The Longitudinal Heavy Quark Structure Function F_{L}^{Q\bar{Q}} in the   Region Q^2 \gg m^2 at O(\alpha_s^3)
  The logarithmic and constant contributions to the Wilson coefficient of the longitudinal heavy quark structure function to $O(\alpha_s^3)$ are calculated using mass factorization techniques in Mellin space. The small $x$ behaviour of the Wilson coefficient is determined. Numerical illustrations are presented. 
J. Bl\"umlein, A. De Freitas, W.L. van Neerven, and S. Klein