The soft graviton theorem factorizes an amplitude with one low-energy graviton into the hard amplitude times a universal sum over external momenta. Gauge invariance of the soft factor requires energy-momentum conservation and universal gravitational coupling.
The Weinberg soft theorem constrains interactions of a massless particle by requiring its soft-emission amplitude to be invariant under shifts of an unphysical polarization. For helicity one it gives charge conservation, for helicity two it gives universal gravitational coupling, and for higher helicity it obstructs generic long-range interactions.
Articles by others on the same topic
The soft graviton theorem is a result in theoretical physics, particularly in the context of quantum gravity and scattering amplitudes. It belongs to a broader class of soft theorems, which describe how physical interactions behave when particles become increasingly low-energy or "soft." Specifically, the soft graviton theorem states that the emission of soft gravitons in scattering processes can be understood in terms of the behavior of the quantum field theory of gravity.