PP-waves in AdS Gauged Supergravities and Supernumerary Supersymmetry
  Purely gravitational pp-waves in AdS backgrounds are described by the generalised Kaigorodov metrics, and they generically preserve 1/4 of the maximum supersymmetry allowed by the AdS spacetimes. We obtain 1/2 supersymmetric purely gravitational pp-wave solutions, in which the Kaigorodov component is set to zero. We construct pp-waves in AdS gauged supergravities supported by a vector field. We find that the solutions in D=4 and D=5 can then preserve 1/2 of the supersymmetry. Like those in ungauged supergravities, the supernumerary supersymmetry imposes additional constraints on the harmonic function associated with the pp-waves. These new backgrounds provide interesting novel features of the supersymmetry enhancement for the dual conformal field theory in the infinite-momentum frame. 
J. Kerimo and H. Lu