Radiation Reaction from Soft Theorems

TL;DR

This paper establishes a novel connection between radiation reaction effects at the third post-Minkowskian order and soft theorems, simplifying calculations and confirming previous results in gravity theories.

Contribution

It introduces a new link between radiation reaction and soft theorems at 3PM order, applicable to Einstein gravity and scalar-tensor theories, bypassing complex loop computations.

Findings

Confirmed agreement with Damour's recent results in Einstein gravity.

Extended the soft theorem connection to Jordan-Brans-Dicke theory.

Supported the general validity of the connection through unitarity and analyticity arguments.

Abstract

Radiation reaction (RR) terms at the third post-Minkowskian (3PM) order have recently been found to be instrumental in restoring smooth continuity between the non-relativistic, relativistic, and ultra-relativistic (including the massless) regimes. Here we propose a new and intriguing connection between RR and soft (bremsstrahlung) theorems which short-circuits the more involved conventional loop computations. Although first noticed in the context of the maximally supersymmetric theory, unitarity and analyticity arguments support the general validity of this 3PM-order connection that we apply, in particular, to Einstein's gravity and to its Jordan-Brans-Dicke extension. In the former case we find full agreement with a recent result by Damour obtained through a very different reasoning.