Universal self-force from an extended object approach

We present a simple approach to determine the self-force acting on an accelerating charged particle. In this approach one considers an extended charged object of finite size $\epsilon ,$ and calculates the overall contribution of the mutual electromagnetic forces at the limit $\overrightarrow{\epsilon }0.$ Previous implementations of this approach often yielded a divergent term $\propto 1/\epsilon$ that could not be cured by mass renormalization. Here we explain the origin of this problem and provide a simple method for fixing it, thereby generalizing and simplifying previous analyses. We obtain a consistent, universal, expression for the extended-object self-force, which conforms with Dirac’s well known formula.