On the role of a nonscalar electron pressure in the collisionless magnetic reconnection

Collisionless tearing instability in a sheared force-free magnetic field is considered in the framework of electron magnetohydrodynamics. A rigorous analytical analysis demonstrates that the bulk inertia of electrons is the dominant reconnection mechanism in a sufficiently low-$β$ plasma, when the reconnection current sheet width exceeds the electron gyroradius. Otherwise a fluidlike approach fails, and fully kinetic treatment of the problem is required. A recently raised issue of the role of the electron gyroviscous cancellation in collisionless reconnection is also addressed.