scholarly journals Holographic principle, cosmological constant and cyclic cosmology

2019 ◽  
Vol 35 (02) ◽  
pp. 1950355
Author(s):  
Claudio Corianò ◽  
Paul H. Frampton
Keyword(s):  
Dark Energy ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Holographic Dark Energy ◽  
Point Of View ◽  
Holographic Principle ◽  
Fine Tuning ◽  
Cyclic Model ◽  
Energy Formula ◽  
Insight Into

The holographic principle provides a deep insight into quantum gravity and resolves the fine-tuning crisis concerning the cosmological constant. Holographic dark energy introduces new ultraviolet (UV) and infrared (IR) cutoffs into quantum gravity which are necessarily strongly related. The equation of state for dark energy [Formula: see text] is discussed from the holographic point of view. The phantom option of [Formula: see text] is resurrected, as in an earlier cyclic cosmology. Such a cyclic model can, however, equally use the cosmological constant with [Formula: see text].

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 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 SECOND-ORDER INVARIANTS AND HOLOGRAPHY

2012 ◽  
Vol 21 (12) ◽  
pp. 1250091 ◽  
Author(s):  
ORLANDO LUONGO ◽  
LUCA BONANNO ◽  
GERARDO IANNONE
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Holographic Dark Energy ◽  
Statistical Tests ◽  
A Priori ◽  
Second Order ◽  
Fine Tuning ◽  
Dark Energy Density ◽  
Event Horizons

Motivated by recent works on the role of the holographic principle in cosmology, we relate a class of second-order Ricci invariants to the IR cutoff characterizing the holographic dark energy density. The choice of second-order invariants provides an invariant way to account the problem of causality for the correct cosmological cutoff, since the presence of event horizons is not an a priori assumption. We find that these models work fairly well, by fitting the observational data, through a combined cosmological test with the use of SNeIa, BAO and CMB. This class of models is also able to overcome the fine-tuning and coincidence problems. Finally, to make a comparison with other recent models, we adopt the statistical tests AIC and BIC.

scholarly journals ACCELERATION AND DECELERATION IN THE CURVATURE-INDUCED PHANTOM MODEL OF THE LATE AND FUTURE UNIVERSE: COSMIC COLLAPSE AND ITS QUANTUM ESCAPE

2009 ◽  
Vol 18 (05) ◽  
pp. 865-887
Author(s):  
S. K. SRIVASTAVA ◽  
J. DUTTA
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Early Universe ◽  
High Energy ◽  
High Energy Density ◽  
Energy Models ◽  
Acceleration And Deceleration ◽  
The Universe

In this paper, the cosmology of the late and future universe is obtained from f(R) gravity with nonlinear curvature terms R2 and R3 (R is the Ricci scalar curvature). It is different from f(R) dark energy models where nonlinear curvature terms are taken as a gravitational alternative to dark energy. In the present model, neither linear nor nonlinear curvature terms are taken as dark energy. Rather, dark energy terms are induced by curvature terms and appear in the Friedmann equation derived from f(R) gravitational equations. This approach has an advantage over f(R) dark energy models in three ways: (i) results are consistent with WMAP observations, (ii) dark matter is produced from the gravitational sector and (iii) the universe expands as ~ t2/3 during dominance of the curvature-induced dark matter, which is consistent with the standard cosmology. Curvature-induced dark energy mimics phantom and causes late acceleration. It is found that transition from matter-driven deceleration to acceleration takes place at the redshift 0.36 at time 0.59 t0 (t0 is the present age of the universe). Different phases of this model, including acceleration and deceleration during the phantom phase, are investigated. It is found that expansion of the universe will stop at the age of 3.87 t0 + 694.4 kyr. After this epoch, the universe will contract and collapse by the time of 336.87 t0 + 694.4 kyr. Further, it is shown that cosmic collapse obtained from classical mechanics can be avoided by making quantum gravity corrections relevant near the collapse time due to extremely high energy density and large curvature analogous to the state of the very early universe. Interestingly, the cosmological constant is also induced here; it is extremely small in the classical domain but becomes very high in the quantum domain. This result explains the largeness of the cosmological constant in the early universe due to quantum gravity effects during this era and its very low value in the present universe due to negligible quantum effect in the late universe.

DARK MATTER AND DARK ENERGY - FACT OR FANTASY?

2004 ◽  
Vol 19 (31) ◽  
pp. 5333-5333
Author(s):  
PHILIP MANNHEIM
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Constant ◽  
Particle Physics ◽  
Einstein Gravity ◽  
Fine Tuning ◽  
Accelerating Universe ◽  
Conformal Invariant ◽  
Invariant Metric ◽  
Conformal Theory

We show that the origin of the dark matter and dark energy problems originates in the assumption of standard Einstein gravity that Newton's constant is fundamental. We discuss an alternate, conformal invariant, metric theory of gravity in which Newton's constant is induced dynamically, with the global induced one which is effective for cosmology being altogether weaker than the local induced one needed for the solar system. We find that in the theory dark matter is no longer needed, and that the accelerating universe data can be fitted without fine-tuning using a cosmological constant as large as particle physics suggests. In the conformal theory then it is not the cosmological constant which is quenched but rather the amount of gravity that it produces.

scholarly journals On the Higgs-like quintessence for dark energy

2014 ◽  
Vol 29 (22) ◽  
pp. 1450117 ◽  
Author(s):  
Sergei V. Ketov ◽  
Natsuki Watanabe
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Scalar Curvature ◽  
Scalar Potential ◽  
Fine Tuning ◽  
Standard Description ◽  
Quintessence Model

We propose a dynamical (quintessence) model of dark energy in the current Universe with a renormalizable (Higgs-like) scalar potential. We prove the viability of our model (after fine-tuning) for the certain range of the average scalar curvature values, and study the cosmological signatures distinguishing our model from the standard description of dark energy in terms of a cosmological constant.

scholarly journals Dark energy and quantum gravity

2019 ◽  
Vol 28 (14) ◽  
pp. 1944018 ◽  
Author(s):  
Per Berglund ◽  
Tristan Hübsch ◽  
Djordje Minić
Keyword(s):  
Dark Energy ◽  
String Theory ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Particle Physics ◽  
Dual Space ◽  
Planck Scale ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Sitter Spacetime

Realizing dark energy and the observed de Sitter spacetime in quantum gravity has proven to be obstructed in almost every usual approach. We argue that additional degrees of freedom of the left- and right-movers in string theory and a resulting doubled, noncommutatively generalized geometric formulation thereof can lead to an effective model of dark energy consistent with de Sitter spacetime. In this approach, the curvature of the canonically conjugate dual space provides for the dark energy inducing a positive cosmological constant in the observed spacetime, whereas the size of the above dual space is the gravitational constant in the same observed de Sitter spacetime. As a hallmark relation owing to a unique feature of string theory which relates short distances to long distances, the cosmological constant scale, the Planck scale and the effective TeV-sized particle physics scale must satisfy a see-saw-like formula — precisely the generic prediction of certain stringy cosmic brane type models.

scholarly journals Rip brane cosmology from a viscous holographic dark fluid

2020 ◽  
Vol 17 (06) ◽  
pp. 2050087 ◽  
Author(s):  
I. Brevik ◽  
A. V. Timoshkin
Keyword(s):  
Dark Energy ◽  
Energy Conservation ◽  
Bulk Viscosity ◽  
Holographic Dark Energy ◽  
Holographic Principle ◽  
De Sitter ◽  
Brane Cosmology ◽  
Viscous Cosmology ◽  
Dark Fluid ◽  
Analytical Expressions

This paper is devoted to the application of the holographic principle to describe Rip brane cosmological models in the presence of a bulk viscosity. We make use of the generalized infrared-cutoff holographic dark energy, introduced by Nojiri and Odintsov. We consider various examples: Rip brane cosmology corresponding to the Little Rip case, asymptotic de Sitter theory, and the so-called Big Freeze theory leading to a singularity. Analytical expressions for infrared cutoffs, as well as the particle and the future horizons at the brane, are obtained. The equations for energy conservation on the brane within the holographic theory are obtained in each case. The correspondence between viscous cosmology and holographic cosmology on the brane is shown.

Reconstructing Tsallis holographic quintessence

2021 ◽  
Author(s):  
Umesh Kumar Sharma ◽  
Vandna Srivastava
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Quantum Gravity ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Energy Model ◽  
Holographic Dark Energy Model ◽  
The Universe ◽  
Modified Entropy

Within the framework of quantum gravity and modified entropy-area formalism, the Tsallis holographic dark energy is an effort to peep into a mysterious content of the Universe, the dark energy, to analyze its nature. The Tsallis parameter [Formula: see text] provides the main characteristic of the Tsallis holographic dark energy. Opting the value of Tsallis parameter [Formula: see text], a quintessence scalar field description of the Tsallis holographic dark energy model can be obtained. In this work, we present this quintessential explanation of the Tsallis holographic dark energy with [Formula: see text] and reconstruct the dynamics of the scalar field and the potential of quintessence.

scholarly journals Holographic dark energy with cosmological constant

2015 ◽  
Vol 2015 (08) ◽  
pp. 012-012 ◽  
Author(s):  
Yazhou Hu ◽  
Miao Li ◽  
Nan Li ◽  
Zhenhui Zhang
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Holographic Dark Energy
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