Related papers: Dark energy models with time-dependent gravitation…
A rare coincidence of scales in standard particle physics is needed to explain why $\Lambda$ or the negative pressure of cosmological dark energy (DE) coincides with the positive pressure $P_0$ of random motion of dark matter (DM) in bright…
Observations provide increasingly strong evidence that the universe is accelerating. This revolutionary advance in cosmological observations confronts theoretical cosmology with a tremendous challenge, which it has so far failed to meet.…
The idea that the cosmological term, Lambda, should be a time dependent quantity in cosmology is a most natural one. It is difficult to conceive an expanding universe with a strictly constant vacuum energy density, namely one that has…
We explore the properties of dark energy from recent observational data, including the Gold Sne Ia, the baryonic acoustic oscillation peak from SDSS, the CMB shift parameter from WMAP3, the X-ray gas mass fraction in cluster and the Hubble…
In this paper a new theory of Dark Matter is proposed. Experimental analysis of several Galaxies show how the non-gravitational contribution to galactic Velocity Rotation Curves can be interpreted as that due to the Cosmological Constant…
Recent observations provide strong evidence that the universe is accelerating. This confronts theory with a severe challenge. Explanations of the acceleration within the framework of general relativity are plagued by difficulties. General…
This thesis investigates late-time cosmic acceleration using modified gravity theories with a focus on $f(Q)$ gravity, as an alternative to the $\Lambda$CDM model. The standard cosmological model attributes the acceleration to a…
Over the last few years, a large family of cosmological attractor models has been discovered, which can successfully match the latest inflation-related observational data. Many of these models can also describe a small cosmological constant…
We have investigated a cosmological model of a phantom energy with a variable cosmological constant ($\Lambda$) depending on the energy density ($\rho$) as $\Lambda\propto \rho^{-\alpha}$, $\alpha=\rm const.$ and a variable gravitational…
Differently from the equivalence time between either matter and radiation or dark energy and matter, the equivalence between dark energy and radiation occurs between two subdominant fluids, since it takes place in the matter dominated…
We study some cosmological constraints on the two phenomenological models of oscillating dark energy. In these scenarios, the equation of state of dark energy varies periodically and may provide a way to unify the early acceleration…
In this paper we consider several phenomenological models of variable $\Lambda$. Model of a flat Universe with variable $\Lambda$ and $G$ is accepted. It is well known, that varying $G$ and $\Lambda$ gives rise to modified field equations…
We study the bending of light for static spherically symmetric (SSS) space-times which include a dark energy contribution. Geometric dark energy models generically predict a correction to the Einstein angle written in terms of the distance…
We investigate the cosmological consequences of a brane-world theory which incorporates time variations in the gravitational coupling G and the cosmological term Lambda. We analyze in detail the model where (dG/dt)/G ~ H and Lambda ~ H^2,…
We investigate Dark Energy by associating it with vacuum energy or Cosmological constant ${\Lambda}$ which is taken to be dynamic in nature. Our approach is phenomenological and falls within the domain of variable-$\Lambda$ Cosmology.…
The current standard cosmological model is constructed within the framework of general relativity with a cosmological constant $\Lambda$, which is often associated with dark energy, and phenomenologically explains the accelerated cosmic…
Is it possible that the current cosmic accelerating expansion will turn into a decelerating one? Can this transition be realized by some viable theoretical model that is consistent with the standard Big Bang cosmology? We study a class of…
We investigate several phenomenological dark energy parameterizations using a joint analysis of late-time cosmological observations, including cosmic-chromatometer measurements of the Hubble parameter, DESI DR2 baryon acoustic oscillation…
We study a gravitational model in which scale transformations play the key role in obtaining dynamical $G$ and $\Lambda$. We take a scale non-invariant gravitational action with a cosmological constant and a gravitational coupling constant.…
In braneworld models a variable vacuum energy may appear if the size of the extra dimension changes during the evolution of the universe. In this scenario the acceleration of the universe is related not only to the variation of the…