. Narison, Nucl Phys. B (Proc. Suppl.

    Extracting the top-quark running mass using ttňČt\bar{t}+1-jet events produced at the Large Hadron Collider

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    We present the calculation of the next-to-leading order QCD corrections for top-quark pair production in association with an additional jet at hadron colliders, using the modified minimal subtraction scheme to renormalize the top-quark mass. The results are compared to measurements at the Large Hadron Collider run I. In particular, we determine the top-quark running mass from a fit of the theoretical results presented here to the LHC data

    Electronic structure of few-electron concentric double quantum rings

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    The ground state structure of few-electron concentric double quantum rings is investigated within the local spin density approximation. Signatures of inter-ring coupling in the addition energy spectrum are identified and discussed. We show that the electronic configurations in these structures can be greatly modulated by the inter-ring distance: At short and long distances the low-lying electron states localize in the inner and outer rings, respectively, and the energy structure is essentially that of an isolated single quantum ring. However, at intermediate distances the electron states localized in the inner and the outer ring become quasi-degenerate and a rather entangled, strongly-correlated system is formed.Comment: 16 pages (preprint format), 6 figure

    Higher dimensional VSI spacetimes

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    We present the explicit metric forms for higher dimensional vanishing scalar invariant (VSI) Lorentzian spacetimes. We note that all of the VSI spacetimes belong to the higher dimensional Kundt class. We determine all of the VSI spacetimes which admit a covariantly constant null vector, and we note that in general in higher dimensions these spacetimes are of Ricci type III and Weyl type III. The Ricci type N subclass is related to the chiral null models and includes the relativistic gyratons and the higher dimensional pp-wave spacetimes. The spacetimes under investigation are of particular interest since they are solutions of supergravity or superstring theory.Comment: 14 pages, changes in second paragraph of the discussio

    Experimental determination of the b quark mass in DELPHI

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    The running mass of the b quark as defined in the MS-bar renormalization scheme, m_b, was measured at the M_Z scale using 2.8 million hadronic Z^0 decays collected by the DELPHI experiment at LEP. The result is m_b(M_Z) = 2.67 +- 0.25 (stat.) +- 0.34 (frag.) +- 0.27(theo.) GeV/c^2 which differs from that obtained at the Upsilon scale, by m_b(M_\Upsilon/2)-m_b(M_Z) = 1.49 +- 0.52 GeV/c^2. This measurement, performed far from the bbňČb\bar{b} production threshold, provides the first experimental observation of the running of the quark masses.Comment: Talk given at the QCD 97 conference held in Montpellier, July 1997. Also available here http://hep.ph.liv.ac.uk/~martis

    InAs/InP single quantum wire formation and emission at 1.5 microns

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    Isolated InAs/InP self-assembled quantum wires have been grown using in situ accumulated stress measurements to adjust the optimal InAs thickness. Atomic force microscopy imaging shows highly asymmetric nanostructures with average length exceeding more than ten times their width. High resolution optical investigation of as-grown samples reveals strong photoluminescence from individual quantum wires at 1.5 microns. Additional sharp features are related to monolayer fluctuations of the two dimensional InAs layer present during the early stages of the quantum wire self-assembling process.Comment: 4 pages and 3 figures submitted to Applied Physics Letter

    Charged particle production in the fragmentation of quark and gluon jets

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    Recent results on the total production and angular distribution of charged particles originated from the fragmentation of quark and gluon jets are presented. Experimental studies of the multiplicity as a function of the quark and gluon jet energy, the inter-jet particle flow and the individual fragmentation fucntions are reviewed and compared to expectations from QCD

    Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire

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    We study the metal-insulator transition in individual self-assembled quantum wires and report optical evidences of metallic liquid condensation at low temperatures. Firstly, we observe that the temperature and power dependence of the single nanowire photoluminescence follow the evolution expected for an electron-hole liquid in one dimension. Secondly, we find novel spectral features that suggest that in this situation the expanding liquid condensate compresses the exciton gas in real space. Finally, we estimate the critical density and critical temperature of the phase transition diagram at nc‚ąľ1√ó105n_c\sim1\times10^5 cm‚ąí1^{-1} and Tc‚ąľ35T_c\sim35 K, respectively.Comment: 4 pages, 5 figure

    Clonal hematopoiesis in cardiovascular disease and therapeutic implications.

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    Clonal hematopoiesis arises from somatic mutations that provide a fitness advantage to hematopoietic stem cells and the outgrowth of clones of blood cells. Clonal hematopoiesis commonly involves mutations in genes that are involved in epigenetic modifications, signaling and DNA damage repair. Clonal hematopoiesis has emerged as a major independent risk factor in atherosclerotic cardiovascular disease, thrombosis and heart failure. Studies in mouse models of clonal hematopoiesis have shown an increase in atherosclerosis, thrombosis and heart failure, involving increased myeloid cell inflammatory responses and inflammasome activation. Although increased inflammatory responses have emerged as a common underlying principle, some recent studies indicate mutation-specific effects. The discovery of the association of clonal hematopoiesis with cardiovascular disease and the recent demonstration of benefit of anti-inflammatory treatments in human cardiovascular disease converge to suggest that anti-inflammatory treatments should be directed to individuals with clonal hematopoiesis. Such treatments could target specific inflammasomes, common downstream mediators such as IL-1ő≤ and IL-6, or mutations linked to clonal hematopoiesis.A.T. and J.J.F. are supported by a grant from the Leducq Foundation (TNE-18CVD04). A.T. is supported by NIH grant 155431. We thank M. A. Zuriaga for assistance with figure design.S
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