Scalar-scalar-graviton vertex from Asymptotic Safety

The unitarity and causality properties of asymptotically safe quantum gravity are still unsettled. Scattering amplitudes provide a direct test, but their computation requires fully momentum-dependent correlation functions. In this light, we compute the full scalar-scalar-graviton vertex from Asymptotic Safety within a mostly analytic approximation. Qualitatively, we find the expected logarithmic branch-cut structure, and we correctly recover the double-eikonal soft divergences predicted by Weinberg’s soft theorem. Quantitatively, we find that non-minimal operators are generally as important as the minimal vertex stemming from the scalar kinetic term.