Multiscale simulations of particle acceleration in astrophysical shocks

Particle acceleration in astrophysical shocks is central to the production of nonthermal radiation from a large variety of astrophysical sources, ranging from supernova remnants to GRB jets. The process of acceleration is an intrinsically multi-scale problem, connecting plasma microphysics at the shock to self-generated instabilities driven by accelerated particles far from the shock. While considerable progress has been made in studying acceleration with ab-initio particle-in-cell (PIC) simulations, future studies will need to address the range of scales with more computationally efficient methods. I will discuss the efforts at studying shock acceleration with fully kinetic and ``hybrid'' simulations, that combine the salient features of PIC schemes with computational efficiency of fluid methods. These methods allow the study of long-term back-reaction of accelerated particles on the shock structure, and the effects of global shock geometry on the local acceleration physics.