Classical spinning soft factors from gauge theory amplitudes

In this short note, we analyse low energy electromagnetic radiation for spinning particles using the KMOC formalism and the quantum soft theorems. In particular, we study low energy electromagnetic radiation emitted by the so-called $\sqrt{\text{Kerr}}$ object. The $\sqrt{\text{Kerr}}$ is a solution of the free Maxwell’s equations with infinite multipole moments expressed solely in terms of the charge(Q), mass(m) and spin(S) of the classical object . We consider the scattering of two $\sqrt{\text{Kerr}}$ particles and using the KMOC formalism generalised to spinning particles, we perturbatively prove the classical subleading soft photon theorem to leading order in the low deflection parameter and to $\mathcal{O}(S_1{S}_2)$ in spin.