Charged test particle scattering and effective one-body metrics with spin

Using recently developed techniques, we consider weak-field test particle scattering angle calculations in two distinct settings: Charged particles spacetimes of charged sources and effective one-body theory with spin. We present up to $\mathcal{O}({G}^{4})$ the Kerr-Newman metric, including electromagnetic interactions second order charge. Coulomb is also discussed, well-known Darwin formula rederived by resummation. An metric for a Kerr-Schwarzschild binary constructed post-Minkowskian framework $\mathcal{O}({G}^{2})$ first Facilitated explicit calculations, our approach equivalent existing literature through gaugelike transformations. Finally, investigate if Newman-Janis algorithm applied an nonspinning binaries represents system