11,664 research outputs found
Density correlators in a self-similar cascade
Multivariate density moments (correlators) of arbitrary order are obtained
for the multiplicative self-similar cascade. This result is based on the
calculation by Greiner, Eggers and Lipa (reference [1]) where the correlators
of the logarithms of the particle densities have been obtained. The density
correlators, more suitable for comparison with multiparticle data, appear to
have even simpler form than those obtained in [1].Comment: 9 pages, 3 figures, uses epsfig.st
Optical counterparts of ROSAT X-ray sources in two selected fields at low vs. high Galactic latitudes
The optical identification of large number of X-ray sources such as those
from the ROSAT All-Sky Survey is challenging with conventional spectroscopic
follow-up observations. We investigate two ROSAT All-Sky Survey fields of size
10 * 10 degrees each, one at galactic latitude b = 83 deg (Com), the other at b
= -5 deg (Sge), in order to optically identify the majority of sources. We used
optical variability, among other more standard methods, as a means of
identifying a large number of ROSAT All-Sky Survey sources. All objects fainter
than about 12 mag and brighter than about 17 mag, in or near the error circle
of the ROSAT positions, were tested for optical variability on hundreds of
archival plates of the Sonneberg field patrol.
The present paper contains probable optical identifications of altogether 256
of the 370 ROSAT sources analysed. In particular, we found 126 AGN (some of
them may be misclassified CVs), 17 likely clusters of galaxies, 16 eruptive
double stars (mostly CVs), 43 chromospherically active stars, 65 stars brighter
than about 13 mag, 7 UV Cet stars, 3 semiregular resp. slow irregular variable
stars of late spectral type, 2 DA white dwarfs, 1 Am star, 1 supernova remnant
and 1 planetary nebula.
X-ray emission is, expectedly, tightly correlated with optical variability,
and thus our new method for optically identifying X-ray sources is demonstrated
to be feasible.Comment: 92 pages, 521 figures, A&A (accepted
Review of the "Bottom-Up" scenario
Thermalization of a longitudinally expanding color glass condensate with
Bjorken boost invariant geometry is investigated within parton cascade BAMPS.
Our main focus lies on the detailed comparison of thermalization, observed in
BAMPS with that suggested in the Bottom-Up scenario. We demonstrate that the
tremendous production of soft gluons via , which is shown in the
Bottom-Up picture as the dominant process during the early preequilibration,
will not occur in heavy ion collisions at RHIC and LHC energies, because the
back reaction hinders the absolute particle multiplication.
Moreover, contrary to the Bottom-Up scenario, soft and hard gluons thermalize
at the same time. The time scale of thermal equilibration in BAMPS calculations
is of order \as^{-2} (\ln \as)^{-2} Q_s^{-1}. After this time the gluon
system exhibits nearly hydrodynamic behavior. The shear viscosity to entropy
density ratio has a weak dependence on and lies close to the lower bound
of the AdS/CFT conjecture.Comment: Quark Matter 2008 Proceeding
Elliptic flow of gluon matter in ultrarelativistic heavy-ion collisions
Employing a perturbative QCD based parton cascade we calculate the elliptic
flow and its transverse momentum dependence for the gluon
matter created in Au+Au collisions at GeV. To make
comparisons with the experimental data at the BNL Relativistic Heavy Ion
Collider (RHIC), parton-hadron duality is assumed. We find that whereas the
integrated matches the experimental data, the gluon (or pion)
is about 20-50% smaller than the experimental data. Hadronization via gluon
fragmentation and quark recombination seems to be the key to explaining the
necessary jump of from the partonic to the hadronic phase. We also
show that the elliptic flow values moderately depend on the chosen freezeout
condition, which will thus constrain the shear viscosity to the entropy density
ratio of the quark gluon plasma created at RHIC.Comment: 20 pages, 7 figures, minor corrections, published versio
Quasi-exact Treatment of the Relativistic Generalized Isotonic Oscillator
We investigate the pseudospin symmetry case of a spin-1/2 particle governed
by the generalized isotonic oscillator, by presenting quasi exact polynomial
solutions to Dirac equation with pseudospin symmetry vector and scalar
potentials. The resulting equation is found to be quasi-exactly solvable owing
to the existence of a hidden algebraic structure. A systematic and
closed form solution to the basic equation is obtained using the Bethe ansatz
method. Analytic expression for the energy is obtain and the wavefunction is
derived in terms of the roots to a set of Bethe ansatz equations
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