A simple property of the Weyl tensor for a shear, vorticity and acceleration-free velocity field

TL;DR

This paper proves a property of the Weyl tensor in higher-dimensional spacetimes with shear-free, vorticity-free, and acceleration-free velocity fields, revealing a link between its divergence and contraction with the velocity.

Contribution

It establishes a new geometric property of the Weyl tensor under specific conditions, extending known results from Robertson-Walker spacetimes to higher dimensions.

Findings

Covariant divergence of Weyl tensor is zero iff contraction with velocity is zero.

Introduces a curvature tensor with a recurrence property.

Extends properties of Robertson-Walker spacetimes to higher dimensions.

Abstract

We prove that, in a space-time of dimension n>3 with a velocity field that is shear-free, vorticity-free and acceleration-free, the covariant divergence of the Weyl tensor is zero if the contraction of the Weyl tensor with the velocity is zero. The other way, if the covariant divergence of the Weyl tensor is zero, then the contraction of the Weyl tensor with the velocity has recurrent geodesic derivative. This partly extends a property found in Generalised Robertson-Walker spacetimes, where the velocity is also eigenvector of the Ricci tensor. Despite the simplicity of the statement, the proof is involved. As a product of the same calculation, we introduce a curvature tensor with an interesting recurrence property.