scholarly journals Can a Chameleon Field Be Identified with Quintessence?

Universe ◽  
2020 ◽  
Vol 6 (12) ◽  
pp. 221
Author(s):  
A. N. Ivanov ◽  
M. Wellenzohn
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Cosmological Constant ◽  
Gravitational Theory ◽  
Einstein Equations ◽  
Late Time ◽  
Dark Energy Density ◽  
Full Extent ◽  
Energy Dynamics

In the Einstein–Cartan gravitational theory with the chameleon field, while changing its mass independently of the density of its environment, we analyze the Friedmann–Einstein equations for the Universe’s evolution with the expansion parameter a being dependent on time only. We analyze the problem of an identification of the chameleon field with quintessence, i.e., a canonical scalar field responsible for dark energy dynamics, and for the acceleration of the Universe’s expansion. We show that since the cosmological constant related to the relic dark energy density is induced by torsion (Astrophys. J.2016, 829, 47), the chameleon field may, in principle, possess some properties of quintessence, such as an influence on the dark energy dynamics and the acceleration of the Universe’s expansion, even in the late-time acceleration, but it cannot be identified with quintessence to the full extent in the classical Einstein–Cartan gravitational theory.

FRW viscous modified cosmic Chaplygin gas cosmology in the presence of cosmological constant

2019 ◽  
Vol 16 (09) ◽  
pp. 1950141 ◽  
Author(s):  
G. S. Khadekar ◽  
Aina Gupta ◽  
Kalpana Pande
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Chaplygin Gas ◽  
Frw Universe ◽  
Dark Energy Density ◽  
Linear Combinations ◽  
Linear Differential ◽  
The Stability ◽  
Cardassian Universe

In this paper, we study viscous Modified Cosmic Chaplygin Gas (MCCG) in the presence of cosmological constant in flat FRW universe. We assume that bulk viscosity [Formula: see text] and cosmological constant [Formula: see text] are the linear combinations of two terms, one is constant and other is a function of dark energy density [Formula: see text]. In this framework, we solve the non-linear differential equation analytically and numerically and obtain time dependent dark energy density. We also consider two separate cases of early and late universe and discussed the evolution of dark energy density. We investigate the effect of viscosity and cosmological constant to the evolution of universe and discuss the stability of the model by square of speed of sound. Finally, we compare our model with Cardassian universe.

scholarly journals SUPERNOVA Ia AND GALAXY CLUSTER GAS MASS FRACTION CONSTRAINTS ON DARK ENERGY

2006 ◽  
Vol 21 (29) ◽  
pp. 2197-2204 ◽  
Author(s):  
KYLE M. WILSON ◽  
GANG CHEN ◽  
BHARAT RATRA
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Mass Fraction ◽  
Galaxy Cluster ◽  
Apparent Magnitude ◽  
Model Parameters ◽  
Dark Energy Density ◽  
Energy Models ◽  
Fraction Versus

We use the Riess et al. (2004)1 supernova Ia apparent magnitude versus redshift data and the Allen et al. (2004)2 galaxy cluster gas mass fraction versus redshift data to constrain dark energy models. These data provide complementary constraints that when combined together significantly restrict model parameters and favor slowly-evolving dark energy density models, close to the Einstein cosmological constant limit of dark energy.

scholarly journals CAN BRANS–DICKE SCALAR FIELD ACCOUNT FOR DARK ENERGY AND DARK MATTER?

2006 ◽  
Vol 21 (15) ◽  
pp. 1241-1248 ◽  
Author(s):  
M. ARIK ◽  
M. C. ÇALIK
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Late Time ◽  
Energy Contribution ◽  
Time Solution ◽  
The Universe

By using a linearized non-vacuum late time solution in Brans–Dicke cosmology, we account for the 75% dark energy contribution but not for approximately 23% dark matter contribution to the present day energy density of the universe.

scholarly journals DARK ENERGY DENSITY IN MODELS WITH SPLIT SUPERSYMMETRY AND DEGENERATE VACUA

2012 ◽  
Vol 27 (11) ◽  
pp. 1250063 ◽  
Author(s):  
C. FROGGATT ◽  
R. NEVZOROV ◽  
H. B. NIELSEN
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Susy Breaking ◽  
Vacuum Energy Density ◽  
Dark Energy Density ◽  
Hidden Sector ◽  
Split Supersymmetry ◽  
Breaking Scale

In N = 1 supergravity supersymmetric and nonsupersymmetric Minkowski vacua originating in the hidden sector can be degenerate. In the supersymmetric phase in flat Minkowski space, nonperturbative supersymmetry breakdown may take place in the observable sector, inducing a nonzero and positive vacuum energy density. Assuming that such a supersymmetric phase and the phase in which we live are degenerate, we estimate the value of the cosmological constant. We argue that the observed value of the dark energy density can be reproduced in the split SUSY scenario of SUSY breaking if the SUSY breaking scale is of order of 1010 GeV.

scholarly journals NEW PHYSICS AT LOW ENERGIES AND DARK MATTER-DARK ENERGY TRANSMUTATION

2005 ◽  
Vol 20 (06) ◽  
pp. 1140-1147 ◽  
Author(s):  
E. I. GUENDELMAN ◽  
A. B. KAGANOVICH
Keyword(s):  
Field Theory ◽  
Dark Matter ◽  
Dark Energy ◽  
Energy Density ◽  
Cold Dark Matter ◽  
Late Time ◽  
Frw Universe ◽  
Dark Energy Density ◽  
Total Energy Density ◽  
Fermion Fields

A field theory is proposed where the regular fermionic matter and the dark fermionic matter can be different states of the same "primordial" fermion fields. In regime of the fermion densities typical for normal particle physics, the primordial fermions split into three families identified with regular fermions. When fermion energy density becomes comparable with dark energy density, the theory allows transition to new type of states. The possibility of such Cosmo-Low Energy Physics (CLEP) states is demonstrated by means of solutions of the field theory equations describing FRW universe filled with homogeneous scalar field and uniformly distributed nonrelativistic neutrinos. Neutrinos in CLEP state are drawn into cosmological expansion by means of dynamically changing their own parameters. One of the features of the fermions in CLEP state is that in the late time universe their masses increase as a3/2 (a=a(t) is the scale factor). The energy density of the cold dark matter consisting of neutrinos in CLEP state scales as a sort of dark energy; this cold dark matter possesses negative pressure and for the late time universe its equation of state approaches that of the cosmological constant. The total energy density of such universe is less than it would be in the universe free of fermionic matter at all.

scholarly journals EXOTIC LOW DENSITY FERMION STATES IN THE TWO MEASURES FIELD THEORY: NEUTRINO DARK ENERGY

2006 ◽  
Vol 21 (21) ◽  
pp. 4373-4406 ◽  
Author(s):  
E. I. GUENDELMAN ◽  
A. B. KAGANOVICH
Keyword(s):  
Field Theory ◽  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Energy Momentum Tensor ◽  
Neutrino Energy ◽  
Momentum Tensor ◽  
Dark Energy Density ◽  
Two Measures ◽  
The Universe

There exist field theory models where the fermionic energy–momentum tensor contains a term proportional to [Formula: see text] which may contribute to the dark energy. We show that this new field theory effect can be achieved in the Two Measures Field Theory (TMT) in the cosmological context. TMT is an alternative gravity and matter field theory where the gravitational interaction of fermionic matter is reduced to that of General Relativity when the energy density of the fermion matter is much larger than the dark energy density. In this case also the fifth force problem is solved automatically. In the opposite limit, where the magnitudes of fermionic energy density and scalar field dark energy density become comparable, nonrelativistic fermions can participate in the cosmological expansion in a very unusual manner. Some of the features of such Cosmo-Low-Energy-Physics (CLEP) states are studied in a toy model of the late time universe filled with homogeneous scalar field and uniformly distributed nonrelativistic neutrinos, and the following results are obtained: neutrino mass increases as m ∝ a3/2 (a is the scale factor); the proportionality factor in the noncanonical contribution to the neutrino energy–momentum tensor (proportional to the metric tensor) approaches a constant as a(t) → ∞ and therefore the noncanonical contribution to the neutrino energy density dominates over the canonical one ~ m/a3 ~ a-3/2 at the late enough universe; hence the neutrino gas equation-of-state approaches w = -1, i.e. neutrinos in the CLEP regime behave as a sort of dark energy as a → ∞; the equation-of-state for the total (scalar field + neutrino) energy density and pressure also approaches w = -1 in the CLEP regime; besides the total energy density of such universe is less than it would be in the universe filled with the scalar field alone. An analytic solution is presented. A domain structure of the dark energy seems to be possible. We speculate that decays of the CLEP state neutrinos may be both an origin of cosmic rays and responsible for a late super-acceleration of the universe. In this sense the CLEP states exhibit simultaneously new physics at very low densities and for very high particle masses.

scholarly journals SOME CONSEQUENCES OF DARK ENERGY DENSITY VARYING EXPONENTIALLY WITH SCALE FACTOR

2005 ◽  
Vol 20 (36) ◽  
pp. 2805-2818
Author(s):  
SANIL UNNIKRISHNAN ◽  
T. R. SESHADRI
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Scale Factor ◽  
Dark Energy Density ◽  
Phantom Field

In this paper we have explored the consequences of a model of dark energy with its energy density varying exponentially with the scale factor. We first consider the model with ρϕ∝eκa, where κ is a constant. This is a kind of generalization of the cosmological constant model with κ=0. We show that such an exponentially varying dark energy density with the scale factor naturally leads to an equivalent phantom field. We also consider a model with ρϕ∝eκ/a and show that this also naturally leads to an equivalent phantom field.

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 Supersymmetric large extra dimensions and the cosmological constant problem

2006 ◽  
Vol 84 (6-7) ◽  
pp. 463-472 ◽  
Author(s):  
C P Burgess
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Present Status ◽  
Extra Dimensions ◽  
Large Extra Dimensions ◽  
Cosmological Constant Problem ◽  
Dark Energy Density ◽  
Higher Dimensional

This article briefly summarizes and reviews the motivations for — and the present status of — the proposal that the small size of the observed Dark Energy density can be understood in terms of the dynamical relaxation of two large extra dimensions within a supersymmetric higher dimensional theory.PACS Nos.: 31.15.Pf, 31.30.Jv, 32.10.Hq

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