16:00
The 4D 4-point scattering amplitude of massless scalars via a massive exchange can be expressed in a basis of conformal primary particle wavefunctions. In this talk I will show that the resulting celestial amplitude admits a decomposition as a sum over 2D conformal blocks. This decomposition is obtained by contour deformation upon expanding the celestial amplitude in a basis of conformal partial waves. The conformal blocks include intermediate exchanges of spinning light-ray states, as well as scalar states with positive integer conformal weights. The conformal block prefactors are found as expected to be quadratic in the celestial OPE coefficients. Finally, I will comment on implications of this result for celestial holography and discuss some open questions.