Classical Gravitational Spinning-Spinless Scattering at O(G^{2}S^{∞}).

Making use of the recently derived, all-spin, opposite-helicity Compton amplitude, we calculate the classical gravitational scattering amplitude for one spinning and one spinless object at O(G^{2}) and all orders in spin. By construction, this amplitude exhibits the spin structure that has been conjectured to describe Kerr black holes. This spin structure alone is not enough to fix all deformations of the Compton amplitude by contact terms, but when combined with considerations of the ultrarelativistic limit we can uniquely assign values to the parameters remaining in the even-in-spin sector.

Relating Gauge and Gravity Theories in the Large Mass Limit.

We show how to double copy heavy quark effective theory (HQET) to heavy black hole effective theory (HBET) for spin s≤1. In particular, the double copy of spin-s HQET with scalar QCD produces spin-s HBET, while the double copy of spin-1/2 HQET with itself gives spin-1 HBET. Finally, we present novel all-order-in-mass Lagrangians for spin-1 heavy particles.