Linear cosmological perturbations in scalar-tensor-vector gravity

Abstract

We investigate the cosmological perturbations in the context of a Scalar-Tensor-Vector theory of Gravity known as MOG in the literature. Although MOG is plagued by ghosts, it does not suffer from tachyonic instability. Therefore it can be considered as a valid theory, at least in the classical limit. In the weak field limit, MOG increases the strength of gravity, and consequently addresses some astrophysical tests, without invoking dark matter particles. Recent investigations show that MOG reproduces a viable background cosmological evolution comparable to ΛCDM. However, the matter dominated era is slightly faster in MOG compared to ΛCDM. In this paper, in order to clarify whether this evolution is compatible with observations, we study the linear matter perturbations and estimate the relevant modified gravity parameters. In contrast to some current claims in the relevant literature, we show that MOG reduces the growth rate of the perturbations. We then compare MOG to the redshift space distortion (RSD) data. We find that MOG yields a much higher value than ΛCDM for the power spectrum parameter σ 8 . Although MOG cannot yet be ruled out by RSD data alone, the low growth and high σ 8 constitute a powerful challenge to the cosmological viability of MOG.

Testing Modified Gravity theory (MOG) with Type Ia Supernovae, Cosmic Chronometers and Baryon Acoustic Oscillations

“…Our results show that none of the predictions of the MOG theory considered here with V G = 0 is in agreement with the data, which is also consistent with previous results [40, 41, JCAP07(2020)015 43,44]. Regarding the SNe Ia data, we have verified that for different non-zero values of V G , the difference between the predictions of the MOG theory is very tiny (in fact, adding more MOG models to figures 2 and 3 would have been confusing due to the superposition of curves).…”

“…As regards the self-interaction potentials, the most simple assumption would be to take them all equal to 0. However, it has been shown that in order to describe properly cosmological quantities such as the age and evolutionary stages of the Universe [42,43], and redshift space distortion (RSD) data [44], V G must be different from 0. Furthermore, previous studies of the MOG theory in the cosmological context [40,41] consider V G > 0.…”

Barred spiral galaxies in modified gravity theories

“…One main issue which should still be addressed by MOG is cosmic structure formation. The evolution of cosmic perturbations has been investigated in Jamali et al (2020). It turns out that MOG is consistent with the redshift distortion data.…”

Dark Matters on the Scale of Galaxies

“…In MOG, the growth rate of the bar in disk galaxies is slower, and the final size of the bar is almost an order of magnitude smaller [622]. Moreover, at cosmological scales, where MOG is supposed to behave like the ΛCDM model, the growth rate of the perturbations is reduced, and the value of the normalization of the power spectrum σ 8 is increased to 1.44 [623], which is inconsistent with σ 8 = 0.802 ± 0.018 obtained by the Planck satellite [63]. Finally, due to the lack of cosmological N-body simulations in the context of the MOG theory, the MSP and PSP can not be currently addressed.…”