Quantum three-dimensional de Sitter space

Abstract

We compute the canonical partition function of 2+1 dimensional de Sitter space using the Euclidean $SU(2)\times SU(2)$ Chern-Simons formulation of 3d gravity with a positive cosmological constant. Firstly, we point out that one can work with a Chern-Simons theory with level $k=l/4G$, and its representations are therefore unitary for integer values of $k$. We then compute explicitly the partition function using the standard character formulae for SU(2) WZW theory and find agreement, in the large $k$ limit, with the semiclassical result. Finally, we note that the de Sitter entropy can also be obtained as the degeneracy of states of representations of a Virasoro algebra with $c=3l/2G$.