Questioning common wisdom on issues of (i) cause of fast magnetic reconnection, (ii) origin and scale of quadrupole magnetic structure, and (iii) physical reality of Sweet-Parker regime

Our recent work brings to question three generally accepted concepts on reconnection: (1) It has been demonstrated that Hall MHD, hybrid, and full particle simulations yield comparable reconnection rates whereas MHD leads to much smaller rates. The cause of fast reconnection observed in non-MHD models has been attributed to the dispersive properties of whistler mode. We show, using Hall-less hybrid simulations, that fast reconnection is achieved due to ion kinetic effects even when whistlers are non-dispersive. (2) It is well known that Hall currents lead to quadrupole magnetic structure in the reconnection process and the observations of such structures in spacecraft data is attributed to Hall physics. We show that (i) linear kinetic theory predicts the presence of the quadrupole structure, (ii) ion kinetics play a significant role in the generation of the quadrupole structure and the resulting quadrupole structure in a collisionless plasma is always wider than that predicted by Hall MHD. (c) Resistive MHD studies have predicted conditions for the occurrence of Sweet-Parker and Petschek regimes. We show that in a kinetic plasma Sweet-Parker is not a stable configuration.