41 research outputs found
Effects of gluon damping rate on the viscosity coefficient of the quark-gluon plasma at finite chemical potential
By considering the Debye screening and damping rate of gluons, the viscosity
coefficient of the quark-gluon plasma was evaluated via real-time finite
temperature QCD in the relaxation time approximation at finite temperature and
chemical potential . The results show that both the damping rate and the
chemical potential cause considerable enhancements to the viscosity coefficient
of hot dense quark-gluon plasma.Comment: Latex, 18 pages plus three figure
Thermal Relaxation Time in Chemically Non-equilibrated Quark- Gluon Plasma
The definition of thermal relaxation time is extended to chemically
non-equilibrated quark-gluon plasma and the chemical non-equilibrated thermal
relaxation times for partons are calculated using the non-equilibrium Debye
mass as the infrared regulator. The dependence of the thermal relaxation time
on the fugacity is given and the influence of the chemical non-equilibration is
discussed. We find that there are threshold fugacities and
for gluons and quarks. For \lambda_g < \lambda_g^* (\lambda_q <
\lambda_q^*), \tau_g^{NEQ}/\tau_g^{EQ} (\tau_q^{NEQ}/\tau_q^{EQ}) decreases
strongly with increasing fugacity, while for ), the ratios are almost 1. It is shown that there is
also the two-stage equilibration in a chemically non-equilibrated plasma. We
also discussed the effect of using the non-equilibrium Deby mass as the
infrared cutoff.Comment: 11 pages, 4 figures, Revtex, submitted to Phys. Rev.
Ward Identities in Non-equilibrium QED
We verify the QED Ward identity for the two- and three -point functions at
non-equilibrium in the HTL limit. We use the Keldysh formalism of real time
finite temperature field theory. We obtain an identity of the same form as the
Ward identity for a set of one loop self-energy and one loop three-point vertex
diagrams which are constructed from HTL effective propagators and vertices.Comment: 19 pages, RevTex, 4 PostScript figures, revised version to be
published in Phys. Rev.
Finite Temperature Retarded and Advanced Fields
By employing retarded and advanced propagators, Aurenche and Becherrawy
showed how to rewrite the real-time thermal Feynman rules so that the
temperature dependence is removed from the free propagators and transferred to
the vertices. The present paper introduces retarded and advanced field
operators and incorporates all temperature dependence into the interaction term
of the Hamiltonian. Perturbative expansions of the Green functions in the
Hamiltonian formulation give the correct results order by order in perturbation
theory.
The spectrum of the temperature-dependent Hamiltonian contains the thermal
quasiparticles that produce poles in the propagators.Comment: 27 pages, latex, no figure
Comprehensive Riser VIV Model Tests in Uniform and Sheared Flow
Despite of considerable research activity during the last decades considerable uncertainties still remain in prediction of Vortex Induced Vibrations (VIV) of risers. Model tests of risers subjected to current have been shown to be a useful method for investigation of the VIV behavior of risers with and without suppression devices. In order to get further insight on VIV of risers, an extensive hydrodynamic test program of riser models subjected to vortex-induced vibrations was undertaken during the winter 2010 by Shell Oil Company. The VIV-model test campaign was performed in the MARINTEK Offshore Basin Laboratory. A new test rig was constructed and showed to give good test conditions. Three different 38m long riser models were towed horizontally at different speeds, simulating uniform and linearly varying sheared current. Measurements were made In-Line (IL) and Cross-Flow (CF) of micro bending strains and accelerations along the risers. The test program compromised about 400 tests, which give a rich test material for further studies. In the present paper the test set-up and program are presented and selected results are reported
Quantum, Multi-Body Effects and Nuclear Reaction Rates in Plasmas
Detailed calculations of the contribution from off-shell effects to the
quasiclassical tunneling of fusing particles are provided. It is shown that
these effects change the Gamow rates of certain nuclear reactions in dense
plasma by several orders of magnitude.Comment: 11 pages; change of content: added clarification of one of the
important steps in the derivatio
Soft Photons from Off-shell Particles in a Hot Plasma
Considering the propagation of off-shell particles in the framework of
thermal field theory, we present the general formalism for the calculation of
the production rate of soft photons and dileptons from a hot plasma. This
approach is illustrated with an electrodynamic plasma. The photon production
rate from strongly interacting quarks in the quark-gluon plasma, which might be
formed in ultrarelativistic heavy ion collisions, is calculated in the
previously unaccessible regime of photon energies of the order of the plasma
temperature within an effective field theory incorporating dynamical chiral
symmetry breaking.Comment: 8 pages in RevTeX format, 3 figures uuencoded postscript added. Also
available by anonymous ftp at ftp://tpri6c.gsi.de/pub/phenning/qh95ga
Transport Theory of Massless Fields
Using the Schwinger-Keldysh technique we discuss how to derive the transport
equations for the system of massless quantum fields. We analyse the scalar
field models with quartic and cubic interaction terms. In the model
the massive quasiparticles appear due to the self-interaction of massless bare
fields. Therefore, the derivation of the transport equations strongly resembles
that one of the massive fields, but the subset of diagrams which provide the
quasiparticle mass has to be resummed. The kinetic equation for the finite
width quasiparticles is found, where, except the mean-field and collision
terms, there are terms which are absent in the standard Boltzmann equation. The
structure of these terms is discussed. In the massless model the
massive quasiparticles do not emerge and presumably there is no transport
theory corresponding to this model. It is not surprising since the
model is anyhow ill defined.Comment: 32 pages, no macro
Wigner functions in covariant and single-time formulations
We will establish the connection between the Lorentz covariant and so-called
single-time formulation for the quark Wigner operator. To this end we will
discuss the initial value problem for the Wigner operator of a field theory and
give a discussion of the gauge-covariant formulation for the Wigner operator
including some new results concerning the chiral limit. We discuss the gradient
or semi-classical expansion and the color and spinor decomposition of the
equations of motion for the Wigner operator. The single-time formulation will
be derived from the covariant formulation by taking energy moments of the
equations for the Wigner operator. For external fields we prove that only the
lowest energy moments of the quark Wigner operator contain dynamical
information.Comment: 92 pages, to appear in Annals of Physics (N.Y.
Landau-Pomeranchuk-Migdal effect in thermal field theory
In recent studies, the production rate of photons or lepton pairs by a quark
gluon plasma has been found to be enhanced due to collinear singularities. This
enhancement pattern is very dependent on rather strict collinearity conditions
between the photon and the quark momenta. It was estimated by neglecting the
collisional width of quasi-particles. In this paper, we study the modifications
of this collinear enhancement when we take into account the possibility for the
quarks to have a finite mean free path. Assuming a mean free path of order
, we find that only low invariant mass photons are
affected. The region where collision effects are important can be interpreted
as the region where the Landau-Pomeranchuk-Migdal effect plays a role in
thermal photon production by bremsstrahlung. It is found that this effect
modifies the spectrum of very energetic photons as well. Based on these results
and on a previous work on infrared singularities, we end this paper by a
reasonable physical picture for photon production by a quark gluon plasma, that
should be useful to set directions for future technical developments.Comment: 28 pages Latex document, 9 postscript figures, typos corrected,
semantics cleanup, final version to appear in Phys. Rev.