348,809 research outputs found

### Glueballs and the Pomeron

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

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

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

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

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?

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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