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 $p_{\perp}$-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 $p_{\perp}$-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 $R(\theta_{{\rm cone}})$ as a universal function of the variable $\theta^2_{{\rm cone}} L^3 \hat q$ where $L$ is the size of the medium and $\hat q$ 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 $e^{\pm}$ beams at arbitrarily small values of the ratio $\delta \varepsilon/\varepsilon$, 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