463 research outputs found
The thermodynamics of the quark-gluon plasma: Self-consistent resummations vs. lattice data
We discuss a recent approach for overcoming the poor convergence of the
perturbative expansion for the thermodynamic potential of QCD. This approach is
based on self-consistent approximations which allow for a gauge-invariant and
manifestly ultraviolet-finite resummation of the essential physics of the hard
thermal/dense loops. The results thus obtained are in good agreement with
available lattice data down to temperatures of about twice the critical
temperature. Calculations for a plasma with finite quark density (i.e., with a
non-zero chemical potential ) are no more difficult than at .Comment: 4 pages LaTeX2e, contribution to the proceedings of the 15th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (QM
2001), Long Island, New York, January 15 - 20, 200
Comparing different hard-thermal-loop approaches to quark number susceptibilities
We compare our previously proposed hard-thermal-loop (HTL) resummed
calculation of quark number susceptibilities using a self-consistent two-loop
approximation to the quark density with a recent calculation of the same
quantity at the one-loop level in a variant of HTL-screened perturbation
theory. Besides pointing out conceptual problems with the latter approach, we
show that it severely over-includes the leading-order interaction effects while
including none of the plasmon term which after all is the reason to construct
improved resummation schemes.Comment: 6 pages, 6 figures. Revised version to appear in Eur. J. Phys.
Thermodynamics of the high-temperature quark-gluon plasma
We review the various methods which have been employed recently to describe
the thermodynamics of the high temperature quark-gluon plasma using weak
coupling techniques, and we compare their results with those of most recent
lattice gauge calculations. Many of the difficulties encountered with
perturbation theory at finite temperature are in fact not specific to QCD but
are present in any field theory at finite temperature and will be discussed
first in the simple example of the scalar field theory. We discuss the merits
and limitations of various techniques which have been used to go beyond
perturbation theory in the soft sector, such as dimensional reduction, screened
perturbation theory or hard-thermal-loop perturbation theory, and Phi-derivable
approximations. In the last part of the review, we focus on the later, which
lead to a remarkably simple expression for the entropy of the quark-gluon
plasma. When complemented with further, physically motivated, approximations,
this approach reproduces accurately the entropy obtained from lattice gauge
calculations at temperatures above 2.5 T_c, where T_c is the deconfinement
temperature. This calculation thus provides also support to the physical
picture of the quark-gluon plasma as a gas of weakly interacting
quasiparticles.Comment: Review for "Quark-Gluon Plasma 3", eds. R.C. Hwa and X.-N. Wang,
World Scientific, Singapore. 63 pages, 21 figures. v2: minor corrections and
2 references adde
Next-to-leading order static gluon self-energy for anisotropic plasmas
In this paper the structure of the next-to-leading (NLO) static gluon self
energy for an anisotropic plasma is investigated in the limit of a small
momentum space anisotropy. Using the Ward identities for the static hard-loop
(HL) gluon polarization tensor and the (nontrivial) static HL vertices, we
derive a comparatively compact form for the complete NLO correction to the
structure function containing the space-like pole associated with magnetic
instabilities. On the basis of a calculation without HL vertices, it has been
conjectured that the imaginary part of this structure function is nonzero,
rendering the space-like poles integrable. We show that there are both positive
and negative contributions when HL vertices are included, highlighting the
necessity of a complete numerical evaluation, for which the present work
provides the basis.Comment: 9 pages, 2 figure
The dynamics of cosmological perturbations in thermal theory
Using a recent thermal-field-theory approach to cosmological perturbations,
the exact solutions that were found for collisionless ultrarelativistic matter
are generalized to include the effects from weak self-interactions in a
model through order . This includes the effects
of a resummation of thermal masses and associated nonlocal gravitational
vertices, thus going far beyond classical kinetic theory. Explicit solutions
for all the scalar, vector, and tensor modes are obtained for a
radiation-dominated Einstein-de Sitter model containing a weakly interacting
scalar plasma with or without the admixture of an independent component of
perfect radiation fluid.Comment: 32 pages, REVTEX, 13 postscript figures included by epsf.st
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