Induced Gluon Radiation in a QCD Medium

TL;DR

Baier, Dokshitzer, Peigné, and Schiff address soft gluon radiation induced by multiple scatterings of a fast parton in a QCD medium, generalizing the Landau-Pomeranchuk-Migdal framework from QED to QCD. They implement the Gyulassy–Wang model of static scattering centers with Debye screening and an eikonal approach to compute the induced gluon spectrum in the soft-gluon regime, emphasizing non-Abelian interference and coherence effects. A key result is coherent suppression relative to the Bethe–Heitler limit, leading to an energy-loss rate that grows with energy as -dE/dz ∝ √E (up to logarithmic factors) and a spectrum with characteristic logarithmic enhancements for the relevant kinematic range. The work also discusses finite-size effects, the large-Nc limit, and the dependence on the medium's transport properties, highlighting implications for parton propagation in quark-gluon plasma and nuclear matter.

Abstract

Soft gluon radiation induced by multiple scattering of a fast quark or gluon propagating through QCD matter is discussed. After revisiting the Landau-Pomeranchuk-Migdal effect in QED we show that large formation times of bremsstrahlung quanta determine the QCD radiation intensity (in analogy to QED) and derive the gluon energy spectrum. Coherent suppression takes place as compared to the Bethe-Heitler situation of independent emissions. As a result the energy loss of fast partons in a QCD medium depends on the incident energy $E$ similarly to QED, $-dE/dz \propto \sqrt{E}$.