Modeling of axion and electromagnetic fields interaction in particle-in-cell simulations

The axion, a theoretically well-motivated particle, has been searched for extensively via its hypothetical interactions with ordinary matter and fields. Recently, a new axion detection approach has been considered utilizing the ultra-intense electromagnetic fields produced by laser–plasma interactions. However, a detailed simulation tool has not hitherto been available to help understand the axion-coupled laser–plasma interactions in such a complex environment. In this paper, we report a custom-developed particle-in-cell (PIC) simulation method that incorporates the axion field, the electromagnetic fields, and their interactions. The axion field equation and modified Maxwell’s equations are numerically solved, with the axion-induced modulation of the electromagnetic field being treated as a first-order perturbation to handle the huge orders of magnitude difference between the two types of field. The simulation is benchmarked with well-studied effects such as axion–photon conversion and the propagation of an extremely weak laser pulse in a magnetized plasma. Such an extended PIC simulation provides a powerful tool to study axions under ultra-intense electromagnetic fields in the laboratory or in astrophysical processes.