CLASSICAL GLUON RADIATION IN ULTRARELATIVISTIC NUCLEUS-NUCLEUS COLLISIONS

The classical Yang-Mills equations are solved perturbatively in covari ant gauge for a collision of two ultrarelativistic nuclei. The nuclei are taken as ensembles of classical color charges on eikonal trajector ies. The classical gluon field is computed in coordinate space up to c ubic order in the coupling constant g, We construct the Feynman diagra ms corresponding to this field and show the equivalence of the classic al and diagrammatic approaches. An argument is given which demonstrate s that at higher orders in g the classical description of the process breaks down. As an application, we calculate the energy, number, and m ultiplicity distributions of produced soft gluons and reproduce earlie r results by Gunion and Bertsch and by Kovner, McLerran, and Weigert.