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The Lambda-CDM model is the best fit to cosmological data, and to the observed galactic rotation curves. However, in the absence of a direct detection of dark matter one should explore theories such as MOND, and perhaps also modified…
We study scalar cosmological perturbations in $f(R, T)$ modified gravity theories being $T$ the trace of the energy-momentum tensor. We provide detailed equations for the matter energy density contrast. We solve then numerically to promote…
We study new consistent scalar-tensor theories of gravity recently introduced by Langlois and Noui with potentially interesting cosmological applications. We derive the conditions for the existence of a primary constraint that prevents the…
Astrophysical data analysis of the weak-field predictions support the claim that modified gravity (MOG) theories provide a self-consistent, scale-invariant, universal description of galaxy rotation curves, without the need of non-baryonic…
We investigate modified theories of gravity in the context of teleparallel geometries with possible Gauss-Bonnet contributions. The possible coupling of gravity with the trace of the energy-momentum tensor is also taken into account. This…
We obtain the action of Moffat's Modified Gravity, (MOG), a scalar-tensor-vector theory of gravitation, by generalizing the Horava-Witten mechanism to fourteen dimensions. We show that the resulting theory is anomaly-free. We propose an…
Over the last few decades, astronomers and cosmologists have accumulated vast amounts of data clearly demonstrating that our current theories of fundamental particles and of gravity are inadequate to explain the observed discrepancy between…
A modified gravitational theory explains early universe and late time cosmology, galaxy and galaxy cluster dynamics. The modified gravity (MOG) theory extends general relativity (GR) by three extra degrees of freedom: a scalar field $G$,…
We investigate inflation in modified gravity framework by introducing a direct coupling term between a scalar field $\phi$ and the trace of the energy momentum tensor $T$ as $f(\phi,T) = 2 \phi( \kappa^{1/2} \alpha T + \kappa^{5/2} \beta…
As an alternative to dark matter models, MOdified Gravity (MOG) theory can compensate for dark matter by a covariant modification of Einstein gravity. The theory introduces two additional scalar fields and one vector field. The aim is to…
MOG is a fully relativistic modified theory of gravity based on an action principle. The MOG field equations are exactly solvable numerically in two important cases. In the spherically symmetric, static case of a gravitating mass, the…
In a modified gravity theory, the propagation equation of gravitational waves will be presented in a non-standard way. Therefore this tenor mode perturbation of time-space, as a complement to the scalar mode perturbation, provides a unique…
The modified Gauss-Bonnet gravity can be motivated by a number of physical reasons, including: the uniqueness of a gravitational Lagrangian in four and higher dimensions and the leading order $\alpha^\prime$ corrections in superstring…
We review the current status of the Lorentz covariance in teleparallel and modified teleparallel theories of gravity, and discuss the controversial features of the different approaches. We also revisit the issue of the remnant Lorentz gauge…
Modified gravity theories on cosmic scales have three key deviations from general relativity. They can cause cosmic acceleration without a physical, highly negative pressure fluid, can cause a gravitational slip between the two metric…
Tensor-scalar theories of gravitation are commonly employed as extensions of General Relativity that allow to describe a much wider phenomenology. They are also naturally generated as low energy limit of higher-dimensional or unified…
Scalar-tensor theories (STTs) are a widely studied alternative to General Relativity (GR) in which gravity is endowed with an additional scalar degree of freedom. Although severely constrained by solar system and pulsar timing experiments,…
This paper is the third in a series on tests of gravity using observations of stars and nearby dwarf galaxies. We carry out four distinct tests using published data on the kinematics and morphology of dwarf galaxies, motivated by the…
Newtonian limit of Extended Theories of Gravity (in particular, higher--order and scalar--tensor theories) is theoretically discussed taking into account recent observational and experimental results.
We study observational bounds in a class of scalar-tensor gravity theories recently proposed. Either an upper or lower bound on a conformal factor in these theories is derived from null observation in composition dependent fifth force…