scholarly journals AGE CONSTRAINTS ON THE COSMIC EQUATION OF STATE

2007 ◽  
Vol 16 (02n03) ◽  
pp. 463-468
Author(s):  
N. PIRES ◽  
J. S. ALCANIZ
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Observational Evidence ◽  
Accelerating Universe ◽  
Observational Constraints ◽  
Energy Component ◽  
Dark Energy Component ◽  
Age Constraints ◽  
Friedmann Robertson Walker ◽  
Age Estimates

A large amount of recent observational evidence strongly suggests that we live in a flat, accelerating universe composed of ≃ 1/3 of matter (barionic + dark) and ≃ 2/3 of an exotic component with large negative pressure, usually called dark energy or "quintessence." In this contribution, we investigate observational constraints on the equation of state of the dark energy from age estimates of galaxy clusters, supernovae observations and CMB measurements. Our results are based on a flat Friedmann–Robertson–Walker (FRW) type models driven by non-relativistic matter plus a smooth dark energy component parametrized by a constant equation of state px = ωωx (ω < 0).

scholarly journals OBSERVATIONAL CONSTRAINTS ON THE GENERALIZED CHAPLYGIN GAS

2009 ◽  
Vol 18 (13) ◽  
pp. 2007-2022 ◽  
Author(s):  
SERGIO DEL CAMPO ◽  
J. R. VILLANUEVA
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
Chaplygin Gas ◽  
Observational Constraints ◽  
Energy Component ◽  
Generalized Chaplygin Gas ◽  
Astronomical Data ◽  
Astronomical Observations ◽  
Dark Energy Component ◽  
Two Parameters

In this paper we study a quintessence cosmological model in which the dark energy component is considered to be the generalized Chaplygin gas and the curvature of the three-geometry is taken into account. Two parameters characterize this sort of fluid: ν and α. We use different astronomical data for restricting these parameters. It is shown that the constraint ν ≲ α agrees well enough with the astronomical observations.

GRAVITATIONAL LENSING CONSTRAINT ON THE COSMIC EQUATION OF STATE

2003 ◽  
Vol 12 (05) ◽  
pp. 953-962 ◽  
Author(s):  
DEEPAK JAIN ◽  
ABHA DEV ◽  
N. PANCHAPAKESAN ◽  
S. MAHAJAN ◽  
V. B. BHATIA
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Gravitational Lensing ◽  
Energy Component ◽  
Distance Measurements ◽  
Dark Energy Component ◽  
Highly Sensitive ◽  
Type Ia ◽  
Image Separation ◽  
Ia Supernovae

Recent redshift-distance measurements of Type Ia supernovae (SNe Ia) at cosmological distances suggest that two-third of the energy density of the universe is dominated by dark energy component with an effective negative pressure. This dark energy component is described by the equation of state px= wρx(w ≥ - 1). We use gravitational lensing statistics to constrain the equation of state of this dark energy. We use n(Δθ), the image separation distribution function of lensed quasars, as a tool to probe w. We find that for the observed range of Ωm~ 0.2–0.4, w should lie between -0.8 ≤ w ≤ -0.4 in order to have five lensed quasars in a sample of 867 optical quasars. This limit is highly sensitive to lens and Schechter parameters and the evolution of galaxies.

scholarly journals THERMODYNAMIC OF THE GHOST DARK ENERGY UNIVERSE

2012 ◽  
Vol 27 (31) ◽  
pp. 1250182 ◽  
Author(s):  
CHAO-JUN FENG ◽  
XIN-ZHOU LI ◽  
XIAN-YONG SHEN
Keyword(s):  
Dark Energy ◽  
Vacuum Energy ◽  
Hawking Temperature ◽  
Frw Universe ◽  
Energy Component ◽  
Ghost Dark Energy ◽  
Dark Energy Component ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Friedmann Robertson Walker

Recently, the vacuum energy of the QCD ghost in a time-dependent background is proposed as a kind of dark energy candidate to explain the acceleration of the Universe. In this model, the energy density of the dark energy is proportional to the Hubble parameter H, which is the Hawking temperature on the Hubble horizon of the Friedmann–Robertson–Walker (FRW) Universe. In this paper, we generalized this model and chose the Hawking temperature on the so-called trapping horizon, which will coincide with the Hubble temperature in the context of flat FRW Universe dominated by the dark energy component. We study the thermodynamics of Universe with this kind of dark energy and find that the entropy-area relation is modified, namely, there is another new term besides the area term.

scholarly journals Thermodynamics of universe with a varying dark energy component

2015 ◽  
Vol 24 (14) ◽  
pp. 1550098 ◽  
Author(s):  
H. Ebadi ◽  
H. Moradpour
Keyword(s):  
Dark Energy ◽  
Apparent Horizon ◽  
Additional Term ◽  
Second Law Of Thermodynamics ◽  
Mutual Interaction ◽  
Frw Universe ◽  
Energy Component ◽  
Horizon Entropy ◽  
Dark Energy Component ◽  
Friedmann Robertson Walker

We consider a Friedmann–Robertson–Walker (FRW) universe filled by a dark energy (DE) candidate together with other possible sources which may include the baryonic and nonbaryonic matters. Thereinafter, we consider a situation in which the cosmos sectors do not interact with each other. By applying the unified first law of thermodynamics on the apparent horizon of the FRW universe, we show that the DE candidate may modify the apparent horizon entropy and thus the Bekenstein limit. Moreover, we generalize our study to the models in which the cosmos sectors have a mutual interaction. Our final result indicates that the mutual interaction between the cosmos sectors may add an additional term to the apparent horizon entropy leading to modify the Bekenstein limit. Relationships with previous works have been addressed throughout the paper. Finally, we investigate the validity of the second law of thermodynamics and its generalized form in the interacting and noninteracting cosmoses.

scholarly journals The Influence of Evolving Dark Energy on Cosmology

2005 ◽  
Vol 22 (4) ◽  
pp. 315-325 ◽  
Author(s):  
Luke Barnes ◽  
Matthew J. Francis ◽  
Geraint F. Lewis ◽  
Eric V. Linder
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Constant ◽  
Energy Exchange ◽  
Observational Evidence ◽  
Cosmological Models ◽  
Observational Constraints ◽  
Expansion Of The Universe ◽  
The Universe

AbstractObservational evidence indicating that the expansion of the universe is accelerating has surprised cosmologists in recent years. Cosmological models have sought to explain this acceleration by incorporating ‘dark energy’, of which the traditional cosmological constant is just one possible candidate. Several cosmological models involving an evolving equation of state of the dark energy have been proposed, as well as possible energy exchange to other components, such as dark matter. This paper summarizes the forms of the most prominent models and discusses their implications for cosmology and astrophysics. Finally, this paper examines the current and future observational constraints on the nature of dark energy.

scholarly journals Emergent Universe as an interaction in the dark sector

2017 ◽  
Vol 32 (28) ◽  
pp. 1750152
Author(s):  
Emiliano Marachlian ◽  
I. E. Sánchez G. ◽  
Osvaldo P. Santillán
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Linear Equation ◽  
Vacuum Energy ◽  
Cosmological Parameters ◽  
Emergent Universe ◽  
Dark Sector ◽  
Cosmological Scenario ◽  
Friedmann Robertson Walker

A cosmological scenario where dark matter interacts with a variable vacuum energy for a spatially flat Friedmann–Robertson–Walker (FRW) spacetime is proposed and analyzed to show that with a linear equation of state and a particular interaction in the dark sector it is possible to get a model of an Emergent Universe. In addition, the viability of two particular models is studied by taking into account the recent observations. The updated observational Hubble data and the JLA supernovae data are used in order to constraint the cosmological parameters of the models and estimate the amount of dark energy in the radiation era. It is shown that the two models fulfil the severe bounds of [Formula: see text] at the 2[Formula: see text] level of Planck.

scholarly journals Holographic cosmology with two coupled fluids in the presence of viscosity

2021 ◽  
pp. 2150149
Author(s):  
I. Brevik ◽  
A. V. Timoshkin
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Holographic Dark Energy ◽  
Exponential Model ◽  
Point Of View ◽  
Accelerating Universe ◽  
Late Time ◽  
Conservation Of Energy ◽  
Analytical Expressions ◽  
Friedmann Robertson Walker

We explore the cosmological models of the late-time universe based on the holographic principle, taking into account the properties of the viscosity of the dark fluid. We use the mathematical formalism of generalized infrared cutoff holographic dark energy, as presented by Nojiri and Odintsov [Covariant generalized holographic dark energy and accelerating universe, Eur. Phys. J. C 77 (2017) 528]. We consider the Little Rip, the Pseudo Rip, and a bounce exponential model, with two interacting fluids, namely dark energy and dark matter in a spatially-flat Friedmann–Robertson–Walker universe. Within these models, analytical expressions are obtained for infrared cutoffs in terms of the particle horizons. The law of conservation of energy is presented, from a holographic point of view.

scholarly journals A Noncommutative Model of Cosmology with Two Metrics

Symmetry ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 435
Author(s):  
Horacio Falomir ◽  
Jorge Gamboa ◽  
Fernando Mendez
Keyword(s):  
Quantum Mechanics ◽  
Dark Energy ◽  
Equation Of State ◽  
Point Of View ◽  
Classical Analog ◽  
Noncommutative Quantum Mechanics ◽  
Friedmann Robertson Walker ◽  
Noncommutative Quantum

We propose a bicosmology model which reduces to the classical analog of noncommutative quantum mechanics. From this point of view, one of the sources in the so modified Friedmann-Robertson- Walker equations is a kind of dark energy governed by a Chapligyn-like equation of state. The parameters of noncommutativity θ and B are interpreted in terms of the Planck area and a magnetic-like field, which presumably acts as a seed for magnetogenesis.

MASS INHOMOGENEITIES AND THE ANGULAR SIZE-REDSHIFT RELATION

2004 ◽  
Vol 13 (07) ◽  
pp. 1309-1313 ◽  
Author(s):  
JAILSON S. ALCANIZ ◽  
JOSÉ A. S. LIMA ◽  
RAIMUNDO SILVA
Keyword(s):  
Dark Energy ◽  
Angular Size ◽  
Matter Density ◽  
Radio Sources ◽  
Density Parameter ◽  
Energy Component ◽  
Dark Energy Component ◽  
Smoothness Parameter ◽  
Best Fit ◽  
Size Data

We investigate the influence of mass inhomogeneities on the angular size-redshift test through a statistical analysis of angular size data for a large sample of milliarcsecond radio sources. The results are based on flat models driven by nonrelativistic matter plus a dark energy component in the form of a relic cosmological constant. To model the mass inhomogeneities we use the Zeldovich–Kantowski distance formula (also known as Dyer–Roeder distance redshift relation) which is characterized by the smoothness parameter α. Marginalizing over the characteristic angular size l and assuming a Gaussian prior on the matter density parameter, i.e., Ωm=0.35±0.07, the best fit model occurs at Ωm=0.35 and α=0.8. For an analysis without priors and minimizing χ2 for the parameters l, Ωm and α we find that a conventional homogeneous scenario (α=1) with Ωm=0.2 and D=22.6h-1 pc constitutes the best fit model for the present angular size data.

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