Cosmic strings from preheating

We investigate nonthermal phase transitions that may occur after post-inflationary preheating in a simple model of a two-component scalar field with the effective potential λ(φi2−v2)2/4, where φ1 is identified with the inflaton field. We use three-dimensional lattice simulations to investigate the full nonlinear dynamics of the model. Fluctuations of the fields generated during and after preheating temporarily make the effective potential convex in the φ1 direction. The subsequent nonthermal phase transition with symmetry breaking leads to formation of cosmic strings even for v≫1016 GeV. This mechanism of string formation, in a modulated (by the oscillating field φ1) phase transition, is different from the usual Kibble mechanism.