GFiRe: a Gauge Field integrator for Reheating

Understand

We present a new numerical algorithm and code, ${\sf GFiRe}$, for solving the non-linear evolution of Abelian gauge fields coupled to complex scalar fields in homogeneous and isotropic spacetimes.

• We adopt a hybrid approach to solving the system: the spatial derivatives are discretized using standard Lattice Gauge Field Theory techniques, whereas the time evolution of the fields and scale factor is implemented with explicit, composite, symplectic integrators.
• An important property of our compound algorithm is that the discretized Gauss constraint is respected exactly, regardless of the order of the symplectic integrator.
• This remains true even when the background expansion is computed "self-consistently"; that is, when the expansion history is computed using spatial averaged components of the energy momentum tensor in the simulation volume.