Manifestly conformally covariant description of spinning and charged particles

It is shown that relativistic particles may be described in terms of conformal 0(2,4)-symmetric actions and that this is the maximal $\mathrm{O}\mathrm{}(m,n)\mathrm{}$ symmetry. The position is given as a six-component object where two are made fictitious by the introduction of two additional local invariances to the conventional reparametrization invariance. Spinning particles are obtained through the superspace technique, and interaction with an external electromagnetic field is obtained through minimal coupling in the case of massless particles.