Scaling of magnetic reconnection in relativistic collisionless plasmas
  Using fully kinetic simulations, we study the scaling of the inflow speed of collisionless magnetic reconnection from the non-relativistic to ultra-relativistic limit. In the anti-parallel configuration, the inflow speed increases with the upstream magnetization parameter $\sigma$ and approaches the light speed when $\sigma > O(100)$, leading to an enhanced reconnection rate. In all regimes, the divergence of pressure tensor is the dominant term responsible for breaking the frozen-in condition at the x-line. The observed scaling agrees well with a simple model that accounts for the Lorentz contraction of the plasma passing through the diffusion region. The results demonstrate that the aspect ratio of the diffusion region remains $\sim 0.1$ in both the non-relativistic and relativistic limits. 
Yi-Hsin Liu, Fan Guo, William Daughton, Hui Li, Michael Hesse
astro-ph.HE physics.plasm-ph