373 research outputs found
Strongly Coupled Quark Gluon Plasma (SCQGP)
We propose that the reason for the non-ideal behavior seen in lattice
simulation of quark gluon plasma (QGP) and relativistic heavy ion collisions
(URHICs) experiments is that the QGP near T_c and above is strongly coupled
plasma (SCP), i.e., strongly coupled quark gluon plasma (SCQGP). It is
remarkable that the widely used equation of state (EoS) of SCP in QED (quantum
electrodynamics) very nicely fits lattice results on all QGP systems, with
proper modifications to include color degrees of freedom and running coupling
constant. Results on pressure in pure gauge, 2-flavors and 3-flavors QGP, are
all can be explained by treating QGP as SCQGP as demonstated here.Energy
density and speed of sound are also presented for all three systems. We further
extend the model to systems with finite quark mass and a reasonably good fit to
lattice results are obtained for (2+1)-flavors and 4-flavors QGP. Hence it is
the first unified model, namely SCQGP, to explain the non-ideal QGP seen in
lattice simulations with just two system dependent parameters.Comment: Revised with corrections and new results, Latex file (11 pages),
postscript file of 7 figure
Application of a new screening model to thermonuclear reactions of the rp process
A new screening model for astrophysical thermonuclear reactions was derived
recently which improved Salpeter's weak-screening one. In the present work we
prove that the new model can also give very reliable screening enhancement
factors (SEFs) when applied to the rp process. According to the results of the
new model, which agree well with Mitler's SEFs, the screened rp reaction rates
can be, at most, twice as fast as the unscreened ones.Comment: 8 RevTex pages + 7 ps figures. (Revised version). Accepted for
publication in Journal of Physics
How Multivalency controls Ionic Criticality
To understand how multivalency influences the reduced critical temperatures,
Tce (z), and densities, roce (z), of z : 1 ionic fluids, we study equisized
hard-sphere models with z = 1-3. Following Debye, Hueckel and Bjerrum,
association into ion clusters is treated with, also, ionic solvation and
excluded volume. In good accord with simulations but contradicting
integral-equation and field theories, Tce falls when z increases while roce
rises steeply: that 80-90% of the ions are bound in clusters near T_c serves to
explain these trends. For z \neq 1 interphase Galvani potentials arise and are
evaluated.Comment: 4 pages, 4 figure
Nuclear Reaction Rates in a Plasma
The problem of determining the effects of the surrounding plasma on nuclear
reaction rates in stars is formulated ab initio, using the techniques of
quantum statistical mechanics. We derive a result that expresses the complete
effects of Coulomb barrier penetration and of the influence of the surrounding
plasma in terms of matrix elements of well defined operators. We find that
possible "dynamical screening" effects that have been discussed in the
literature are absent. The form of our results suggests that an approach that
relies on numerical calculations of the correlation functions in a classical
Coulomb gas, followed by construction of an effective two body potential and a
quantum barrier penetration calculation, will miss physics that is as important
as the physics that it includes.Comment: 66 pages, revtex, Errors Fixed, Explanation Adde
Kinetic theory and dynamic structure factor of a condensate in the random phase approximation
We present the microscopic kinetic theory of a homogeneous dilute Bose
condensed gas in the generalized random phase approximation (GRPA), which
satisfies the following requirements: 1) the mass, momentum and energy
conservation laws; 2) the H-theorem; 3) the superfluidity property and 4) the
recovery of the Bogoliubov theory at zero temperature \cite{condenson}. In this
approach, the condensate influences the binary collisional process between the
two normal atoms, in the sense that their interaction force results from the
mediation of a Bogoliubov collective excitation traveling throughout the
condensate. Furthermore, as long as the Bose gas is stable, no collision
happens between condensed and normal atoms. In this paper, we show how the
kinetic theory in the GRPA allows to calculate the dynamic structure factor at
finite temperature and when the normal and superfluid are in a relative motion.
The obtained spectrum for this factor provides a prediction which, compared to
the experimental results, allows to validate the GRPA.
PACS numbers:03.75.Hh, 03.75.Kk, 05.30.-dComment: 6 pages, 1 figures, QFS2004 conferenc
Kinetic properties of particle-in-cell simulations compromised by Monte Carlo collisions
he particle-in-cell method with Monte Carlo collisions is frequently used when a detailed kinetic simulation of a weakly collisional plasma is required. In such cases, one usually desires, inter alia, an accurate calculation of the particle distribution functions in velocity space. However, velocity space diffusion affects most, perhaps all, kinetic simulations to some degree, leading to numerical thermalization (i.e., relaxation of the velocity distribution toward a Maxwellian), and consequently distortion of the true velocity distribution functions, among other undesirable effects. The rate of such thermalization can be considered a figure of merit for kinetic simulations. This article shows that, contrary to previous assumption, the addition of Monte Carlo collisions to a one-dimensional particle-in-cell simulation seriously degrades certain properties of the simulation. In particular, the thermalization time can be reduced by as much as three orders of magnitude. This effect makes obtaining strictly converged simulation results difficult in many cases of practical interest
Klein-Gordon Equation in Hydrodynamical Form
We follow and modify the Feshbach-Villars formalism by separating the
Klein-Gordon equation into two coupled time-dependent Schroedinger equations
for particle and antiparticle wave function components with positive
probability densities. We find that the equation of motion for the probability
densities is in the form of relativistic hydrodynamics where various forces
have their classical counterparts, with the additional element of the quantum
stress tensor that depends on the derivatives of the amplitude of the wave
function. We derive the equation of motion for the Wigner function and we find
that its approximate classical weak-field limit coincides with the equation of
motion for the distribution function in the collisionless kinetic theory.Comment: 13 page
Probing Color Response - Wakes in a Color Plasma
The wake induced in a hot QCD medium by a high momentum parton (jet
precursor) is calculated in the framework of linear response theory. Two
different scenarios are discussed: a weakly coupled quark gluon plasma (pQGP)
as described by hard-thermal loop (HTL) perturbation theory and a strongly
cupled QGP (sQGP) with the properties of a quantum liquid. In the latter case
the wake could exhibit a pronounced Mach cone structure. This physical
mechanism could be important for the understanding of preliminary data from the
PHENIX and STAR experiments at RHIC on the angular distribution of low-pt
secondaries stemming from the away-side jet which indicate maxima at
.Comment: Prepared for: Workshop on Correlations and Fluctuations in
Relativistic Nuclear Collisions, MIT, Cambridge, Massachusetts, USA, 21-23
April 200
On the Ground State of Electron Gases at Negative Compressibility
Two- and three-dimensional electron gases with a uniform neutralizing
background are studied at negative compressibility. Parametrized expressions
for the dielectric function are used to access this strong-coupling regime,
where the screened Coulomb potential becomes overall attractive for like
charges. Closely examining these expressions reveals that the ground state with
a periodic modulation of the charge density, albeit exponentially damped,
replaces the homogeneous one at positive compressibility. The wavevector
characterizing the new ground state depends on the density and is complex,
having a positive imaginary part, as does the homogeneous ground state, and
real part, as does the genuine charge density wave.Comment: 6 double-column pages, 2 figures. 2nd version is an extension of the
1st one, giving more detail
Dislocation-Mediated Melting: The One-Component Plasma Limit
The melting parameter of a classical one-component plasma is
estimated using a relation between melting temperature, density, shear modulus,
and crystal coordination number that follows from our model of
dislocation-mediated melting. We obtain in good agreement
with the results of numerous Monte-Carlo calculations.Comment: 8 pages, LaTe
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