Related papers: The Cosmological Flatness Problem and Limits on Da…
The uncertainty principle is a cornerstone of modern physics, and its implications have a fundamental impact on theoretical and applied quantum mechanics. The aim of this thesis is to study and apply the uncertainty relations between time…
Our universe is observed to be accelerating due to the dominant dark energy with negative pressure. The dark energy equation of state (w) holds a key to understanding the ultimate fate of the universe. The cosmic voids behave like bubbles…
The Cosmological Principle states that the universe is both homogeneous and isotropic. This, alone, is not enough to specify the global geometry of the spacetime. If we were able to measure both the Hubble constant and the energy density we…
The lower limit on the age of the universe derived from globular cluster dating techniques, which previously strongly motivated a non-zero cosmological constant, has now been dramatically reduced, allowing consistency for a flat matter…
We study the possibility that dark energy decays in the future and the universe stops accelerating. The fact thatthe cosmological observations prefer an equation of state of dark energy smaller than -1 can be a signal that dark energy will…
We present cosmological constraints arising from the first measurement of the radial (line-of-sight) baryon acoustic oscillations (BAO) scale in the large scale structure traced by the galaxy distribution. Here we use these radial BAO…
How much can we know about our Universe? All of our observations are restricted to a finite volume, and therefore our estimates of presumably global cosmological parameters are necessarily based on incomplete information. Even assuming that…
Recent cosmological observations suggest that nearly seventy per cent of the energy density in the universe is unclustered and has negative pressure. Several conceptual issues related to the modeling of this component (`dark energy'), which…
We propose a novel parameterization of the dark energy density. It is particularly well suited to describe a non-negligible contribution of dark energy at early times and contains only three parameters, which are all physically meaningful:…
In axion quintessence, the cosmological era with an energy contrast in dark energy 0.1 < Omega_DE < 0.9 may represent a significant fraction of the universe's lifetime if the minimum of the axion potential is negative (unstable axion…
A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic…
Astronomical measurements of the Omegas for mass density, cosmological constant lambda and curvature k are shown to be sufficient to produce a unique and detailed cosmological model describing dark energy influences based on the Friedman…
Over the past decade, the disparity between the value of the cosmic expansion rate directly determined from measurements of distance and redshift or instead from the standard $\Lambda$CDM cosmological model calibrated by measurements from…
The principles of General Relativity allow for a non-vanishing cosmological constant, which can possibly be interpreted at least partially in terms of quantum-fluctuations of matter fields. Depending on sign and magnitude it can cause…
Cosmological observations strongly suggest the presence of dark energy which comprises the majority of the current energy density of the universe. The equation of state relating the pressure and energy density of this dark energy, p = w…
Under four assumptions such that 1) Einstein's theory of gravity is correct, 2) existence of foliation by geodesic slicing, 3) the trace of the extrinsic curvature, $K$, is negative at the present time in observed region, that is, the…
Although big bang cosmology effectively models even the most puzzling observational data, it offers no insight into why the cosmological expansion should occur at all. In this paper it is suggested that a finite Universe poses particular…
One of the greatest challenges in cosmology today is to determine the nature of dark energy, the source of the observed present acceleration of the universe. High precision experiments are being developed to reduce the uncertainties in the…
We use Type Ia supernovae studied by the High-Z Supernova Search Team to constrain the properties of an energy component which may have contributed to accelerating the cosmic expansion. We find that for a flat geometry the equation of state…
The idea that the vacuum energy density $\rho_{\Lambda}$ could be time dependent is a most reasonable one in the expanding Universe; in fact, much more reasonable than just a rigid cosmological constant for the entire cosmic history. Being…