Possible fates for the accelerating Universe

2006 ◽  
Vol 84 (6-7) ◽  
pp. 583-589
Author(s):  
V Faraoni
Keyword(s):  
Stability Analysis ◽  
Modified Gravity ◽  
Accelerating Universe ◽  
Late Time ◽  
De Sitter ◽  
Recent Proposal ◽  
Time Dynamics ◽  
Big Rip ◽  
Exponential Expansion ◽  
General Potential

The accelerating Universe may end in eternal de Sitter expansion, in a Big Rip, or in super-exponential expansion. We discuss a gauge-independent stability analysis of de Sitter space in scalar–tensor and in modified gravity, the late-time dynamics of a phantom Universe with general potential, and the recent proposal of evading the Big Rip through wormhole tunneling.PACS Nos.: 98.80.–k, 04.50.+h, 04.20.–q

Some late-time cosmological aspects of a Gauss–Bonnet gravity with nonminimal coupling à la Brans–Dicke: solutions and perspectives

2013 ◽  
Vol 91 (4) ◽  
pp. 300-321 ◽  
Author(s):  
Rami Ahmad El-Nabulsi
Keyword(s):  
Scalar Field ◽  
String Theory ◽  
Modified Gravity ◽  
Cosmological Models ◽  
Gravity Theory ◽  
Accelerating Universe ◽  
Late Time ◽  
Nonminimal Coupling ◽  
Bonnet Gravity ◽  
Time Dynamics

In this paper, we study modified homogeneous and isotropic cosmological models based on the Gauss–Bonnet invariant term as models of an accelerating universe. We discuss and criticize the late-time dynamics of six independent cosmological models: in the first model, we discuss the case of the modified gravity f(R) ∝ R1+δ for δ = −1/2 and 1 augmented by the Gauss–Bonnet invariant term; in the second model, we discuss the general case of f(R) ∝ R1+δ accompanied by a nonminimal coupling between the scalar field and the Ricci curvature as well as the Gauss–Bonnet invariant; in the third model, we discuss a generalized modified gravity model that includes the Einstein–Hilbert action, a dynamical cosmological constant, and an effective gravitational coupling constant; in the fourth model, we discuss a more generalized modified scalar–tensor cosmology that includes in addition to the Gauss–Bonnet invariant term, stringy corrections motivated from string and heterotic superstring arguments; in the fifth model, we discuss the cosmological dynamics of a nonminimal scalar Gauss–Bonnet gravity theory motivated from string theory; and finally in the sixth model, we discuss the possibility of having an extension of the generalized modified gravity theory, free from nonminimal coupling with δ = 0, with a Hubble expansion rate and an equation of state parameter that depend on the Gauss–Bonnet invariant term. In the first five models, we conjecture that the Hubble parameter is related to the scalar field by the relation [Formula: see text], which is applied merely to the late time epoch. This ansatz is in fact motivated by some recent advances in scalar–tensor theory and string theory. All of the six models reveal interesting consequences, which are discussed in some detail. Our main objective in this work is to analyze, criticize, and differentiate between viable realistic models and those that are not. Many critical points are discussed in some detail.

scholarly journals Averaging generalized scalar field cosmologies II: locally rotationally symmetric Bianchi I and flat Friedmann–Lemaître–Robertson–Walker models

2021 ◽  
Vol 81 (6) ◽  
Author(s):  
Genly Leon ◽  
Sebastián Cuéllar ◽  
Esteban González ◽  
Samuel Lepe ◽  
Claudio Michea ◽  
...  
Keyword(s):  
Scalar Field ◽  
Nonlinear Dynamical Systems ◽  
Perturbation Parameter ◽  
Time Dependent ◽  
Late Time ◽  
De Sitter ◽  
Time Dynamics ◽  
Locally Rotationally Symmetric ◽  
Bianchi I ◽  
Rotationally Symmetric

AbstractScalar field cosmologies with a generalized harmonic potential and a matter fluid with a barotropic equation of state (EoS) with barotropic index $$\gamma $$ γ for the locally rotationally symmetric (LRS) Bianchi I and flat Friedmann–Lemaître–Robertson–Walker (FLRW) metrics are investigated. Methods from the theory of averaging of nonlinear dynamical systems are used to prove that time-dependent systems and their corresponding time-averaged versions have the same late-time dynamics. Therefore, the simplest time-averaged system determines the future asymptotic behavior. Depending on the values of $$\gamma $$ γ , the late-time attractors of physical interests are flat quintessence dominated FLRW universe and Einstein-de Sitter solution. With this approach, the oscillations entering the system through the Klein–Gordon (KG) equation can be controlled and smoothed out as the Hubble parameter H – acting as time-dependent perturbation parameter – tends monotonically to zero. Numerical simulations are presented as evidence of such behavior.

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 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 Averaging generalized scalar field cosmologies I: locally rotationally symmetric Bianchi III and open Friedmann–Lemaître–Robertson–Walker models

2021 ◽  
Vol 81 (5) ◽  
Author(s):  
Genly Leon ◽  
Esteban González ◽  
Samuel Lepe ◽  
Claudio Michea ◽  
Alfredo D. Millano
Keyword(s):  
Scalar Field ◽  
Nonlinear Dynamical Systems ◽  
Time Dependent ◽  
Late Time ◽  
De Sitter ◽  
Time Dynamics ◽  
Locally Rotationally Symmetric ◽  
Rotationally Symmetric ◽  
Bianchi Iii ◽  
Flrw Universe

AbstractScalar field cosmologies with a generalized harmonic potential and a matter fluid with a barotropic Equation of State (EoS) with barotropic index $$\gamma $$ γ for locally rotationally symmetric (LRS) Bianchi III metric and open Friedmann–Lemaître–Robertson–Walker (FLRW) metric are investigated. Methods from the theory of averaging of nonlinear dynamical systems are used to prove that time-dependent systems and their corresponding time-averaged versions have the same late-time dynamics. Therefore, simple time-averaged systems determine the future asymptotic behavior. Depending on values of barotropic index $$\gamma $$ γ late-time attractors of physical interests for LRS Bianchi III metric are Bianchi III flat spacetime, matter dominated FLRW universe (mimicking de Sitter, quintessence or zero acceleration solutions) and matter-curvature scaling solution. For open FLRW metric late-time attractors are a matter dominated FLRW universe and Milne solution. With this approach, oscillations entering nonlinear system through Klein–Gordon (KG) equation can be controlled and smoothed out as the Hubble factor H – acting as a time-dependent perturbation parameter – tends monotonically to zero. Numerical simulations are presented as evidence of such behaviour.

scholarly journals Unitarity at the late time boundary of de Sitter

2020 ◽  
Vol 2020 (6) ◽  
Author(s):  
Gizem Şengör ◽  
Constantinos Skordis
Keyword(s):  
Late Time ◽  
De Sitter ◽  
Time Boundary

scholarly journals Late-time quantum radiation by a uniformly accelerated detector in de Sitter spacetime

2018 ◽  
Vol 98 (10) ◽  
Author(s):  
Shumpei Yamaguchi ◽  
Rumi Tatsukawa ◽  
Shih-Yuin Lin ◽  
Kazuhiro Yamamoto
Keyword(s):  
Late Time ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Sitter Spacetime ◽  
Quantum Radiation ◽  
Time Quantum

scholarly journals Holographic cosmology with two coupled fluids in the presence of viscosity

2021 ◽  
pp. 2150149
Author(s):  
I. Brevik ◽  
A. V. Timoshkin
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Holographic Dark Energy ◽  
Exponential Model ◽  
Point Of View ◽  
Accelerating Universe ◽  
Late Time ◽  
Conservation Of Energy ◽  
Analytical Expressions ◽  
Friedmann Robertson Walker

We explore the cosmological models of the late-time universe based on the holographic principle, taking into account the properties of the viscosity of the dark fluid. We use the mathematical formalism of generalized infrared cutoff holographic dark energy, as presented by Nojiri and Odintsov [Covariant generalized holographic dark energy and accelerating universe, Eur. Phys. J. C 77 (2017) 528]. We consider the Little Rip, the Pseudo Rip, and a bounce exponential model, with two interacting fluids, namely dark energy and dark matter in a spatially-flat Friedmann–Robertson–Walker universe. Within these models, analytical expressions are obtained for infrared cutoffs in terms of the particle horizons. The law of conservation of energy is presented, from a holographic point of view.

scholarly journals The little sibling of the big rip singularity

2015 ◽  
Vol 24 (10) ◽  
pp. 1550078 ◽  
Author(s):  
Mariam Bouhmadi-López ◽  
Ahmed Errahmani ◽  
Prado Martín-Moruno ◽  
Taoufik Ouali ◽  
Yaser Tavakoli
Keyword(s):  
Blow Up ◽  
Energy Condition ◽  
Cosmic Time ◽  
Energy Conditions ◽  
Accelerating Universe ◽  
Hubble Rate ◽  
Big Rip ◽  
The Status ◽  
The Universe ◽  
Nonlinear Energy

In this paper, we present a new cosmological event, which we named the little sibling of the big rip. This event is much smoother than the big rip singularity. When the little sibling of the big rip is reached, the Hubble rate and the scale factor blow up, but the cosmic derivative of the Hubble rate does not. This abrupt event takes place at an infinite cosmic time where the scalar curvature explodes. We show that a doomsday à la little sibling of the big rip is compatible with an accelerating universe, indeed at present it would mimic perfectly a ΛCDM scenario. It turns out that, even though the event seems to be harmless as it takes place in the infinite future, the bound structures in the universe would be unavoidably destroyed on a finite cosmic time from now. The model can be motivated by considering that the weak energy condition should not be strongly violated in our universe, and it could give us some hints about the status of recently formulated nonlinear energy conditions.

scholarly journals Universal late-time dynamics in isolated one-dimensional statistical systems with topological excitations

2020 ◽  
Vol 101 (10) ◽  
Author(s):  
Alvise Bastianello ◽  
Alessio Chiocchetta ◽  
Leticia F. Cugliandolo ◽  
Andrea Gambassi
Keyword(s):  
Late Time ◽  
One Dimensional ◽  
Topological Excitations ◽  
Time Dynamics ◽  
Statistical Systems
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