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Investigation of Light Propagation in Inhomogeneous Cosmic Spacetimes

Parsi Mood, Mojahed | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 46108 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Mansouri, Reza
  7. Abstract:
  8. In this work we investigate the propagattion of light in inhomogenous cosmic spacetime within general relativity framework. We use Lemaitr-Tolaman-Bondi metric for modeling inhomogenous spacetime. For investigation of gravitational lensing we need to solve geodesic equaions in this model. Beacuse of nonlinearity and complexity of these equations we should apply numerical methods. At first we used Runge-Kutta method with adaptive step size, but beacuse of stiffness of these equaions, the results of this method did not match to approximation methods for low deflection angles. So we try semi-implicit Rosenbrock method. Then for inspection of thin lens approximation for the first time; we compare the result of this exact solution to the results of thin lens approximation, which we see good agreement between them. In addition we study some quasi-local masses which are defined in general relativity by our model. Our aim was to investigate the feasibility of comparision of these relativistic masses to measurment of mass by gravitaional lengs. Finally by gluing many of these inhomogenous structures, we construct a Swiss cheese model. Then by solving optical-scalar equations in this model, we compute angular diameter distance in terms of redshift. So we obtain the effect of inhomogenities in the path of light on cosmological distances. The excess of distances which is achived in this model is approximatly 10-15 percent of the increase that is observed, which is induced by dark energy. So it seems that this model can not solve dark energy problem. However in future observations for dark energy the contibution of this effect should be consider to increase the accuracy
  9. Keywords:
  10. Inhomogeneous Space Time ; Geodesic Equations ; Numerical Solution of Differential Equations ; Gravitational Lensing ; Swiss Cheese Model

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