Electromagnetic drift

We define, by a natural way, a velocity field at a space region occupied by an electromagnetic field. By using that velocity field we can obtain a relativistic expression for drift velocity of an electrically charged particle in presence of an electromagnetic field. Taking in account temporal components and the temporal space of the energy momentum tensor of electromagnetic field, and also his Lorentz invariants, it is possible to define the concept of electromagnetic field “mass density in rest”. Then, we can obtain a very important expression for the velocity field in terms of electromagnetic field energy density and mass density. Also we can show that if we calculate the drift velocity for an electromagnetic field such that ⃗E · ⃗B = 0 and B = √εE with ε the dielectrically permittivity of a transparent media, then drift velocity is the same as light velocity in such media.