scholarly journals SCALAR NONLUMINOUS MATTER IN GALAXIES

2002 ◽  
Vol 17 (04) ◽  
pp. 555-560 ◽  
Author(s):  
BYUNG JOO LEE ◽  
TAE HOON LEE
Keyword(s):  
Rotational Velocity ◽  
Scalar Potential ◽  
Scalar Fields ◽  
Global Symmetry ◽  
Late Time ◽  
Complex Scalar ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Static Space ◽  
Quintessence Model

As a candidate for dark matter in galaxies, we study an SU(3) triplet of complex scalar fields which are nonminimally coupled to gravity. In the spherically symmetric static space–time where the flat rotational velocity curves of stars in galaxies can be explained, we find simple solutions of scalar fields with SU(3) global symmetry broken to U(1) × U(1), in an exponential scalar potential, which will be useful in a quintessence model of the late-time acceleration of the universe.

scholarly journals A LATE TIME ACCELERATION OF THE UNIVERSE WITH TWO SCALAR FIELDS: MANY POSSIBILITIES

2006 ◽  
Vol 21 (35) ◽  
pp. 2663-2670 ◽  
Author(s):  
NARAYAN BANERJEE ◽  
SUDIPTA DAS
Keyword(s):  
Scalar Field ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
The Other ◽  
Field Conditions ◽  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

In the present work, an attempt has been made to explain the recent cosmic acceleration of the universe with two mutually interacting scalar fields, one being the Brans–Dicke scalar field and the other a quintessence scalar field. Conditions have been derived for which the quintessence scalar field has an early oscillation and it grows during a later time to govern the dynamics of the universe.

scholarly journals Chameleon field and the late time acceleration of the Universe

Pramana ◽  
2010 ◽  
Vol 74 (3) ◽  
pp. 481-489 ◽  
Author(s):  
Narayan Banerjee ◽  
Sudipta Das ◽  
Koyel Ganguly
Keyword(s):  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

scholarly journals RADION POTENTIAL AND BRANE DYNAMICS

2001 ◽  
Vol 16 (24) ◽  
pp. 1583-1595 ◽  
Author(s):  
L. MERSINI
Keyword(s):  
Inflation Rate ◽  
Vacuum Energy ◽  
Density Perturbation ◽  
Scalar Fields ◽  
Fine Tuning ◽  
Late Time ◽  
Frw Universe ◽  
Strong Suppression ◽  
Dynamic Setting ◽  
The Universe

We examine the cosmology of Randall–Sundrum model in a dynamic setting where scalar fields are present in the bulk as well as the branes. This generates a mechanism similar to that of Goldberger–Wise for radion stabilization and the recovery of late-time cosmology features on the branes. Due to the induced radion dynamics, the inflating branes roll towards the minimum of the radion potential, thereby exiting inflation and reheating the universe. In the slow roll part of the potential, the TeV branes have maximum inflation rate and energy as their coupling to the radion and bulk modes have minimum suppression. Hence, when rolling down the steep end of the potential towards the stable point, the radion field (which appears as the inflaton of the effective 4-D theory in the branes) decays very fast and reheats the universe. This process results in a decrease of the brane's canonical vacuum energy, Λ4. However, at the minimum of the potential Λ4 is small but not necessarily zero and the fine-tuning issue remains. Density perturbation constraints introduce an upper bound on Λ4. Due to the large radion mass and strong suppression to the bulk modes, moduli problems and bulk reheating do not occur. The reheat temperature and a sufficient number of e-folding constraints for the brane-universe are also satisfied. The model therefore recovers the radiation dominated FRW universe.

Five-dimensional Brans–Dicke compactified universe dominated by a varying speed of light

2020 ◽  
Vol 35 (30) ◽  
pp. 2050252
Author(s):  
Rami Ahmad El-Nabulsi
Keyword(s):  
Killing Vector ◽  
Scalar Fields ◽  
Analytic Solutions ◽  
Accelerated Expansion ◽  
Late Time ◽  
Speed Of Light ◽  
Orthogonal Space ◽  
Spacetime Curvature ◽  
The Universe ◽  
Data Analytic

We extend the model of a 5D Brans–Dicke gravity theory reduced to 4D through the presence of a hypersurface-orthogonal space-like killing vector field in the underlying 5D spacetime by including a varying speed of light. The resulting model is characterized by the presence of two scalar fields. We focus on late-time power law solutions which emerge in general when scalar fields couple to spacetime curvature and do not contradict the SNIa astrophysical data. Analytic solutions in 4-dimensions are derived and late-time accelerated expansion was found. The universe is dominated by dark energy, free from phantom field and is characterized by a decaying energy matter density, decaying scalar fields, and a decreasing celerity of light. The model is confronted with astrophysical observations and is found to fit these data.

scholarly journals Cosmological dynamics of f(R) models in dynamical system analysis

2020 ◽  
Vol 35 (22) ◽  
pp. 2050124
Author(s):  
Parth Shah ◽  
Gauranga C. Samanta
Keyword(s):  
Dynamical System ◽  
Asymptotic Behavior ◽  
Critical Points ◽  
System Analysis ◽  
Late Time ◽  
Field Equations ◽  
Acceleration Phase ◽  
First Case ◽  
Acceleration Of The Universe ◽  
The Universe

In this work we try to understand the late-time acceleration of the universe by assuming some modification in the geometry of the space and using dynamical system analysis. This technique allows to understand the behavior of the universe without analytically solving the field equations. We study the acceleration phase of the universe and stability properties of the critical points which could be compared with observational results. We consider an asymptotic behavior of two particular models [Formula: see text] and [Formula: see text] with [Formula: see text], [Formula: see text], [Formula: see text] for the study. As a first case we fix the value of [Formula: see text] and analyze for all [Formula: see text]. Later as second case, we fix the value of [Formula: see text] and calculation are done for all [Formula: see text]. At the end all the calculations for the generalized case have been shown and results have been discussed in detail.

Cosmic acceleration with tachyon field

2018 ◽  
Vol 33 (34) ◽  
pp. 1850199 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
De Sitter ◽  
Tachyon Field ◽  
Minimal Coupling ◽  
Acceleration Of The Universe ◽  
The Universe

In this study, we examine two models of the scalar field, that is, a normal scalar field and a tachyon scalar field in [Formula: see text] gravity to describe cosmic acceleration of the universe, where [Formula: see text], [Formula: see text] and [Formula: see text] are Ricci curvature scalar, trace of energy–momentum tensor and kinetic energy of scalar field [Formula: see text], respectively. Using the minimal-coupling Lagrangian [Formula: see text], for both the scalar models we obtain a viable cosmological system, where [Formula: see text] and [Formula: see text] are real constants. While a normal scalar field gives a system describing expansion from the deceleration to the late-time acceleration, tachyon field together with [Formula: see text] in the system produces a quintessential expansion which is very close to de Sitter point, where we find a new condition [Formula: see text] for inflation.

A new pressure-parametric cosmological model

2020 ◽  
Vol 35 (25) ◽  
pp. 2050209
Author(s):  
Yan-Hong Yao ◽  
Xin-He Meng
Keyword(s):  
Scalar Fields ◽  
Model Parameters ◽  
Acoustic Oscillations ◽  
Dark Sector ◽  
Type Ia ◽  
Phantom Scalar ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
Ia Supernovae ◽  
The Universe

We put forward a pressure-parametric model to study the tiny deviation from cosmological constant(CC) behavior of the dark sector accelerating the expansion of the Universe. Data from cosmic microwave background (CMB) anisotropies, baryonic acoustic oscillations (BAO), Type Ia supernovae (SN Ia) observation are applied to constrict the model parameters. The constraint results show that such model suffers with [Formula: see text] tension as well. To realize this model more physically, we reconstruct it with the quintessence and phantom scalar fields, and find out that although the model predicts a quintessence-induced acceleration of the Universe at past and present, at some moment of the future, dark energy’s density have a disposition to increase.

scholarly journals SOME ASPECTS OF SPHERICAL SYMMETRIC EXTREMAL DYONIC BLACK HOLES IN 4D N = 1 SUPERGRAVITY

2013 ◽  
Vol 28 (18) ◽  
pp. 1350084 ◽  
Author(s):  
BOBBY E. GUNARA ◽  
FREDDY P. ZEN ◽  
FIKI T. AKBAR ◽  
AGUS SUROSO ◽  
ARIANTO
Keyword(s):  
Black Hole ◽  
Scalar Potential ◽  
Local Existence ◽  
Scalar Fields ◽  
Asymptotic Region ◽  
De Sitter ◽  
Complex Scalar ◽  
Symmetric Black Hole ◽  
Scalar Potentials ◽  
Nonzero Scalar

In this paper, we study several aspects of extremal spherical symmetric black hole solutions of four-dimensional N = 1 supergravity coupled to vector and chiral multiplets with the scalar potential turned on. In the asymptotic region, the complex scalars are fixed and regular which can be viewed as the critical points of the black hole and the scalar potentials with vanishing scalar charges. It follows that the asymptotic geometries are of a constant and nonzero scalar curvature which are generally not Einstein. These spaces could also correspond to the near horizon geometries which are the product spaces of a two anti-de Sitter surface and the two sphere if the value of the scalars in both regions coincide. In addition, we prove the local existence of nontrivial radius dependent complex scalar fields which interpolate between the horizon and the asymptotic region. We finally give some simple ℂn-models with both linear superpotential and gauge couplings.

scholarly journals Accelerating cosmology in modified gravity: From convenient F(R) or string-inspired theory to bimetric F(R) gravity

2014 ◽  
Vol 11 (02) ◽  
pp. 1460006 ◽  
Author(s):  
Shin'ichi Nojiri ◽  
Sergei D. Odintsov
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Early Time ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Reconstruction Method ◽  
Free Theory ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Unified Description

We consider modified gravity which may describe the early-time inflation and/or late-time cosmic acceleration of the universe. In particular, we discuss the properties of F(R), F(G), string-inspired and scalar-Einstein–Gauss–Bonnet gravities, including their FRW equations and fluid or scalar-tensor description. Simplest accelerating cosmologies are investigated and possibility of unified description of the inflation with dark energy is described. The cosmological reconstruction program which permits to get the requested universe evolution from modified gravity is developed. As some extension, massive F(R) bigravity which is ghost-free theory is presented. Its scalar-tensor form turns out to be the easiest formulation. The cosmological reconstruction method for such bigravity is presented. The unified description of inflation with dark energy in F(R) bigravity turns out to be possible.

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.

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