The need to improve our analytical knowledge of the gravitational waveforms emitted by binary systems has recently sparked fervent activity in the application of (classical and/or quantum) post-Minkowskian methods (i.e., perturbative expansions in powers of G) to the study of gravitational dynamics and radiation in the relativistic two-body problem. In this talk, we shall address two recent puzzles that have emerged in this context regarding the angular momentum flux from the system at O(G^2): (1) The physical nature of this term is in question as it can be removed via a suitable supertranslation, and (2) the standard formula of DeWitt-Thorne does not agree with recent quantum-field-theoretic computations, except in the binary’s center-of-mass frame. After a short review of the Bondi-Sachs formalism, we show how the resolution of both puzzles lies in the correct definition of angular momentum. We propose a new balance law for the angular momentum of the system at all orders in G that (1) is supertranslation invariant and (2) agrees with the recent computations based on quantum field theory.
Host: Walter Goldberger (walter.goldberger@yale.edu)