We apply a parameterization-independent approach to fitting the dark energy equation-of-state (EOS). Utilizing the latest type Ia supernova data, combined with results from the cosmic microwave background and baryon acoustic oscillations, we find that the dark energy is consistent with a cosmological constant. We establish independent estimates of the evolution of the dark energy EOS by diagona...

Here, cosmology of the late and future universe is obtained from f(R)− gravity with non-linear curvature terms R and R (R being the Ricci scalar curvature). It is different from f(R)−dark energy models [6] where non-linear curvature terms are taken as gravitational alternative of dark energy. In the present model, neither linear nor non-linear curvature terms are taken as dark energy. Rather, d...

We examine the linear density contrast at collapse time, δc, for large-scale structure in dynamical dark energy cosmologies, including models with early dark energy. Contrary to previous results, we find that as long as dark energy is homogeneous on small scales, δc is insensitive to dark energy properties for parameter values fitting current data, including the case of early dark energy. This ...

We study a cosmological model in which phantom dark energy has an interaction with dark matter by introducing a term in the equations of motion of dark energy and dark matter. Such a term is parameterized by a product of a dimensionless coupling function δ, Hubble parameter and the energy density of dark matter, and it manifests an energy flow between the dark energy and dark matter. We discuss...

In models of coupled dark energy and dark matter the mass of the dark matter particle depends on the cosmological evolution of the dark energy field. In this note we exemplify in a simple model the effects of this mass variation on the relic abundance of cold dark matter. We still do not know the origin and composition of the cold dark matter (CDM) in the universe. Recent precision measurements...

Recent observations on Type-Ia supernovae and low density (Ωm = 0.3) measurement of matter including dark matter suggest that the presentday universe consists mainly of repulsive-gravity type ‘exotic matter’ with negative-pressure often said ‘dark energy’ (Ωx = 0.7). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the dark energy, a...

Recent observations on Type-Ia supernovae and low density (Ωm = 0.3) measurement of matter including dark matter suggest that the presentday universe consists mainly of repulsive-gravity type ‘exotic matter’ with negative-pressure often said ‘dark energy’ (Ωx = 0.7). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the dark energy, a...

We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and dark energy are investigated using the cosmological observations of cosmic microwave background, baryon acoustic oscillations and type Ia suprenovae. When one investigates dark energy, the Hubble c...