348,809 research outputs found

    Glueballs and the Pomeron

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    We present our latest results on the glueball spectrum of SU(N) gauge theories in 2+1 dimensions for spins ranging from 0 to 6 inclusive, as well as preliminary results for SU(3) in 3+1 dimensions. Simple glueball models and the relation of the even-spin spectrum to the 'Pomeron' are discussed.Comment: LAT03 proceedings (spectrum), 3 pages, 3 figures, talk by H.Meye

    The formation of the coronal flow/ADAF

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    We develop a new method to describe the accretion flow in the corona above a thin disk around a black hole in vertical and radial extent. The model is based on the same physics as the earlier one-zone model, but now modified including inflow and outflow of mass, energy and angular momentum from and towards neighboring zones. We determine the radially extended coronal flow for different mass flow rates in the cool disk resulting in the truncation of the thin disk at different distance from the black hole. Our computations show how the accretion flow gradually changes to a pure vertically extended coronal or advection-dominated accretion flow (ADAF). Different regimes of solutions are discussed. For some cases wind loss causes an essential reduction of the mass flow.Comment: 8 pages, 4 figures, accepted for publication in A&

    C*-Algebras over Topological Spaces: Filtrated K-Theory

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    We define the filtrated K-theory of a C*-algebra over a finite topological space X and explain how to construct a spectral sequence that computes the bivariant Kasparov theory over X in terms of filtrated K-theory. For finite spaces with totally ordered lattice of open subsets, this spectral sequence becomes an exact sequence as in the Universal Coefficient Theorem, with the same consequences for classification. We also exhibit an example where filtrated K-theory is not yet a complete invariant. We describe a space with four points and two C*-algebras over this space in the bootstrap class that have isomorphic filtrated K-theory but are not KK(X)-equivalent. For this particular space, we enrich filtrated K-theory by another K-theory functor, so that there is again a Universal Coefficient Theorem. Thus the enriched filtrated K-theory is a complete invariant for purely infinite, stable C*-algebras with this particular spectrum and belonging to the appropriate bootstrap class.Comment: Changes to theorem and equation numbering

    Combable groups have group cohomology of polynomial growth

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    Group cohomology of polynomial growth is defined for any finitely generated discrete group, using cochains that have polynomial growth with respect to the word length function. We give a geometric condition that guarantees that it agrees with the usual group cohomology and verify this condition for a class of combable groups. Our condition involves a chain complex that is closely related to exotic cohomology theories studied by Allcock and Gersten and by Mineyev.Comment: 19 pages, typo corrected in version

    Late evolution of cataclysmic variables: the loss of AM Her systems

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    The white dwarf in AM Her systems is strongly magnetic and keeps in synchronous rotation with the orbit by magnetic coupling to the secondary star. As the latter evolves through mass loss to a cool, degenerate brown dwarf it can no longer sustain its own magnetic field and coupling is lost. Angular momentum accreted then spins up the white dwarf and the system no longer appears as an AM Her system. Possible consequences are run-away mass transfer and mass ejection from the system. Some of the unusual cataclysmic variable systems at low orbital periods may be the outcome of this evolution.Comment: 6 pages, 1 figure, Proceedings of "Cataclysmic Variables", Symposium in Honour of Brian Warner, Oxford 1999, eds. P.Charles, A.King, O'Donoghue, to appea

    The relation between radio and X-ray luminosity of black hole binaries: affected by inner cool disks?

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    Observations of the black hole X-ray binaries GX 339-4 and V404 Cygni have brought evidence of a strong correlation between radio and X-ray emission during the hard spectral state; however, now more and more sources, the so-called `outliers', are found with a radio emission noticeably below the established `standard' relation. Several explanations have already been considered, but the existence of dual tracks is not yet fully understood. We suggest that in the hard spectral state re-condensation of gas from the corona into a cool, weak inner disk can provide additional soft photons for Comptonization, leading to a higher X-ray luminosity in combination with rather unchanged radio emission, which presumably traces the mass accretion rate. As an example, we determined how much additional luminosity due to photons from an underlying disk would be needed to explain the data from the representative outlier source H1743-322. From the comparison with calculations of Compton spectra with and without the photons from an underlying disk, we find that the required additional X-ray luminosity lies well in the range obtained from theoretical models of the accretion flow. The radio/X-ray luminosity relation resulting from Comptonization of additional photons from a weak, cool inner disk during the hard spectral state can explain the observations of the outlier sources, especially the data for H1743-322, the source with the most detailed observations. The existence or non-existence of weak inner disks on the two tracks might point to a difference in the magnetic fields of the companion stars. These could affect the effective viscosity and the thermal conductivity, hence also the re-condensation process.Comment: 7 pages, 2 figures. Accepted for publication in A &
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