The acceleration-dependent mass increase and acceleration limit of a charged sphere in uniform circular motion*

The equation of motion for a charged particle, though well established, still has many problems. In particular, when the particle is located in strong electromagnetic fields, the equation of motion becomes unsolvable because of the strong radiation reaction (the self-force). Such strong fields can be observed frequently in astrophysical conditions. Nowadays it is becoming feasible to generate such strong fields in laboratories owing to the rapid development of laser technologies. Naturally, it motivates researchers to investigate the radiation reaction experimentally as well as theoretically. We recently published a new theoretical model of the self-force of a charged sphere undergoing uniform acceleration [Phys. Lett. A 407 (2021) 127445]. In this new model, we tried to resolve the historical paradox about the radiation emission of a uniformly accelerated charge by assuming that a particle is a charged sphere embedded with an image of a point charge on its surface. From this assumption, we have found that the effective mass of the sphere increases by its acceleration (not velocity). The radiation reaction on a uniformly accelerated charged particle, missing in the classical model, could be explained by the acceleration-dependent mass increase. In this talk, we present the self-force of a charged sphere in a uniform circular motion. It will be shown that the effective mass of the sphere in the circular motion also increases by the acceleration. We investigate a physical origin of the acceleration-dependent mass increase. Furthermore, we show that the acceleration in a uniform circular motion can potentially have an upper limit, which is an interesting unexpected consequence of the charged-sphere model. Possible link to the Schwinger limit will be discussed briefly.