PP-waves, Israel's Matching conditions, Brane-world scenarios and BPS   states in gravity
  The matching between two 4-dimensional PP-waves is discussed by using Israel's matching conditions. Physical consequences on the dynamics of (cosmic) strings are analyzed. The extension to space-time of arbitrary dimension is discussed and some interesting features related to the brane world scenario, BPS states in gravity and Dirac-like quantization conditions are briefly described. 
F. Canfora, G. Vilasi