Preacceleration in classical electrodynamics

As is well known, the Lorentz-Dirac equation follows by means of a hypothesis of simplicity. When this hypothesis is ruled out, several additional terms can be added to the one that appears in the Lorentz-Dirac equation. We study the equation that considers the two terms explicitly shown by Dirac in his paper. It is shown, on general grounds, that the additional terms are not related to the radiation emitted by the electron; which is fully taken into account by the Larmor term of the Lorentz-Dirac equation. This result is explicitly verified by means of an exact solution of the enlarged Lorentz-Dirac equation that corresponds to a monoenergetic electron in circular orbit. Also it is shown that the additional term diminishes the effect of preacceleration in comparison with the one that comes from the Lorentz-Dirac equation.