scholarly journals Interacting holographic Ricci dark energy as running vacuum

2019 ◽  
Vol 28 (04) ◽  
pp. 1950060 ◽  
Author(s):  
Paxy George ◽  
V. Mohammed Shareef ◽  
Titus K. Mathew
Keyword(s):  
System Analysis ◽  
Component Model ◽  
Coupling Constant ◽  
De Sitter ◽  
Ricci Dark Energy ◽  
Macroscopic System ◽  
Two Component ◽  
Cosmological Data ◽  
End Stage ◽  
The Universe

Earlier studies have shown that in a two component model of the universe with dark matter and the running vacuum energy, which is phenomenologically a combination of [Formula: see text] and [Formula: see text] either eternal deceleration or acceleration is produced in the absence of a bare constant in the density of the running vacuum. In this paper, we have shown that in the interaction scenario, where the interaction between matter and vacuum is introduced through a phenomenological term, the two component model is capable of causing a transition from a prior decelerated to a later accelerated epoch without a bare constant in the running vacuum density. On contrasting the model with the cosmological data, we have found that the interaction coupling constant is small enough for a slow decay of the running vacuum. The model is subjected to dynamical system analysis, which revealed that the end de Sitter phase of the model is a stable one. We did an analysis on the thermal behavior of the system, which shows that the entropy is bounded at the end stage so that the system behaves like an ordinary macroscopic system. Apart from these, we have also performed the state finder diagnostic analysis which implies the quintessence nature of running vacuum and confirms that the model will approach the standard [Formula: see text]CDM in the future.

scholarly journals An interacting holographic dark energy model within an induced gravity brane

2020 ◽  
Vol 29 (09) ◽  
pp. 2050066
Author(s):  
Moulay-Hicham Belkacemi ◽  
Zahra Bouabdallaoui ◽  
Mariam Bouhmadi-López ◽  
Ahmed Errahmani ◽  
Taoufik Ouali
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Late Time ◽  
De Sitter ◽  
Ricci Dark Energy ◽  
Induced Gravity ◽  
Big Rip ◽  
Dark Energy Component ◽  
Braneworld Model ◽  
The Universe

In this paper, we present a model for the late-time evolution of the universe where a dark energy-dark matter interaction is invoked. Dark energy is modeled through an holographic Ricci dark energy component. The model is embedded within an induced gravity braneworld model. For suitable choices of the interaction coupling, the big rip and little rip induced by the holographic Ricci dark energy, in a relativistic model and in an induced gravity braneworld model, are removed. In this scenario, the holographic dark energy will have a phantom like behavior even though the brane is asymptotically de Sitter.

scholarly journals INTERACTING MODIFIED HOLOGRAPHIC RICCI DARK ENERGY MODEL AND STATEFINDER DIAGNOSIS IN FLAT UNIVERSE

2014 ◽  
Vol 23 (03) ◽  
pp. 1450024 ◽  
Author(s):  
PRASEETHA PANKUNNI ◽  
TITUS K. MATHEW
Keyword(s):  
Dark Energy ◽  
Equations Of State ◽  
State Parameter ◽  
Chaplygin Gas ◽  
De Sitter ◽  
Ricci Dark Energy ◽  
Future Evolution ◽  
Standard Models ◽  
The Universe ◽  
Far Future

In this paper, we have considered the modified holographic Ricci dark energy interacting with dark matter through a nongravitational coupling. We took three phenomenological forms for the interaction term Q in the model, where, in general, it is proportional to the Hubble parameter and densities of the dark sectors, that Q = ρde+ρm, ρmand ρde, respectively. We have obtained analytical solutions for the three interacting models, and studied the evolutions of equations of state parameter and deceleration parameter. The results are compared with the observationally constrained values for the best parameters of the model. In general, we have shown that the equation of state of models are showing a de Sitter type behavior, in the far future evolution of the universe. We have also done the statefinder analysis of the model to discriminate it from other standard models of dark energy and have shown that the present r–s values of the models were in the range of the r–s value of the Chaplygin gas model of dark energy.

scholarly journals Dynamics in Interacting Scalar-Torsion Cosmology

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 244
Author(s):  
Andronikos Paliathanasis
Keyword(s):  
Special Interest ◽  
System Analysis ◽  
Stable Solution ◽  
Gravitational Theory ◽  
De Sitter ◽  
Dark Sector ◽  
Background Space ◽  
Qualitative Evolution ◽  
De Sitter Universe ◽  
The Universe

In a spatially flat Friedmann–Lemaître–Robertson–Walker background space, we consider a scalar-torsion gravitational model which has similar properties to the dilaton theory. This teleparallel model is invariant under a discrete transformation similar to the Gasperini–Veneziano duality transformation. Moreover, in the gravitational action integral, we introduce the Lagrangian function of a pressureless fluid source which is coupled to the teleparallel dilaton field. This specific gravitational theory with interaction in the dark sector of the universe was investigated by using methods of the dynamical system analysis. We calculate that the theory provides various areas of special interest for the evolution of the cosmological history. Inflationary scaling solutions and the de Sitter universe are recovered. Furthermore, we calculate that there exist an attractor which provides a stable solution where the two fluid components, the scalar field and the pressureless matter, contribute in the cosmological fluid. This solution is of special interest because it can describe the present epoch. Finally, the qualitative evolution of the cosmographic parameters is discussed.

scholarly journals Diagnostics for generalized power-law torsion–matter coupling f(T) model

2019 ◽  
Vol 28 (02) ◽  
pp. 1950031
Author(s):  
Rui-Hui Lin ◽  
Qiang Wen ◽  
Xiang-Hua Zhai ◽  
Xin-Zhou Li
Keyword(s):  
Dark Energy ◽  
Power Law ◽  
System Analysis ◽  
Coupling Model ◽  
Chaplygin Gas ◽  
Accelerated Expansion ◽  
De Sitter ◽  
Matter Coupling ◽  
Energy Models ◽  
The Universe

The currently accelerated expansion of our universe is unarguably one of the most intriguing problems in today’s physics research. Two realistic nonminimal torsion–matter coupling [Formula: see text] models have been established and studied in our previous papers [C. J. Feng, F. F. Ge, X. Z. Li, R. H. Lin and X. H. Zhai, Phys. Rev. D 92 (2015) 104038; R. H. Lin, X. H. Zhai and X. Z. Li, Eur. Phys. J. C 77 (2017) 504] aiming to explain this “dark energy” problem. In this paper, we study the generalized power-law torsion–matter coupling [Formula: see text] model. Dynamical system analysis shows that the three expansion phases of the universe, i.e. the radiation-dominated era, the matter-dominated era and the dark energy-dominated era, can all be reproduced in this generalized model. By using the statefinder and [Formula: see text] diagnostics, we find that the different cases of the model can be distinguished from each other and from other dark energy models such as the two models in our previous papers, [Formula: see text]CDM, quintessence and Chaplygin gas. Furthermore, the analyses also show that all kinds of generalized power-law torsion–matter coupling model are able to cross the [Formula: see text] divide from below to above, which is a realization of quintom scenario. The decrease of the energy density resulting from the crossing of [Formula: see text] will make the catastrophic fate of the universe avoided and a de Sitter expansion fate in the future will be approached.

scholarly journals Characteristic properties of two different viscous cosmology models for the future universe

2017 ◽  
Vol 32 (04) ◽  
pp. 1750026 ◽  
Author(s):  
Ben David Normann ◽  
Iver Brevik
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Component Model ◽  
De Sitter ◽  
A Value ◽  
Small Constant ◽  
Two Component ◽  
The Future ◽  
State Formula ◽  
The One

We analyze characteristic properties of two different cosmological models: (i) a one-component dark energy model where the bulk viscosity [Formula: see text] is associated with the fluid as a whole, and (ii) a two-component model where [Formula: see text] is associated with a dark matter component [Formula: see text] only, the dark energy component considered inviscid. Shear viscosity is omitted. We assume throughout the simple equation-of-state [Formula: see text] with [Formula: see text] a constant. In the one-component model, we consider two possibilities, either to take [Formula: see text] proportional to the scalar expansion (equivalent to the Hubble parameter), in which case the evolution becomes critically dependent on the value of the small constant [Formula: see text] and the magnitude of [Formula: see text], or we consider the case [Formula: see text], where a de Sitter final stage is reached in the future. In the two-component model, we consider only the case where the dark matter viscosity [Formula: see text] is proportional to the square of [Formula: see text], where again a de Sitter form is found in the future. In this latter case, the formalism is supplemented by a phase space analysis. As a general result of our considerations, we suggest that a value [Formula: see text] for the present viscosity is reasonable, and that the two-component model seems to be favored.

scholarly journals The non-minimal coupling constant and the primordial de Sitter state

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
Orest Hrycyna
Keyword(s):  
Scalar Field ◽  
Potential Functions ◽  
Constant Parameter ◽  
Coupling Constant ◽  
De Sitter ◽  
Dimensional Theory ◽  
Minimal Coupling ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Friedmann Robertson Walker

AbstractDynamical systems methods are used to investigate dynamics of a flat Friedmann–Robertson–Walker cosmological model with the non-minimally coupled scalar field and a potential function. Performed analysis distinguishes the value of non-minimal coupling constant parameter $$\xi =\frac{3}{16}$$ ξ = 3 16 , which is the conformal coupling in five dimensional theory of gravity. It is shown that for a monomial potential functions at infinite values of the scalar field there exist generic de Sitter and Einstein–de Sitter states. The de Sitter state is unstable with respect to expansion of the Universe for potential functions which do not change faster than linearly. This leads to a generic cosmological evolution without the initial singularity.

Radiometric Chronology of Neh–nar Glacier, Kashmir

1982 ◽  
Vol 28 (98) ◽  
pp. 91-105 ◽  
Author(s):  
V. N. Nijampurkar ◽  
N. Bhandari ◽  
C. P. Vohra ◽  
V. Krishnan
Keyword(s):  
Average Rate ◽  
Component Model ◽  
Vertical Profiles ◽  
Kashmir Valley ◽  
Movement Rate ◽  
Accumulation Zone ◽  
Core Samples ◽  
Surface Samples ◽  
Two Component

AbstractSurface and core samples of Neh–nar Glacier in the Kashmir Valley have been analysed for the radionuclides 32Si. 210Pb, 40K, and 137Cs. The lateral and vertical profiles (at an altitude of about 4 140 m) reveal:(1)32Si activity decreasing slowly from the accumulation zone to 4 050 m altitude and then abruptly towards the snout.(2)Five zones of alternating high and low 210Pb activity in the surface samples.(3)An horizon at between 2 and 3 m depth containing 210Pb activity above natural levels. This horizon is also associated with 137Cs and a maximum in total ß activity.The ice samples have been dated on the basis of a simplified two–component model, the “fresh“contribution determined by 2l0Pb and the old component by 32Si. The following conclusions can be drawn from these observations:(1)The model age of the snout ice is c. 850 years.(2)The average rate of ice movement in the lower glacier is about 2 m/year, which compares well with the annual movement rate of 2.65 m/year observed since 1974.

Cosmological spacetimes

2018 ◽  
Author(s):  
Nathalie Deruelle ◽  
Jean-Philippe Uzan
Keyword(s):  
Cosmological Model ◽  
Large Scale ◽  
Cosmic Time ◽  
De Sitter ◽  
Matter Distribution ◽  
Observable Universe ◽  
Cosmological Principle ◽  
Riemannian Spacetime ◽  
The Universe ◽  
Copernican Principle

This chapter provides a few examples of representations of the universe on a large scale—a first step in constructing a cosmological model. It first discusses the Copernican principle, which is an approximation/hypothesis about the matter distribution in the observable universe. The chapter then turns to the cosmological principle—a hypothesis about the geometry of the Riemannian spacetime representing the universe, which is assumed to be foliated by 3-spaces labeled by a cosmic time t which are homogeneous and isotropic, that is, ‘maximally symmetric’. After a discussion on maximally symmetric space, this chapter considers spacetimes with homogenous and isotropic sections. Finally, this chapter discusses Milne and de Sitter spacetimes.

scholarly journals Estimation of Galactic Model Parameters by Interval Method

1996 ◽  
Vol 169 ◽  
pp. 713-714
Author(s):  
S. A. Kutuzov
Keyword(s):  
Mutual Interaction ◽  
Component Model ◽  
Model Parameters ◽  
Interval Method ◽  
Two Component ◽  
The Galaxy ◽  
Galactic Model

The interval method of estimating model parameters (MPs) for the Galaxy was suggested earlier (Kutuzov 1988). Intervals are proposed to be used both for observational estimates of galactic parameters (GPs) and for the values of MPs. In this work we consider a model as a tool for studying mutual interaction of GPs. Two-component model is considered (Kutuzov, Ossipkov 1989). We have to estimate the array P of eight MPs.

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