A New Covariant Formalism for Kinetic Plasma Simulations in Curved Spacetimes

Low-density astrophysical plasmas are characterized by a large separation of scales between the gyromotion of particles around the magnetic fields and the scales of the system, often making global kinetic simulations computationally intractable. The guiding center formalism, which approximates the trajectory of a charged particle by following its guiding center motion (or drift motion) is a powerful tool to bridge the gap between scales. Despite its usefulness, the guiding center approach has been formulated successfully only in flat spacetimes, limiting its applicability in astrophysical settings. In this talk, I will present a new covariant formalism that leads to kinetic equations in the guiding center limit that are valid in arbitrary spacetimes. I will show results of various numerical experiments demonstrating that the new equations capture all known guiding center drifts while overcoming one severe limitation imposed on numerical algorithms by the fast timescales of the particle gyromotions. I will then discuss an application of this formalism related to the trapping of non-thermal particles in quasi-coherent structures in black-hole accretion flows and their relation to the bright flares observed from them.