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Boost symmetries in spatially compact spacetimes with a cosmological constant

The author characterizes those boost symmetric spacetimes which, in addition to de Sitter space, admit spatially compact, (locally) conformally flat, time symmetric Cauchy hypersurfaces and satisfy Einstein's vacuum field equations with a cosmological constant. The Cauchy surfaces all turn out to be (finite quotients of) Riemannian products and warped products of (S1,dy2) with (S2, gamma k) where gamma k is the canonical metric of constant positive sectional curvature k.