Aspects of Plane Wave (Matrix) String Dynamics
  We analyse two issues that arise in the context of (matrix) string theories in plane wave backgrounds, namely (1) the use of Brinkmann- versus Rosen-variables in the quantum theory for general plane waves (which we settle conclusively in favour of Brinkmann variables), and (2) the regularisation of the quantum dynamics for a certain class of singular plane waves (discussing the benefits and limitations of regularisations of the plane-wave metric itself). 
Matthias Blau, Martin O'Loughlin, Lorenzo Seri
hep-th gr-qc