Stringent magnetic field limits from early universe dynamos cosmology
  with torsion
  Earlier Bamba et al [JCAP (2012)] have obtained cosmological magnetic fields
in teleparallel torsion theories of gravity that are not compatible with
galactic dynamos. This result agrees with previous ones obtained by the author
which shows [Phys Lett B (2012)] that anti-dynamo generalised theorem to
torsion theories forbides such kind of dynamos to explain galactic magnetic
fields of the order of ${\mu}$G. More recently the author has suggested [IJAA
(2012)] that a sort of Biermann battery could be obtained in torsioned
cosmology. Nevertheless in this paper we show that this can be a particular
result, since the second author did not took into account mean field dynamo
equations in torsion field background. Actually it is shown that amplification
or not of the magnetic field depends upon handness sign of the torsion field
vector. It is shown that density fluctuations of spin-torsion density implies
also a possibility of amplification of the cosmic magnetic fields. From WMAP
data it is possible to estimate the spin-torsion fluctuation as $10^{-6}$ which
represents an order of magnitude lower than the matter density. By making use
of the gravitational couling of type $RF^{2}$ one obtains $10^{37}G$ for the
Planck era magnetic field, which is a much more stringent limit than the ones
obtained earlier. The magnetic field obtained today is $10^{-23}G$ is obtained
which is able to seed galactic dynamos.
