769 research outputs found
Quark number susceptibilities of hot QCD up to g^6ln(g)
The pressure of hot QCD has recently been determined to the last
perturbatively computable order g^6 ln(g) by Kajantie et al. using
three-dimensional effective theories. A similar method is applied here to the
pressure in the presence of small but non-vanishing quark chemical potentials,
and the result is used to derive the quark number susceptibilities in the limit
mu = 0. The diagonal quark number susceptibility of QCD with n_f flavours of
massless quarks is evaluated to order g^6ln(g) and compared with recent lattice
simulations. It is observed that the results qualitatively resemble the lattice
ones, and that when combined with the fully perturbative but yet undetermined
g^6 term they may well explain the behaviour of the lattice data for a wide
range of temperatures.Comment: 11 pages, 3 figures Typos corrected, references added, figures
modifie
Jacobi Fields on Statistical Manifolds of Negative Curvature
Two entropic dynamical models are considered. The geometric structure of the
statistical manifolds underlying these models is studied. It is found that in
both cases, the resulting metric manifolds are negatively curved. Moreover, the
geodesics on each manifold are described by hyperbolic trajectories. A detailed
analysis based on the Jacobi equation for geodesic spread is used to show that
the hyperbolicity of the manifolds leads to chaotic exponential instability. A
comparison between the two models leads to a relation among statistical
curvature, stability of geodesics and relative entropy-like quantities.
Finally, the Jacobi vector field intensity and the entropy-like quantity are
suggested as possible indicators of chaoticity in the ED models due to their
similarity to the conventional chaos indicators based on the Riemannian
geometric approach and the Zurek-Paz criterion of linear entropy growth,
respectively.Comment: 22 page
Emission of thermal photons and the equilibration time in Heavy-Ion collisions
The emission of hard real photons from thermalized expanding hadronic matter
is dominated by the initial high-temperature expansion phase. Therefore, a
measurement of photon emission in ultrarelativistic heavy-ion collisions
provides valuable insights into the early conditions realized in such a
collision. In particular, the initial temperature of the expanding fireball or
equivalently the equilibration time of the strongly interacting matter are of
great interest. An accurate determination of these quantities could help to
answer the question whether or not partonic matter (the quark gluon plasma) is
created in such collisions. In this work, we investigate the emission of real
photons using a model which is based on the thermodynamics of QCD matter and
which has been shown to reproduce a large variety of other observables. With
the fireball evolution fixed beforehand, we are able to extract limits for the
equilibration time by a comparison with photon emission data measured by WA98.Comment: 12 pages, 5 figures, accepted for publication at Phys. Rev.
Level spacing statistics of classically integrable systems -Investigation along the line of the Berry-Robnik approach-
By extending the approach of Berry and Robnik, the limiting level spacing
distribution of a system consisting of infinitely many independent components
is investigated. The limiting level spacing distribution is characterized by a
single monotonically increasing function of the level spacing
. Three cases are distinguished: (i) Poissonian if ,
(ii) Poissonian for large , but possibly not for small if
, and (iii) sub-Poissonian if .
This implies that, even when energy-level distributions of individual
components are statistically independent, non-Poissonian level spacing
distributions are possible.Comment: 19 pages, 4 figures. Accepted for publication in Phys. Rev.
Parton rescattering and screening in Au+Au collisions at RHIC
We study the microscopic dynamics of quarks and gluons in relativistic heavy
ion collisions in the framework of the Parton Cascade Model. We use lowest
order perturbative QCD cross sections with fixed lower momentum cutoff p_0. We
calculate the time-evolution of the Debye-screening mass for Au+Au collisions
at sqrt(s)=200 GeV per nucleon pair. The screening mass is used to determine a
lower limit for the allowed range of p_0. We also determine the energy density
reached through hard and semi-hard processes at RHIC, obtain a lower bound for
the rapidity density of charged hadrons produced by semihard interactions, and
analyze the extent of perturbative rescattering among partons.Comment: 6 pages, 4 figures, uses RevTeX 4.0; revised version with minor
corrections and one updated figur
Duality properties of Gorringe-Leach equations
In the category of motions preserving the angular momentum's direction,
Gorringe and Leach exhibited two classes of differential equations having
elliptical orbits. After enlarging slightly these classes, we show that they
are related by a duality correspondence of the Arnold-Vassiliev type. The
specific associated conserved quantities (Laplace-Runge-Lenz vector and
Fradkin-Jauch-Hill tensor) are then dual reflections one of the othe
Wavepacket Dynamics in Yang-Mills Theory
We discuss the results of numerical simulations of colliding wavepackets in
Yang--Mills theory. We investigate their behavior as a function of
amplitude and momentum distribution. We find regions in our parameter space in
which initial wave packets scatter into final configurations with dramatically
different momentum distributions. These results constitute new classical
trajectories with multiparticle boundary conditions. We explain their relevance
for the calculation of scattering amplitudes in the semiclassical
approximation. Finally, we give directions for future work.Comment: 11 pgs. text, 11 optional figs using PiCTeX and epsf, new version
contains improved discussion of scaling properties of results and one
additional figure
Quark-Gluon Plasma Fireball
Lattice-QCD results provide an opportunity to model, and extrapolate to
finite baryon density, the properties of the quark-gluon plasma (QGP). Upon
fixing the scale of the thermal coupling constant and vacuum energy to the
lattice data, the properties of resulting QGP equations of state (EoS) are
developed. We show that the physical properties of the dense matter fireball
formed in heavy ion collision experiments at CERN-SPS are well described by the
QGP-EoS we presented. We also estimate the properties of the fireball formed in
early stages of nuclear collision, and argue that QGP formation must be
expected down to 40A GeV in central Pb--Pb interactions.Comment: 10 pages, 9 postscript figures, 1 table, uses revtex, V3: introduced
difference between n_f and n_s; fireball restframe energy corrected,
references added. Publisched version in press Phys. Rev.
Perturbations of anti-de Sitter black holes
I review perturbations of black holes in asymptotically anti-de Sitter space.
I show how the quasi-normal modes governing these perturbations can be
calculated analytically and discuss the implications on the hydrodynamics of
gauge theory fluids per the AdS/CFT correspondence. I also discuss phase
transitions of hairy black holes with hyperbolic horizons and the dual
superconductors emphasizing the analytical calculation of their properties.Comment: 25 pages, 4 figures, prepared for the proceedings of the 5th Aegean
Summer School "From Gravity to Thermal Gauge Theories: the AdS/CFT
Correspondence," Milos, Greece, September 2009
The pressure of hot QCD up to g^6 ln(1/g)
The free energy density, or pressure, of QCD has at high temperatures an
expansion in the coupling constant g, known so far up to order g^5. We compute
here the last contribution which can be determined perturbatively, g^6 ln(1/g),
by summing together results for the 4-loop vacuum energy densities of two
different three-dimensional effective field theories. We also demonstrate that
the inclusion of the new perturbative g^6 ln(1/g) terms, once they are summed
together with the so far unknown perturbative and non-perturbative g^6 terms,
could potentially extend the applicability of the coupling constant series down
to surprisingly low temperatures.Comment: 18 pages. Small clarifications added. To appear in Phys.Rev.
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