1. Kibble, T.W.B. [1976], ‘Topology of cosmic domains and strings’, J.Phys. A9, 1387. Kibble, T.W.B. [1980], ‘Some implications of a cosmological phase transition’, Phys. Rep. 67, 183.
2. Vilenkin, A. [1981], ‘Cosmological density fluctuations produced by vacuum strings’, Phys. Rev. Lett. 46, 1169. Erratum: Phys. Rev. Lett. 46, 1496.
3. Zel’dovich, Ya.B. [1980], ‘Cosmological fluctuations produced near a singularity’, M. N. R. A. S. 192, 663.
4. Barriola, M., & Vilenkin, A. [1989], ‘Gravitational field of a global monopole’, Phys. Rev. Lett. 63, 341.
5. Turok,N. [1989b],’Global texture as the origin of cosmic structure’, Phys. Rev. Lett. 63,2625.