Interparticle-Fields Amplified Radiation Reaction

The trajectories of relativistic particles in an intense electromagnetic field can be described by the Landau-Lifshitz (LL) equation, where radiation reaction (RR) is accounted for via a self-force, and interparticle fields are often neglected as an approximation. Yet, the inclusion of interparticle fields is necessary to ensure energy-momentum conservation, in particular during coherent emission. We present a simple generalization of the LL equation for many bodies, which includes coherence effects in the self-force. This theory is shown both analytically and numerically to satisfy energy-momentum conservation as expected. By simulating a neutral, relativistic bunch of electrons and positrons ($e^-/e^+$) colliding with a laser pulse, we show that the inclusion of interparticle fields can significantly affect the particle dynamics and the emission spectrum, even though the external field dominates over the interparticle fields.
Comment: 13 pages, 3 figures