Atomic ground state energy in multiply connected universes

A hydrogen atom interacting with electromagnetic vacuum fluctuations in a variety of multiply connected universes is considered and to order e2, the shift in energy of its ground state from the value it would take in Minkowski space is calculated. The classical dipole self-interaction is also included and, for investigation, universes with underlying manifolds R1 x T3,R1 x B1 and R1 x G2 are chosen upon each of which a flat metric is imposed. In all cases, the energy shift is found to be proportional to the atom's static polarizability. (author)