“…It is interesting that the Sommerfeld formula predicts the rate of the energy loss due to superluminal electron vacuum radiation which is close to the results of modern calculations for the Cherenkov radiation by a finite-size, "spherically symmetric" charged tachyon, see [22,23,24]. Note, it is rather high, but one can expect that such a radiation will be strongly suppressed in a high energy range (for the photon energies comparable with the energy of the tachyon) after introduction of a longitudinal tachyon form-factor [25] (see also Appendix B), and due to quantum selection rules [1].…”