The membrane at the end of the (de Sitter) universe

The original membrane at the end of the universe corresponds to a probe M2-brane of signature (2, 1) occupying the S-2 x S-1 boundary of the (10, 1) spacetime AdS(4) x S-7, and is described by an OSp(4/8) SCFT. However, it was subsequently generalized to other worldvolume signatures (s, t) and other spacetime signatures (S, T). An interesting special case is provided by the (3, 0) brane at the end of the cle Sitter universe dS(4) which has recently featured in the dS/CFT correspondence. The resulting CFT contains the one recently proposed as the holographic dual of a four-dimensional de Sitter cosmology. Supersymmetry restricts S, T, s, t by requiring that the corresponding bosonic symmetry O(s + 1, t + 1) x O(S - s, T - t) be a subgroup of a superconformal group. The case of dS(4) x AdS(7) is 'doubly holographic' and may be regarded as the near horizon geometry of N-2 M2-branes or equivalently, under interchange of conformal and R-symmetry, of N-5 M5-branes, provided N-2 = 2N5(2). The same correspondence holds in the pp-wave limit of conventional M-theory. (C) 2006 Published by Elsevier B.V.