4,659 research outputs found
Self-consistent parametrization of the two-flavor isotropic color-superconducting ground state
Lack of Lorentz invariance of QCD at finite quark chemical potential in
general implies the need of Lorentz non-invariant condensates for the
self-consistent description of the color-superconducting ground state.
Moreover, the spontaneous breakdown of color SU(3) in this state naturally
leads to the existence of SU(3) non-invariant non-superconducting expectation
values. We illustrate these observations by analyzing the properties of an
effective 2-flavor Nambu-Jona-Lasinio type Lagrangian and discuss the
possibility of color-superconducting states with effectively gapless fermionic
excitations. It turns out that the effect of condensates so far neglected can
yield new interesting phenomena.Comment: 16 pages, 3 figure
Dead Time Compensation for High-Flux Ranging
Dead time effects have been considered a major limitation for fast data
acquisition in various time-correlated single photon counting applications,
since a commonly adopted approach for dead time mitigation is to operate in the
low-flux regime where dead time effects can be ignored. Through the application
of lidar ranging, this work explores the empirical distribution of detection
times in the presence of dead time and demonstrates that an accurate
statistical model can result in reduced ranging error with shorter data
acquisition time when operating in the high-flux regime. Specifically, we show
that the empirical distribution of detection times converges to the stationary
distribution of a Markov chain. Depth estimation can then be performed by
passing the empirical distribution through a filter matched to the stationary
distribution. Moreover, based on the Markov chain model, we formulate the
recovery of arrival distribution from detection distribution as a nonlinear
inverse problem and solve it via provably convergent mathematical optimization.
By comparing per-detection Fisher information for depth estimation from high-
and low-flux detection time distributions, we provide an analytical basis for
possible improvement of ranging performance resulting from the presence of dead
time. Finally, we demonstrate the effectiveness of our formulation and
algorithm via simulations of lidar ranging.Comment: Revision with added estimation results, references, and figures, and
modified appendice
Dileptons in High-Energy Heavy-Ion Collisions
The current status of our understanding of dilepton production in
ultrarelativistic heavy-ion collisions is discussed with special emphasis on
signals from the (approach towards) chirally restored and deconfined phases. In
particular, recent results of the CERN-SPS low-energy runs are compared to
model predictions and interpreted. Prospects for RHIC experiments are given.Comment: Invited talk at ICPAQGP, Jaipur, India, Nov. 26-30, 2001; 1 Latex and
9 eps-/ps-files Reoprt No.: SUNY-NTG-02-0
-Process simulations with a modified reaction library
We have performed -process simulations with the most recent stellar
cross sections from the "Karlsruhe Astrophysical Database of
Nucleosynthesis in Stars" project (version v0.2,
http://nuclear-astrophysics.fzk.de/kadonis). The simulations were carried out
with a parametrized supernova type II shock front model (`` process'')
of a 25 solar mass star and compared to recently published results. A decrease
in the normalized overproduction factor could be attributed to lower cross
sections of a significant fraction of seed nuclei located in the Bi and Pb
region around the =126 shell closure.Comment: 5 pages, 1 figure Proceedings "Nuclear Physics in Astrophysics
NPA-III", Dresden/Germany (2007
Photon and dilepton emission rates from high density quark matter
We compute the rates of real and virtual photon (dilepton) emission from
dense QCD matter in the color-flavor locked (CFL) phase, focusing on results at
moderate densities (3-5 times the nuclear saturation density) and temperatures
MeV. We pursue two approaches to evaluate the electromagnetic
(e.m.) response of the CFL ground state: (i) a direct evaluation of the photon
self energy using quark particle/-hole degrees of freedom, and (ii) a Hidden
Local Symmetry (HLS) framework based on generalized mesonic excitations where
the meson is introduced as a gauge boson of a local SU(3) color-flavor
group. The coupling to generalized two-pion states induces a finite
width and allows to address the issue of vector meson dominance (VMD) in the
CFL phase. We compare the calculated emissivities (dilepton rates) to those
arising from standard hadronic approaches including in-medium effects. For
rather large superconducting gaps (several tens of MeV at moderate densities),
as suggested by both perturbative and nonperturbative estimates, the dilepton
rates from CFL quark matter turn out to be very similar to those obtained in
hadronic many-body calculations, especially for invariant masses above
GeV. A similar observation holds for (real) photon production.Comment: 18 pages, 12 figure
Statistical Complexity and Nontrivial Collective Behavior in Electroencephalografic Signals
We calculate a measure of statistical complexity from the global dynamics of
electroencephalographic (EEG) signals from healthy subjects and epileptic
patients, and are able to stablish a criterion to characterize the collective
behavior in both groups of individuals. It is found that the collective
dynamics of EEG signals possess relative higher values of complexity for
healthy subjects in comparison to that for epileptic patients. To interpret
these results, we propose a model of a network of coupled chaotic maps where we
calculate the complexity as a function of a parameter and relate this measure
with the emergence of nontrivial collective behavior in the system. Our results
show that the presence of nontrivial collective behavior is associated to high
values of complexity; thus suggesting that similar dynamical collective process
may take place in the human brain. Our findings also suggest that epilepsy is a
degenerative illness related to the loss of complexity in the brain.Comment: 13 pages, 3 figure
Interferometry of direct photons in Pb+Pb collisions at 158 AGeV
We present final results from the WA98 experiment which provide first
measurements of Bose-Einstein correlations of direct photons in
ultrarelativistic heavy ion collisions. Invariant interferometric radii were
extracted in the range MeV/c and compared to interferometric
radii of charged pions. The yield of direct photons for MeV/c was
extracted from the correlation strength parameter and compared to the yield of
direct photons measured in WA98 at higher with the statistical
subtraction method, and to predictions of a fireball model.Comment: 4 pages, 3 figures, proceedings for Quark Matter 200
Hadro-Chemistry and Evolution of (Anti-) Baryon Densities at RHIC
The consequences of hadro-chemical freezeout for the subsequent hadron gas
evolution in central heavy-ion collisions at RHIC and LHC energies are
discussed with special emphasis on effects due to antibaryons. Contrary to
naive expectations, their individual conservation, as implied by experimental
data, has significant impact on the chemical off-equilibrium composition of
hadronic matter at collider energies. This may reflect on a variety of
observables including source sizes and dilepton spectra.Comment: 4 pages ReVTeX incl. 3 ps-figs, submitted to PR
Consideration of permanent tidal deformation in the orbit determination and data analysis for the Topex/Poseidon mission
The effects of the permanent tidal effects of the Sun and Moon with specific applications to satellite altimeter data reduction are reviewed in the context of a consistent definition of geoid undulations. Three situations are applicable not only for altimeter reduction and geoid definition, but also for the second degree zonal harmonic of the geopotential and the equatorial radius. A recommendation is made that sea surface heights and geoid undulations placed on the Topex/Poseidon geophysical data record should be referred to the mean Earth case (i.e., with the permanent effects of the Sun and Moon included). Numerical constants for a number of parameters, including a flattening and geoid geopotential, are included
Signatures of Thermal Dilepton Radiation at RHIC
The properties of thermal dilepton production from heavy-ion collisions in
the RHIC energy regime are evaluated for invariant masses ranging from 0.5 to 3
GeV. Using an expanding thermal fireball to model the evolution through both
quark-gluon and hadronic phases various features of the spectra are addressed.
In the low-mass region, due to an expected large background, the focus is on
possible medium modifications of the narrow resonance structures from
and mesons, whereas in the intermediate-mass region the old idea of
identifying QGP radiation is reiterated including effects of chemical
under-saturation in the early stages of central Au+Au collisions.Comment: 17 pages ReVTeX including 16 figure
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