Baryogenesis in a magnetized universe

We examine the cosmic baryon asymmetry generated by an almost uniform fossil magnetic field that is twisted on a scale larger than the present cosmological horizon. No extension of the Standard Model of particle physics is assumed or required. At high temperatures where the electroweak symmetry is restored, a hypercharge U(1)Y magnetic field retains net helicity even in the presence of SU(2) sphalerons that cancel baryon and lepton number from the primordial plasma. When the electroweak symmetry breaks, the hypercharge magnetic field decomposes into a U(1)em piece and a second Z0 piece that is not stable within the minimal Standard Model. The helical component of the hypercharge gauge field then induces a large potential through its coupling to fermions, which drives production of baryon number via the axial anomaly. The resulting baryon density is gauge invariant because the vacuum behaves like a superconductor in regions containing Z0-magnetic flux. The magnetic flux density required to generate the observed baryon asymmetry is B0∼10−25(LH0/c)−1/2 G, and decreases with increasing twist length L. This model does not strictly require that the electroweak symmetry was originally restored by thermal effects, and can in principle evade the washout of baryon number associated with a heavy Higgs and a weakly first order phase transition. Indeed, the enormous baryonic charge Nb within the twist volume L3 can be related to the mass hierarchy Mpl/MEW in a simple inflationary model in which the reheating temperature is very low, Trh