Two-loop integrals for $t\bar{t}γ$ production at hadron colliders in the leading-colour approximation

Abstract

We complete the calculation of the two-loop Feynman integrals required for the next-to-next-to-leading order QCD corrections to on-shell top--antitop production in association with a photon at hadron colliders, in the leading-colour approximation. The same integrals also enter the subleading-colour corrections to top--antitop production in association with a jet. We construct integral bases that satisfy algebraic differential equations. These are largely in canonical form; the exceptions are a few entries, associated with elliptic curves or nested square roots, that depend at most quadratically on the dimensional regulator $ε$. We solve the differential equations in terms of a tailored set of special functions, which will enable the analytic extraction of the two-loop finite remainder. We evaluate these functions by numerically solving the differential equations they satisfy, and show that the resulting routine is fast and stable enough in the physical region for phenomenological applications.