Loop-corrected subleading soft theorem and the celestial stress-tensor

TL;DR

The paper shows that loop-corrected subleading soft graviton theorems follow automatically from the conservation of extended BMS charges when hard and soft fluxes each realize the extended algebra. By constructing an extended radiative phase space with a hard/soft split that factorizes the symplectic form, the authors derive canonical generators matching the BMS fluxes and demonstrate that one-loop corrections are encoded in these fluxes without requiring IR-divergent counterterms. They reformulate the subleading soft theorem as a Ward identity for a celestial stress tensor, deriving a loop-corrected celestial T and proving the associated central charge vanishes to all orders. The results bolster celestial holography as a consistent framework for quantum gravity in asymptotically flat spacetimes and clarify how quantum corrections sit inside the asymptotic symmetry structure.

Abstract

We demonstrate that the one-loop exact subleading soft graviton theorem automatically follows from conservation of the BMS charges, provided that the hard and soft fluxes separately represent the extended BMS algebra at null infinity. This confirms that superrotations are genuine symmetries of the gravitational $\mathcal{S}$-matrix beyond the semiclassical regime. In contrast with a previous proposal, the celestial stress-tensor accounting for the one-loop corrections follows from the gravitational phase space analysis and does not require the addition of divergent counterterms. In addition, we show that the symplectic form on the radiative phase space factorises into hard and soft sectors, and that the resulting canonical generators precisely coincide with the correct BMS fluxes.