  A new quantization scheme for a massive scalar field in de Sitter spacetime
is proposed, based on the general boundary formulation of quantum field theory.
We show that the general interacting theory can be consistently described in
terms of the S-matrix for spatial asymptotic states. The new S-matrix results
to be equivalent to the standard one in situations where both apply. This is
due to the existence of an isomorphism between the corresponding asymptotic
state spaces.
