A Comment on Boundary Correlators: Soft Omissions and the Massless S-Matrix

Abstract

We revisit the extrapolate dictionary for massless scattering in flat spacetime and identify a soft contribution that is typically dropped from the saddle point approximation. We show how to consistently regulate the extrapolation to include both the soft and hard components and identify the boundary correlation functions as a combination of electric and magnetic branch Carrollian correlators. This implies in particular that there are contributions to these boundary correlators that are non-distributional on the celestial sphere. Finally, we close by exploring the utility of the magnetic branch for extracting celestial data from low point correlators: connecting our results to recent work on flat space extrapolate dictionaries and celestial shadow amplitudes.