Angular Momentum Loss at Fourth Post-Minkowskian Order

Abstract

We calculate the total loss of angular momentum for a gravitational scattering of two non-spinning point-like objects at $\mathcal{O}(G^4)$. Our methodology combines use of both amplitudes and worldline-based methods. We derive the integrand from two copies of the gravitational waveform with cuts on massive lines arising naturally from the worldline. We then glue these two copies and evaluate the resulting phase-space integrals using reverse unitarity, in the amplitudes spirit. We obtain separately the radiated angular momentum and the static contribution that, at this order, is entirely determined by the initial shear and the linear memory. Combining these two terms, we derive relativistic expressions for the angular momentum loss and for the infrared-finite component of the mass dipole loss, which in the low-velocity limit match results available in the literature. We also use this result to derive the conservative deflection angle at $\mathcal{O}(G^5)$ and first self-force order.