2,916 research outputs found
Effective degrees of freedom and gluon condensation in the high temperature deconfined phase
The Equation of State and the properties of matter in the high temperature
deconfined phase are analyzed by a quasiparticle approach for . In
order to fix the parameters of our model we employ the lattice QCD data of
energy density and pressure. First we consider the pure SU(3) gluon plasma and
it turns out that such a system can be described in terms of a gluon condensate
and of gluonic quasiparticles whose effective number of degrees of freedom and
mass decrease with increasing temperature. Then we analyze QCD with finite
quark masses. In this case the numerical lattice data for energy density and
pressure can be fitted assuming that the system consists of a mixture of gluon
quasiparticles, fermion quasiparticles, boson correlated pairs (corresponding
to in-medium mesonic states) and gluon condensate. We find that the effective
number of boson degrees of freedom and the in-medium fermion masses decrease
with increasing temperature. At only the correlated pairs
corresponding to the mesonic nonet survive and they completely disappear at . The temperature dependence of the velocity of sound of the
various quasiparticles, the effects of the breaking of conformal invariance and
the thermodynamic consistency are discussed in detail.Comment: 18 pages, 9 figure
The Hagedorn temperature Revisited
The Hagedorn temperature, T_H is determined from the number of hadronic
resonances including all mesons and baryons. This leads to a stable result T_H
= 174 MeV consistent with the critical and the chemical freeze-out temperatures
at zero chemical potential. We use this result to calculate the speed of sound
and other thermodynamic quantities in the resonance hadron gas model for a wide
range of baryon chemical potentials following the chemical freeze-out curve. We
compare some of our results to those obtained previously in other papers.Comment: 13 pages, 4 figure
Stabilizing Hadron Resonance Gas Models against Future Discoveries
We examine the stability of hadron resonance gas models by extending them to
take care of undiscovered resonances through the Hagedorn formula. We find that
the influence of unknown resonances on thermodynamics is large but bounded.
Hadron resonance gases are internally consistent up to a temperature higher
than the cross over temperature in QCD; but by examining quark number
susceptibilities we find that their region of applicability seems to end even
below the QCD cross over. We model the decays of resonances and investigate the
ratios of particle yields in heavy-ion collisions. We find that observables
such as hydrodynamics and hadron yield ratios change little upon extending the
model. As a result, heavy-ion collisions at RHIC and LHC are insensitive to a
possible exponential rise in the hadronic density of states, thus increasing
the stability of the predictions of hadron resonance gas models
Kappa-deformed Statistics and the Formation of a Quark-Gluon Plasma
The effect of the non-extensive form of statistical mechanics proposed by
Tsallis on the formation of a quark-gluon plasma (QGP) has been recently
investigated in ref. \cite{1}. The results show that for small deviations
() from Boltzmann-Gibbs (BG) statistics in the QGP phase, the
critical temperature for the formation of a QGP does not change substantially
for a large variation of the chemical potential. In the present effort we use
the extensive -deformed statistical mechanics constructed by Kaniadakis
to represent the constituents of the QGP and compare the results with ref. [1].Comment: 2 Figure
Instability of Boost-invariant hydrodynamics with a QCD inspired bulk viscosity
We solve the relativistic Navier-Stokes equations with homogeneous
boost-invariant boundary conditions, and perform a stability analysis of the
solution. We show that, if the bulk viscosity has a peak around as
inferred from QCD-based arguments, the background solution "freezes" at
to a nearly constant temperature state. This state is however highly unstable
with respect to certain inhomogeneous modes. Calculations show that these modes
have enough time to blow up and tear the system into droplets. We conjecture
that this is how freeze-out occurs in the QGP created in heavy ion collisions,
and perhaps similar transitions in the early universe.Comment: Accepted for publication, Rapid Communication in Physical Review C
Discussion extended, derivation and conclusions not change
N=(1,1) super Yang--Mills theory in 1+1 dimensions at finite temperature
We present a formulation of N=(1,1) super Yang-Mills theory in 1+1 dimensions
at finite temperature. The partition function is constructed by finding a
numerical approximation to the entire spectrum. We solve numerically for the
spectrum using Supersymmetric Discrete Light-Cone Quantization (SDLCQ) in the
large-N_c approximation and calculate the density of states. We find that the
density of states grows exponentially and the theory has a Hagedorn
temperature, which we extract. We find that the Hagedorn temperature at
infinite resolution is slightly less than one in units of (g^(2) N_c/pi)^(1/2).
We use the density of states to also calculate a standard set of thermodynamic
functions below the Hagedorn temperature. In this temperature range, we find
that the thermodynamics is dominated by the massless states of the theory.Comment: 16 pages, 8 eps figures, LaTe
Energy and system size dependence of chemical freeze-out in relativistic nuclear collisions
We present a detailed study of chemical freeze-out in p-p, C-C, Si-Si and
Pb-Pb collisions at beam momenta of 158A GeV as well as Pb-Pb collisions at
beam momenta of 20A, 30A, 40A and 80A GeV. By analyzing hadronic multiplicities
within the statistical hadronization model, we have studied the parameters of
the source as a function of the number of the participating nucleons and the
beam energy. We observe a nice smooth behaviour of temperature, baryon chemical
potential and strangeness under-saturation parameter as a function of energy
and nucleus size. Interpolating formulas are provided which allow to predict
the chemical freeze-out parameters in central collisions at centre-of-mass
energies > 4.5 GeV and for any colliding ions. Specific discrepancies between
data and model emerge in particle ratios in Pb-Pb collisions at SPS between 20A
and 40A GeV of beam energy which cannot be accounted for in the considered
model schemes.Comment: 22 pages, 10 figures. References added and updated. Table correcte
The real black power : Mattie Coney and the pragmatic politics of black conservatism
This project examines the life and activism of Mattie Rice Coney, a black civic leader from Indianapolis, Indiana. Coney founded the Citizens Forum, Inc., in July 1964 to facilitate the smooth implementation of recently enacted civil rights legislation such as the 1964 Civil Rights Act and Indianapolis\u27s Open Housing Ordinance. Employing a language of racial uplift and civic duty, Coney deftly crafted an image of black conservatism that appealed to moderate white conservatives. In articulating a quiet, alternative civil rights agenda centered on individual improvement, Coney legitimized her sociopolitical status among whites as a respectable black leader. This status helped Coney secure funds and recognition for her organization, which combatted the effects of poverty through neighborhood cleanup and beautification, job training and placement, and voter registration and education. ^ I argue that Coney\u27s embrace of conservatism was pragmatic as it enabled her to advocate openly for meaningful black equality post 1965. The history of Mattie Coney\u27s life and activism sheds light on the various ways in which African Americans struggled to gain meaningful equality at the grassroots level in the wake of federal civil right policy changes. Moreover, this study offers a more nuanced history of the long civil rights movement by examining the intersections of civil rights and modern conservatism, in effect revealing the varied forms of civil rights activism—including black conservatism—after 1965
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