26,653 research outputs found

    Semisimple Weakly Symmetric Pseudo--Riemannian Manifolds

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    We develop the classification of weakly symmetric pseudo--riemannian manifolds G/HG/H where GG is a semisimple Lie group and HH is a reductive subgroup. We derive the classification from the cases where GG is compact, and then we discuss the (isotropy) representation of HH on the tangent space of G/HG/H and the signature of the invariant pseudo--riemannian metric. As a consequence we obtain the classification of semisimple weakly symmetric manifolds of Lorentz signature (n1,1)(n-1,1) and trans--Lorentz (conformal Lorentz) signature (n2,2)(n-2,2).Comment: This arXiv version 3 adds a reference to version 2 and tweaks the Introduction accordingl

    The Inverse-Compton And Extragalactic Components Of The Diffuse Gamma-Ray Emission

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    We present spectra of the inverse-Compton and extragalactic components of the high-energy gamma-radiation based on an analysis of the emission at high galactic latitudes (\vertb\vert \geq 30deg30\deg). We correlate the gamma-ray intensity with a model consisting of an isotropic component, a component proportional to the 408 MHz synchrotron radiation, and a component proportional to atomic hydrogen (H I) column density with different emissivities in eight galactic octants. The spectrum of gamma-radiation that is correlated with the H I column density indicates that this component originates in cosmic-ray/matter interactions. The cosmic-ray electrons which produce the 408 MHz radio continuum emission also produce gamma-radiation through inverse-Compton interactions with interstellar photons. By correlating the gamma-radiation with the 408 MHz continuum, we measure the spectrum and absolute intensity of the IC emission. The isotropic component gives us the spectrum and intensity of the extragalactic gamma-radiation. We discuss interpretation of the extragalactic spectrum.Comment: 21 page Postscript file, 10 Postscript figure

    Downside Risk and the Momentum Effect

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    Stocks with greater downside risk, which is measured by higher correlations conditional on downside moves of the market, have higher returns. After controlling for the market beta, the size effect and the book-to-market effect, the average rate of return on stocks with the greatest downside risk exceeds the average rate of return on stocks with the least downside risk by 6.55% per annum. Downside risk is important for explaining the cross-section of expected returns. In particular of the profitability of investing in momentum strategies can be explained as compensation for bearing high exposure to downside risk.

    Journey to the Center of the Fuzzball

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    We study two-charge fuzzball geometries, with attention to the use of the proper duality frame. For zero angular momentum there is an onion-like structure, and the smooth D1-D5 geometries are not valid for typical states. Rather, they are best approximated by geometries with stringy sources, or by a free CFT. For non-zero angular momentum we find a regime where smooth fuzzball solutions are the correct description. Our analysis rests on the comparison of three radii: the typical fuzzball radius, the entropy radius determined by the microscopic theory, and the breakdown radius where the curvature becomes large. We attempt to draw more general lessons.Comment: 22 pages, 1 figur
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