scholarly journals Dynamical relaxation of dark energy: A solution to early inflation, late-time acceleration and the cosmological constant problem

2006 ◽  
Vol 638 (2-3) ◽  
pp. 94-99 ◽  
Author(s):  
Ishwaree P. Neupane ◽  
Benedict M.N. Carter
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Late Time ◽  
Cosmological Constant Problem ◽  
Late Time Acceleration

The possibility of a stable flat dark energy-dominated Swiss-cheese brane-world universe

2020 ◽  
Vol 17 (05) ◽  
pp. 2050075
Author(s):  
Nasr Ahmed ◽  
Kazuharu Bamba ◽  
F. Salama
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Cosmological Models ◽  
Brane World ◽  
Fine Tuning ◽  
Energy Conditions ◽  
Late Time ◽  
Swiss Cheese ◽  
Black Strings ◽  
The Stability

In this paper, we study the possibility of obtaining a stable flat dark energy-dominated universe in a good agreement with observations in the framework of Swiss-cheese brane-world cosmology. Two different brane-world cosmologies with black strings have been introduced for any cosmological constant [Formula: see text] using two empirical forms of the scale factor. In both models, we have performed a fine-tuning between the brane tension and the cosmological constant so that the Equation of state (EoS) parameter [Formula: see text] for the current epoch, where the redshift [Formula: see text]. We then used these fine–tuned values to calculate and plot all parameters and energy conditions. The deceleration–acceleration cosmic transition is allowed in both models, and the jerk parameter [Formula: see text] at late-times. Both solutions predict a future dark energy-dominated universe in which [Formula: see text] with no crossing to the phantom divide line. While the pressure in the first solution is always negative, the second solution predicts a better behavior of cosmic pressure where the pressure is negative only in the late-time accelerating era but positive in the early-time decelerating era. Such a positive-to-negative transition in the evolution of pressure helps to explain the cosmic deceleration–acceleration transition. Since black strings have been proved to be unstable by some authors, this instability can actually reflect doubts on the stability of cosmological models with black strings (Swiss-cheese type brane-worlds cosmological models). For this reason, we have carefully investigated the stability through energy conditions and sound speed. Because of the presence of quadratic energy terms in Swiss-cheese type brane-world cosmology, we have tested the new nonlinear energy conditions in addition to the classical energy conditions. We have also found that a negative tension brane is not allowed in both models of the current work as the energy density will no longer be well defined.

scholarly journals Fine Structure of Dark Energy and New Physics

2007 ◽  
Vol 2007 ◽  
pp. 1-14 ◽  
Author(s):  
Vishnu Jejjala ◽  
Michael Kavic ◽  
Djordje Minic
Keyword(s):  
Fine Structure ◽  
Quantum Theory ◽  
Dark Energy ◽  
Cosmological Constant ◽  
New Physics ◽  
Blackbody Radiation ◽  
Cosmological Constant Problem ◽  
Radiation Problem ◽  
Specific Proposal ◽  
Dual Quantum

Following our recent work on the cosmological constant problem, in this letter we make a specific proposal regarding the fine structure (i.e., the spectrum) of dark energy. The proposal is motivated by a deep analogy between the blackbody radiation problem, which led to the development of quantum theory, and the cosmological constant problem, for which we have recently argued calls for a conceptual extension of the quantum theory. We argue that the fine structure of dark energy is governed by a Wien distribution, indicating its dual quantum and classical nature. We discuss observational consequences of such a picture of dark energy and constrain the distribution function.

scholarly journals A COSMOLOGICAL MODEL WITH FERMIONIC FIELD

2010 ◽  
Vol 25 (13) ◽  
pp. 2735-2746 ◽  
Author(s):  
R. RAKHI ◽  
G. V. VIJAYAGOVINDAN ◽  
K. INDULEKHA
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
The Self ◽  
Late Time ◽  
Fermionic Field ◽  
Energy Field ◽  
Late Time Acceleration ◽  
Higher Order Terms ◽  
Interaction Term ◽  
M Theory

In this work, a cosmological model inspired by string/M-theory with fermionic field is taken into consideration. Here it is investigated whether the introduction of a non-Dirac fermionic field — characterized by an interaction term — affects the cosmological evolution. The self-interaction potential is considered as a combination of the scalar and pseudoscalar invariants. It is observed that the fermionic field under consideration behaves like an inflation field for the early universe and later on, as a dark energy field. The late time acceleration becomes more prominent by the addition of the interaction term. There is a slight decrease for the inflation peak as well as for the energy density. We see that the addition of higher-order terms to the fermionic part of Lagrangian does not significantly change either the inflation or the late time acceleration behavior.

scholarly journals Magnetized dark energy and the late time acceleration

2012 ◽  
Vol 127 (10) ◽  
Author(s):  
A. K. Yadav ◽  
F. Rahaman ◽  
S. Ray ◽  
G. K. Goswami
Keyword(s):  
Dark Energy ◽  
Late Time ◽  
Late Time Acceleration

scholarly journals Late-time cosmic acceleration: ABCD of dark energy and modified theories of gravity

2016 ◽  
Vol 25 (12) ◽  
pp. 1630031 ◽  
Author(s):  
M. Sami ◽  
R. Myrzakulov
Keyword(s):  
Dark Energy ◽  
Scalar Fields ◽  
Massive Gravity ◽  
Cosmic Acceleration ◽  
Modified Theories Of Gravity ◽  
Late Time ◽  
Cosmological Constant Problem ◽  
Chameleon Mechanism ◽  
Theories Of Gravity ◽  
Basic Ideas

We briefly review the problems and prospects of the standard lore of dark energy. We have shown that scalar fields, in principle, cannot address the cosmological constant problem. Indeed, a fundamental scalar field is faced with a similar problem dubbed naturalness. In order to keep the discussion pedagogical, aimed at a wider audience, we have avoided technical complications in several places and resorted to heuristic arguments based on physical perceptions. We presented underlying ideas of modified theories based upon chameleon mechanism and Vainshtein screening. We have given a lucid illustration of recently investigated ghost-free nonlinear massive gravity. Again, we have sacrificed rigor and confined to the basic ideas that led to the formulation of the theory. The review ends with a brief discussion on the difficulties of the theory applied to cosmology.

scholarly journals Cosmological constant from the emergent gravity perspective

2014 ◽  
Vol 23 (06) ◽  
pp. 1430011 ◽  
Author(s):  
T. Padmanabhan ◽  
Hamsa Padmanabhan
Keyword(s):  
Cosmological Constant ◽  
Sufficient Conditions ◽  
Integration Constant ◽  
Dimensionless Number ◽  
Late Time ◽  
Field Equations ◽  
Cosmological Constant Problem ◽  
Emergent Gravity ◽  
Background Material ◽  
The Universe

Observations indicate that our universe is characterized by a late-time accelerating phase, possibly driven by a cosmological constant Λ, with the dimensionless parameter [Formula: see text], where LP= (Għ/c3)1/2is the Planck length. In this review, we describe how the emergent gravity paradigm provides a new insight and a possible solution to the cosmological constant problem. After reviewing the necessary background material, we identify the necessary and sufficient conditions for solving the cosmological constant problem. We show that these conditions are naturally satisfied in the emergent gravity paradigm in which (i) the field equations of gravity are invariant under the addition of a constant to the matter Lagrangian and (ii) the cosmological constant appears as an integration constant in the solution. The numerical value of this integration constant can be related to another dimensionless number (called CosMIn) that counts the number of modes inside a Hubble volume that cross the Hubble radius during the radiation and the matter-dominated epochs of the universe. The emergent gravity paradigm suggests that CosMIn has the numerical value 4π, which, in turn, leads to the correct, observed value of the cosmological constant. Further, the emergent gravity paradigm provides an alternative perspective on cosmology and interprets the expansion of the universe itself as a quest towards holographic equipartition. We discuss the implications of this novel and alternate description of cosmology.

scholarly journals Dark energy in modified Gauss-Bonnet gravity: Late-time acceleration and the hierarchy problem

2006 ◽  
Vol 73 (8) ◽  
Author(s):  
Guido Cognola ◽  
Emilio Elizalde ◽  
Shin’ichi Nojiri ◽  
Sergei D. Odintsov ◽  
Sergio Zerbini
Keyword(s):  
Dark Energy ◽  
Late Time ◽  
Hierarchy Problem ◽  
Bonnet Gravity ◽  
Late Time Acceleration

scholarly journals DARK ENERGY IN PRACTICE

2010 ◽  
Vol 25 (29) ◽  
pp. 5253-5331 ◽  
Author(s):  
DOMENICO SAPONE
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Complete List ◽  
Late Time ◽  
Evolution Of The Universe ◽  
Late Time Acceleration ◽  
Energy Models ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Alternative Theories

In this paper we review a part of the approaches that have been considered to explain the extraordinary discovery of the late time acceleration of the Universe. We discuss the arguments that have led physicists and astronomers to accept dark energy as the current preferable candidate to explain the acceleration. We highlight the problems and the attempts to overcome the difficulties related to such a component. We also consider alternative theories capable of explaining the acceleration of the Universe, such as modification of gravity. We compare the two approaches and point out the observational consequences, reaching the sad but foresightful conclusion that we will not be able to distinguish between a Universe filled by dark energy or a Universe where gravity is different from General Relativity. We review the present observations and discuss the future experiments that will help us to learn more about our Universe. This is not intended to be a complete list of all the dark energy models but this paper should be seen as a review on the phenomena responsible for the acceleration. Moreover, in a landscape of hardly compelling theories, it is an important task to build simple measurable parameters useful for future experiments that will help us to understand more about the evolution of the Universe.

scholarly journals f(R) dual theories of quintessence: expansion-collapse duality

2021 ◽  
Vol 2021 (12) ◽  
pp. 016
Author(s):  
Dipayan Mukherjee ◽  
H.K. Jassal ◽  
Kinjalk Lochan
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Einstein Frame ◽  
Time Limit ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
Jordan Frame ◽  
Late Time ◽  
Perturbative Solution ◽  
The Universe

Abstract The accelerated expansion of the universe demands presence of an exotic matter, namely the dark energy. Though the cosmological constant fits this role very well, a scalar field minimally coupled to gravity, or quintessence, can also be considered as a viable alternative for the cosmological constant. We study f(R) gravity models which can lead to an effective description of dark energy implemented by quintessence fields in Einstein gravity, using the Einstein frame-Jordan frame duality. For a family of viable quintessence models, the reconstruction of the f(R) function in the Jordan frame consists of two parts. We first obtain a perturbative solution of f(R) in the Jordan frame, applicable near the present epoch. Second, we obtain an asymptotic solution for f(R), consistent with the late time limit of the Einstein frame if the quintessence field drives the universe. We show that for certain class of viable quintessence models, the Jordan frame universe grows to a maximum finite size, after which it begins to collapse back. Thus, there is a possibility that in the late time limit where the Einstein frame universe continues to expand, the Jordan frame universe collapses. The condition for this expansion-collapse duality is then generalized to time varying equations of state models, taking into account the presence of non-relativistic matter or any other component in the Einstein frame universe. This mapping between an expanding geometry and a collapsing geometry at the field equation level may have interesting potential implications on the growth of perturbations therein at late times.

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