FROM DE SITTER TO DE SITTER: A NON-SINGULAR INFLATIONARY UNIVERSE DRIVEN BY VACUUM

A semi-classical analysis of vacuum energy in the expanding space–time suggests that the cosmological term decays with time, with a concomitant matter production. For early times we find, in Planck units, Λ ≈ H4, where H is the Hubble parameter. The corresponding cosmological solution has no initial singularity, existing since an infinite past. During an infinitely long period we have a quasi-de Sitter, inflationary universe, with H ≈ 1. However, at a given time, the expansion undertakes a phase transition, with H and Λ decreasing to nearly zero in a few Planck times, producing a huge amount of radiation. On the other hand, the late-time scenario is similar to the standard model, with the radiation phase followed by a dust era, which tends asymptotically to a de Sitter universe, with vacuum dominating again.

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Holographic Ricci dark energy as running vacuum

Modern Physics Letters A ◽

10.1142/s0217732316500759 ◽

2016 ◽

Vol 31 (13) ◽

pp. 1650075 ◽

Cited By ~ 5

Author(s):

Paxy George ◽

Titus K. Mathew

Keyword(s):

Dark Energy ◽

Vacuum Energy ◽

Additive Constant ◽

Late Time ◽

De Sitter ◽

Energy Status ◽

Ricci Dark Energy ◽

Future Singularity ◽

Expansion Of The Universe ◽

De Sitter Universe

Holographic Ricci dark energy (DE) that has been proposed ago has faced problems of future singularity. In the present work, we consider the Ricci DE with an additive constant in its density as running vacuum energy. We have analytically solved the Friedmann equations and also the role played by the general conservation law followed by the cosmic components together. We have shown that the running vacuum energy status of the Ricci DE helps to remove the possible future singularity in the model. The additive constant in the density of the running vacuum played an important role, such that, without that, the model predicts either eternal deceleration or eternal acceleration. But along with the additive constant, equivalent to a cosmological constant, the model predicts a late time acceleration in the expansion of the universe, and in the far future of the evolution it tends to de Sitter universe.

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COSMOLOGY IN SCALAR–TENSOR THEORY AND ASYMPTOTICALLY de SITTER UNIVERSE

Modern Physics Letters A ◽

10.1142/s021773230100442x ◽

2001 ◽

Vol 16 (20) ◽

pp. 1303-1313 ◽

Cited By ~ 53

Author(s):

A. A. SEN ◽

S. SEN

Keyword(s):

Accelerated Expansion ◽

Late Time ◽

Scalar Tensor Theory ◽

Dilaton Field ◽

De Sitter ◽

Positive Cosmological Constant ◽

Expansion Phase ◽

Tensor Theory ◽

Sitter Universe ◽

De Sitter Universe

We have investigated the cosmological scenarios with a four-dimensional effective action which is connected with multidimensional, supergravity and string theories. The solution for the scale factor is such that initially universe undergoes a decelerated expansion but in late times it enters into the accelerated expansion phase. In fact, it asymptotically becomes a de Sitter universe. The dilaton field in our model is a decreasing function of time and it becomes a constant in late time resulting the exit from the scalar–tensor theory to the standard Einstein's gravity. Also the dilaton field results in the existence of a positive cosmological constant in late times.

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THE RETURN OF A STATIC UNIVERSE AND THE END OF COSMOLOGY

International Journal of Modern Physics D ◽

10.1142/s0218271808012449 ◽

2008 ◽

Vol 17 (03n04) ◽

pp. 685-690 ◽

Cited By ~ 4

Author(s):

LAWRENCE M. KRAUSS ◽

ROBERT J. SCHERRER

Keyword(s):

Coordinate System ◽

Vacuum Energy ◽

Big Bang ◽

Light Elements ◽

De Sitter ◽

True Nature ◽

Static Universe ◽

Hubble Expansion ◽

De Sitter Universe ◽

The Universe

We demonstrate that as we extrapolate the current ΛCDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our "island universe" will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented.

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Evolution of Inhomogeneities in the Inflationary Universe -No Hair Theorem or Multi-Production of Universes?-

Symposium - International Astronomical Union ◽

10.1017/s0074180900135867 ◽

1988 ◽

Vol 130 ◽

pp. 67-75

Author(s):

Katsuhiko Sato

Keyword(s):

Critical Length ◽

High Density ◽

Density Contrast ◽

Inflationary Universe ◽

De Sitter ◽

Inhomogeneous Universe ◽

Sitter Universe ◽

De Sitter Universe ◽

The Universe

Recent investigations on the evolution of the inhomogeneities in the inflationary universe are reviewed. 1) Strict cosmological no hair theorem does not hold, but the class of inhomogeneous universe which evolve to homogeneous de Sitter universe is finite, i.e, “weak cosmic no hair theorem” holds. 2) High density regions in the inhomogeneous universe evolve to wormholes provided that i) the size of the regions is greater than the horizon length, but smaller than a critical length which is the function of the density contrast, and ii) the density is three times higher than that of surrounding region. 3) If wormholes are formed copiously in the period of inflation, they evolve to causally disconnected “child- universes”. In this scenario, the universe we are now observing is one of the locally flat regions.

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Phase space analysis and singularity classification for linearly interacting dark energy models

The European Physical Journal C ◽

10.1140/epjc/s10052-020-7671-x ◽

2020 ◽

Vol 80 (2) ◽

Author(s):

Muhsin Aljaf ◽

Daniele Gregoris ◽

Martiros Khurshudyan

Keyword(s):

Dark Energy ◽

Equation Of State ◽

Cosmological Parameters ◽

State Parameter ◽

Late Time ◽

De Sitter ◽

Effective Equation ◽

De Sitter Universe ◽

Friedmann Cosmological Models ◽

Interacting Dark Energy Models

Abstract In this paper, applying the Hartman–Grobman theorem we carry out a qualitative late-time analysis of some unified dark energy-matter Friedmann cosmological models, where the two interact through linear energy exchanges, and the dark energy fluid obeys to the dynamical equation of state of Redlich–Kwong, Modified Berthelot, and Dieterici respectively. The identification of appropriate late-time attractors allows to restrict the range of validity of the free parameters of the models under investigation. In particular, we prove that the late-time attractors which support a negative deceleration parameter correspond to a de Sitter universe. We show that the strength of deviation from an ideal fluid for the dark energy does not influence the stability of the late-time attractors, as well as the values of all the cosmological parameters at equilibrium, but for the Hubble function (which represents the age of the universe). Our analysis also shows that a singularity in the effective equation of state parameter for the dark energy fluid is not possible within this class of models.

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De Sitter and bounce solutions from anisotropy in extended gravity cosmology

Modern Physics Letters A ◽

10.1142/s0217732319503218 ◽

2019 ◽

Vol 34 (39) ◽

pp. 1950321 ◽

Cited By ~ 3

Author(s):

B. Mishra ◽

G. Ribeiro ◽

P. H. R. S. Moraes

Keyword(s):

Big Bang ◽

Late Time ◽

Type I ◽

De Sitter ◽

Field Equations ◽

Extended Gravity ◽

Numerical Fitting ◽

De Sitter Universe ◽

The Big Bang ◽

The Universe

We investigate the consequences of incepting the Bianchi type I metric in the [Formula: see text] gravity theory field equations. We particularly derive solutions for a matter-dominated universe. From such a scenario, it is possible to predict a late-time de Sitter universe. Moreover, depending on the numerical fitting function for the scale factor, the universe is predicted to bounce and evade the Big Bang singularity.

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FROM INFLATION TO DARK ENERGY THROUGH A DYNAMICAL Λ: AN ATTEMPT AT ALLEVIATING FUNDAMENTAL COSMIC PUZZLES

International Journal of Modern Physics D ◽

10.1142/s021827181342008x ◽

2013 ◽

Vol 22 (12) ◽

pp. 1342008 ◽

Cited By ~ 34

Author(s):

SPYROS BASILAKOS ◽

JOSÉ ADEMIR SALES LIMA ◽

JOAN SOLÀ

Keyword(s):

Energy Density ◽

Vacuum Energy ◽

Big Bang ◽

Vacuum Energy Density ◽

Late Time ◽

De Sitter ◽

New Class ◽

Sitter Spacetime ◽

Inflationary Phase ◽

De Sitter Vacuum

After decades of successful hot big-bang paradigm, cosmology still lacks a framework in which the early inflationary phase of the universe smoothly matches the radiation epoch and evolves to the present "quasi" de Sitter spacetime. No less intriguing is that the current value of the effective vacuum energy density is vastly smaller than the value that triggered inflation. In this paper, we propose a new class of cosmologies capable of overcoming, or highly alleviating, some of these acute cosmic puzzles. Powered by a decaying vacuum energy density, the spacetime emerges from a pure nonsingular de Sitter vacuum stage, "gracefully" exits from inflation to a radiation phase followed by dark matter and vacuum regimes, and, finally, evolves to a late-time de Sitter phase.

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Cosmological inflationary studying around the type IV singularity within f(T) gravity

International Journal of Geometric Methods in Modern Physics ◽

10.1142/s0219887820501959 ◽

2020 ◽

Vol 17 (14) ◽

pp. 2050195

Author(s):

M. G. Ganiou ◽

M. J. S. Houndjo ◽

H. F. Abadji ◽

J. Tossa

Keyword(s):

Dynamical Instability ◽

Theoretical Formula ◽

Inflationary Universe ◽

Late Time ◽

De Sitter ◽

Type Iv ◽

Flow Parameters ◽

Additional Constant ◽

Text Model ◽

Hubble Flow

In this paper, we investigate the effects of Type IV singularity through [Formula: see text] gravity description of inflationary Universe, where [Formula: see text] denotes the torsion scalar. With the Friedmann equations of the theory, we reconstruct a [Formula: see text] model according to a given Hubble rate susceptible to describe the inflationary era near the Type IV singularity. One obtains an interesting well-known [Formula: see text] model but with additional constant parameter [Formula: see text] staying as the Type IV singularity contribution. Moreover, we calculate the Hubble flow parameters in order to determine the dynamical evolution of the cosmological system. The results show that some of the Hubble flow parameters are small near the Type IV singularity and become singular at Type IV singularity, indicating that a dynamical instability of the cosmological system occurs at that point. This means that the dynamical cosmological evolution up to that point ceases to be the final attractor since the system is abruptly interrupted. Furthermore, by considering the [Formula: see text] trace anomaly equation, the previous result on the Type IV singularity is consolidated by the conditional instability coming from the de Sitter inflationary description of the reconstructed [Formula: see text] model. The model leads to instability strongly governed by the Type IV singularity parameter [Formula: see text] is viewed as the graceful exit from inflation. Our theoretical [Formula: see text] description based on slow-roll parameters not only confirms some observational data on spectral index and the scalar-to-tensor ratio from Planck data and BICEP[Formula: see text]/Keck-Array data, but also shows the property of [Formula: see text] gravity in describing the early and late-time evolution of our Universe.

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