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UBC Theses and Dissertations

Gravitational effects of cosmic strings Vollick, Daniel


Cosmic strings are line-like distributions of energy which may have formed in the early universe. Recent simulations of the evolution of cosmic string networks show that strings have a significant amount of small scale structure (i.e. wiggles). In this thesis we will examine some of the gravitational effects produced by wiggly cosmic strings. One intriguing possibility is that cosmic strings produced the density perturbations which triggered the formation of galaxies and large scale structure. Calculations by others which neglect the wiggles suggest that this scenario is ruled out. Using the Zel’dovich approximation and taking the wiggles into account I found that the wakes produced by the strings in cold dark matter can account for the observed large scale structure of the universe. Using the Gilbert equation I found that the size of the structure produced in hot dark matter is smaller but comparable to the size of the observed large scale structure. I also found that the wiggles can fragment the wakes into pieces which have the mass of a galaxy. One of the interesting observational effects of cosmic strings is the production of double images through gravitational lensing. The gravitational field of a wiggly string differs from the field of a straight string in that the curvature tensor outside a straight string is zero, whereas the curvature tensor diverges as one approaches a wiggly string. Could this make a significant observational difference? To examine this I calculated the effect of a wave pulse on the images of objects located behind the string and found that differences exist, but are small.

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