300,256 research outputs found

    Homogeneous Lorentzian manifolds of a semisimple group

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    We describe the structure of dd-dimensional homogeneous Lorentzian GG-manifolds M=G/HM=G/H of a semisimple Lie group GG. Due to a result by N. Kowalsky, it is sufficient to consider the case when the group GG acts properly, that is the stabilizer HH is compact. Then any homogeneous space G/HˉG/\bar H with a smaller group HˉH\bar H \subset H admits an invariant Lorentzian metric. A homogeneous manifold G/HG/H with a connected compact stabilizer HH is called a minimal admissible manifold if it admits an invariant Lorentzian metric, but no homogeneous GG-manifold G/H~G/\tilde H with a larger connected compact stabilizer H~H\tilde H \supset H admits such a metric. We give a description of minimal homogeneous Lorentzian nn-dimensional GG-manifolds M=G/HM = G/H of a simple (compact or noncompact) Lie group GG. For n11n \leq 11, we obtain a list of all such manifolds MM and describe invariant Lorentzian metrics on MM

    Fermionic topological charge of families of lattice gauge fields

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    Topological charge of families of lattice gauge fields is defined fermionically via families index theory for the overlap Dirac operator. Certain obstructions to gauge invariance of the overlap chiral fermion determinant, as well as the lattice analogues of certain obstructions to gauge fixings without the Gribov problem, have natural descriptions in this context.Comment: 4p., Lattice2002(chiral) (+ one paragraph not included in the proceedings version for length reasons

    Jet Studies in STAR via Di-jet Triggered (2+1) Multi-hadron Correlations

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    We explore jet-medium interactions via the recently developed multi-hadron correlation or "2+1" technique. We restrict the di-jet kinematics by selecting a pair of approximately back-to-back high pT hadron triggers and study associated particles. Here we present our study of di-jet systematics comparing the measurements of associate yields and spectra in 200 GeV Au+Au and d+Au collisions in two different scenarios. We present Sum(pT) as an estimate for energy loss. First findings indicate little to no energy loss in the symmetric "2+1" scenario whereas model predictions are about 2 GeV.Comment: 4 pages, 3 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

    The RHIC azimuth quadrupole: "perfect liquid" or gluonic radiation?

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    Large elliptic flow at RHIC seems to indicate that ideal hydrodynamics provides a good description of Au-Au collisions, at least at the maximum RHIC energy. The medium formed has been interpreted as a nearly perfect (low-viscosity) liquid, and connections have been made to gravitation through string theory. Recently, claimed observations of large flow fluctuations comparable to participant eccentricity fluctuations seem to confirm the ideal hydro scenario. However, determination of the azimuth quadrupole with 2D angular autocorrelations, which accurately distinguish ``flow'' (quadrupole) from ``nonflow'' (minijets), contradicts conventional interpretations. Centrality trends may depend only on the initial parton geometry, and methods used to isolate flow fluctuations are sensitive instead mainly to minijet correlations. The results presented in this paper suggest that the azimuth quadrupole may be a manifestation of gluonic multipole radiation.Comment: 11 pages, 6 figure

    Elliptic Flow arising from Ridges due to Semi-hard Scattering

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    Azimuthal anisotropy in heavy-ion collisions is studied by taking into account the ridges generated by semi-hard scattering of intermediate-momentum partons, which can be sensitive to the initial spatial configuration of the medium in non-central collisions. In a simple treatment of the problem where the recombination of only thermal partons is considered, analytical formulas can be derived that yield results in accord with the data on v_2 for p_T <1-2 GeV/c. Centrality dependence is described by a geometrical factor. Ridge phenomenology is used to determine the initial slopes of v_2 at low p_T for both pion and proton. For higher p_T, shower partons from high-p_T jets must be included, but they are not considered here.Comment: revised version with new title and expanded discussion, to be published in Phys. Lett.

    Event anisotropy v2v_{2} at STAR

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    Collective flow reflects the dynamical evolution in high-energy heavy ion collisions. In particular, the elliptic flow reflects early collision dynamics.We present a systematic analysis of elliptic flow (v2v_{2}) for identified particles measured in Au + Au and Cu + Cu collisions at sNN\sqrt{s_{NN}} = 200 GeV. Number of quark scaling is tested in the intermediate pTp_{T} region and in the smaller system (Cu + Cu). The Cu + Cu collisions results are compared with those from ideal hydrodynamic model calculations.Comment: 4 pages, 3 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

    Improving the locality of the overlap Dirac operator via approximate solutions of the Ginsparg-Wilson relation

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    We determine the free field hypercubic Dirac operator which is optimally close to satisfying the Ginsparg-Wilson relation. Inserting this operator into the overlap formula, we show that the analytic locality bound on the resulting overlap Dirac operator is substantially stronger than in the standard case. This improvement generally persists in gauge backgrounds when the plaquette variables are all close to unity.Comment: 3 pages, contributed to Proceedings of Lattice2003(chiral

    Environmental Justice: Where are the Fracking Sites?

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    This paper looks at the variables that determine the location of hydraulic fracturing wells. Using cross-sectional data on Texas counties, we test whether county income level and the percentage of the population that is minority are significant indicators of well location. This study mirrors other studies that focus on the location of undesirable land uses such as landfills. Our study finds that income level and the size of the minority population are not statistically significant indicators of hydraulic fracturing well location

    Urban Land Reform Briefing Paper No 6: Explaining Urban Partnership Zones

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    This is one of six briefing papers prepared by Professor David Adams of the University of Glasgow to help explain key proposals for urban land reform made in 2014 by the Scottish Government’s Land Reform Review Group (LRRG) to whom he acted as an independent adviser. This paper focuses on the LRRG’s recommendations “that the well-established international practice of property land readjustment or land-pooling provides another effective means of addressing fragmented or multiple ownership of land. The Group recommends that the Scottish Government investigates the potential of introducing an Urban Partnership Zone mechanism in Scotland” (see pages 126-128 of the LRRG report)
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