The energy-momentum complex in non-local gravity

TL;DR

This paper extends the concept of gravitational energy-momentum pseudotensors to non-local gravity theories, deriving a conserved energy-momentum complex using Noether's theorem and exploring its properties and weak field limit.

Contribution

It introduces a generalized energy-momentum pseudotensor for non-local gravity theories based on the Noether theorem, ensuring local conservation and affine transformation properties.

Findings

Derived a conserved energy-momentum pseudotensor for non-local gravity.

Established the invariance and conservation laws in non-local gravitational theories.

Performed the weak field limit analysis for astrophysical applications.

Abstract

In General Relativity, the issue of defining the gravitational energy contained in a given spatial region is still unresolved, except for particular cases of localized objects where the asymptotic flatness holds for a given spacetime. In principle, a theory of gravity is not self-consistent, if the whole energy content is not uniquely defined in a specific volume. Here we generalize the Einstein gravitational energy-momentum pseudotensor to non-local theories of gravity where analytic functions of the non-local integral operator $\Box^{-1}$ are taken into account. We apply the Noether theorem to a gravitational Lagrangian, supposed invariant under the one-parameter group of diffeomorphisms, that is, the infinitesimal rigid translations. The invariance of non-local gravitational action under global translations leads to a locally conserved Noether current, and thus, to the definition of a gravitational energy-momentum pseudotensor, which is an affine object transforming like a tensor under affine transformations. Furthermore, the energy-momentum complex remains locally conserved, thanks to the non-local contracted Bianchi identities. The continuity equations for the gravitational pseudotensor and the energy-momentum complex, taking into account both gravitational and matter components, can be derived. Finally, the weak field limit of pseudotensor is performed to lowest order in metric perturbation in view of astrophysical applications.