  Spontaneous breaking of Lorentz invariance may take place in string theories,
possibly endowing the photon with a mass. This leads to the breaking of the
conformal symmetry of the electromagnetic action allowing for the generation
within inflationary scenarios of magnetic fields over $Mpc$ scales. We show
that the generated fields are consistent with amplification by the galactic
dynamo processes and can be as large as to explain the observed galactic
magnetic fields through the collapse of protogalactic clouds.
