相关论文: Cardassian Expansion: Dark Energy Density from Mod…
Recent observations confirm that our universe is flat and consists of a dark energy component $\Omega_{DE}\simeq 0.7$. This dark energy is responsible for the cosmic acceleration as well as determines the feature of future evolution of the…
In a recent paper, a cosmological model based on El Naschie {\it E} infinity cantorian spacetime was presented [Iovane, G.; Chaos, Solitons and Fractals, 20: 657-667, (2004)]. In that work it was claimed that the present accelerated…
The standard procedure to explain the accelerated expansion of the Universe is to assume the existence of an exotic component with negative pressure, generically called dark energy. Here, we propose a new accelerating flat cosmology without…
Astronomical observations indicate an accelerated cosmic expansion, the cause of which is explained by the action of `dark energy'. Here we show that in discrete expanding space-time, only a tiny fraction of the vacuum fluctuations can…
The acceleration of the cosmic expansion is a fundamental challenge to standard models of particle physics and cosmology. The new physics of dark energy may lie in the nature of gravity, the quantum vacuum, or extra dimensions. I give a…
Recent astronomical observations indicate that the Universe is presently almost flat and undergoing a period of accelerated expansion. Basing on Einstein's general relativity all these observations can be explained by the hypothesis of a…
The nature of the fuel that drives today's cosmic acceleration is an open and tantalizing mystery. We entertain the suggestion that the acceleration is not the manifestation of yet another new ingredient in the cosmic gas tank, but rather a…
A novel idea that the cosmic acceleration can be understood from the perspective that spacetime dynamics is an emergent phenomena was proposed by T. Padmanabhan. The Friedmann equations of FRW universe can be derived from different gravity…
The four-dimensional Friedman flat universe, filled with an ideal fluid with a linear (oscillating) inhomogeneous equation of state (EoS) depending on time, is studied. The equations of motion are solved. It is shown that in some cases…
The traditional "explanation" for the observed acceleration of the universe is the existence of a positive cosmological constant. However, this can hardly be a truly convincing explanation, as an expanding universe is not expected to have a…
The present study is based on a generalized form of Brans-Dicke (BD) theory where, the dimensionless BD parameter is regarded as a function of the scalar field, which is reciprocal of the gravitational constant. The field equations have…
Recent supernovae of type Ia measurements and other astronomical observations suggest that our universe is in accelerating phase of evolution at the present epoch. While a dark energy of unknown form is usually proposed as the most feasible…
In a recent paper [arXiv:1206.4916] by T. Padmanabhan, it was argued that our universe provides an ideal setup to stress the issue that cosmic space is emergent as cosmic time progresses and that the expansion of the universe is due to the…
In this work, a way to consider together two originally different corrections to the Friedmann equations is presented. The first is the Barrow entropy, which imposes a fractal structure on the black hole horizon area. While the second is…
It is shown that a first-order relativistic perturbation theory for the open, flat or closed Friedmann-Lemaitre-Robertson-Walker universe admits one, and only one, gauge-invariant quantity which describes the perturbation to the energy…
This thesis focuses on late-time cosmic acceleration within modified theories of gravity, using various observational data sets and statistical analysis. The Universe is assumed to be spatially homogeneous and isotropic and is described by…
The accelerated expansion of the universe implies the existence of an energy contribution known as dark energy. Associated with the cosmological constant in the standard model of cosmology, the nature of this dark energy is still unknown.…
Within the standard cosmological scenario the Universe is found to be filled by obscure components (dark matter and dark energy) for ~95% of its energy budget. In particular, almost all the matter content in the Universe is given by dark…
A highly excited Friedmann universe filled with a scalar field and radiation has been considered. On the basis of a direct solution to the quantum-mechanical problem with a well-defined time variable, it has been shown that such a universe…
The physical process leading to the acceleration of the expansion of the universe is unknown. It may involve new high energy physics or extensions to gravitation. Calling this generically dark energy, we examine the consistencies and…