Benchmarking semiclassical approaches to strong-field QED*

The recoil exerted due to photon emission plays a key role in particle dynamics in ultrastrong electromagnetic fields. In laser-matter interactions beyond the current intensity frontier, or in astrophysical environments such as neutron magnetospheres, individual photons of the emitted radiation have energies comparable to that of the electron, making it necessary to take quantum effects into account. However, calculating the scattering matrix element directly from strong-field QED is not possible for many scenarios of interest due to high multiplicity and the complex structure of the electromagnetic fields. Numerical modelling of these interactions is therefore based upon a semiclassical approach, in which probabilistic emission events are coupled to classical electrodynamics using rates calculated in the locally constant field approximation. We discuss recent work in which we provide comprehensive benchmarking of this approach against exact QED results.