3,936 research outputs found
Shear and bulk viscosities of the gluon plasma in a quasiparticle description
Shear and bulk viscosities of deconfined gluonic matter are investigated
within an effective kinetic theory by describing the strongly interacting
medium phenomenologically in terms of quasiparticle excitations with
medium-dependent self-energies. We show that the resulting transport
coefficients reproduce the parametric dependencies on temperature and coupling
obtained in perturbative QCD at large temperatures and small running coupling.
The extrapolation into the non-perturbative regime results in a decreasing
specific shear viscosity with decreasing temperature, exhibiting a minimum in
the vicinity of the deconfinement transition, while the specific bulk viscosity
is sizeable in this region falling off rapidly with increasing temperature. The
temperature dependence of specific shear and bulk viscosities found within this
quasiparticle description of the pure gluon plasma is in agreement with
available lattice QCD results.Comment: Sep 2011. 24pp. 6 figures. revised journal versio
Dynamical screening in hot systems away from (chemical) equilibrium
Within the Closed Time Path Formalism of Thermal Field Theory we calculate
the hard photon emission rate as well as the collisional energy-loss rate for a
quark-gluon plasma away from chemical equilibrium. Mass singularities are shown
to be dynamically screened within HTL-resummed perturbation theory also away
from equilibrium. Additional (pinch) singularities are absent and well defined
results are obtained.Comment: Talk given at the Japanese Workshop on Thermal Quantum Field Theories
and their Applications, Kyoto, Japan, 25.-27. August 1999, 6 page
Viscosities in the Gluon-Plasma within a Quasiparticle Model
A phenomenological quasiparticle model, featuring dynamically generated
self-energies of excitation modes, successfully describes lattice QCD results
relevant for the QCD equation of state and related quantities both at zero and
non-zero net baryon density. Here, this model is extended to study bulk and
shear viscosities of the gluon-plasma within an effective kinetic theory
approach. In this way, the compatibility of the employed quasiparticle ansatz
with the apparent low viscosities of the strongly coupled deconfined gluonic
medium is shown.Comment: 4 pages, 1 figure. To appear in the conference proceedings for Quark
Matter 2009, March 30 - April 4, Knoxville, Tennessee, US
Dynamical screening away from equilibrium: hard photon production and collisional energy loss
We investigate the production rate for hard real photons and the collisional
energy loss in the quark-gluon plasma away from chemical equilibrium. Applying
the Hard-Thermal-Loop resummation scheme away from equilibrium, we can show
that Landau damping provides dynamical screening for both fermion and boson
exchange present in the two quantities.Comment: 5 pages RevTeX, 2 figures, remarks for clarification and one
reference added, typos correcte
Transport Coefficients in Gluodynamics: From Weak Coupling towards the Deconfinement Transition
We study the ratio of bulk to shear viscosity in gluodynamics within a
phenomenological quasiparticle model. We show that at large temperatures this
ratio exhibits a quadratic dependence on the conformality measure as known from
weak coupling perturbative QCD. In the region of the deconfinement transition,
however, this dependence becomes linear as known from specific strongly coupled
theories. The onset of the strong coupling behavior is located near the maximum
of the scaled interaction measure. This qualitative behavior of the viscosity
ratio is rather insensitive to details of the equation of state.Comment: Oct 2011. 3 pages. 3 figures. Contribution to the proceedings of the
19th Particles and Nuclei International Conference (PANIC11
Probability distributions in statistical ensembles with conserved charges
The probability distributions for charged particle numbers and their
densities are derived in statistical ensembles with conservation laws. It is
shown that if this limit is properly taken then the canonical and grand
canonical ensembles are equivalent. This equivalence is proven on the most
general, probability distribution level.Comment: 5 pages. A little bit shorter version due to some editorial and
language changes. To be published in Phys. Rev.
One Loop Effects in Various Dimensions and D-Branes
We calculate some one loop corrections to the effective action of theories in
dimensions that arise on the dimensional reduction of a Weyl fermion in
dimensions. The terms that we are interested in are of a topological nature.
Special attention is given to the effective actions of the super Yang Mills
theories that arise on dimensional reduction of the N=1 theory in six
dimensions or on the dimensional reduction of the N=1 theory in ten dimensions.
In the latter case we suggest an interpretation of the quantum effect as a
coupling of the gauge field on the brane to a relative background gauge field.Comment: 18 pages, LaTe
Some Relations for Quark Confinement and Chiral Symmetry Breaking in QCD
We analytically study the relation between quark confinement and spontaneous
chiral-symmetry breaking in QCD. In terms of the Dirac eigenmodes, we derive
some formulae for the Polyakov loop, its fluctuations, and the string tension
from the Wilson loop. We also investigate the Polyakov loop in terms of the
eigenmodes of the Wilson, the clover and the domain wall fermion kernels,
respectively. For the confinement quantities, the low-lying Dirac/fermion
eigenmodes are found to give negligible contribution, while they are essential
for chiral symmetry breaking. These relations indicate no direct one-to-one
correspondence between confinement and chiral symmetry breaking in QCD, which
seems to be natural because confinement is realized independently of the quark
mass
Dirac spectrum representation of Polyakov loop fluctuations in lattice QCD
Dirac spectrum representations of the Polyakov loop fluctuations are derived
on the temporally odd-number lattice, where the temporal length is odd with the
periodic boundary condition. We investigate the Polyakov loop fluctuations
based on these analytical relations. It is semianalytically and numerically
found that the low-lying Dirac eigenmodes have little contribution to the
Polyakov loop fluctuations, which are sensitive probe for the quark
deconfinement. Our results suggest no direct one-to-one corresponding between
quark confinement and chiral symmetry breaking in QCD.Comment: 7 pages and 1 figure. Proceeding of the 33rd International Symposium
on Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe International
Conference Center, Kobe, Japan. Also regarded as the Proceeding of the 4th
International Conference on new Frontiers in Physics (ICNFP 2015), 23-30
August 2015, Conference Center of the Orthodox Academy of Crete, Crete,
Greec
Relating Quark Confinement and Chiral Symmetry Breaking in QCD
We study the relation between quark confinement and chiral symmetry breaking
in QCD. Using lattice QCD formalism, we analytically express the various
"confinement indicators", such as the Polyakov loop, its fluctuations, the
Wilson loop, the inter-quark potential and the string tension, in terms of the
Dirac eigenmodes. In the Dirac spectral representation, there appears a power
of the Dirac eigenvalue such as , which behaves
as a reduction factor for small . Consequently, since this reduction
factor cannot be cancelled, the low-lying Dirac eigenmodes give negligibly
small contribution to the confinement quantities,while they are essential for
chiral symmetry breaking. These relations indicate no direct, one-to-one
correspondence between confinement and chiral symmetry breaking in QCD. In
other words, there is some independence of quark confinement from chiral
symmetry breaking, which can generally lead to different transition
temperatures/densities for deconfinement and chiral restoration. We also
investigate the Polyakov loop in terms of the eigenmodes of the Wilson, the
clover and the domain-wall fermion kernels, respectively, and find the similar
results. The independence of quark confinement from chiral symmetry breaking
seems to be natural, because confinement is realized independently of quark
masses and heavy quarks are also confined even without the chiral symmetry.Comment: 20 pages, 10 figures. arXiv admin note: text overlap with
arXiv:1611.0874
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