Ground state energy and topological mass in spacetimes with nontrivial topology.

In this paper, we study the ground state energy of a massless scalar field and generation of topological mass by considering a quasi-periodically identified Minkowski spacetime and the "half-Einstein universe", that is, an Einstein universe where the massless scalar field satisfies the Dirichlet boundary condition. The analysis is performed considering one and two-loop contributions to the effective potential in both cases. We also compare our results with earlier studies. [ABSTRACT FROM AUTHOR]