Topics in Particle Physics and String Theory.

We did the calculations which revealed that both the multi-Higgs model and the supersymmetry theory are likely to produce a neutron electric dipole moment that can be measured by experiments in the near future. We studied the one-loop anomaly of Bosonic string theory. We calculated the decay rate of a macroscopic string. We studied the spacetime duality of string theory and using duality we discovered new extended objects which we named as D-brane and Orientifold that couples with strings and found the evidence that open and closed string theory, oriented and non-oriented string theory, are in fact the same theory on different vacua.