New developments in magnetic reconnection theory.

Although two-dimensional reconnection is now fairly well understood, there have recently been some interesting new developments. Four distinct types of reconnection are possible, namely: viscous (or kinematic) reconnection; extra-slow (or linear) reconnection; slow (or Sweet-Parker) reconnection; and fast (Almost-uniform or Nonuniform) reconnection. An antireconnection theorem has been discovered which states that steady two-dimensional reconnection (with flow across the separatrices) is impossible for slow inviscid flow (and it has also been generalised to three dimensions). Solutions for linear reconnection have been presented and a new theory for the self-consistent time-dependent collapse of an X-point to form a reconnecting current sheet has been developed. The new field of three-dimensional reconnection is only just beginning. Reconnection at null points is discussed.