Primordial magnetic fields via spontaneous breaking of Lorentz invariance

Spontaneous breaking of Lorentz invariance compatible with observational li mits may realistically take place in the context of string theories, possib ly endowing the photon with a mass. In this process the conformal symmetry of the electromagnetic action is broken allowing for the possibility of gen erating large scale (similar to Mpc) magnetic fields within inflationary sc enarios. We show that for reheating temperatures safe from the point of vie w of the gravitino and moduli problem, T-RH less than or similar to 10(9) G eV for m(3/2) approximate to 1 TeV, the strength of the generated seed fiel ds is, in our mechanism, consistent with amplification by the galactic dyna mo processes and can be even as large as to explain the observed galactic m agnetic fields through the collapse of protogalactic clouds. (C) 1999 Elsev ier Science B.V. All rights reserved.