Classical Observables from the Exponential Representation of the Gravitational S-Matrix

TL;DR

This paper demonstrates that the two-body scattering angle in gravity can be derived from the exponential representation of the S-matrix, with explicit calculations up to the fourth Post-Minkowskian order, including radiation effects.

Contribution

It introduces a novel approach combining the KMOC formalism with exponential S-matrix representation to compute scattering angles in gravity to high order.

Findings

Scattering angle expressed as a matrix element of the exponential S-matrix.

Explicit fourth Post-Minkowskian order results including radiation effects.

Systematic expansion of momentum kick illustrating iterative structure.

Abstract

By combining the KMOC-formalism with the exponential representation of the scattering matrix we show that the two-body scattering angle is given by the corresponding matrix element of the exponential representation. This holds to all orders in the Post-Minkowskian expansion of gravity when restricted to the conservative sector. Once gravitational radiation is taken into account new terms correcting this relationship appear starting at fourth Post-Minkowskian order. A systematic expansion of the momentum kick is provided to any order, thus illustrating the iterative structure that partly recycles terms from lower orders in the Post-Minkowskian expansion. We provide explicit results for this computation to fourth Post-Minkowskian order, the first complete calculation at this order based on scattering amplitudes.