Topological defects from Kibble mechanism; scaling solution with reconnection
Cosmic strings form when a U(1) symmetry breaks during a cosmological phase transition (Kibble 1976). The network evolves toward a scaling solution: the characteristic length ξ ∝ t grows with the Hubble time. Loops shrink by radiating gravitational waves with power P = ΓGμ²c, where Γ ≈ 50.