Vector field models of modified gravity and the dark sector

TL;DR

This paper explores vector field models of modified gravity, constraining their parameters using cosmological data, and finds that some models can explain dark energy but not dark matter.

Contribution

It provides a comprehensive analysis of Generalized Einstein-Aether models, constraining their parameters with cosmological observations and identifying issues with dark matter candidates.

Findings

Dark matter candidate models do not fit the data.

Dark energy candidate models are consistent with observations.

The kinetic index parameter $n_{ae}$ can significantly differ from $\\Lambda$CDM.

Abstract

We present a comprehensive investigation of cosmological constraints on the class of vector field formulations of modified gravity called Generalized Einstein-Aether models. Using linear perturbation theory we generate cosmic microwave background and large-scale structure spectra for general parameters of the theory, and then constrain them in various ways. We investigate two parameter regimes: a dark-matter candidate where the vector field sources structure formation, and a dark-energy candidate where it causes late-time acceleration. We find that the dark matter candidate does not fit the data, and identify five physical problems that can restrict this and other theories of dark matter. The dark energy candidate does fit the data, and we constrain its fundamental parameters; most notably we find that the theory's kinetic index parameter $n_{\mathrm{ae}}$ can differ significantly from its $\Lambda$CDM value.