Casimir energy density in closed hyperbolic universes
  The original Casimir effect results from the difference in the vacuum energies of the electromagnetic field, between that in a region of space with boundary conditions and that in the same region without boundary conditions. In this paper we develop the theory of a similar situation, involving a scalar field in spacetimes with compact spatial sections of negative spatial curvature. 
Daniel Muller (Instituto de Fisica, Universidade de Brasilia,   Brasilia) and Helio V. Fagundes (Instituto de Fisica Teorica...