8,829 research outputs found
The impact of viscosity on the morphology of gaseous flows in semidetached binary systems
Results of 3D gas dynamical simulation of mass transfer in binaries are
presented for systems with various values of viscosity. Analysis of obtained
solutions shows that in the systems with low value of viscosity the flow
structure is qualitatively similar to one for systems with high viscosity.
Presented calculations confirm that there is no shock interaction between the
stream from L1 and the forming accretion disk (`hot spot') at any value of
viscosity.Comment: LaTeX, 18 pages, 15 eps-figures, Astron. Reports, in pres
Localizations at infinity and essential spectrum of quantum Hamiltonians: I. General theory
We isolate a large class of self-adjoint operators H whose essential spectrum
is determined by their behavior at large x and we give a canonical
representation of their essential spectrum in terms of spectra of limits at
infinity of translations of H. The configuration space is an arbitrary abelian
locally compact not compact group.Comment: 63 pages. This is the published version with several correction
The structure of cool accretion disc in semidetached binaries
We present the results of qualitative consideration of possible changes
occurring during the transition from the hot accretion disc to the cool one. We
argue the possible existence of one more type of spiral density waves in the
inner part of the disc where gasdynamical perturbations are negligible. The
mechanism of formation of such a wave as well as its parameters are considered.
We also present the results of 3D gasdynamical simulation of cool accretion
discs. These results confirm the hypothesis of possible formation of the spiral
wave of a new, "precessional" type in the inner regions of the disc. Possible
observational manifestations of this wave are discussed.Comment: LaTeX, 16 pages, 8 figures, to be published in Astron. Z
Projective Ribbon Permutation Statistics: a Remnant of non-Abelian Braiding in Higher Dimensions
In a recent paper, Teo and Kane proposed a 3D model in which the defects
support Majorana fermion zero modes. They argued that exchanging and twisting
these defects would implement a set R of unitary transformations on the zero
mode Hilbert space which is a 'ghostly' recollection of the action of the braid
group on Ising anyons in 2D. In this paper, we find the group T_{2n} which
governs the statistics of these defects by analyzing the topology of the space
K_{2n} of configurations of 2n defects in a slowly spatially-varying gapped
free fermion Hamiltonian: T_{2n}\equiv {\pi_1}(K_{2n})$. We find that the group
T_{2n}= Z \times T^r_{2n}, where the 'ribbon permutation group' T^r_{2n} is a
mild enhancement of the permutation group S_{2n}: T^r_{2n} \equiv \Z_2 \times
E((Z_2)^{2n}\rtimes S_{2n}). Here, E((Z_2)^{2n}\rtimes S_{2n}) is the 'even
part' of (Z_2)^{2n} \rtimes S_{2n}, namely those elements for which the total
parity of the element in (Z_2)^{2n} added to the parity of the permutation is
even. Surprisingly, R is only a projective representation of T_{2n}, a
possibility proposed by Wilczek. Thus, Teo and Kane's defects realize
`Projective Ribbon Permutation Statistics', which we show to be consistent with
locality. We extend this phenomenon to other dimensions, co-dimensions, and
symmetry classes. Since it is an essential input for our calculation, we review
the topological classification of gapped free fermion systems and its relation
to Bott periodicity.Comment: Missing figures added. Fixed some typos. Added a paragraph to the
conclusio
Paramaterizations of inclusive cross sections for pion production in proton-proton collisions. II. Comparison to new data
A set of new, precise data have recently been made available by the NA49
collaboration for charged pion production in proton-proton and proton-Carbon
reactions at 158 GeV. The current paper compares this new data to five
currently available arithmetic parameterizations. Although a precise fit is not
expected, two of the parameterizations do not work very well but the other
three are able to provide a moderately good, but not precise fit to the
proton-proton data. The best two of these three parameterizations are scaled to
the proton-Carbon data and again provide a moderately good, but not precise
fit.Comment: 11 pages, 13 figures, Accepted for publication in Physical Review
A New Determination of the High Redshift Type Ia Supernova Rates with the Hubble Space Telescope Advanced Camera for Surveys
We present a new measurement of the volumetric rate of Type Ia supernova up
to a redshift of 1.7, using the Hubble Space Telescope (HST) GOODS data
combined with an additional HST dataset covering the North GOODS field
collected in 2004. We employ a novel technique that does not require
spectroscopic data for identifying Type Ia supernovae (although spectroscopic
measurements of redshifts are used for over half the sample); instead we employ
a Bayesian approach using only photometric data to calculate the probability
that an object is a Type Ia supernova. This Bayesian technique can easily be
modified to incorporate improved priors on supernova properties, and it is
well-suited for future high-statistics supernovae searches in which
spectroscopic follow up of all candidates will be impractical. Here, the method
is validated on both ground- and space-based supernova data having some
spectroscopic follow up. We combine our volumetric rate measurements with low
redshift supernova data, and fit to a number of possible models for the
evolution of the Type Ia supernova rate as a function of redshift. The data do
not distinguish between a flat rate at redshift > 0.5 and a previously proposed
model, in which the Type Ia rate peaks at redshift >1 due to a significant
delay from star-formation to the supernova explosion. Except for the highest
redshifts, where the signal to noise ratio is generally too low to apply this
technique, this approach yields smaller or comparable uncertainties than
previous work.Comment: Accepted for publication in Ap
Aperture synthesis for gravitational-wave data analysis: Deterministic Sources
Gravitational wave detectors now under construction are sensitive to the
phase of the incident gravitational waves. Correspondingly, the signals from
the different detectors can be combined, in the analysis, to simulate a single
detector of greater amplitude and directional sensitivity: in short, aperture
synthesis. Here we consider the problem of aperture synthesis in the special
case of a search for a source whose waveform is known in detail: \textit{e.g.,}
compact binary inspiral. We derive the likelihood function for joint output of
several detectors as a function of the parameters that describe the signal and
find the optimal matched filter for the detection of the known signal. Our
results allow for the presence of noise that is correlated between the several
detectors. While their derivation is specialized to the case of Gaussian noise
we show that the results obtained are, in fact, appropriate in a well-defined,
information-theoretic sense even when the noise is non-Gaussian in character.
The analysis described here stands in distinction to ``coincidence
analyses'', wherein the data from each of several detectors is studied in
isolation to produce a list of candidate events, which are then compared to
search for coincidences that might indicate common origin in a gravitational
wave signal. We compare these two analyses --- optimal filtering and
coincidence --- in a series of numerical examples, showing that the optimal
filtering analysis always yields a greater detection efficiency for given false
alarm rate, even when the detector noise is strongly non-Gaussian.Comment: 39 pages, 4 figures, submitted to Phys. Rev.
From Gravitons to Giants
We discuss exact quantization of gravitational fluctuations in the half-BPS
sector around AdSS background, using the dual super Yang-Mills
theory. For this purpose we employ the recently developed techniques for exact
bosonization of a finite number of fermions in terms of bosonic
oscillators. An exact computation of the three-point correlation function of
gravitons for finite shows that they become strongly coupled at
sufficiently high energies, with an interaction that grows exponentially in
. We show that even at such high energies a description of the bulk physics
in terms of weakly interacting particles can be constructed. The single
particle states providing such a description are created by our bosonic
oscillators or equivalently these are the multi-graviton states corresponding
to the so-called Schur polynomials. Both represent single giant graviton states
in the bulk. Multi-particle states corresponding to multi-giant gravitons are,
however, different, since interactions among our bosons vanish identically,
while the Schur polynomials are weakly interacting at high enough energies.Comment: v2-references added, minor changes and typos corrected; 24 pages,
latex, 3 epsf figure
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