Slow decay of cosmic magnetic fields superadiabatically in curvature-torsion scales

Abstract

Recently Barrow, and Tsagas [Phys Rev D 77: 107302, (2008)] have shown that slow decay of cosmological magnetic slowly decay in FRW universes on curvature scales as $B\sim{a^{-1}}$ in the context of general relativity (GR). This helps possible amplification of cosmic magnetic fields. In this paper starting from dynamo equations in spacetimes with torsion we obtain also slow decay of magnetic fields naturally on curvature-torsion scales of Riemann-Cartan spacetime on a de Sitter universe. In this case the constant of proportionality between the magnetic field and the curvature scale is the torsion in the present universe. Thus the B-field becomes $B\sim{\frac{{\eta}}{H_{0}}Ta^{-1}}$ where T is torsion vector modulus, $H_{0}$ is the Hubble constant and $\eta$ is the diffusive scale.