15,420 research outputs found

    Calculation of epsilon'/epsilon

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    I shortly review the present status of the theoretical calculations of epsilon'/epsilon and the comparison with the present experimental results. I discuss the role of higher order chiral corrections and in general of non-factorizable contributions for the explanation of the Delta I = 1/2 selection rule and direct CP violation in kaon decays. Still lacking reliable lattice calculations, analytic methods and phenomenological approaches are helpful in understanding correlations among theoretical effects and the experimental data. Substantial progress from lattice QCD is expected in the coming years.Comment: 10 pages, Invited talk at the 9th Int. Symposium on Heavy Flavour Physics, Pasadena, CA, 10-13 September 2001 Comments added on Table

    Aspects of symmetry breaking in SO(10) GUTs

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    I review some recent results on the Higgs sector of minimal SO(10) grand unified theories both with and without supersymmetry. It is shown that nonsupersymmetric SO(10) with just one adjoint triggering the first stage of the symmetry breaking does provide a successful gauge unification when radiative corrections are taken into account in the scalar potential, while in the supersymmetric case it is argued that the troubles in achieving a phenomenologically viable breaking with representations up to the adjoint are overcome by considering the flipped SO(10) embedding of the hypercharge.Comment: 8 pages, 1 figure; prepared for the proceedings of DISCRETE'10 - Symposium on Prospects in the Physics of Discrete Symmetrie

    N=1 Super QCD and Fractional Branes

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    We show how to get the one-loop beta function and the chiral anomaly of N=1 Super QCD from a stack of fractional N D3-branes localized inside the world-volume of 2M fractional D7-branes on the orbifold C^3/(Z_2 x Z_2). They are obtained by analyzing the classical supergravity background generated by such a brane configuration, in the spirit of the gauge/gravity correspondence.Comment: 4 pages, LaTeX. Talk given at the IXth International Symposium on Particles, Strings and Cosmology PASCOS '03, Mumbai-India, January 3-8 2003. To appear in a special issue of Praman

    More Anomalies from Fractional Branes

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    In this note we show how the anomalies of both pure and matter coupled N=1,2 supersymmetric gauge theories describing the low energy dynamics of fractional branes on orbifolds can be derived from supergravity.Comment: 11 pages, latex; v2: minor typos fixe

    The Gauge/Gravity Correspondence for Non-Supersymmetric Theories

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    We review the string construction of the ``orientifold field theories'' and we show that for these theories the gauge/gravity correspondence is only valid for a large number of colours.Comment: 7 pages, Latex, Talk given at 37. International Symposium Ahrenshoop, Berlin, August 2004. Added references and acknowledgements; corrected typo

    Evolutionary urban transportation planning? An exploration

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    For urban transportation planners these are challenging times. Mounting practical concerns are mirrored by more fundamental critiques. The latter come together in the observation that conventional approaches do not adequately account for the irreducible uncertainty of future developments. The central aim of this paper is to explore if and how an evolutionary approach can help overcome this limit. Two core-hypotheses are formulated. The first is that the urban transportation system behaves in an evolutionary fashion. The second hypothesis is that because of this, urban transportation planning needs also to focus on enhancing the resilience and adaptability of the system. Changes in transport and land use development patterns and policies and in the broader context in the post-war period in the Amsterdam region are analysed in order to illustrate the two core-hypotheses. In the conclusions more general implications are drawn.evolutionary economics, urban economics, transportation planning
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