New Variables, the Gravitational Action, and Boosted Quasilocal Stress-energy-momentum *

This paper presents a complete set of quasilocal densities which describe the stress-energy-momentum content of the gravitational field and which are built with Ashtekar variables. The densities are defined on a two-surface B which bounds a generic spacelike hypersurface Σ of spacetime. The method used to derive the set of quasilocal densities is a Hamilton-Jacobi analysis of a suitable covariant action principle for the Ashtekar variables. As such, the theory presented here is an Ashtekar-variable reformulation of the metric theory of quasilocal stress-energy-momentum originally due to Brown and York. This work also investigates how the quasilocal densities behave under generalized boosts, i. e. switches of the Σ slice spanning B. It is shown that under such boosts the densities behave in a manner which is similar to the simple boost law for energy-momentum four-vectors in special relativity. The developed formalism is used to obtain a collection of two-surface or boost invariants. With these invariants, one may “build” several different mass definitions in general relativity, such as the Hawking expression. Also discussed in detail in this paper is the canonical action principle as applied to bounded spacetime regions with “sharp corners.” Vienna, March 1996 Typeset using REVTEX Revised version, to appear in Classical and Quantum Gravity. Previously at the Institute of Field Physics, Department of Physics & Astronomy, University of North Carolina, Chapel Hill, NC 27599–3255 USA.