| Astronomical observations, when combined with Einstein's theory of general relativity, indicate that the Universe we observe today has evolved from a much denser, hotter and homogeneous state about thirteen and a half billion years ago. Our current knowledge of particle physics - derived from accelerator experiments - implies that, as this young Universe expanded and cooled, there were episodes when its ground state changed in a number of phase transitions analogous to the water-to-ice or the conductor-to-superconductor transition. During such transitions, remnants of the hotter phase can get trapped in what is generically known as topological defects or extended objects. The trapping is due to frustration in the long-range order of the underlying microscopic fields (thus the name defects), so the experimental investigation of defects provides a unique window into the microscopic theory. This idea has already been used successfully in low-temperature systems such as superfluid helium, and is the basis of a new interdisciplinary area known as Laboratory Cosmology. We plan to exploit the window provided by extended objects in a cosmological context to place new contraints on some of the particle physics models currently favoured in the high energy physics literature (favoured by their agreement with experiments or, if not directly testable, by other - more theoretical - considerations). The novelty of the approach comes from the range of techniques involved, which include laboratory cosmology, detailed analytic studies of the microscopic degrees of freedom (using field theory and supersymmetry techniques) and state-of-the-art numerical simulations. |
