We compute the O(λ) correction to the Casimir energy for the massive
λϕ4 model confined between a pair of parallel plates. The
calculations are made with Dirichlet and Neumann boundary conditions. The
correction is shown to be sensitive to the boundary conditions, except in the
zero mass limit, in which case our results agree with those found in the
literature.Comment: 6 pages. Work presented at the XXIII Brazilian National Meeting on
Particles and Fields (Aguas de Lindoia, Brazil, 15-19 Oct 2002). Also
available at http://www.sbf1.if.usp.br/eventos/enfpc/xxiii/procs/RES142.pd