Quantum graviton scattering with definite helicities in the null surface formulation, Part II: Third-order scattering and the exchange channels \author{C.~N.~Kozameh \and G.~O.~Depaola}

Abstract

We derive the graviton scattering map in the null-surface formulation (NSF) through third order in perturbations of Minkowski spacetime. The rational structure of the exact NSF equations allows a recursive perturbative construction of the cut function, conformal factor, and geometric sources. At third order, matching future and past null-surface reconstructions determines the cubic correction $\delta a^{\mathrm{out}}_{3,\lambda}$ to the outgoing graviton operators. We then study the connected one-loop contribution from $\delta a^{\mathrm{out}}_3 \delta a^{\mathrm{out}}_3$. Delta functions enforce total three-momentum conservation and reduce internal integrations to a single loop momentum. The ultraviolet scaling is controlled by the radiative mode weight $\nu(\omega)=8\pi^2\sqrt{4\pi G}\,\omega^{-3/2}$. As a result, each normalized vertex scales as $\mathcal{O}(K^{-2})$, yielding a radially convergent UV tail bounded by $\int^\infty dK/K^4$. The plane-wave kernel is therefore radially UV finite, while smooth wave packets define the physical domain of the operator distributions. Finally, the corrections preserve Hermitian conjugation and are compatible order by order with a unitary Baker--Campbell--Hausdorff representation of the asymptotic scattering map.