ON THE THERMODYNAMICS OF DARK ENERGY

2007 ◽  
Vol 16 (02n03) ◽  
pp. 469-473 ◽  
Author(s):  
R. SILVA ◽  
J. S. ALCANIZ ◽  
J. A. S. LIMA
Keyword(s):  
Dark Energy ◽  
Negative Pressure ◽  
Energy Content ◽  
Phantom Energy ◽  
Energy Component ◽  
Astronomical Observations ◽  
Thermodynamic Behavior ◽  
Dark Energy Component ◽  
Ultimate Fate ◽  
The Universe

Recent astronomical observations suggest that the bulk of energy in the Universe is repulsive and appears like a dark energy component (which accounts for ~2/3 of the energy content of the Universe) with negative pressure (ω ≡ px/ρx < 0). In this work, we discuss the thermodynamic behavior by considering three different parametrizations, describing the dark energy component: (1) Model 1: [Formula: see text]; (2) Model 2: ω(z) = ω0 + ω2 z; (3) Model 3: ω(z) = ω0 - ω3 ln (1 + z). It is found that its energy and temperature grow during the evolution of the Universe since work is done on the system. The case of phantom energy (ω < -1), however, seems to be physically meaningless because its entropy is negative. Our analysis also implies that the ultimate fate of the Universe may be considerably modified. Actually, the future of the Universe depends on the kind of parametrization. For Models 1 and 3, the Universe will becoming increasingly hot, while for Model 2 it cools during evolution.

scholarly journals WMAPing THE UNIVERSE: SUPERSYMMETRY, DARK MATTER, DARK ENERGY, PROTON DECAY AND COLLIDER PHYSICS

2003 ◽  
Vol 12 (09) ◽  
pp. 1529-1591 ◽  
Author(s):  
A. B. LAHANAS ◽  
N. E. MAVROMATOS ◽  
D. V. NANOPOULOS
Keyword(s):  
Dark Energy ◽  
Particle Physics ◽  
Energy Content ◽  
Unknown Origin ◽  
Precise Determination ◽  
Minimal Models ◽  
Energy Component ◽  
Dark Energy Component ◽  
Supersymmetric Models ◽  
The Universe

In this review we critically discuss constraints on minimal supersymmetric models of particle physics as implied by the recent astrophysical observations of WMAP satellite experiment. Although the prospects of detecting supersymmetry increase dramatically, at least within the context of the minimal models, and 90% of the available parameter space can safely be reached by the sensitivity of future colliders, such as Tevatron, LHC and linear colliders, nevertheless we pay particular emphasis on discussing regions of the appropriate phase diagrams, which — if realized in nature — would imply that detection of supersymmetry, at least in the context of minimal models, could be out of colliders reach. We also discuss the importance of a precise determination of the radiative corrections to the muon anomalous magnetic moment, gμ-2, both theoretically and experimentally, which could lead to elimination of such "out of reach" regions in case of a confirmed discrepancy of gμ-2 from the standard model value. Finally, we briefly commend upon recent evidence, supported by observations, on a dark energy component of the Universe, of as yet unknown origin, covering 73% of its energy content. To be specific, we discuss how supergravity quintessence (relaxation) models can be made consistent with recent observations, which may lead to phenomenologically correct constrained supersymmetric models, accounting properly for this dark energy component. We also outline their unresolved problems.

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.

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 GRAVITATIONAL LENSING STATISTICAL PROPERTIES IN GENERAL FRW COSMOLOGIES WITH DARK ENERGY COMPONENT(S): ANALYTIC RESULTS

2000 ◽  
Vol 09 (05) ◽  
pp. 591-600 ◽  
Author(s):  
ZONG-HONG ZHU
Keyword(s):  
Dark Energy ◽  
Gravitational Lensing ◽  
Cosmological Models ◽  
Distance Measures ◽  
Energy Component ◽  
Dark Energy Component ◽  
Image Separation ◽  
Cosmological Tests ◽  
Age Of The Universe ◽  
The Universe

Various astronomical observations have been consistently making a strong case for the existence of a component of dark energy with negative pressure in the universe. It is now necessary to take the dark energy component(s) into account in gravitational lensing statistics and other cosmological tests. By using the comoving distance we derive analytic but simple expressions for the optical depth of multiple image, the expected value of image separation and the probability distribution of image separation caused by an assemble of singular isothermal spheres in general FRW cosmological models with dark energy component(s). We also present the kinematical and dynamical properties of these kinds of cosmological models and calculate the age of the universe and the distance measures, which are often used in classical cosmological tests. In some cases we are able to give formulae that are simpler than those found elsewhere in the literature, which could make the cosmological tests for dark energy component(s) more convenient.

scholarly journals Dark Energy: Nature and Robustness

2005 ◽  
Vol 192 ◽  
pp. 573-578
Author(s):  
A. Blanchard ◽  
Y. Zolnierowski
Keyword(s):  
Dark Energy ◽  
Energy Component ◽  
Dark Energy Component ◽  
Cosmological Data ◽  
The Universe ◽  
Accepted Form

SummarySupernovae have provided the evidence for the existence of a dominant dark energy component of the Universe. The commonly accepted form of such a component is the quintessence. Here, we show that the possible nature of this component is rather well constrained by combining the various existing observational cosmological data. However, relaxing some of the various hypothesis can lead to somewhat different results.

scholarly journals QUANTUM EFFECTS AND SUPERQUINTESSENCE IN THE NEW AGE OF PRECISION COSMOLOGY

2004 ◽  
Vol 13 (10) ◽  
pp. 2255-2259 ◽  
Author(s):  
E. GUNZIG ◽  
ALBERTO SAA
Keyword(s):  
Experimental Data ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Classical Approach ◽  
Constant Ratio ◽  
Energy Component ◽  
Dark Energy Component ◽  
Type Ia ◽  
The Universe

Recent observations of Type Ia supernova at high redshifts establish that the dark energy component of the universe has (a probably constant) ratio between pressure and energy density [Formula: see text]. The conventional quintessence models for dark energy are restricted to the range -1≤w<0, with the cosmological constant corresponding to w=-1. Conformally coupled quintessence models are the simplest ones compatible with the marginally allowed superaccelerated regime (w<-1). However, they are known to be plagued with anisotropic singularities. We argue here that the extension of the classical approach to the semiclassical one, with the inclusion of quantum counterterms necessary to ensure the renormalization, can eliminate the anisotropic singularities preserving the isotropic behavior of conformally coupled superquintessence models. Hence, besides of having other interesting properties, they are consistent candidates to describe the superaccelerated phases of the universe compatible with the present experimental data.

scholarly journals Taxonomy of Dark Energy Models

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 163
Author(s):  
Verónica Motta ◽  
Miguel A. García-Aspeitia ◽  
Alberto Hernández-Almada ◽  
Juan Magaña ◽  
Tomás Verdugo
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Energy Component ◽  
The Past ◽  
Energy Models ◽  
The Status ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

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.

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 CAN THE EXISTENCE OF DARK ENERGY BE DIRECTLY DETECTED?

2009 ◽  
Vol 24 (18n19) ◽  
pp. 3426-3436 ◽  
Author(s):  
MARTIN L. PERL
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Total Mass ◽  
Mass Density ◽  
Mass Energy ◽  
Dark Energy Density ◽  
Astronomical Observations ◽  
Expansion Of The Universe ◽  
The Universe

Over the last decade, astronomical observations show that the acceleration of the expansion of the universe is greater than expected from our understanding of conventional general relativity, the mass density of the visible universe, the size of the visible universe and other astronomical measurements. The additional expansion has been attributed to a variety of phenomenon that have been given the general name of dark energy. Dark energy in the universe seems to comprise a majority of the energy in the visible universe amounting to about three times the total mass energy. But locally the dark energy density is very small. However it is not zero. In this paper I describe the work of others and myself on the question of whether dark energy density can be directly detected. This is a work-in-progress and I have no answer at present.

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