Revision 1

Accepted · first revision · record

Title: Bootstrap-ready scattering observables with soft photons and gravitons
Plain: In four dimensions, every scattering of charged particles or gravitons emits unlimited numbers of very low-energy photons or gravitons, so the usual scattering amplitude is ill-defined. A replacement object with the properties bootstrap methods need has not been established.
Precise: For 4D theories with massless gauge bosons or gravitons, define nonperturbatively asymptotic observables (dressed amplitudes, Faddeev-Kulish states, or inclusive cross sections) that are infrared finite and obey unitarity, analyticity and crossing in a form usable for numerical bootstrap. An answer is such a definition with proofs of these properties, or a demonstration that one of them must fail.
Settled by: A definition with nonperturbative proofs of unitarity, analyticity and crossing, used in a working numerical bootstrap.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: open
Status note: Generalized crossing relations between different asymptotic observables were proven at tree level in 2023 (Caron-Huot, Giroux, Hannesdottir, Mizera, arXiv:2310.12199).
Posed since: (empty)