3,181 research outputs found

### Hadronic Equation of State and Speed of Sound in Thermal and Dense Medium

The equation of state $p(\epsilon)$ and speed of sound squared $c_s^2$ are
studied in grand canonical ensemble of all hadron resonances having masses
$\leq 2\,$GeV. This large ensemble is divided into strange and non-strange
hadron resonances and furthermore to pionic, bosonic and femionic sectors. It
is found that the pions represent the main contributors to $c_s^2$ and other
thermodynamic quantities including the equation of state $p(\epsilon)$ at low
temperatures. At high temperatures, the main contributions are added in by the
massive hadron resonances. The speed of sound squared can be calculated from
the derivative of pressure with respect to the energy density, $\partial
p/\partial \epsilon$, or from the entropy-specific heat ratio, $s/c_v$. It is
concluded that the physics of these two expressions is not necessarily
identical. They are distinguishable below and above the critical temperature
$T_c$. This behavior is observed at vanishing and finite chemical potential. At
high temperatures, both expressions get very close to each other and both of
them approach the asymptotic value, $1/3$. In the HRG results, which are only
valid below $T_c$, the difference decreases with increasing the temperature and
almost vanishes near $T_c$. It is concluded that the HRG model can very well
reproduce the results of the lattice quantum chromodynamics (QCD) of $\partial
p/\partial \epsilon$ and $s/c_v$, especially at finite chemical potential. In
light of this, energy fluctuations and other collective phenomena associated
with the specific heat might be present in the HRG model. At fixed
temperatures, it is found that $c_s^2$ is not sensitive to the chemical
potential.Comment: 19 pages, 6 figures with 13 eps graph

### 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

### 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 $T> 1.2~T_c$. 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 $T \simeq 1.5 ~T_c$ only the correlated pairs
corresponding to the mesonic nonet survive and they completely disappear at $T
\simeq 2 ~T_c$. 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

### Negative electrode catalyst for the iron chromium redox energy storage system

A redox cell which operates at elevated temperatures and which utilizes the same two metal couples in each of the two reactant fluids is disclosed. Each fluid includes a bismuth salt and may also include a lead salt. A low cost, cation permselective membrane separates the reactant fluids

### Quantum Collective QCD String Dynamics

The string breaking model of particle production is extended in order to help
explain the transverse momentum distribution in elementary collisions. Inspired
by an idea of Bialas', we treat the string using a collective coordinate
approach. This leads to a chromo-electric field strength which fluctuates, and
in turn implies that quarks are produced according to a thermal distribution.Comment: 6 pages. Presented at SQM 2006. Submitted to J. Phys. G for
publication in proceedings. Vers. 2: Minor revisions; final hadron spectrum
calculation include

### Micro-canonical pentaquark production in \ee annihilations

The existence of pentaquarks, namely baryonic states made up of four quarks
and one antiquark, became questionable, because the candidates, i.e. the
$\Theta^+$ peak, are seen in certain reactions, i.e. p+p collisions, but not in
others, i.e. \ee annihilations. In this paper, we estimate the production of
$\Theta ^{+}(1540)$ and $\Xi^{--} (1860)$ in \ee annihilations at different
energies using Fermi statistical model as originally proposed in its
microcanonical form. The results is compared with that from pp collisions at
SPS and RHIC energies. We find that, if pentaquark states exist, the production
is highly possible in \ee annihilations. For example, at LEP energy
$\sqrt{s}$=91.2 GeV, both $\Theta ^{+}(1540)$ and $\Xi^{--} (1860)$ yield more
than in pp collisions at SPS and RHIC energy.Comment: 7 pages 2 figure

### Large Nc Continuum Reduction and the Thermodynamics of QCD

It is noted that if large Nc continuum reduction applies to an observable,
then that observable is independent of temperature for all temperatures below
some critical value. This fact, plus the fact that mesons and glueballs are
weakly interacting at large Nc is used as the basis for a derivation of large
Nc continuum reduction for the chiral condensate. The structure of this
derivation is quite general and can be extended to a wide class of observables

### Spectrum and thermodynamic properties of two-dimensional N=(1,1) super Yang-Mills theory with fundamental matter and a Chern-Simons term

We consider N=(1,1) super Yang-Mills theory in 1+1 dimensions with
fundamentals at large-N_c. A Chern-Simons term is included to give mass to the
adjoint partons. Using the spectrum of the theory, we calculate thermodynamic
properties of the system as a function of the temperature and the Yang-Mills
coupling. In the large-N_c limit there are two non-communicating sectors, the
glueball sector, which we presented previously, and the meson-like sector that
we present here. We find that the meson-like sector dominates the
thermodynamics. Like the glueball sector, the meson sector has a Hagedorn
temperature T_H, and we show that the Hagedorn temperature grows with the
coupling. We calculate the temperature and coupling dependence of the free
energy for temperatures below T_H. As expected, the free energy for weak
coupling and low temperature grows quadratically with the temperature. Also the
ratio of the free energies at strong coupling compared to weak coupling,
r_{s-w}, for low temperatures grows quadratically with T. In addition, our data
suggest that r_{s-w} tends to zero in the continuum limit at low temperatures.Comment: 34 p

### 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

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