1,114 research outputs found
Dileptons in a coarse-grained transport approach
We calculate dilepton spectra in heavy-ion collisions using a coarse-graining
approach to the simulation of the created medium with the UrQMD transport
model. This enables the use of dilepton-production rates evaluated in
equilibrium quantum-field theory at finite temperatures and chemical
potentials.Comment: 4 pages, 2 figures, contribution to the proceedings of "The 15th
International Conference on Strangeness in Quark Matter" (SQM 2015), 06-11
July in Dubna, Russi
Renormalization of a gapless Hartree-Fock approximation to a theory with spontaneously broken O(N)-symmetry
The renormalization of a gapless Phi-derivable Hartree--Fock approximation to
the O(N)-symmetric lambda*phi^4 theory is considered in the spontaneously
broken phase. This kind of approach was proposed by three of us in a previous
paper in order to preserve all the desirable features of Phi-derivable
Dyson-Schwinger resummation schemes (i.e., validity of conservation laws and
thermodynamic consistency) while simultaneously restoring the Nambu--Goldstone
theorem in the broken phase. It is shown that unlike for the conventional
Hartree--Fock approximation this approach allows for a scale-independent
renormalization in the vacuum. However, the scale dependence still persists at
finite temperatures. Various branches of the solution are studied. The
occurrence of a limiting temperature inherent in the renormalized Hartree--Fock
approximation at fixed renormalization scale mu is discussed.Comment: 11 pages, 14 figures / Version accepted by Phys. Rev. D: title and
one reference change
Interpretation of Recent SPS Dilepton Data
We summarize our current theoretical understanding of in-medium properties of
the electromagnetic current correlator in view of recent dimuon data from the
NA60 experiment in In(158 AGeV)-In collisions at the CERN-SPS. We discuss the
sensitivity of the results to space-time evolution models for the hot and dense
partonic and hadronic medium created in relativistic heavy-ion collisions and
the contributions from different sources to the dilepton-excess spectra.Comment: To appear in the proceedings of the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2006) v2:
references added, minor typos correcte
Renormalization in Self-Consistent Approximation schemes at Finite Temperature III: Global Symmetries
We investigate the symmetry properties for Baym's -derivable schemes.
We show that in general the solutions of the dynamical equations of motion,
derived from approximations of the -functional, do not fulfill the
Ward-Takahashi identities of the symmetry of the underlying classical action,
although the conservation laws for the expectation values of the corresponding
Noether currents are fulfilled exactly for the approximation. Further we prove
that one can define an effective action functional in terms of the
self-consistent propagators which is invariant under the operation of the same
symmetry group representation as the classical action. The requirements for
this theorem to hold true are the same as for perturbative approximations: The
symmetry has to be realized linearly on the fields and it must be free of
anomalies, i.e., there should exist a symmetry conserving regularization
scheme. In addition, if the theory is renormalizable in Dyson's narrow sense,
it can be renormalized with counter terms which do not violate the symmetry.Comment: 32 papges, 3 figures, uses ReVTeX 4, V2: Added one more reference,
V3: Corrected some typos, added two more sections about the large-N expansio
Soft Modes, Resonances and Quantum Transport
Effects of the propagation of particles, which have a finite life-time and an
according width in their mass spectrum, are discussed in the context of
transport description. First, the importance of coherence effects
(Landau-Pomeranchuk-Migdal effect) on production and absorption of field quanta
in non-equilibrium dense matter is considered. It is shown that classical
diffusion and Langevin results correspond to re-summation of certain
field-theory diagrams formulated in terms of full non-equilibrium Green's
functions. Then the general properties of broad resonances in dense and hot
systems are discussed in the framework of a self-consistent and conserving
Phi-derivable method of Baym at the examples of the rho-meson in hadronic
matter and the pion in dilute nuclear matter. Further we address the problem of
a transport description that properly accounts for the damping width of the
particles. The Phi-derivable method generalized to the real-time contour
provides a self-consistent and conserving kinetic scheme. We derive a
generalized expression for the non-equilibrium kinetic entropy flow, which
includes corrections from fluctuations and mass-width effects. In special cases
an H-theorem is proved. Memory effects in collision terms give contributions to
the kinetic entropy flow that in the Fermi-liquid case recover the famous
bosonic type T^3 ln T correction to the specific heat of liquid Helium-3. At
the example of the pion-condensate phase transition in dense nuclear matter we
demonstrate important part played by the width effects within the quantum
transport.Comment: submitted to Phys. At. Nucl. (Rus.), the volume dedicated to the
memory of A.B. Migdal. 31 pages, 5 figure
Soft Modes, Quantum Transport and Kinetic Entropy
The effects of the propagation of particles which have a finite life-time and
an according width in their mass spectrum are discussed in the context of
transport descriptions. In the first part the coupling of soft photon modes to
a source of charged particles is studied in a classical model which can be
solved completely in analytical terms. The solution corresponds to a
re-summation of certain field theory diagrams. The general properties of broad
resonances in dense finite temperature systems are discussed at the example of
the -meson in hadronic matter. The second part addresses the problem of
transport descriptions which also account for the damping width of the
particles. The Kadanoff--Baym equation after gradient approximation together
with the -derivable method of Baym provides a self-consistent and
conserving scheme. Memory effects appearing in collision term diagrams of
higher order are discussed. We derive a generalized expression for the
nonequilibrium kinetic entropy flow, which includes corrections from
fluctuations and mass-width effects. In special cases an -theorem is proved.
Memory effects in collision terms provide contributions to the kinetic entropy
flow that in the Fermi-liquid case recover the famous bosonic type
correction to the specific heat of liquid Helium-3.Comment: Contribution to Proc. of Int. Workshop "Kadanoff-Baym Equations -
Progress and Perspectives for Many-Body Physics" Rostock (Germany), September
20-24 1999, ed. M.Bonitz, World Scientific (2000
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