4,184 research outputs found
Stopping distance for high energy jets in weakly-coupled quark-gluon plasmas
We derive a simple formula for the stopping distance for a high-energy quark
traveling through a weakly-coupled quark gluon plasma. The result is given to
next-to-leading-order in an expansion in inverse logarithms ln(E/T), where T is
the temperature of the plasma. We also define a stopping distance for gluons
and give a leading-log result. Discussion of stopping distance has a
theoretical advantage over discussion of energy loss rates in that stopping
distances can be generalized to the case of strong coupling, where one may not
speak of individual partons.Comment: 20 pages, 4 figures [change from v1: fixed embarrassing reference
error
Inhomogeneous quadratic congruences
We investigate the density of integer solutions to certain binary
inhomogeneous quadratic congruences and use this information to detect almost
primes on a singular del Pezzo surface of degree 6.Comment: 24 page
How does transverse (hydrodynamic) flow affect jet-broadening and jet-quenching ?
We give the modification of formulas for -broadening and energy
loss which are necessary to calculate parton interactions in a medium with
flow. Arguments are presented leading to the conclusion that for large
-spectra observed in heavy ion collisions at RHIC, the influence of
transverse flow on the determination of the "quenching power" of the produced
medium is small. This leaves open the question of the interpretation of data in
a consistent perturbative framework.Comment: 8 pages and 4 figures; version v2 includes more consistent notations
and correction of fig.2; version v3 contains a misprint correction, an added
sentence in section 3C and in the Introduction as well as in section 4 a
rephrasing of comments about references [31,32,35
Medium-induced radiative energy loss; equivalence between the BDMPS and Zakharov formalisms
We extend the BDMPS formalism for calculating radiative energy loss to the
case when the radiated gluon carries a finite fraction of the quark momentum.
Some virtual terms, previously overlooked, are now included. The equivalence
between the formalism of BDMPS and that of B.Zakharov is explicitly
demonstrated.Comment: 23 pages, 7 eps figures; uses amsmat
On the Angular Dependence of the Radiative Gluon Spectrum
The induced momentum spectrum of soft gluons radiated from a high energy
quark produced in and propagating through a QCD medium is reexamined in the
BDMPS formalism. A mistake in our published work (Physical Review C60 (1999)
064902) is corrected. The correct dependence of the fractional induced loss
as a universal function of the variable
where is the size of the medium and
the transport coefficient is presented. We add the proof that the
radiated gluon momentum spectrum derived in our formalism is equivalent with
the one derived in the Zakharov-Wiedemann approach.Comment: LaTex, 5 pages, 1 figur
Laser-dressed vacuum polarization in a Coulomb field
We investigate quantum electrodynamic effects under the influence of an
external, time-dependent electromagnetic field, which mediates dynamic
modifications of the radiative corrections. Specifically, we consider the
quantum electrodynamic vacuum-polarization tensor under the influence of two
external background fields: a strong laser field and a nuclear Coulomb field.
We calculate the charge and current densities induced by a nuclear Coulomb
field in the presence of a laser field. We find the corresponding induced
scalar and vector potentials. The induced potential, in first-order
perturbation theory, leads to a correction to atomic energy levels. The
external laser field breaks the rotational symmetry of the system.
Consequently, the induced charge density is not spherically symmetric, and the
energy correction therefore leads to a "polarized Lamb shift." In particular,
the laser generates an additional potential with a quadrupole moment. The
corresponding laser-dressed vacuum-polarization potential behaves like 1/r**3
at large distances, unlike the Uehling potential that vanishes exponentially
for large r. Our investigation might be useful for other situations where
quantum field theoretic phenomena are subjected to external fields of a rather
involved structure.Comment: 13 pages, RevTe
Saturation and shadowing in high-energy proton-nucleus dilepton production
We discuss the inclusive dilepton cross section for proton (quark)-nucleus
collisions at high energies in the very forward rapidity region. Starting from
the calculation in the quasi-classical approximation, we include low-x
evolution effects in the nucleus and predict leading twist shadowing together
with anomalous scaling behaviour.Comment: 32 pages, LaTex, 6 figures, a few modifications of the tex
Coulomb effects in the spin-dependent contribution to the intra-beam scattering rate
Coulomb effects in the intra-beam scattering are taken into account in a way
providing correct description of the spin-dependent contribution to the beam
loss rate. It allows one to calculate this rate for polarized beams
at arbitrarily small values of the ratio ,
characterizing relative change of the electron energy in the laboratory system
during scattering event.Comment: 8 pages, 2 figure
Does parton saturation at high density explain hadron multiplicities at LHC?
An addendum to our previous papers in Phys. Lett. B539 (2002) 46 and Phys.
Lett. B502 (2001) 51, contributed to the CERN meeting "First data from the LHC
heavy ion run", March 4, 2011Comment: 6 pages, contribution to the CERN meeting "First data from the LHC
heavy ion run", March 4, 201
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