Solvable N=(4,4) Type IIA String Theory in Plane-Wave Background and   D-Branes
  We study various aspects of N=(4,4) type IIA GS superstring theory in the pp-wave background, which arises as the compactification of maximally supersymmetric eleven-dimensional pp-wave geometry along the spacelike isometry direction. We show the supersymmetry algebra of N=(4,4) worldsheet supersymmetry as well as non-linearly realized supersymmetry. We also give quantization of closed string and open string incorporating various boundary conditions. From the open string boundary conditions, we find configurations of D-branes which preserve half the supersymmetries. Among these we identify D4 brane configurations with longitudinal five brane configurations in matrix model on the eleven-dimensional pp-wave geometry. 
Seungjoon Hyun, Hyeonjoon Shin