Current sheet bifurcation and collapse in electron magnetohydrodynamics.

Inertial effects in nonlinear magnetic reconnection are studied within the context of two-dimensional electron magnetohydrodynamics with resistive and viscous dissipation. Families of nonlinear solutions for relevant current sheet parameters are predicted and confirmed numerically in all regimes of interest. Electron inertia becomes important for current sheet thicknesses δ below the inertial length d_e. In this case, in the absence of electron viscosity, the sheet thickness experiences a nonlinear collapse to arbitrarily small scales. Viscosity regularizes solutions at small scales. The transition between resistive and viscous regimes features a hysteresis bifurcation that describes suitable current sheet solutions and reconnection rates. Away from transition, the nonlinear reconnection rate is found not to be explicitly dependent on the electron inertia or dissipation coefficients. [ABSTRACT FROM AUTHOR]