The Stephani Universe, k-essence and strings in the 5-th dimension

TL;DR

This paper explores the Stephani universe as an inhomogeneous alternative to Lambda-CDM, revealing its connection to a special form of k-essence derived from 5-dimensional string-like theories and non-linear electrodynamics.

Contribution

It demonstrates that the exotic fluid in the Stephani universe is a linear velocity k-essence obtained via dimensional reduction from a 5D non-linear electrodynamics model.

Findings

The Stephani universe can be embedded in 5D Minkowski space.

The k-essence corresponds to a reduction of a 5D strongly coupled non-linear electrodynamics.

The non-linear electrodynamics resembles Nielsen-Olesen string field theory.

Abstract

The Stephani universe is an inhomogeneous alternative to $\Lambda{\rm CDM}$ .We show that the exotic fluid driving the Stephani exact solution of Einstein's equations is an unusual form of k-essence that is linear in "velocity". Much as the Stephani universe can be embedded into (a section of) flat 5-d Minkowski space-time, we show that the k-essence obtains through dimensional reduction of a 5-d strongly coupled non-linear "electrodynamics" that, in the empty Stephani universe, is similar to the Nielsen-Olesen field theory of the dual string.