Two-loop leading-color helicity amplitudes for three-photon production at the LHC

We calculate all planar contributions to the two-loop massless helicity amplitudes for process $q\bar q\to \gamma\gamma\gamma$. The results are presented in fully analytic form terms of functional basis proposed recently by Chicherin and Sotnikov. With this publication we provide already used us NNLO QCD calculation LHC $pp\to \gamma\gamma\gamma$ [Chawdhry et al. (2019)]. Our agree with a recent same amplitude [Abreu (2020)] which was performed using different techniques. combine several modern computational techniques, notably, solutions IBP identities, finite-field reconstruction techniques as well approach [Chen (2019)] efficiently projecting amplitudes. framework appears well-suited multileg complete sets master integrals exist.