Birth of Cosmic Strings

The great success of gauge theory in elementary particle physics naturally led to the notion that the Grand Unified Theory is a feature of an earlier and hotter Universe. Since we have smaller pieces of symmetry ( ) today, the spontaneous symmetry breaking process is believed to have taken place at a very early time. Production of topological defects such as the monopole, cosmic strings, and domain walls are inevitable.

The Kibble Mechanism is responsible for producing topological defects during the symmetry breaking. When regions are causally uncorrelated, scalar field values assigned in these regions have to be uncorrelated also. As those regions grow and are in contact, there are discrete jumps in the field values, and topological defects are produced at the border of two uncorrelated regions - playing the role of buffer zone.

Figure 1. Kibble mechanism: symmetry breaking of a complex scalar field produces cosmic strings [1]. (a) patches with true vacuum energies start growing  as the symmetry is broken. Gray region represents false vacua. (b) As the patches with true vacua merge, false vacuum regions are squeezed and form topological defects.