Exact Solutions In Radiation Reaction And The Radiation-Free Direction

We present new exact solutions of the Landau-Lifshitz (LL) and higher-order LL equations describing particle motion, with radiation reaction, in intense electromagnetic fields. Through these solutions and others we compare the phenomenological predictions of different equations in the context of the conjectured 'radiation-free direction' (RFD). We confirm analytically in several cases that particle orbits predicted by the LL equation indeed approach the RFD at extreme intensities, and give time-resolved signals of this behaviour in radiation spectra.