2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/13999In these lectures, I describe the formation of defect distributions in first-order phase transitions, then briefly discuss the relevance of defect interactions after a phase transition and the observational signatures of cosmic strings. Some open questions are also discussed.20 pages; Les Houches lecturesAstrophysicsCondensed MatterHigh Energy Physics - Phenomenologytext