26,653 research outputs found
Semisimple Weakly Symmetric Pseudo--Riemannian Manifolds
We develop the classification of weakly symmetric pseudo--riemannian
manifolds where is a semisimple Lie group and is a reductive
subgroup. We derive the classification from the cases where is compact, and
then we discuss the (isotropy) representation of on the tangent space of
and the signature of the invariant pseudo--riemannian metric. As a
consequence we obtain the classification of semisimple weakly symmetric
manifolds of Lorentz signature and trans--Lorentz (conformal Lorentz)
signature .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
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 (b ). 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
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
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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