Asymptotic symmetries of gravity and soft theorems for massive particles

TL;DR

This work extends the generalized BMS symmetry ${\cal G}$ to act on time-like infinity and develops a coherent asymptotic phase space for gravity plus massive scalars. By constructing boundary-to-bulk Green's functions that relate null-infinity generators to time-like infinity, the authors derive hard/soft charge decompositions and prove Ward identities that are equivalent to the Weinberg leading and subleading soft graviton theorems, as well as the Cachazo–Strominger subleading theorem for massive external states. The results establish a unified symmetry-soft theorem correspondence in the presence of massive matter and clarify how Green's functions encode the soft factors, while highlighting IR-dressing subtleties that remain to be resolved. The framework provides a consistent picture linking asymptotic symmetries, soft theorems, and massive scattering data, with clear avenues for addressing infrared issues and dressing in future work.

Abstract

The existing equivalence between (generalized) BMS Ward identities with leading and subleading soft graviton theorems is extended to the case where the scattering particles are massive scalars. By extending the action of generalized BMS group off null infinity at late times, we show that there is a natural action of such group not only on the radiative data at null infinity but also on the scattering data of the massive scalar field. This leads to a formulation of Ward identities associated to the generalized BMS group when the scattering states are massive scalars or massless gravitons and we show that these Ward identities are equivalent to the leading and subleading soft graviton theorems.