title: Positivity of quasilocal mass.
abstract: Motivated by the important work of Brown and York on quasilocal energy, we propose definitions of quasilocal energy and momentum surface energy of a spacelike 2-surface with a positive intrinsic curvature in a spacetime. We show that the quasilocal energy of the boundary of a compact spacelike hypersurface which satisfies the local energy condition is strictly positive unless the spacetime is flat along the spacelike hypersurface.
authors.affiliation: Harvard University, Department of Mathematics, One Oxford Street, Cambridge, MA 02138, USA. ccliu@math.harvard.edu
authors.forename: Chiu-Chu Melissa
authors.initials: CC
authors.lastname: Liu
authors.forename: Shing-Tung
authors.initials: ST
authors.lastname: Yau