Hall current effects in mean-field dynamo theory
  The role of the Hall term on large scale dynamo action is investigated by
means of the First Order Smoothing Approximation. It is shown that the standard
$\alpha$ coefficient is altered, and is zero when a specific double Beltrami
state is attained, in contrast to the Alfv\'enic state for MHD dynamos. The
$\beta$ coefficient is no longer positive definite, and thereby enables dynamo
action even if $\alpha$-quenching were to operate. The similarities and
differences with the (magnetic) shear-current effect are pointed out, and a
mechanism that may be potentially responsible for $\beta < 0$ is advanced. The
results are compared against previous studies, and their astrophysical
relevance is also highlighted.
