Recent measurements of the global curvature of space-time, using distant supernovae as distance indicators, favor a positive cosmological constant, associated with an accelerating universal expansion . However, these results by themselves still allow an open universe with low mass density and zero cosmological constant. We show here that this degeneracy is removed by independent constraints fro...

We point out that the expansion of the universe leads to a cosmological time evolution of the vacuum expectation of the Higgs boson. Within the standard model of particle physics, the cosmological time evolution of the vacuum expectation of the Higgs leads to a cosmological time evolution of the masses of the fermions and of the electroweak gauge bosons while the scale of Quantum Chromodynamics...

We review the study of inhomogeneous perturbations about a homogeneous and isotropic background cosmology. We adopt a coordinate based approach, but give geometrical interpretations of metric perturbations in terms of the expansion, shear and curvature of constant-time hypersurfaces and the orthogonal timelike vector field. We give the gauge transformation rules for metric and matter variables ...

Variability in gravitationally lensed quasars can be due to intrinsic fluctuations of the quasar or due to " microlensing " by compact objects along the line of sight. If disentangled from each other, microlens-induced variability can be used to study two cosmological issues of great interest, the size and brightness profile of quasars on one hand, and the distribution of compact (dark) matter ...

Motivated by the recent observations for the cosmic acceleration and the suitable evolution of the Universe provided an interaction (decay of dark energy to matter) is incorporated in a cosmological model, we study the cosmological evolution of the Interacting Holographic Dark Energy scenario. Critical points are derived and their corresponding cosmological models are presented. The dynamical c...

Cosmological implications of clusters of galaxies are discussed with particular attention to their importance in probing the cosmological parameters. More specifically we compute the number counts of clusters of galaxies, LogN–LogS relation, in X-ray and submm bands on the basis of the Press–Schechter theory. We pay particular attention to a set of theoretical models which well reproduce the RO...

Duality under inversion of the cosmological scale factor is discussed both for the classical motion of strings in cosmological backgrounds and for genus zero, low energy effective actions. The string-modified, Einstein-Friedmann equations are then shown to possess physically-inequivalent, duality-related solutions which generically describe the ”decay” of an initial, perturbative, flat D = 10 s...

The dark energy cosmology with the equation of state w = constant is considered in this paper. The ΩDE−ΩM plane has been used to study the present state and expansion history of the universe. Through the mathematical analysis, we give the theoretical constraint of cosmological parameters. Together with some observations such as the transition redshift from deceleration to acceleration, more pre...

The dissipation of energy from local velocity perturbations in the cosmological fluid affects the time evolution of spatially averaged fluid dynamic fields and the cosmological solution of Einstein's field equations. We show how this backreaction effect depends on shear and bulk viscosity and other material properties of the dark sector, as well as the spectrum of perturbations. If sufficiently...