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We describe a new type of gravity-matter models where gravity couples in a non-conventional way to two distinct scalar fields providing a unified Lagrangian action principle description of: (a) the evolution of both "early" and "late"…
Recent attempts to explain the dark matter and energy content of the universe have involved some radical extensions of standard physics, including quintessence, phantom energy, additional space dimensions and variations in the speed of…
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…
Gravitation might make a preferred frame appear, and with it a clear space/time separation--the latter being, a priori, needed by quantum mechanics (QM) in curved space-time. Several models of gravitation with an ether are discussed: they…
In this paper, we investigate the cosmological dynamics of teleparallel dark energy in the presence of nonzero spatial geometry. Extending previous analyses of nonminimal scalar-tensor theories in the torsion-based framework, we consider…
Considering the vacuum as characterized by the presence of only the gravitational field, we show that the vacuum energy density of the de Sitter space, in the realm of the teleparallel equivalent of general relativity, can acquire…
The two apparently distinct phenomena of dark energy (or late-time cosmic acceleration) and quantum gravity dominate physics on extremely low, and extremely high energies, but do not seem to have any apparent empirical connection.…
In order to explain the Late-times accelerated expansion of the Universe we must appeal to some form of Dark Energy. In the standard model of cosmology, the latter is interpreted as a Cosmological Constant $\Lambda$. However, for a number…
In a recent paper (V\'an, P.; Abe, S. Physica A 2022, 588, 126505), it has been discovered that a scalar field coupled to a fluid and allowed to be a thermodynamic variable in consistency with the second law of thermodynamics is only…
The non-relativistic self-gravitating gas in thermal equilibrium in the presence of a positive cosmological constant Lambda (dark energy) is investigated. The dark energy introduces a force pushing outward all particles with strength…
The observed excess of gravitational forces in galaxies and galactic clusters is usually referred as the existence of "dark matter particles" of unknown origin. An alternative explanation of the dark matter effect is presented here by…
The Abnormally Weighting Energy (AWE) hypothesis consists of assuming that the dark sector of cosmology violates the weak equivalence principle (WEP) on cosmological scales, which implies a violation of the strong equivalence principle for…
The physical nature of the presently dominating enigmatic dark energy in the expanding universe is demonstrated to be explainable as an excess of the kinetic energy with respect to its potential energy. According to traditional Friedman…
Apart from the familiar structure firmly-rooted in the general relativistic field equations where the energy--momentum tensor has a null divergence i.e., it conserves, there exists a considerable number of extended theories of gravity…
Modified gravity has garnered interest as a backstop against dark matter and dark energy (DE). As one possible modification, the graviton can become massive, which introduces a new scalar field - here with a Galileon-type symmetry. The…
It has been suggested that Einstein's theory of General Relativity can be modified to accomodate mismatches between the gravitational field and luminous matter on a wide range of scales. Covariant theories of modified gravity generically…
We show that mass varying neutrinos (MaVaNs) can behave as a negative pressure fluid which could be the origin of the cosmic acceleration. We derive a model independent relation between the neutrino mass and the equation of state parameter…
We review the increasing evidence for the cosmological relevance of the cold local Hubble flow. New observations, N-body simulations and other theoretical arguments are discussed, supporting our previous suggestion that the cosmological…
The method of non-Riemannian (metric-independent) spacetime volume-forms (alternative generally-covariant integration measure densities) is applied to construct a modified model of gravity coupled to a single scalar field providing an…
We introduce a modified divergence law for the energy-momentum tensor in the theory of unimodular relativity. Consequently, an additional equation for the measure field follows from the divergence of the field equations. The equations of…