Universal field equations for metric-affine theories of gravity

TL;DR

This paper demonstrates that most metric-affine gravity theories lead to Einstein equations with a cosmological constant, and explores the inclusion of Weyl vector fields for anisotropy, analyzing their astrophysical viability.

Contribution

It shows that nearly all metric-affine theories reduce to Einstein equations with a cosmological constant and discusses conditions for including Weyl vector fields.

Findings

Most metric-affine theories produce Einstein equations with a non-zero cosmological constant

Inclusion of Weyl vector fields introduces anisotropy into the models

The viability of these models is assessed against recent astrophysical data

Abstract

We show that almost all metric--affine theories of gravity yield Einstein equations with a non--null cosmological constant $\Lambda$. Under certain circumstances and for any dimension, it is also possible to incorporate a Weyl vector field $W_\mu$ and therefore the presence of an anisotropy. The viability of these field equations is discussed in view of recent astrophysical observations.