Type IIB tensionless superstrings in a pp-wave background
  We solve the tensionless string in a constant plane wave background and obtain a hugely degenerate spectrum. This is the case for a large class of plane wave backgrounds. We show that the solution can also be derived as a consistent limit of the quantized tensile theory of IIB strings in a pp-wave. This is in contrast to the situation for several other backgrounds. 
Andreas Bredthauer, Ulf Lindstrom, Jonas Persson, Linus Wulff