Speaker
Description
Celestial scattering amplitudes for massless particles are Mellin transforms of momentum-space scattering amplitudes with respect to the energies of the external particles, and behave as conformal correlators on the celestial sphere. However, there are few explicit cases of well-defined celestial amplitudes, particularly for gravitational theories: the mixing between low- and high-energy scales induced by the Mellin transform generically yields divergent integrals. In this talk, I will describe the results of a recent paper(in coll. with Tim Adamo, Wei Bu and Bin Zhu) where we argue that the most natural object to consider is the gravitational amplitude dressed by an oscillating phase arising from semi-classical effects known as eikonal exponentiation. This leads to gravitational celestial amplitudes which are analytic, apart from a set of poles at integer negative conformal dimensions, whose degree and residues we characterize. I'll also present the large conformal dimension limits, and provide an asymptotic series representation for these celestial eikonal amplitudes. Our investigation covered two different frameworks, related by eikonal exponentiation: 2→2 scattering of scalars in flat spacetime and 1→1 scattering of a probe scalar particle in a curved, stationary spacetime. These provide data which any putative celestial dual for Minkowski, shockwave or black hole spacetimes must reproduce. I'll finally comment on dispersion and monodromy relations that these celestial amplitudes obey and mention the Carrollian situation.
