Coherent medium-induced gluon radiation in hard forward $1\to 1$ partonic processes

Abstract

We revisit the medium-induced coherent radiation associated to hard and forward (small angle) scattering of an energetic parton through a nuclear medium. We consider all $1\to 1$ hard forward processes ($g\to g$, $q\to q$, $q\to g$ and $g\to q$), and derive the energy spectrum of induced coherent radiation rigorously to all orders in the opacity expansion and for the specific case of a Coulomb scattering potential. We obtain a simple general formula for the induced coherent spectrum, which encompasses the results corresponding to previously known special cases.

Comments: 35 pages, 10 figures; title changed, introduction developed and references added, detailed discussion added in Section VI, all results unchanged; version v2 corresponds to the published version