A new constraint on mean-field galactic dynamo theory
  Appealing to an analytical result from mean-field theory, we show, using a
generic galaxy model, that galactic dynamo action can be suppressed by
small-scale magnetic fluctuations. This is caused by the magnetic analogue of
the R\"{a}dler or $\Omega\times J$ effect, where rotation-induced corrections
to the mean-field turbulent transport result in what we interpret to be an
effective reduction of the standard $\alpha$ effect in the presence of
small-scale magnetic fields.
