Brown-York charges at null boundaries

Abstract

The Brown-York stress tensor provides a means for defining quasilocal gravitational charges in subregions bounded by a timelike hypersurface. We consider the generalization of this stress tensor to null hypersurfaces. Such a stress tensor can be derived from the on-shell subregion action of general relativity associated with a Dirichlet variational principle, which fixes an induced Carroll structure on the null boundary. The formula for the mixed-index tensor $T{}^i{}_j$ takes a remarkably simple form that is manifestly independent of the choice of auxiliary null vector at the null surface, and we compare this expression to previous proposals for null Brown-York stress tensors. The stress tensor we obtain satisfies a covariant conservation equation with respect to any connection induced from a rigging vector at the hypersurface, as a result of the null constraint equations. For transformations that act covariantly on the boundary structures, the Brown-York charges coincide with canonical charges constructed from a version of the Wald-Zoupas procedure. For anomalous transformations, the charges differ by an intrinsic functional of the boundary geometry, which we explicity verify for a set of symmetries associated with finite null hypersurfaces. Applications of the null Brown-York stress tensor to symmetries of asymptotically flat spacetimes and celestial holography are discussed.

22 pages + appendix; v2: fixed sign conventions, references added; v3 references added, matches published version

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Cited by in corpus (10)

• Carrollian Perspective on Celestial Holography
• Null boundary phase space: slicings, news and memory
• Complexity Equals Anything II
• Carrollian hydrodynamics from symmetries
• Carrollian manifolds and null infinity: A view from Cartan geometry
• Non-linear black hole dynamics and Carrollian fluids
• Wald-Zoupas prescription with (soft) anomalies
• Celestial Klein Spaces
• Relativistic Fluids, Hydrodynamic Frames and their Galilean versus Carrollian Avatars
• Cost of holographic path integrals