Two-loop tensor integral coefficients in OpenLoops

Understand

We present a new and fully general algorithm for the automated construction of the integrands of two-loop scattering amplitudes.

• This is achieved through a generalisation of the open-loops method to two loops.
• The core of the algorithm consists of a numerical recursion, where the various building blocks of two-loop diagrams are connected to each other through process-independent operations that depend only on the Feynman rules of the model at hand.
• This recursion is implemented in terms of tensor coefficients that encode the polynomial dependence of loop numerators on the two independent loop momenta.