scholarly journals A FIVE-DIMENSIONAL MODEL WITH A FIFTH DIMENSION AS FUNDAMENTAL AS TIME IN TERMS OF A COSMOLOGICAL APPROACH

2013 ◽  
Vol 28 (21) ◽  
pp. 1350095 ◽  
Author(s):  
GIZEM ŞENGÖR ◽  
METIN ARIK
Keyword(s):  
Dark Energy ◽  
The Other ◽  
Accelerated Expansion ◽  
Internal Space ◽  
Conformally Flat ◽  
Dimensional Model ◽  
Time Dimension ◽  
Flat Spacetime ◽  
Fifth Dimension ◽  
Five Dimensional Model

In five-dimensional cosmological models, the convention is to include the fifth dimension in a way similar to the other space dimensions. In this paper, we attempt to introduce the fifth dimension in a way that a time dimension would be introduced. With such an internal space, we are able to obtain accelerated expansion without introducing dark energy. We obtain a five-dimensional flat, meaning both Ricci flat and conformally flat, spacetime into which all relevant four-dimensional cosmologies can be locally embedded. We also argue on the choice of the cosmological frame. The choice that is simplest and most convenient in terms of dimensional analysis, amounts to a linearly expanding universe.

scholarly journals DARK ENERGY FROM FIFTH-DIMENSIONAL BRANS–DICKE THEORY

2013 ◽  
Vol 22 (10) ◽  
pp. 1350070 ◽  
Author(s):  
AMIR F. BAHREHBAKHSH ◽  
MEHRDAD FARHOUDI ◽  
HAJAR VAKILI
Keyword(s):  
Dark Energy ◽  
Energy Momentum Tensor ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Conservation Equation ◽  
Scale Factor ◽  
The State ◽  
The Other ◽  
Distance Modulus ◽  
Fifth Dimension

Following the approach of the induced-matter theory, we investigate the cosmological implications of a five-dimensional Brans–Dicke (BD) theory, and propose to explain the acceleration of the universe. After inducing in a four-dimensional hypersurface, we classify the energy–momentum tensor into two parts in a way that, one part represents all kind of the matter (the baryonic and dark) and the other one contains every extra terms emerging from the scale factor of the fifth dimension and the scalar field, which we consider as the energy–momentum tensor of dark energy. We also separate the energy–momentum conservation equation into two conservation equations, one for matter and the other for dark energy. We perform this procedure for different cases, without interacting term and with two particular (suitable) interacting terms between the two parts. By assuming the parameter of the state equation for dark energy to be constant, the equations of the model admit the power-law solutions. Though, the noninteracting case does not give any accelerated universe, but the interacting cases give both decelerated and accelerated universes. For the interacting cases, we figure out analytically the acceptable ranges of some parameters of the model, and also investigate the data analysis to test the model parameter values consistency with the observational data of the distance modulus of 580 SNe Ia compiled in Union2.1. For one of these interacting cases, the best fitted values suggest that BD coupling constant (ω) is ≃ -7.75, however, it also gives the state parameter of dark energy (wX) equal to ≃ -0.67. In addition, the model gives the Hubble and deceleration parameters at the present time to be H◦ ≃ 69.4 (km/s)/Mpc and q◦ ≃ -0.38 (within their confidence intervals), where the scale factor of the fifth dimension shrinks with the time.

scholarly journals FIELD CONFIGURATIONS AND THEIR INSTABILITY INDUCED BY HIGHER DIMENSIONS OF SPACE–TIME: AN EXAMPLE

1999 ◽  
Vol 14 (34) ◽  
pp. 2393-2401 ◽  
Author(s):  
LAURA MERSINI
Keyword(s):  
Higher Dimensions ◽  
Energy Difference ◽  
Field Configuration ◽  
The Other ◽  
Four Dimensions ◽  
Fifth Dimension ◽  
True Vacuum ◽  
Twisted Field ◽  
Five Dimensional Model ◽  
The Stability

We use the model of L. Randall et al.3 to investigate the stability of allowed quantum field configurations. Firstly, we find that due to the topology of this five-dimensional model, there are two possible configurations of the scalar field, untwisted and twisted. They give rise to two types of instability. Secondly, when allowed to interact in the brane, the untwisted field is shown to be unstable even if it is at the true vacuum ground state as a result of one-loop corrections that arise from coupling with the twisted field. On the other hand, the twisted field can make the two three-branes (that are otherwise identical in their properties and geometry) distinguishable therefore causing an energy difference between them. That is due to the antiperiodicity of the twisted fields, when rotating with π to go from one three-brane to the other. This energy difference between the branes renders the fifth dimension unstable. This toy model is simple enough to use to illustrate a point that can be important for the general case of any high dimension model, namely: higher dimensions, besides many other effects can also induce more than one field configuration and that can have consequences (e.g. instabilities) even after reducing the problem to four dimensions.

scholarly journals Harnessing Dark Energy in Five-dimensional Brans-Dicke Universe

2021 ◽  
Vol 31 (3) ◽  
Author(s):  
Kangujam Priyokumar Singh ◽  
Koijam Manihar Singh
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Fifth Dimension ◽  
Big Rip ◽  
Expansion Of The Universe ◽  
New Type ◽  
The Universe ◽  
Accepted Form

In trying to explain the present accelerated expansion of the universe in the light of a five-dimensional Brans-Dicke theory, it is found that the fifth dimension itself here acts as a source of dark energy. It may be taken as a curvature-induced form of dark energy, in one case of which it behaves similar to that form of dark energy arising out of the cosmological constant which is the most commonly accepted form of dark energy. It is also found that this new type of dark energy is free from big rip singularity and may be taken as a viable form of dark energy which can explain some of physical mysteries of the universe.

scholarly journals INCONSISTENCES IN INTERACTING AGEGRAPHIC DARK ENERGY MODELS

2011 ◽  
Vol 26 (40) ◽  
pp. 3055-3066
Author(s):  
CHENG-YI SUN ◽  
YU SONG
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
The Other ◽  
Accelerated Expansion ◽  
Agegraphic Dark Energy ◽  
Energy Models

It is found that the origin agegraphic dark energy tracks the matter in the matter-dominated epoch and then the subsequent dark-energy-dominated epoch becomes impossible. It is argued that the difficulty can be removed when the interaction between the agegraphic dark energy and dark matter is considered. In the note, by discussing three different interacting models, we find that the difficulty still stands even in the interacting models. Furthermore, we find that in the interacting models, there exists the other serious inconsistence that the existence of the radiation/matter-dominated epoch contradicts the ability of agegraphic dark energy in driving the accelerated expansion. The contradiction can be avoided in one of the three models if some constraints on the parameters hold.

Cosmological constant

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Vacuum Fluctuations ◽  
Present Epoch ◽  
Modify Gravity ◽  
Expansion Of The Universe ◽  
The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

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.

scholarly journals Forest and Society’s Welfare: Impact Assessment in Lithuania

2021 ◽  
Vol 13 (10) ◽  
pp. 5598
Author(s):  
Stasys Mizaras ◽  
Diana Lukmine
Keyword(s):  
Impact Assessment ◽  
Forest Policy ◽  
Assessment Model ◽  
Dimensional Model ◽  
Important Goal ◽  
Welfare Impact ◽  
Global Problem ◽  
Five Dimensional Model ◽  
Welfare Index ◽  
The Impact

Effective formation and implementation of forest policy can only be achieved with orientation to the most important goal—increasing society’s welfare. The global problem is, at present, that the impact of forests on society welfare indexes have not been identified. The aim of the study is to design an assessment model and assess the impact of Lithuanian forests on the society welfare index. The impact of forests was determined by multiplying the country’s welfare of society index by the forest contribution coefficient. In this study, to assess the index of the welfare of Lithuanian society, a five-dimensional model with 16 indicators was applied. The study is based on the Eurostat database and on Lithuanian forestry statistics. The Lithuanian welfare of society index calculated according to the model was 51.4% and the contribution of forests in this index was 3.9%. It represented 7.6% of the index of the welfare of society. Forests have the greatest impact in the environmental dimension, according to the assessment results.

scholarly journals FORMATION OF DARK MATTER HALOES IN A HOMOGENEOUS DARK ENERGY UNIVERSE

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1397-1403
Author(s):  
L. MARASSI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Large Scale ◽  
State Parameter ◽  
Mass Function ◽  
Accelerated Expansion ◽  
X Ray ◽  
Energy Models ◽  
Dark Energy Component ◽  
Standard Press

Several independent cosmological tests have shown evidences that the energy density of the universe is dominated by a dark energy component, which causes the present accelerated expansion. The large scale structure formation can be used to probe dark energy models, and the mass function of dark matter haloes is one of the best statistical tools to perform this study. We present here a statistical analysis of mass functions of galaxies under a homogeneous dark energy model, proposed in the work of Percival (2005), using an observational flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our analysis, the standard Press–Schechter (PS) approach (where a Gaussian distribution is used to describe the primordial density fluctuation field of the mass function), and the PL (power–law) mass function (where we apply a non-extensive q-statistical distribution to the primordial density field). We conclude that the PS mass function cannot explain at the same time the X-ray and the CMB data (even at 99% confidence level), and the PS best fit dark energy equation of state parameter is ω = -0.58, which is distant from the cosmological constant case. The PL mass function provides better fits to the HIFLUGCS X-ray galaxy data and the CMB data; we also note that the ω parameter is very sensible to modifications in the PL free parameter, q, suggesting that the PL mass function could be a powerful tool to constrain dark energy models.

FRW viscous fluid cosmological model with time-dependent inhomogeneous equation of state

2017 ◽  
Vol 15 (01) ◽  
pp. 1830001 ◽  
Author(s):  
G. S. Khadekar ◽  
Deepti Raut
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Quadratic Form ◽  
State Parameter ◽  
The Other ◽  
Time Dependent ◽  
Inhomogeneous Equation ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Viscous Models

In this paper, we present two viscous models of non-perfect fluid by avoiding the introduction of exotic dark energy. We consider the first model in terms of deceleration parameter [Formula: see text] has a viscosity of the form [Formula: see text] and the other model in quadratic form of [Formula: see text] of the type [Formula: see text]. In this framework we find the solutions of field equations by using inhomogeneous equation of state of form [Formula: see text] with equation of state parameter [Formula: see text] is constant and [Formula: see text].

Sign in / Sign up

Export Citation Format

Share Document