  A new regime of fast magnetic reconnection with an out-of-plane (guide)
magnetic field is reported in which the key role is played by an electron
pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations
of state in the generalized Ohm's law, which even dominates the Hall term. A
description of the physical cause of this behavior is provided and
two-dimensional fluid simulations are used to confirm the results. The electron
pressure anisotropy causes the out-of-plane magnetic field to develop a
quadrupole structure of opposite polarity to the Hall magnetic field and gives
rise to dispersive waves. In addition to being important for understanding what
causes reconnection to be fast, this mechanism should dominate in plasmas with
low plasma beta and a high in-plane plasma beta with electron temperature
comparable to or larger than ion temperature, so it could be relevant in the
solar wind and some tokamaks.
