Cosmological magnetic fields as string dynamo seeds and axion fields in torsioned spacetime

Abstract

In this paper two examples of the generation cosmological magnetic fields (CMF) are given. The first is the string dynamo seed cosmological magnetic field estimated as Bseed∼10-24 Gauss from a static spin polarised cylinder in Einstein-Cartan-Maxwell spacetime. The string dynamo seeds from a static spin polarised cylinder is given by B∼σ2R2 where σ is the spin-torsion density while R is the string radius. The B-field value above is able to seed galactic dynamo. In the BBN the magnetic fields around 1012 Gauss give rise to a string radius as small as 1017lP where lP is the Planck length. The second is the CMF from axionic torsion field which is given by Bseed∼10-27 Gauss which is stronger than the primordial magnetic field BBICEP2∼10-30 Gauss from the BICEP2 recent experiment on primordial gravitational waves and cosmological inflation to axionic torsion. The interaction Lagrangean between axionic torsion scalar ϕ and magnetic fields used in this last example is given by f2(ϕ)FμνFμν. A similar lagrangean has been used by K. Bamba et al. [JCAP 10 (2012) 058] so generate magnetic fields without dynamo action. Since axionic torsion can be associated with axionic domain walls both examples discussed here could be consider as topological defects examples of the generation of primordial magnetic fields in universes endowed with spacetime torsion.