Vacuum Energy of Quantum Fields in Classical Background Configurations

The ground state energy of a quantum field in the background of classical field configurations is considered. The subject of the ground state energy in framework of the quantum field theory is explained. The short review of calculation methods (generalized zeta function and heat kernel expansion) and their mathematical foundations is given. We use the zeta-functional regularization and express the ground state energy as an integral involving the Jost function of a two dimensional scattering problem.We perform the renormalization by subtracting the contributions from first several heat kernel coefficients. The ground state energy is presented as a convergent expression suited for numerical evaluation. The investigation for three models has been carried out: scalar quantum field on the background of scalar string with rectangular shape, spinor vacuum polarized by magnetic string of the similar shape and spinor vacuum interacting with the Nielsen-Olesen vortex. Using the uniform asymptotic expansion of the special functions entering the Jost function we are also able to calculate higher order heat kernel coefficients. Several features of vacuum energy have been investigated numerically. We discuss corresponding numerical results.