Résumé:
In this thesis, we study the effects of cosmic strings on the particle pair creation phenomenon.In the first part, we investigate particle creation caused by the Coulomb potential of an external electric field in the presence of a gravitational field of astatic cosmic string.To accomplish this, we solve the generalized Klein-Gordon and Dirac equations, and by using the Bogoliubov transformation we calculate the probability and the number density of the created particles. Our results show that the presence of the cosmic string amplifies the production of particles. Specifically, in the case of the grand unified theory (GUT) cosmic string, the production of spinless particles is feasible when the nucleus charge of the Coulomb potentiel satisfies Z ≥206, and for spin-1/2 particles if Z ≥275.
In the second part, we analyze the phenomenon of particle creation by the Coulomb potential of an external electric field in the presence of a scalar potential in the background of a spinning cosmic string. By solving the Klein-Gordon equation, we have obtained then number density of particlec reation in term of the parameters of the two potentials and the spinning cosmic string. It is shown that the angular momentum quantum number l is shifted to an effective angular momentum, leff= 1(l−kJ0), which depends on the cosmic string parameters J0 and α.We also shown that the scalar and Coulomb potentials, along with the spinning parameter, reduce the rate of the number density, in contrast with the cosmic string parameter α.
