scholarly journals Gauss–Bonnet modified gravity models with bouncing behavior

2016 ◽  
Vol 31 (17) ◽  
pp. 1650108 ◽  
Author(s):  
Anna Escofet ◽  
Emilio Elizalde
Keyword(s):  
Modified Gravity ◽  
Physical Nature ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
De Sitter ◽  
Eos Parameter ◽  
Energy Models ◽  
De Sitter Universe ◽  
The Universe ◽  
Modified Gravity Models

The following issue is addressed: How the addition of a Gauss–Bonnet term (generically coming from most fundamental theories, as string and M theories), to a viable model, can change the specific properties, and even the physical nature, of the corresponding cosmological solutions? Specifically, brand new original dark energy models are obtained in this way with quite interesting properties, which exhibit, in a unified fashion, the three distinguished possible cosmological phases corresponding to phantom matter, quintessence and ordinary matter, respectively. A model, in which the equation of state (EoS) parameter, w, is a function of time, is seen to lead either to a singularity of the Big Rip kind or to a bouncing solution which evolves into a de Sitter universe with w = −1. Moreover, new Gauss–Bonnet modified gravity models with bouncing behavior in the early stages of the universe evolution are obtained and tested for the validity and stability of the corresponding solutions. They allow for a remarkably natural, unified description of a bouncing behavior at early times and accelerated expansion at present.

scholarly journals THEORETICAL MODELS OF DARK ENERGY

2012 ◽  
Vol 21 (12) ◽  
pp. 1230002 ◽  
Author(s):  
JAEWON YOO ◽  
YUKI WATANABE
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Modified Gravity ◽  
Fine Tuning ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
Late Time ◽  
Spatial Homogeneity ◽  
The Universe ◽  
Modified Gravity Models

Mounting observational data confirm that about 73% of the energy density consists of dark energy which is responsible for the current accelerated expansion of the Universe. We present observational evidences and dark energy projects. We then review various theoretical ideas that have been proposed to explain the origin of dark energy; they contain the cosmological constant, modified matter models, modified gravity models and the inhomogeneous model. The cosmological constant suffers from two major problems: one regarding fine-tuning and the other regarding coincidence. To solve them there arose modified matter models such as quintessence, k-essence, coupled dark energy and unified dark energy. We compare those models by presenting attractive aspects, new rising problems and possible solutions. Furthermore, we review modified gravity models that lead to late-time accelerated expansion without invoking a new form of dark energy; they contain f(R) gravity and the Dvali–Gabadadze–Porrati (DGP) model. We also discuss observational constraints on those models and on future modified gravity theories. Finally we review the inhomogeneous Lemaître–Tolman–Bondi (LTB) model that drops an assumption of the spatial homogeneity of the Universe. We also present basics of cosmology and scalar field theory, which are useful especially for students and novices to understand dark energy models.

Pilgrim dark energy models in fractal universe

2016 ◽  
Vol 26 (06) ◽  
pp. 1750049 ◽  
Author(s):  
Abdul Jawad ◽  
Shamaila Rani ◽  
Ines G. Salako ◽  
Faiza Gulshan
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Freezing And Thawing ◽  
Eos Parameter ◽  
Pilgrim Dark Energy ◽  
Energy Models ◽  
Expansion Behavior ◽  
The Universe

We discuss the cosmological implications of interacting pilgrim dark energy (PDE) models (with Hubble, Granda–Oliveros and generalized ghost cutoffs) with cold dark matter ([Formula: see text]CDM) in fractal cosmology by assuming the flat universe. We observe that the Hubble parameter lies within observational suggested ranges while deceleration parameter represents the accelerated expansion behavior of the universe. The equation of state (EoS) parameter ([Formula: see text]) corresponds to the quintessence region and phantom region for different cases of [Formula: see text]. Further, we can see that [Formula: see text]–[Formula: see text] (where prime indicates the derivative with respect to natural logarithmic of scale factor) plane describes the freezing and thawing regions and also corresponds to [Formula: see text] limit for some cases of [Formula: see text] (PDE parameter). It is also noted that the [Formula: see text]–[Formula: see text] (state-finder parameters) plane corresponds to [Formula: see text] limit and also shows the Chaplygin as well as phantom/quintessence behavior. It is observed that pilgrim dark energy models in fractal cosmology expressed the consistent behavior with recent observational schemes.

F(G) gravity models based on the ordinary and entropy-corrected holographic dark energy models

2013 ◽  
Vol 91 (2) ◽  
pp. 134-139
Author(s):  
M.R. Setare ◽  
B. Malakolkalami ◽  
N. Mohammadipour
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Holographic Dark Energy ◽  
Gravity Models ◽  
Energy Models ◽  
Friedmann Robertson Walker ◽  
Modified Gravity Models

The ordinary and entropy-corrected versions of the holographic dark energy models in the spatially flat Friedmann–Robertson–Walker universe are considered. Then the F(G) modified gravity models as a candidates of dark energy are reconstructed according to the ordinary and entropy-corrected versions of the holographic dark energy models. The EoS parameters corresponding to the F(G) gravity models are obtained. The validity phantom or quintessence models in this framework of the modified gravity are investigated.

scholarly journals de Sitter limit analysis for dark energy and modified gravity models

2017 ◽  
Vol 96 (2) ◽  
Author(s):  
Antonio De Felice ◽  
Noemi Frusciante ◽  
Georgios Papadomanolakis
Keyword(s):  
Dark Energy ◽  
Limit Analysis ◽  
Modified Gravity ◽  
Gravity Models ◽  
De Sitter ◽  
Modified Gravity Models

Reconstructions of f(P) gravity from (m,n) type ordinary and entropy-corrected holographic and Pilgrim dark energy models

2021 ◽  
Author(s):  
Rahul Ghosh ◽  
Ujjal Debnath ◽  
Shuvendu Chakraborty
Keyword(s):  
Dark Energy ◽  
Power Law ◽  
Holographic Dark Energy ◽  
Gravity Models ◽  
Pilgrim Dark Energy ◽  
Energy Models ◽  
Ordinary Power ◽  
Age Of The Universe ◽  
The Universe ◽  
Modified Gravity Models

Modified gravity models are popular among cosmologists, as they can describe the cosmological evolution quite efficiently. Reconstruction of newly introduced [Formula: see text] gravity, with the help of ordinary, power-law entropy corrected and logarithmic entropy-corrected versions of Holographic dark energy (HDE) and Pilgrim dark energy (PDE) models have been studied in this work. For such reconstruction, we have considered the power-law scale factor [Formula: see text]. Further, the classical stabilities (the squared speed of sound method) of such reconstructions and their implications on the nature of the equation of state (EoS) parameters and deceleration parameter with respect to red-shift have also been examined. Finally, we have computed the age of the universe for reconstructed models.

scholarly journals RECONSTRUCTION OF MODIFIED GRAVITY WITH GHOST DARK ENERGY MODELS

2012 ◽  
Vol 27 (18) ◽  
pp. 1250100 ◽  
Author(s):  
A. KHODAM-MOHAMMADI ◽  
M. MALEKJANI ◽  
M. MONSHIZADEH
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Modified Gravity ◽  
Deceleration Parameter ◽  
Accelerated Expansion ◽  
Ghost Dark Energy ◽  
Energy Models ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Generalized Ghost Dark Energy

In this work, we reconstruct the f(R) modified gravity for different ghost and generalized-ghost dark energy (DE) models in FRW flat universe, which describes the accelerated expansion of the universe. The equation of state and deceleration parameter of reconstructed f(R) gravity have been calculated. The equation of state and deceleration parameter of reconstructed f(R)-ghost/generalized-ghost DE, have been calculated. We show that the corresponding f(R) gravity of ghost/generalized-ghost DE model can behave like phantom or quintessence. Also the transition between deceleration to acceleration regime is indicated by deceleration parameter diagram for reconstructed f(R) generalized-ghost DE model.

scholarly journals Unified Inflation and Late-Time Accelerated Expansion with Exponential and R2 Corrections in Modified Gravity

Symmetry ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 794
Author(s):  
Luis Granda
Keyword(s):  
Modified Gravity ◽  
Initial Conditions ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
Late Time ◽  
Time Behavior ◽  
De Sitter ◽  
Cosmological Observations ◽  
Leading Term ◽  
The Stability

Modified gravity models with and exponential function of curvature and R 2 corrections are proposed. At low curvature, the model explains the matter epoch and the late time accelerated expansion while at the inflation epoch the leading term is R 2 . At R → 0 the cosmological constant disappears, giving unified description of inflation and dark energy in pure geometrical context. The models satisfy the stability conditions, pass local tests and are viable in the ( r , m ) -plane, where the trajectories connect the saddle matter dominated critical point ( r = − 1 , m = 0 ) with the late time de Sitter attractor at r = − 2 and 0 < m ≤ 1 . Initial conditions were found, showing that the density parameters evolve in a way consistent with current cosmological observations, predicting late time behavior very close to the Λ CDM with future universe evolving towards the de Sitter attractor.

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 Probing modified gravity in cosmic filaments

2018 ◽  
Vol 619 ◽  
pp. A122 ◽  
Author(s):  
Alex Ho ◽  
Max Gronke ◽  
Bridget Falck ◽  
David F. Mota
Keyword(s):  
Modified Gravity ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
Radial Density ◽  
Post Process ◽  
Global Properties ◽  
Modified Gravity Theories ◽  
Expansion Of The Universe ◽  
Gravity Theories ◽  
The Universe

Multiple modifications of general relativity (GR) have been proposed in the literature in order to understand the nature of the accelerated expansion of the Universe. However, thus far all the predictions of GR have been confirmed with constantly increasing accuracy. In this work, we study the imprints of a particular class of models – “screened” modified gravity theories – on cosmic filaments. We have utilized the N-body code ISIS/RAMSES to simulate the symmetron model and the Hu–Sawicky f(R) model, and we post-process the output with DisPerSE to identify the filaments of the cosmic web. We investigated how the global properties of the filaments – such as their lengths, masses, and thicknesses – as well as their radial density and speed profiles change under different gravity theories. We find that filaments are, on average, shorter and denser in modified gravity models compared to in ΛCDM. We also find that the speed profiles of the filaments are enhanced, consistent with theoretical expectations. Overall, our results suggest that cosmic filaments can be an effective complementary probe of screened modified gravity theories on Mpc scales.

scholarly journals POLYTROPIC AND CHAPLYGIN f(R)-GRAVITY MODELS

2012 ◽  
Vol 21 (12) ◽  
pp. 1250083 ◽  
Author(s):  
K. KARAMI ◽  
M. S. KHALEDIAN
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
De Sitter Space ◽  
Chaplygin Gas ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
De Sitter ◽  
Expansion Of The Universe ◽  
The Universe

We reconstruct different f(R)-gravity models corresponding to the polytropic, standard Chaplygin, generalized Chaplygin, modified Chaplygin and modified variable Chaplygin gas dark energy (DE) models. We also obtain the equation of state (EoS) parameters of the corresponding f(R)-gravity models which describe the accelerated expansion of the universe. We conclude that although the EoS parameters of the obtained f(R)-gravities can behave like phantom or quintessence DE models, they cannot justify the transition from the quintessence state to the phantom regime. Furthermore, the polytropic and Chaplygin f(R)-gravity models in de Sitter space can satisfy the inflation condition.

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