Kinetic-Alfvén-wave turbulence in the low beta limit: tearing mediation and electron Landau damping

We report analytical and numerical investigations of sub-ion scale turbulence in weakly collisional, low beta plasmas using a hybrid fluid-kinetic model. Assuming that the energy cascade is mediated by the tearing instability, we derive scalings for the energy spectrum and for the eddy three-dimensional anisotropy. The use of a Hermite formalism to express the velocity space dependence of the electron distribution function allows us to obtain an analytical, zeroth order solution for the Hermite moments of the distribution, which is borne out by numerical simulations. Electron Landau damping is found to play an important role in energy dissipation, enabled by the local weakening of nonlinearities in current sheets.