SELF INTERACTING BRANS–DICKE COSMOLOGY AND QUINTESSENCE

Recent cosmological observations reveal that we are living in a flat accelerated expanding universe. In this work we have investigated the nature of the potential compatible with the power law expansion of the universe in a self interacting Brans–Dicke cosmology with a perfect fluid background and have analyzed whether this potential supports the accelerated expansion. It is found that positive power law potential is relevant in this scenario and can drive accelerated expansion for negative Brans–Dicke coupling parameter ω. The evolution of the density perturbation is also analyzed in this scenario and is seen that the model allows growing modes for negative ω.

Download Full-text

PRESENT ACCELERATION OF THE UNIVERSE, HOLOGRAPHIC ENERGY AND BRANS–DICKE THEORY

Modern Physics Letters A ◽

10.1142/s0217732309030205 ◽

2009 ◽

Vol 24 (22) ◽

pp. 1785-1792 ◽

Cited By ~ 24

Author(s):

B. NAYAK ◽

L. P. SINGH

Keyword(s):

Dark Energy ◽

Power Law ◽

Dark Energy Model ◽

Holographic Dark Energy ◽

Accelerated Expansion ◽

Temporal Behavior ◽

Holographic Dark Energy Model ◽

Acceleration Of The Universe ◽

Expansion Of The Universe ◽

The Universe

The present-day accelerated expansion of the universe is naturally addressed within the Brans–Dicke theory just by using holographic dark energy model with inverse of Hubble scale as IR cutoff and power law temporal behavior of scale factor. It is also concluded that if the universe continues to expand, then one day it might be completely filled with dark energy.

Download Full-text

COSMOLOGICAL DYNAMICS OF f(R) GRAVITY SCALAR DEGREE OF FREEDOM IN EINSTEIN FRAME

International Journal of Modern Physics D ◽

10.1142/s0218271813500831 ◽

2013 ◽

Vol 22 (14) ◽

pp. 1350083 ◽

Cited By ~ 9

Author(s):

UMANANDA DEV GOSWAMI ◽

KABITA DEKA

Keyword(s):

Scalar Field ◽

Power Law ◽

Einstein Frame ◽

Degree Of Freedom ◽

Gravity Models ◽

Accelerated Expansion ◽

Power Law Model ◽

Starobinsky Model ◽

Expansion Of The Universe ◽

The Universe

f(R) gravity models belong to an important class of modified gravity models where the late time cosmic accelerated expansion is considered as a manifestation of the large scale modification of the force of gravity. f(R) gravity models can be expressed in terms of a scalar degree of freedom by redefinition of model's variable. The conformal transformation of the action from Jordan frame to Einstein frame makes the scalar degree of freedom more explicit and can be studied conveniently. We have investigated the features of the scalar degree of freedoms and the consequent cosmological implications of the power-law (ξRn) and the Starobinsky (disappearing cosmological constant) f(R) gravity models numerically in the Einstein frame. Both the models show interesting behavior of their scalar degree of freedom and could produce the accelerated expansion of the universe in the Einstein frame with the negative equation of state of the scalar field. However, the scalar field potential for the power-law model is the well-behaved function of the field, whereas the potential becomes flat for higher value of field in the case of the Starobinsky model. Moreover, the equation of state of the scalar field for the power-law model is always negative and less than -1/3, which corresponds to the behavior of the dark energy, that produces the accelerated expansion of the universe. This is not always the case for the Starobinsky model. At late times, the Starobinsky model behaves as cosmological constant Λ as behaves by power-law model for the values of n → 2 at all times.

Download Full-text

ACCELERATED EXPANSION IN MODIFIED GRAVITY WITH A YUKAWA-LIKE TERM

International Journal of Modern Physics D ◽

10.1142/s0218271807009838 ◽

2007 ◽

Vol 16 (04) ◽

pp. 687-697 ◽

Cited By ~ 23

Author(s):

K. ATAZADEH ◽

H. R. SEPANGI

Keyword(s):

Power Law ◽

Modified Gravity ◽

Newtonian Limit ◽

Accelerated Expansion ◽

Palatini Formalism ◽

Expansion Of The Universe ◽

Tensor Formulation ◽

The Universe ◽

Yukawa Term

We discuss the Palatini formulation of modified gravity including a Yukawa-like term. It is shown that in this formulation, the Yukawa term offers an explanation for the current exponential accelerated expansion of the universe and reduces to the standard Friedmann cosmology in the appropriate limit. We then discuss the scalar-tensor formulation of the model as a metric theory and show that the Yukawa term predicts a power-law acceleration at late-times. The Newtonian limit of the theory is also discussed in context of the Palatini formalism.

Download Full-text

Cosmological constant

10.1093/oso/9780198802877.003.0026 ◽

2018 ◽

Author(s):

Michael Kachelriess

Keyword(s):

Dark Energy ◽

Cosmological Constant ◽

Accelerated Expansion ◽

Vacuum Fluctuations ◽

Present Epoch ◽

Modify Gravity ◽

Expansion Of The Universe ◽

The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

Download Full-text

Taxonomy of Dark Energy Models

Universe ◽

10.3390/universe7060163 ◽

2021 ◽

Vol 7 (6) ◽

pp. 163

Author(s):

Verónica Motta ◽

Miguel A. García-Aspeitia ◽

Alberto Hernández-Almada ◽

Juan Magaña ◽

Tomás Verdugo

Keyword(s):

Dark Energy ◽

Cold Dark Matter ◽

Accelerated Expansion ◽

Energy Component ◽

The Past ◽

Energy Models ◽

The Status ◽

Expansion Of The Universe ◽

The Universe ◽

Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

Download Full-text

INFLATION, QUINTESSENCE PROBLEM AND VARYING SPEED OF LIGHT

Modern Physics Letters A ◽

10.1142/s0217732302006370 ◽

2002 ◽

Vol 17 (05) ◽

pp. 295-302

Author(s):

SUBENOY CHAKRABORTY

Keyword(s):

Cosmological Constant ◽

Accelerated Expansion ◽

Speed Of Light ◽

Expansion Of The Universe ◽

The Universe

In this paper it is shown that the present accelerated expansion of the Universe can be explained only by considering variation of the speed of light, without taking into account the cosmological constant or quintessence matter.

Download Full-text

Heuristic determination of the cosmological constant

Modern Physics Letters A ◽

10.1142/s0217732321501145 ◽

2021 ◽

pp. 2150114

Author(s):

Manuel Urueña Palomo ◽

Fernando Pérez Lara

Keyword(s):

Field Theory ◽

Energy Density ◽

Cosmological Constant ◽

Accelerated Expansion ◽

Fundamental Constants ◽

Quantum Field ◽

Brute Force ◽

Expansion Of The Universe ◽

The Universe

The vacuum catastrophe results from the disagreement between the theoretical value of the energy density of the vacuum in quantum field theory and the estimated one observed in cosmology. In a similar attempt in which the ultraviolet catastrophe was solved, we search for the value of the cosmological constant by brute-force through computation. We explore combinations of the fundamental constants in physics performing a dimensional analysis, in search of an equation resulting in the measured energy density of the vacuum or cosmological constant that is assumed to cause the accelerated expansion of the universe.

Download Full-text

Can accelerated expansion of the universe be due to spacetime vorticity?

Modern Physics Letters A ◽

10.1142/s0217732318502401 ◽

2018 ◽

Vol 33 (40) ◽

pp. 1850240

Author(s):

Babur M. Mirza

Keyword(s):

Magnetic Field ◽

Accelerated Expansion ◽

Newtonian Gravity ◽

Hubble’S Parameter ◽

Cosmic Expansion ◽

Zero Curvature ◽

Expansion Of The Universe ◽

General Relativistic ◽

The Universe ◽

The Magnetic Field

We present here a general relativistic mechanism for accelerated cosmic expansion and the Hubble’s parameter. It is shown that spacetime vorticity coupled to the magnetic field density in galaxies causes the galaxies to recede from one another at a rate equal to the Hubble’s constant. We therefore predict an oscillatory universe, with zero curvature, without assuming violation of Newtonian gravity at large distances or invoking dark energy/dark matter hypotheses. The value of the Hubble’s constant, along with the scale of expansion, as well as the high isotropy of CMB radiation are deduced from the model.

Download Full-text