2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/55821We study the problem of a Dirac field in the background of an Aharonov-Bohm flux string. We exclude the origin by imposing spectral boundary conditions at a finite radius then shrinked to zero. Thus, we obtain a behaviour of the eigenfunctions which is compatible with the self-adjointness of the radial Hamiltonian and the invariance under integer translations of the reduced flux. After confining the theory to a finite region, we check the consistency with the index theorem, and discuss the vacuum fermionic number and Casimir energy.To appear in Proceedings of "Fourth Workshop on Quantum Field Theory under the influence of External Conditions"High Energy Physics - Theorytext