Quadratic Gravity, double layers and non-conservative energy-momentum tensor

TL;DR

This paper explores the conservation laws in Quadratic Gravity, showing that while the total energy-momentum tensor is conserved in the bulk, singular hypersurfaces can lead to matter creation, with derived conditions for such phenomena.

Contribution

It derives conservative conditions on singular hypersurfaces in Quadratic Gravity and demonstrates the possibility of matter creation at these interfaces.

Findings

Total energy-momentum tensor is conserved in the bulk.

Singular hypersurfaces can induce matter creation.

Derived conditions for conservation on hypersurfaces.

Abstract

In the present paper we investigate the conservative conditions in Quadratic Gravity. It is shown explicitly that the Bianchi identities lead to the conservative condition of the left-hand-side of the (gravitational) field equation. Therefore, the total energy-momentum tensor is conservative in the bulk (like in General Relativity). However, in Quadratic Gravity it is possible to have singular hupersurfaces separating the bulk regions with different behavior of the matter energy-momentum tensor or different vacua. They require special consideration. We derived the conservative conditions on such singular hypersurfaces and demonstrated the very possibility of the matter creation. In the remaining part of the paper we considered some applications illustrating the obtained results.