scholarly journals Non-Extensive Thermodynamics Effects in the Cosmology of f(T) Gravity

Symmetry ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 75
Author(s):  
Asmaa G. Shalaby ◽  
Vasilis K. Oikonomou ◽  
Gamal G. L. Nashed
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Energy Equation ◽  
State Parameter ◽  
Gravitational Theory ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Equation Of State Parameter ◽  
Relativistic Matter

Using f(T) gravitational theory, we construct modified cosmological models via the first law of thermodynamics by using the non-extensive thermodynamics framework, the effects of which are captured by the parameter δ. The resulting cosmological equations are modified compared to the standard Einstein-Hilbert ones, with the modifications coming from the f(T) gravitational theory and from the non-extensive parameter which quantifies the non-extensive thermodynamics effects quantified by the parameter δ, which when is set equal to unity, one recovers the field equations of f(T) gravity. We study in detail the cosmological evolution of the model in the presence of collisionless non-relativistic matter case, and we derive the exact forms of the dark energy density parameter and of the dark energy equation of state parameter, from which we impose constraints on the non-extensive thermodynamics parameter, δ, by using the Planck 2018 data on cosmological parameters. Accordingly, we repeat our calculations after including the relativistic matter along with the non-relativistic one, and we derive the new forms of the dark energy density parameter and of the dark energy equation of state parameter. Our study shows that the inclusion of non-extensive thermodynamic effects, quantified by the parameter δ, for a flat Friedmann-Robertson-Walker Universe, has measurable differences compared with the normal thermodynamics case. We confront our results with Type Ia supernovae observations for z≥0.4 and we obtain reasonably agreement with the observational data.

scholarly journals PARAMETRIZATION OF THE DARK ENERGY EQUATION OF STATE

2007 ◽  
Vol 16 (10) ◽  
pp. 1581-1591 ◽  
Author(s):  
VINOD B. JOHRI ◽  
P. K. RATH
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Comparative Study ◽  
Energy Equation ◽  
Critical Evaluation ◽  
Density Parameter ◽  
Dark Energy Density ◽  
History Of ◽  
The Universe

A comparative study of various parametrizations of the dark energy equation of state is made. Astrophysical constraints from LSS, CMB and BBN are laid down to test the physical viability and cosmological compatibility of these parametrizations. A critical evaluation of the four-index parametrizations reveals that Hannestad–Mörtsell as well as Lee parametrizations are simple and transparent in probing the evolution of the dark energy during the expansion history of the universe and they satisfy the LSS, CMB and BBN constraints on the dark energy density parameter.

Chaplygin scalar field reconstruction of the modified ghost dark energy model

2015 ◽  
Vol 93 (8) ◽  
pp. 855-861
Author(s):  
Kayoomars Karami
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Energy Density ◽  
Dark Energy Model ◽  
State Parameter ◽  
Energy Model ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Ghost Dark Energy

Within the framework of Einstein gravity, we establish a correspondence between the Chaplygin scalar field model and the modified ghost dark energy model. We consider a spatially non-flat Friedmann–Robertson–Walker universe containing modified ghost dark energy and dark matter that are in interaction with each other. We solve the differential equation governing the dimensionless modified ghost dark energy density parameter numerically. Then we obtain the evolutionary behaviors of both the energy density and equation of state parameters of the modified ghost dark energy. More interesting is that the equation of state parameter at the present time can cross the phantom divide line provided the interaction parameter b2 > 0.15 is compatible with the observations. Furthermore, we reconstruct both the Chaplygin gas scalar field and potential according to the evolutionary behavior of the modified ghost dark energy model.

scholarly journals DARK ENERGY IN GLOBAL BRANE UNIVERSE

2007 ◽  
Vol 16 (10) ◽  
pp. 1633-1640 ◽  
Author(s):  
YONGLI PING ◽  
LIXIN XU ◽  
CHENGWU ZHANG ◽  
HONGYA LIU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Exact Solutions ◽  
Deceleration Parameter ◽  
Mass Density ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Friedmann Equations

We discuss the exact solutions of brane universes and the results indicate that the Friedmann equations on the branes are modified with a new density term. Then, we assume the new term as the density of dark energy. Using Wetterich's parametrization equation of state (EOS) of dark energy, we obtain that the new term varies with the redshift z. Finally, the evolutions of the mass density parameter Ω2, dark energy density parameter Ωx and deceleration parameter q2 are studied.

A study on the modified holographic Ricci dark energy in logarithmic f(T) gravity

2013 ◽  
Vol 91 (4) ◽  
pp. 351-354 ◽  
Author(s):  
Antonio Pasqua ◽  
Surajit Chattopadhyay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Modified Gravity ◽  
State Parameter ◽  
Ricci Dark Energy ◽  
Equation Of State Parameter ◽  
Interaction Term ◽  
The Universe

In this paper, we have studied and investigated the behavior of a modified holographic Ricci dark energy (DE) model interacting with pressureless dark matter (DM) under the theory of modified gravity, dubbed logarithmic f(T) gravity. We have chosen the interaction term between DE and DM in the form Q = 3γHρm and investigated the behavior of the torsion, T, the Hubble parameter, H, the equation of state parameter, ωDE, the energy density of DE, ρDE, and the energy density contribution due to torsion, ρT, as functions of the redshift, z. We have found that T increases with the redshift, z, H increases with the evolution of the universe, ωDE has a quintessence-like behavior, and both energy densities increase going from higher to lower redshifts.

scholarly journals DILATON COUPLED QUINTESSENCE MODEL IN THE ω - ω′ PLANE

2007 ◽  
Vol 16 (07) ◽  
pp. 1109-1117 ◽  
Author(s):  
Z. G. HUANG ◽  
H. Q. LU ◽  
W. FANG
Keyword(s):  
Dark Energy ◽  
Field Equation ◽  
Scalar Field ◽  
Equation Of State ◽  
State Parameter ◽  
Equation Of Motion ◽  
Gravitational Theory ◽  
Scalar Field Equation ◽  
Equation Of State Parameter ◽  
Quintessence Model

In this paper, we regard the dilaton in Weyl-scaled induced gravitational theory as a coupled quintessence. Based on this consideration, we investigate the dilaton coupled quintessence (DCQ) model in the ω - ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). We find the scalar field equation of motion in the ω - ω′ plane, and show mathematically the properties of attractor solutions which correspond to ωσ ~ -1, ωσ = 1. Finally, we find that our model is a tracking one which belongs to "freezing" type models classified in the ω - ω′ plane.

scholarly journals Reconstruction of interaction rate in holographic dark energy model with Hubble horizon as the infrared cut-off

2017 ◽  
Vol 26 (11) ◽  
pp. 1750136 ◽  
Author(s):  
Abdulla Al Mamon
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Energy Equation ◽  
Present Model ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Model Parameters ◽  
Interaction Rate ◽  
Equation Of State Parameter

This work is the reconstruction of the interaction rate of holographic dark energy whose infrared cut-off scale is set by the Hubble length. We have reconstructed the interaction rate between dark matter and the holographic dark energy for a specific parameterization of the effective equation-of-state parameter. We have obtained observational constraints on the model parameters using the latest type Ia supernova (SNIa), baryon acoustic oscillations (BAO) and cosmic microwave background (CMB) radiation datasets. We have found that for the present model, the interaction rate increases with expansion and remains positive throughout the evolution. For a comprehensive analysis, we have also compared the reconstructed results of the interaction rate with other well-known holographic dark energy models. The nature of the deceleration parameter, the statefinder parameters and the dark energy equation-of-state parameter have also been studied for the present model. It has been found that the deceleration parameter favors the past decelerated and recent accelerated expansion phase of the universe. It has also been found that the dark energy equation-of-state parameter shows a phantom nature at the present epoch.

scholarly journals GRAVITATIONAL LENSING STATISTICS AS A PROBE OF DARK ENERGY

2000 ◽  
Vol 15 (16) ◽  
pp. 1023-1029 ◽  
Author(s):  
ZONG-HONG ZHU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Cosmological Model ◽  
Gravitational Lensing ◽  
Mass Density ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Analytic Expression ◽  
Cosmic Mass

By using the comoving distance, we derive an analytic expression for the optical depth of gravitational lensing, which depends on the redshift to the source and the cosmological model characterized by the cosmic mass density parameter Ωm, the dark energy density parameter Ωm and its equation of state ωx = px/ρx. It is shown that, the larger the dark energy density and the more negative its pressure, the higher is the gravitational lensing probability. This fact can provide an independent constraint for dark energy.

scholarly journals Modified cosmology through Kaniadakis horizon entropy

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Andreas Lymperis ◽  
Spyros Basilakos ◽  
Emmanuel N. Saridakis
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Equation ◽  
State Parameter ◽  
De Sitter ◽  
Single Model ◽  
Dark Energy Density ◽  
Horizon Entropy ◽  
Analytical Expressions ◽  
The Universe

AbstractWe apply the gravity-thermodynamics conjecture, namely the first law of thermodynamics on the Universe horizon, but using the generalized Kaniadakis entropy instead of the standard Bekenstein–Hawking one. The former is a one-parameter generalization of the classical Boltzmann–Gibbs–Shannon entropy, arising from a coherent and self-consistent relativistic statistical theory. We obtain new modified cosmological scenarios, namely modified Friedmann equations, which contain new extra terms that constitute an effective dark energy sector depending on the single model Kaniadakis parameter K. We investigate the cosmological evolution, by extracting analytical expressions for the dark energy density and equation-of-state parameters and we show that the Universe exhibits the usual thermal history, with a transition redshift from deceleration to acceleration at around 0.6. Furthermore, depending on the value of K, the dark energy equation-of-state parameter deviates from $$\Lambda $$ Λ CDM cosmology at small redshifts, while lying always in the phantom regime, and at asymptotically large times the Universe always results in a dark-energy dominated, de Sitter phase. Finally, even in the case where we do not consider an explicit cosmological constant the resulting cosmology is very interesting and in agreement with the observed behavior.

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