  The dS/CFT correspondence is illuminated through an analysis of massive
scalar field theory in d-dimensional de Sitter space. We consider a
one-parameter family of dS-invariant vacua related by Bogolyubov
transformations and compute the corresponding Green functions. It is shown that
none of these Green functions correspond to the one obtained by analytic
continuation from AdS. Among this family of vacua are in (out) vacua which have
no incoming (outgoing) particles on past (future) infinity. Surprisingly, it is
shown that in odd spacetime dimensions the in and out vacua are the same,
implying the absence of particle production for this state. The correlators of
the boundary CFT, as defined by the dS/CFT correspondence, are shown to depend
on the choice of vacuum state - the correlators with all points on past
infinity vanish in the in vacuum. For dS_3 we argue that this bulk vacuum
dependence of the correlators is dual to a deformation of the boundary CFT_2 by
a specific marginal operator. It is also shown that Witten's non-standard de
Sitter inner product (slightly modified) reduces to the standard inner product
of the boundary field theory. Next we consider a scalar field in the Kerr-dS_3
Euclidean vacuum. A density matrix is constructed by tracing out over modes
which are causally inaccessible to a single geodesic observer. This is shown to
be a thermal state at the Kerr-dS_3 temperature and angular potential. It is
further shown that, assuming Cardy's formula, the microscopic entropy of such a
thermal state in the boundary CFT precisely equals the Bekenstein-Hawking value
of one quarter the area of the Kerr-dS_3 horizon.
