3-loop Massive $O(T_F^2)$ Contributions to the DIS Operator Matrix   Element $A_{gg}$
  Contributions to heavy flavour transition matrix elements in the variable flavour number scheme are considered at 3-loop order. In particular a calculation of the diagrams with two equal masses that contribute to the massive operator matrix element $A_{gg,Q}^{(3)}$ is performed. In the Mellin space result one finds finite nested binomial sums. In $x$-space these sums correspond to iterated integrals over an alphabet containing also square-root valued letters. 
J. Ablinger, J. Bl\"umlein, A. De Freitas, A. Hasselhuhn, A. von   Manteuffel, M. Round and C. Schneider
hep-ph