Triple-real contribution to the quark beam function in QCD at next-to-next-to-next-to-leading order

We compute the three-loop master integrals required for the calculation of the triple-real contribution to the N${}^3$LO quark beam function due to the splitting of a quark into a virtual quark and three collinear gluons, $q \to q^*+ggg$. This provides an important ingredient for the calculation of the leading-color contribution to the quark beam function at N${}^3$LO.