23 research outputs found
Hard parton damping in hot QCD
The gluon and quark collisional widths in hot QCD plasmas are discussed with
emphasis on temperatures near Tc, where the coupling is large. Considering the
effect on the entropy, which is known from lattice calculations, it is argued
that the width of the partons, which in the perturbative limit is given by
gamma ~ g^2 ln(1/g) T, should be sizeable at intermediate temperatures but has
to be small close to Tc. This behavior implies a substantial reduction of the
radiative energy loss of jets near Tc.Comment: invitetd talk given at 'Hot Quarks 04', July 18-24 2004, Taos Valley,
NM, US
Collisional Energy Loss of a Fast Muon in a Hot QED Plasma
We calculate the collisional energy loss of a muon of high energy in a
hot QED plasma beyond logarithmic accuracy, i.e., we determine the constant
terms of order O(1) in . Considering first the
-channel contribution to , we show that the terms are
sensitive to the full kinematic region for the momentum exchange in elastic
scattering, including large values . We thus redress a previous
calculation by Braaten and Thoma, which assumed and could not find the
correct constant (in the large limit). The relevance of 'very hard'
momentum transfers then requires, for consistency, that and -channel
contributions from Compton scattering must be included, bringing a second
modification to the Braaten-Thoma result. Most importantly, Compton scattering
yields an additional large logarithm in . Our results might have
implications in the QCD case of parton collisional energy loss in a quark gluon
plasma.Comment: 26 pages, 3 figures, JHEP styl
Turning on the Charm
We argue that the strong jet quenching of heavy flavors observed in heavy-ion
collisions is to a large extent due to binary scatterings in the quark-gluon
plasma. It can be understood from first principles: the charm collision
probability beyond logarithmic accuracy and Markov evolution.Comment: 4 pages, 5 figure
Comment on `Pressure of Hot QCD at large N_f'
It is argued why quasiparticle models can be useful to describe the
thermodynamics of hot QCD excluding, however, the case of a large number of
flavors, for which exact results have been calculated by Moore.Comment: 5 pages, 2 figures (version accepted for publication
HTL Resummation of the Thermodynamic Potential
Starting from the Phi-derivable approximation scheme at leading-loop order,
the thermodynamical potential in a hot scalar theory, as well as in QED and
QCD, is expressed in terms of hard thermal loop propagators. This
nonperturbative approach is consistent with the leading-order perturbative
results, ultraviolet finite, and, for gauge theories, explicitly
gauge-invariant. For hot QCD it is argued that the resummed approximation is
applicable in the large-coupling regime, down to almost twice the transition
temperature.Comment: minor changes, to appear in PRD, 27 pages, 15 eps figure
Collisional energy loss of a fast heavy quark in a quark-gluon plasma
We discuss the average collisional energy loss dE/dx of a heavy quark
crossing a quark-gluon plasma, in the limit of high quark energy E >> M^2/T,
where M is the quark mass and T >> M is the plasma temperature. In the fixed
coupling approximation, at leading order dE/dx \propto \alpha_s^2, with a
coefficient which is logarithmically enhanced. The soft logarithm arising from
t-channel scattering off thermal partons is well-known, but a collinear
logarithm from u-channel exchange had previously been overlooked. We also
determine the constant beyond those leading logarithms. We then generalize our
calculation of dE/dx to the case of running coupling. We estimate the remaining
theoretical uncertainty of dE/dx, which turns out to be quite large under RHIC
conditions. Finally, we point out an approximate relation between dE/dx and the
QCD Debye mass, from which we derive an upper bound to dE/dx for all quark
energies.Comment: 6 page
Hard gluon damping in hot QCD
The gluon collisional width in hot QCD plasmas is discussed with emphasis on
temperatures near , where the coupling is large. Considering its effect on
the entropy, which is known from lattice calculations, it is argued that the
width, which in the perturbative limit is given by , should be sizeable at intermediate temperatures but has to be small close
to . Implications of these results for several phenomenologically relevant
quantities, such as the energy loss of hard jets, are pointed out.Comment: uses RevTex and graphic
Quark Dispersion Relation and Dilepton Production in the Quark-Gluon Plasma
Under very general assumptions we show that the quark dispersion relation in
the quark-gluon plasma is given by two collective branches, of which one has a
minimum at a non-vanishing momentum. This general feature of the quark
dispersion relation leads to structures (van Hove singularities, gaps) in the
low mass dilepton production rate, which might provide a unique signature for
the quark-gluon plasma formation in relativistic heavy ion collisions.Comment: 6 pages, Revtex, 2 PostScript figures, revised version to be
published in Phys. Rev. Let