2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/196932The 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.16 pages, no figures. Accepted for pubblication on Classical and Quantum GravityGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext