scholarly journals Phantom dark energy from nonlocal infrared modifications of general relativity

2014 ◽  
Vol 89 (4) ◽  
Author(s):  
Michele Maggiore
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Phantom Dark Energy

BOUNDS ON f(G) GRAVITY FROM ENERGY CONDITIONS

2010 ◽  
Vol 25 (27) ◽  
pp. 2325-2332 ◽  
Author(s):  
PUXUN WU ◽  
HONGWEI YU
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Modified Gravity ◽  
Energy Conditions ◽  
Model Parameters ◽  
Effective Energy ◽  
Raychaudhuri Equation ◽  
Accelerating Expansion

The f(G) gravity is a theory to modify the general relativity and it can explain the present cosmic accelerating expansion without the need of dark energy. In this paper the f(G) gravity is tested with the energy conditions. Using the Raychaudhuri equation along with the requirement that the gravity is attractive in the FRW background, we obtain the bounds on f(G) from the SEC and NEC. These bounds can also be found directly from the SEC and NEC within the general relativity context by the transformations: ρ → ρm + ρE and p → pm + pE, where ρE and pE are the effective energy density and pressure in the modified gravity. With these transformations, the constraints on f(G) from the WEC and DEC are obtained. Finally, we examine two concrete examples with WEC and obtain the allowed region of model parameters.

scholarly journals Phantom dark energy as an effect of bulk viscosity

2013 ◽  
Vol 88 (12) ◽  
Author(s):  
Hermano Velten ◽  
Jiaxin Wang ◽  
Xinhe Meng
Keyword(s):  
Dark Energy ◽  
Bulk Viscosity ◽  
Phantom Dark Energy

scholarly journals Some Cosmological Solutions of a New Nonlocal Gravity Model

Symmetry ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 917
Author(s):  
Ivan Dimitrijevic ◽  
Branko Dragovich ◽  
Alexey S. Koshelev ◽  
Zoran Rakic ◽  
Jelena Stankovic
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Analytic Function ◽  
Cosmological Constant ◽  
Explicit Form ◽  
Gravity Model ◽  
Necessary Conditions ◽  
Equations Of Motion ◽  
Nonlocal Operator ◽  
Cosmological Solutions

In this paper, we investigate a nonlocal modification of general relativity (GR) with action S = 1 16 π G ∫ [ R − 2 Λ + ( R − 4 Λ ) F ( □ ) ( R − 4 Λ ) ] − g d 4 x , where F ( □ ) = ∑ n = 1 + ∞ f n □ n is an analytic function of the d’Alembertian □. We found a few exact cosmological solutions of the corresponding equations of motion. There are two solutions which are valid only if Λ ≠ 0 , k = 0 , and they have no analogs in Einstein’s gravity with cosmological constant Λ . One of these two solutions is a ( t ) = A t e Λ 4 t 2 , that mimics properties similar to an interference between the radiation and the dark energy. Another solution is a nonsingular bounce one a ( t ) = A e Λ t 2 . For these two solutions, some cosmological aspects are discussed. We also found explicit form of the nonlocal operator F ( □ ) , which satisfies obtained necessary conditions.

Brans–Dicke type teleparallel scalar–tensor theory

2017 ◽  
Vol 32 (34) ◽  
pp. 1750183 ◽  
Author(s):  
Mustafa Salti ◽  
Oktay Aydogdu ◽  
Hilmi Yanar ◽  
Figen Binbay
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Scalar Field ◽  
Noether Symmetry ◽  
Scalar Tensor Theory ◽  
Minimal Coupling ◽  
Energy Effect ◽  
New Model ◽  
Symmetry Approach ◽  
Tensor Theory

The teleparallel alternative of general relativity which is based on torsion instead of curvature is considered as the gravitational sector to explore the dark universe. Inspired from the well-known Brans–Dicke gravity, here, we introduce a new proposal for the galactic dark energy effect. The new model includes a scalar field with self-interacting potential and a non-minimal coupling between the gravity and scalar field. Additionally, we analyze the idea via the Noether symmetry approach and thermodynamics.

scholarly journals Properties of singularities in the (phantom) dark energy universe

2005 ◽  
Vol 71 (6) ◽  
Author(s):  
Shin’ichi Nojiri ◽  
Sergei D. Odintsov ◽  
Shinji Tsujikawa
Keyword(s):  
Dark Energy ◽  
Phantom Dark Energy

scholarly journals Generalized Phenomenological Models of Dark Energy

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Prasenjit Paul ◽  
Rikpratik Sengupta
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Phenomenological Models ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Free Parameters ◽  
The Universe ◽  
Matter Energy

It was first observed at the end of the last century that the universe is presently accelerating. Ever since, there have been several attempts to explain this observation theoretically. There are two possible approaches. The more conventional one is to modify the matter part of the Einstein field equations, and the second one is to modify the geometry part. We shall consider two phenomenological models based on the former, more conventional approach within the context of general relativity. The phenomenological models in this paper consider a Λ term firstly a function of a¨/a and secondly a function of ρ, where a and ρ are the scale factor and matter energy density, respectively. Constraining the free parameters of the models with the latest observational data gives satisfactory values of parameters as considered by us initially. Without any field theoretic interpretation, we explain the recent observations with a dynamical cosmological constant.

Exact solution of phantom dark energy model

2010 ◽  
Vol 19 (11) ◽  
pp. 119801 ◽  
Author(s):  
Wen-Fu Wang ◽  
Zheng-Wei Shui ◽  
Bin Tang
Keyword(s):  
Exact Solution ◽  
Dark Energy ◽  
Dark Energy Model ◽  
Energy Model ◽  
Phantom Dark Energy

Evolution of the Universe with two rotating fluids

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040042
Author(s):  
V. F. Panov ◽  
O. V. Sandakova ◽  
E. V. Kuvshinova ◽  
D. M. Yanishevsky
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Scalar Field ◽  
Bianchi Type ◽  
Relativity Theory ◽  
Anisotropic Fluid ◽  
Rotating Fluids ◽  
General Relativity Theory ◽  
Exponential Expansion ◽  
The Universe

An anisotropic cosmological model with expansion and rotation and the Bianchi type IX metric has been constructed within the framework of general relativity theory. The first inflation stage of the Universe filled with a scalar field and an anisotropic fluid is considered. The model describes the Friedman stage of cosmological evolution with subsequent transition to accelerated exponential expansion observed in the present epoch. The model has two rotating fluids: the anisotropic fluid and dust-like fluid. In the approach realized in the model, the anisotropic fluid describes the rotating dark energy.

Sign in / Sign up

Export Citation Format

Share Document