5,298 research outputs found
Supercooling of rapidly expanding quark-gluon plasma
We reexamine the scenario of homogeneous nucleation of the quark-gluon plasma
produced in ultra-relativistic heavy ion collisions. A generalization of the
standard nucleation theory to rapidly expanding system is proposed. The
nucleation rate is derived via the new scaling parameter . It is
shown that the size distribution of hadronic clusters plays an important role
in the dynamics of the phase transition. The longitudinally expanding system is
supercooled to about 3-6%, then it is reheated, and the hadronization is
completed within 6-10 fm/c, i.e. 5-10 times faster than it was estimated
earlier, in a strongly nonequilibrium way.Comment: 12 pages, LaTeX, 3 eps figure
Charmonium Suppression with cc~ Dissociation by Strings
We study the production of cc~ pairs in nuclear reactions at SPS energies
within the covariant transport approach HSD. The production of cc~ is treated
perturbatively employing experimental cross sections while the interactions of
cc~ pairs with baryons are included by conventional cascade-type two-body
collisions. Adopting 6 mb for the cc~-baryon cross sections the data on J/\Psi
suppression in p+A reactions are reproduced in line with calculations based on
the Glauber model. Additionally the dissociation of the cc~ pairs by strings is
included in a purely geometrical way. We find good agreement with experimental
data from the NA38 and NA50 collaboration with an estimate for the string
radius of ~0.2-0.3 fm.Comment: 9 pages (LaTeX), 5 PS figure
Fluctuations and Correlations in Nucleus-Nucleus Collisions within Transport Models
Particle number fluctuations and correlations in nucleus-nucleus collisions
at SPS and RHIC energies are studied within microscopic transport approaches.
In this review we focus on the Hadron-String-Dynamics (HSD) and
Ultra-relativistic-Quantum-Molecular-Dynamics (UrQMD) models The obtained
results are compared with the available experimental data as well as with the
statistical models and the model of independent sources. In particular the role
of the experimental centrality selection and acceptance is discussed in detail
for a variety of experimental fluctuations and correlation observables with the
aim to extract information on the critical point in the plane of
strongly interacting matter
The highly ionized disk wind of GRO J1655-40
Aims: The galactic superluminal microquasar GRO J1655-40 started a new
outburst in February 2005, after seven years in quiescence, rising to a
high/soft state in March 2005. In this paper we study the X-ray spectra during
this rise. Methods: We observed GRO J1655-40 with XMM-Newton, on 27 February
2005, in the low/hard state, and on three consecutive days in March 2005,
during the rise of the source to its high/soft state. The EPIC-pn camera was
used in the fast-read Burst mode to avoid photon pile-up. Results: First, we
contributed to the improvement of the calibration of the EPIC-pn, since the
high flux received from the source required some refinements in the correction
of the Charge Transfer Efficiency of the camera.Second, we find that the X-ray
spectrum of GRO J1655-40 is dominated in the high/soft state by the thermal
emission from the accretion disk, with an inner radius of 13-14(D/3.2kpc)km and
a maximum temperature of 1.3 keV. Two absorption lines are detected in the
EPIC-pn spectra, at 6.7-6.8 and 7.8-8.0 keV, which can be identified either as
blended Fe XXV and Fe XXVI K-alpha and K-beta lines, or as blueshifted Fe XXV.
We find no orbital dependence on the X-ray properties, which provides an upper
limit for the inclination of the system of 73 degr. The RGS spectrometers
reveal interstellar absorption features at 17.2AA, 17.5AA (Fe L edges) and
23.54AA (OI K-alpha). Finally, while checking the interstellar origin of the OI
line, we find a general correlation of the OI K-alpha line equivalent width
with the hydrogen column density using several sources available in the
literature.Comment: 10 pages, 7 figures, 4 tables. Revised version with important change
Zitterbewegung of optical pulses in nonlinear frequency conversion
Pulse walk-off in the process of sum frequency generation in a nonlinear
crystal is shown to be responsible for pulse jittering which is
reminiscent to the Zitterbewegung (trembling motion) of a relativistic freely
moving Dirac particle. An analytical expression for the pulse center of mass
trajectory is derived in the no-pump-depletion limit, and numerical examples of
Zitterbewegung are presented for sum frequency generation in periodically-poled
lithium niobate. The proposed quantum-optical analogy indicates that frequency
conversion in nonlinear optics could provide an experimentally accessible
simulator of the Dirac equation.Comment: to be published in Journal of Physics B: Atomic, Molecular & Optical
Physic
A New Study of the Transition to Uniform Nuclear Matter in Neutron Stars and Supernovae
A comprehensive microscopic study of the properties of bulk matter at
densities just below nuclear saturation g
cm, zero and finite temperature and high neutron fraction, is outlined,
and preliminary results presented. Such matter is expected to exist in the
inner crust of neutron stars and during the core collapse of massive stars with
$M \gtrsim 8M_{\odot}Comment: 4 pages, 2 figures. Participant Contribution at the ``Dense Matter in
Heavy Ion Collisions and Astrophysics" Summer School, JINR, Dubna, Aug. 21 -
Sept. 1, 2006. To be published in PEPAN letter
Proof that the Hydrogen-antihydrogen Molecule is Unstable
In the framework of nonrelativistic quantum mechanics we derive a necessary
condition for four Coulomb charges ,
where all masses are assumed finite, to form the stable system. The obtained
stability condition is physical and is expressed through the required minimal
ratio of Jacobi masses. In particular this provides the rigorous proof that the
hydrogen-antihydrogen molecule is unstable. This is the first result of this
sort for four particles.Comment: Submitted to Phys.Rev.Let
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