ELKO applications in cosmology

2014 ◽  
Vol 23 (14) ◽  
pp. 1444008 ◽  
Author(s):  
S. H. Pereira ◽  
A. Pinho S. S.
Keyword(s):  
Dark Matter ◽  
Spinor Field ◽  
System Approach ◽  
State Parameter ◽  
Simple Application ◽  
Different Types ◽  
Acceleration Of The Universe ◽  
Interaction Term ◽  
Elko Spinors ◽  
The Universe

A brief review is presented about the ELKO spinor field applied to cosmology, with the main results and limitations of the theory. As a simple application, we have analyzed a model involving the interaction of the ELKO spinor field with dark matter in the universe from a dynamical system approach. When the system is rewritten in terms of the deceleration parameter q and under the assumption that such parameter is nearly constant for some different stages of the evolution, stability points were found for different types of interaction between dark matter and ELKO spinors. Within this new analysis several interesting scenarios are possible, depending on the interaction term. For example, if it is assumed that the equation of the state parameter of the ELKO field is of the phantom type, ωϕ < -1, the current acceleration of the universe can be driven by the decay of dark matter particles into ELKO field. Furthermore, even for ωϕ > 0, the inflationary period can be driven by the decay of the inflaton field (described by the ELKO spinor) into dark matter particles.

scholarly journals INTERACTION BETWEEN DARK ENERGY AND DARK MATTER: OBSERVATIONAL CONSTRAINTS FROM OHD, BAO, CMB AND SNe Ia

2013 ◽  
Vol 22 (14) ◽  
pp. 1350082 ◽  
Author(s):  
SHUO CAO ◽  
NAN LIANG
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Observational Constraints ◽  
Coincidence Problem ◽  
Cosmological Constraints ◽  
Coincidence Index ◽  
Acceleration Of The Universe ◽  
Interaction Term ◽  
Negative Coupling ◽  
The Universe

In order to test if there is energy transfer between dark energy (DE) and dark matter (DM), we investigate cosmological constraints on two forms of nontrivial interaction between the DM sector and the sector responsible for the acceleration of the universe, in light of the newly revised observations including OHD, CMB, BAO and SNe Ia. More precisely, we find the same tendencies for both phenomenological forms of the interaction term Q = 3γHρ, i.e. the parameter γ to be a small number, |γ| ≈ 10-2. However, concerning the sign of the interaction parameter, we observe that γ > 0 when the interaction between dark sectors is proportional to the energy density of dust matter, whereas the negative coupling (γ < 0) is preferred by observations when the interaction term is proportional to DE density. We further discuss two possible explanations to this incompatibility and apply a quantitative criteria to judge the severity of the coincidence problem. Results suggest that the γm IDE model with a positive coupling may alleviate the coincidence problem, since its coincidence index C is smaller than that for the γd IDE model, the interacting quintessence and phantom models by four orders of magnitude.

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 On generalized Lemaitre–Tolman–Bondi metric: Fractal matter at the end of matter–antimatter recombination

2021 ◽  
pp. 2150086
Author(s):  
Sergio L. Cacciatori ◽  
Alessio Marrani ◽  
Federico Re
Keyword(s):  
Dark Matter ◽  
Relativistic Effects ◽  
Partial Explanation ◽  
First Order ◽  
Acceleration Of The Universe ◽  
Particular Solution ◽  
Ancient Times ◽  
The Universe ◽  
Recombination Epoch ◽  
Ltb Metric

Many recent researches have investigated the deviations from the Friedmannian cosmological model, as well as their consequences on unexplained cosmological phenomena, such as dark matter and the acceleration of the Universe. On one hand, a first-order perturbative study of matter inhomogeneity returned a partial explanation of dark matter and dark energy, as relativistic effects due to the retarded potentials of far objects. On the other hand, the fractal cosmology, now approximated by a Lemaitre–Tolman–Bondi (LTB) metric, results in distortions of the luminosity distances of SNe Ia, explaining the acceleration as apparent. In this work, we extend the LTB metric to ancient times. The origin of the fractal distribution of matter is explained as the matter remnant after the matter–antimatter recombination epoch. We show that the evolution of such a inhomogeneity necessarily requires a dynamical generalization of LTB, and we propose a particular solution.

The accelerating universe and dark energy

2014 ◽  
Vol 23 (06) ◽  
pp. 1430012 ◽  
Author(s):  
Charles Baltay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Parameters ◽  
Accelerating Universe ◽  
Heavy Particles ◽  
Familiar World ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Present Understanding

The recent discovery by Riess et al.1 and Perlmutter et al.2 that the expansion of the universe is accelerating is one of the most significant discoveries in cosmology in the last few decades. To explain this acceleration a mysterious new component of the universe, dark energy, was hypothesized. Using general relativity (GR), the measured rate of acceleration translates to the present understanding that the baryonic matter, of which the familiar world is made of, is a mere 4% of the total mass-energy of the universe, with nonbaryonic dark matter making up 24% and dark energy making up the majority 72%. Dark matter, by definition, has attractive gravity, and even though we presently do not know what it is, it could be made of the next heavy particles discovered by particle physicists. Dark energy, however, is much more mysterious, in that even though we do not know what it is, it must have some kind of repulsive gravity and negative pressure, very unusual properties that are not part of the present understanding of physics. Investigating the nature of dark energy is therefore one of the most important areas of cosmology. In this review, the cosmology of an expanding universe, based on GR, is discussed. The methods of studying the acceleration of the universe, and the nature of dark energy, are presented. A large amount of experimentation on this topic has taken place in the decade since the discovery of the acceleration. These are discussed and the present state of knowledge of the cosmological parameters is summarized in Table 7 below. A vigorous program to further these studies is under way. These are presented and the expected results are summarized in Table 10 below. The hope is that at the end of this program, it would be possible to tell whether dark energy is due to Einstein's cosmological constant or is some other new constituent of the universe, or alternately the apparent acceleration is due to some modification of GR.

scholarly journals CONSTRAINING TEVES GRAVITY AS EFFECTIVE DARK MATTER AND DARK ENERGY

2007 ◽  
Vol 16 (12a) ◽  
pp. 2055-2063 ◽  
Author(s):  
HONGSHENG ZHAO
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Elliptical Galaxies ◽  
Dual Roles ◽  
Acceleration Of The Universe ◽  
The Universe

The phenomena customarily described with the standard ΛCDM model are broadly reproduced by an extremely simple model in TeVeS, Bekenstein's1 modification of general relativity motivated by galaxy phenomenology. Our model can account for the acceleration of the Universe seen at SNeIa distances without a cosmological constant, and the accelerations seen in rotation curves of nearby spiral galaxies and gravitational lensing of high-redshift elliptical galaxies without cold dark matter. The model is consistent with BBN and the neutrino mass between 0.05 eV to 2 eV. The TeVeS scalar field is shown to play the effective dual roles of dark matter and dark energy, with the amplitudes of the effects controlled by a μ function of the scalar field, called the μ essence here. We also discuss outliers to the theory's predictions on multiimaged galaxy lenses and outliers on the subgalaxy scale.

scholarly journals Thermodynamical description of the ghost dark energy model

2015 ◽  
Vol 24 (07) ◽  
pp. 1550048 ◽  
Author(s):  
M. Honarvaryan ◽  
A. Sheykhi ◽  
H. Moradpour
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Dark Energy Model ◽  
State Parameter ◽  
Thermal Fluctuations ◽  
Mutual Interaction ◽  
Coincidence Problem ◽  
Ghost Dark Energy ◽  
Equation Of State Parameter ◽  
The Universe

In this paper, we point out thermodynamical description of ghost dark energy (GDE) and its generalization to the early universe. Thereinafter, we find expressions for the entropy changes of these dark energy (DE) candidates. In addition, considering thermal fluctuations, thermodynamics of the DE component interacting with a dark matter (DM) sector is addressed. We will also find the effects of considering the coincidence problem on the mutual interaction between the dark sectors, and thus the equation of state parameter of DE. Finally, we derive a relation between the mutual interaction of the dark components of the universe, accelerated with the either GDE or its generalization, and the thermodynamic fluctuations.

Generalized interaction term inspired dark energy model in fractal universe

2020 ◽  
Vol 35 (15) ◽  
pp. 2050126
Author(s):  
Abdul Jawad ◽  
Saba Qummer ◽  
Shamaila Rani ◽  
M. Younas
Keyword(s):  
Dark Energy ◽  
Dark Energy Model ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Energy Model ◽  
Linear Term ◽  
Accelerated Expansion ◽  
Linear Interaction ◽  
Interaction Term ◽  
The Universe

By assuming generalized nonlinear and linear interaction term between dark matter and dark energy, we investigate the cosmic accelerated expansion of the universe. For this reason, we suppose a flat fractal universe platform as well as Tsallis holographic dark energy model. The Hubble horizon is being adopted as an infrared cutoff and extracted different cosmological parameters as well as plane. It is observed that equation-of-state parameter exhibits the quintom-like nature while ([Formula: see text]–[Formula: see text]) lies in thawing and freezing regions for different parametric values for both the cases. Furthermore, the squared sound speed shows stable behavior for nonlinear interaction term but shows the partially stable behavior for linear term. For both cases, the deceleration parameter leads to the accelerated phase of the universe and the consequences are comparable with observational data. The results for [Formula: see text]–[Formula: see text] plane, leads to the quintessence and phantom region of the universe for nonlinear case while this plane represents the Chaplygin gas behavior for linear term. The [Formula: see text] diagnostic also shows the satisfying results.

scholarly journals A COSMOLOGICAL MODEL WITH FERMIONIC FIELD AND GAUSS–BONNET TERM

2010 ◽  
Vol 25 (06) ◽  
pp. 1267-1278 ◽  
Author(s):  
R. RAKHI ◽  
G. V. VIJAYAGOVINDAN ◽  
K. INDULEKHA ◽  
NOBLE P. ABRAHAM
Keyword(s):  
Cosmological Model ◽  
State Parameter ◽  
The Self ◽  
Late Time ◽  
Fermionic Field ◽  
New Type ◽  
Interaction Term ◽  
The Stability ◽  
The Universe ◽  
Bonnet Term

In this work, a cosmological model inspired by string theory with Gauss–Bonnet term coupled to the fermionic field is taken into consideration. The self-interaction potential is considered as a combination of the scalar and pseudoscalar invariants. Here the cosmological contribution of the coupling of Gauss–Bonnet term with a non-Dirac fermionic field — characterized by an interaction term[Formula: see text] — is investigated. It is observed that the new type of coupling plays a significant role in the accelerating behavior of the universe. Specifically, in addition to the late time acceleration for the universe, [Formula: see text] produces an early decelerating behavior. The behavior of the equation-of-state parameter (w) is such that it guarantees the stability of the theory.

scholarly journals Ghost Dark Energy in the DGP Braneworld

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
M. Abdollahi Zadeh ◽  
A. Sheykhi
Keyword(s):  
Dark Energy ◽  
Sound Speed ◽  
State Parameter ◽  
Late Time ◽  
Ghost Dark Energy ◽  
Equation Of State Parameter ◽  
Interaction Term ◽  
The Stability ◽  
The Universe ◽  
Dgp Braneworld

We investigate the ghost model of dark energy in the framework of DGP braneworld. We explore the cosmological consequences of this model by determining the equation of state parameter, ωD, the deceleration, and the density parameters. We also examine the stability of this model by studying the squared of the sound speed in the presence/absence of interaction term between dark energy and dark matter. We find out that in the absence of interaction between two dark sectors of the universe we have ωD→-1 in the late time, while in the presence of interaction ωD can cross the phantom line -1. In both cases the squared of sound speed vs2 does not show any signal of stability. We also determine the statefinder diagnosis of this model as well as the ωD-ωD′ plane and compare the results with the ΛCDM model. We find that ωD-ωD′ plane meets the freezing region in the absence of interaction between two dark sectors, while it meets both the thawing and the freezing regions in the interacting case.

scholarly journals Modified holographic energy density-driven inflation and some cosmological outcomes

2020 ◽  
Vol 17 (05) ◽  
pp. 2050066
Author(s):  
Gargee Chakraborty ◽  
Surajit Chattopadhyay
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Bulk Viscosity ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Late Time ◽  
Effective Equation ◽  
Inflationary Scenario ◽  
Acceleration Of The Universe ◽  
The Universe

Motivated by the work of Nojiri et al. [S. Nojiri, S. D. Odintsov and E. N. Saridakis, Holographic inflation, Phys. Lett. B 797 (2019) 134829], this study reports a model of inflation under the consideration that the inflationary regime is originated by a type of holographic energy density. The infrared cutoff has been selected based on the modified holographic model that is a particular case of Nojiri–Odintsov holographic dark energy [S. Nojiri and S. D. Odintsov, Unifying phantom inflation with late-time acceleration: Scalar phantom–non-phantom transition model and generalized holographic dark energy, Gen. Relativ. Gravit. 38 (2006) 1285] that unifies phantom inflation with the acceleration of the universe on late time. On getting an analytical solution for Hubble parameter we considered the presence of bulk viscosity and the effective equation of state parameter appeared to be consistent with inflationary scenario with some constraints. It has also being observed that in the inflationary scenario the contribution of bulk viscosity is not of much significance and its influence is increasing with the evolution of the universe. Inflationary observables have been computed for the model and the slow-roll parameters have been computed. Finally, it has been observed that the trajectories in [Formula: see text] are compatible with the observational bound found by Planck. It has been concluded that the tensor to scalar ratio for this model can explain the primordial fluctuation in the early universe as well.

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