Stochastic reacceleration of relativistic electrons by turbulent
  reconnection: a mechanism for cluster-scale radio emission ?
  In this paper we investigate a situation where relativistic particles are
reaccelerated diffusing across regions of reconnection and magnetic dynamo in
super-Alfvenic, incompressible large-scale turbulence. We present an
exploratory study of this mechanism in the intra-cluster-medium (ICM). In view
of large-scale turbulence in the ICM we adopt a reconnection scheme that is
based on turbulent reconnection and MHD turbulence. In this case particles are
accelerated and decelerated in a systematic way in reconnecting and
magnetic-dynamo regions, respectively, and on longer time-scales undergo a
stochastic process diffusing across these sites (similar to second-order
Fermi). Our study extends on larger scales numerical studies that focused on
the acceleration in and around turbulent reconnecting regions. We suggest that
this mechanism may play a role in the reacceleration of relativistic electrons
in galaxy clusters providing a new physical scenario to explain the origin of
cluster-scale diffuse radio emission. Indeed differently from current turbulent
reacceleration models proposed for example for radio halos this mechanism is
based on the effect of large-scale incompressible and super-Alfvenic
turbulence. In this new model turbulence governs the interaction between
relativistic particles and magnetic field lines that diffuse, reconnect and are
stretched in the turbulent ICM.
