A no-depolarization theorem for rotator-aided resonance crossing

An rf frequency rotator magnet provides a useful tool for manipulating particle spins in any accelerator or storage ring with polarized beams. This note briefly demonstrates the general idea of the rotator-aided crossing of spin resonance and sketches the proof of a general theorem about the process. The important question of whether this technique can be useful for a specific spin resonance at a particular accelerator involves a detailed analysis of the impact of the rotator on a range of machine parameters