Cosmic strings are non-trivial configurations of scalar (and vector) fields that are stable on account of a topological conservation law.
They can be formed in the early universe as it cools after the Big Bang.
The scalar fields required to form cosmic strings arise naturally if Nature is supersymmetric at high energies. A common feature of supersymmetric theories are directions in the scalar potential that are extremely flat. Combining these two ingredients, the cosmic strings associated with supersymmetric flat directions are qualitatively different from ordinary cosmic strings.
In particular, flat-direction strings have very stable higher-winding modes, and are very wide relative to the scale of their energy density.
These novel features have important implications for the formation and evolution of a network of flat-direction cosmic strings in the early universe. They also affect the observational signatures of the strings, which include gravity waves, dark matter, and modifications to the nuclear abundances and the blackbody spectrum of the microwave background radiation