Energy of cosmological spacetimes and perturbations: a quasilocal approach

TL;DR

This paper applies quasilocal stress-energy-momentum definitions to cosmology, analyzing energy and conservation in FLRW spacetimes with and without scalar perturbations, highlighting the role of vacuum energy and the cosmological constant.

Contribution

It provides a detailed application of the Brown-York quasilocal tensor to cosmological models, clarifying energy concepts and conservation laws in perturbed and unperturbed FLRW spacetimes.

Findings

Vacuum energy plays a crucial role in quasilocal energy calculations.

The approach relates to and clarifies effective local energy treatments in cosmology.

Results offer insights into the cosmological constant and back-reaction issues.

Abstract

Quasilocal definitions of stress-energy-momentum -- that is, in the form of boundary densities (rather than local volume densities) -- have proven generally very useful in formulating and applying conservation laws in general relativity. In this paper, we present a detailed application of such definitions to cosmology, specifically using the Brown-York quasilocal stress-energy-momentum tensor for matter and gravity combined. We compute this tensor, focusing on the energy and its associated conservation law, for FLRW spacetimes with no pertubrations and with scalar cosmological perturbations. For unperturbed FLRW spacetimes, we emphasize the importance of the vacuum energy (for both flat and curved space), which is almost universally underappreciated (and usually "subtracted"), and discuss the quasilocal interpretation of the cosmological constant. For the perturbed FLRW spacetime, we show how our results recover or relate to the more typical effective local treatment of energy in cosmology, with a view towards better studying the issues of the cosmological constant and of cosmological back-reactions.