Influence of a cosmic string on the rate of pairs produced by the Coulomb potential

We study particle creation phenomenon by the Coulomb potential of an external electric field in the presence of a gravitational field of a static cosmic string. For that, the generalized Klein-Gordon and Dirac equations are solved, and by using the Bogoliubov transformation we calculate the probability and the number density of created particles. It is shown that the presence of the cosmic string enhances the particle production. For the grand unified theory (GUT) cosmic string, the production of spinless particles is possible if the Coulomb potential nucleus charge $Z\ge 206$, and for spin-1/2 particles if $Z\ge 275$.