On the cosmology of scalar-tensor-vector gravity theory

Abstract

We consider the cosmological consequences of a special scalar-tensor-vector theory of gravity, known as MOG (for MOdified Gravity), proposed to address the dark matter problem. This theory introduces two scalar fields $G(x)$ and $\mu (x)$, and one vector field ${\varphi }_{\alpha }(x)$, in addition to the metric tensor. We set the corresponding self-interaction potentials to zero, as in the standard form of MOG. Then using the phase space analysis in the flat Friedmann-Robertson-Walker background, we show that the theory possesses a viable sequence of cosmological epochs with acceptable time dependency for the cosmic scale factor. We also investigate MOG's potential as a dark energy model and show that extra fields in MOG cannot provide a late time accelerated expansion. Furthermore, using a dynamical system approach to solve the non-linear field equations numerically, we calculate the angular size of the sound horizon, i.e. ${\theta }_{\text{s}}$, in MOG. We find that $8\times 10^{-3}\text{rad}<{\theta }_{\text{s}}<8.2\times 10^{-3}\text{rad}$ which is way outside the current observational bounds. Finally, we generalize MOG to a modified form called mMOG, and we find that mMOG passes the sound-horizon constraint. However, mMOG also cannot be considered as a dark energy model un;ess one adds a cosmological constant, and more importantly, the matter dominated era is still slightly different from the standard case.

Accepted version for publication in JCAP

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• Gravitational Theory of Cosmology, Galaxies and Galaxy Clusters
• Compact stars in the Einstein dark energy model
• Does modified gravity predict fast stellar bars in spiral galaxies?
• Linear cosmological perturbations in Scalar-tensor-vector gravity
• Exact cosmological black hole solutions in Scalar Tensor Vector Gravity
• A Modified Dynamical Model of Cosmology I. Theory
• Accretion Process as a Probe of Extra Dimensions in MOG Compact Object Spacetimes
• Scattering of quantum fields by a MOG Black Hole