scholarly journals CONSTRAINING THE RUNAWAY DILATON AND QUINTESSENTIAL DARK ENERGY

2010 ◽  
Vol 19 (03) ◽  
pp. 367-394 ◽  
Author(s):  
ISHWAREE P. NEUPANE ◽  
HOLLY TROWLAND
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Cosmological Parameters ◽  
Scalar Fields ◽  
Current Data ◽  
Gravity Models ◽  
Model Parameters ◽  
Dilaton Field ◽  
The Universe

Dark energy is some of the weirdest and most mysterious stuff in the universe that tends to increase the rate of expansion of the universe. Two commonly known forms of dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli whose energy density can vary with time. We explore one particular model for dynamic dark energy: quintessence driven by a scalar dilaton field. We propose an ansatz for the form of the dilaton field, |ϕ(a)|mP ≡ α1 ln t + α2tn = α ln a + βa2ζ, where a is the scale factor and α and ζ are parameters of the model. This phenomenological ansatz for ϕ can be motivated by generic solutions of a scalar dilaton field in many effective string theory and string-inspired gravity models in four dimensions. Most of the earlier discussions in the literature correspond to the choice that ζ = 0 so that ϕ(t) ∝ ln t or ϕ(t) ∝ ln a(t). Using a compilation of current data including type Ia supernovae, we impose observational constraints on the slope parameters like α and ζ and then discuss the relation of our results to analytical constraints on various cosmological parameters, including the dark energy equation of state. Some useful constraints are imposed on model parameters like α and ζ as well as on the dark energy/dark matter couplings using results from structure formation. The constraints of this model are shown to encompass the cosmological constant limit within 1σ error bars.

Late time cosmology in f(R,G)- gravity with interacting fluids

2022 ◽  
Author(s):  
Bikash Chandra Paul ◽  
A. Chanda ◽  
Sunil Maharaj ◽  
Aroonkumar Beesham
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Cosmological Parameters ◽  
Accelerating Universe ◽  
Model Parameters ◽  
Density Parameter ◽  
Late Time ◽  
First Case ◽  
The Universe

Abstract Cosmological models are obtained in a $f(R)$ modified gravity with a coupled Gauss-Bonnet (GB) terms in the gravitational action. The dynamical role of the GB terms is explored with a coupled dilaton field in two different cases (I) $f(R)= R + \gamma R^2- \lambda \left( \frac{R}{3m_s^2} \right)^{\delta}$ where $\gamma$, $\lambda$ and $\delta$ are arbitrary constants and (II) $f(R)=R$ and estimate the constraints on the model parameters. In the first case we choose GB terms coupled with a free scalar field in the presence of interacting fluid and in the second case GB terms coupled with scalar field in a self interacting potential to compare the observed universe. The evolutionary scenario of the universe is obtained adopting a numerical technique as the field equations are highly non-linear. Defining a new density parameter $\Omega_{H}$, a ratio of the dark energy density to the present energy density of the non-relativistic matter, we look for a late accelerating universe. The state finder parameters $\Omega_{H}$, deceleration parameter ($q$), jerk parameter ($j$) are plotted. It is noted that a non-singular universe with oscillating cosmological parameters for a given strength of interactions is admitted in Model-I. The gravitational coupling constant $\lambda$ is playing an important role. The Lagrangian density of $f(R)$ is found to dominate over the GB terms when oscillating phase of dark energy arises. In Model-II, we do not find oscillation of the cosmological parameters as the universe evolves. In the presence of interaction the energy from radiation sector of matter cannot flow to the other two sectors of fluid. The range of values of the strengths of interaction of the fluids are estimated for a stable universe assuming the primordial gravitational wave speed equal to unity.

scholarly journals Generalized Phenomenological Models of Dark Energy

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Prasenjit Paul ◽  
Rikpratik Sengupta
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Phenomenological Models ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Free Parameters ◽  
The Universe ◽  
Matter Energy

It was first observed at the end of the last century that the universe is presently accelerating. Ever since, there have been several attempts to explain this observation theoretically. There are two possible approaches. The more conventional one is to modify the matter part of the Einstein field equations, and the second one is to modify the geometry part. We shall consider two phenomenological models based on the former, more conventional approach within the context of general relativity. The phenomenological models in this paper consider a Λ term firstly a function of a¨/a and secondly a function of ρ, where a and ρ are the scale factor and matter energy density, respectively. Constraining the free parameters of the models with the latest observational data gives satisfactory values of parameters as considered by us initially. Without any field theoretic interpretation, we explain the recent observations with a dynamical cosmological constant.

scholarly journals SUPERNOVA Ia AND GALAXY CLUSTER GAS MASS FRACTION CONSTRAINTS ON DARK ENERGY

2006 ◽  
Vol 21 (29) ◽  
pp. 2197-2204 ◽  
Author(s):  
KYLE M. WILSON ◽  
GANG CHEN ◽  
BHARAT RATRA
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Mass Fraction ◽  
Galaxy Cluster ◽  
Apparent Magnitude ◽  
Model Parameters ◽  
Dark Energy Density ◽  
Energy Models ◽  
Fraction Versus

We use the Riess et al. (2004)1 supernova Ia apparent magnitude versus redshift data and the Allen et al. (2004)2 galaxy cluster gas mass fraction versus redshift data to constrain dark energy models. These data provide complementary constraints that when combined together significantly restrict model parameters and favor slowly-evolving dark energy density models, close to the Einstein cosmological constant limit of dark energy.

Observational and astrophysical cosmology: 1980–2018

2019 ◽  
pp. 375-423
Author(s):  
Malcolm S. Longair
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Constant ◽  
Large Scale ◽  
Cosmological Parameters ◽  
Semiconductor Detectors ◽  
Empirical Knowledge ◽  
Global Geometry ◽  
The Universe ◽  
Large Scale Structure Formation

Since 1980, our empirical knowledge of the universe has advanced tremendously and precision cosmology has become a reality. These developments have been largely technology-driven, the result of increased computer power, new generations of telescopes for all wavebands, new types of semiconductor detectors, such as CCDs, and major investments by many nations in superb observing facilities. The discipline also benefitted from the influx of experimental and theoretical physicists into the cosmological arena. The accuracy and reliability of the values of the cosmological parameters has improved dramatically, many of them now being known to about 1%. The ΛCDM model provides a remarkable fit to all the observational data, demonstrating that the cosmological constant is non-zero and that the global geometry of the universe is flat. The underlying physics of galaxy and large-scale structure formation has advanced dramatically and demonstrated the key roles played by dark matter and dark energy.

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.

scholarly journals WHAT ARE THE BUILDING BLOCKS OF OUR UNIVERSE?

2008 ◽  
Vol 17 (05) ◽  
pp. 817-825
Author(s):  
KAMESHWAR C. WALI
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Total Energy ◽  
High Energy Physics ◽  
Cosmological Parameters ◽  
Building Blocks ◽  
High Energy ◽  
Total Energy Density ◽  
The Universe ◽  
Energy Physics

We are living in a Golden Age of Astronomy. Cosmological Parameters are found with an unprecedented accuracy comparable to high energy physics. Yet, the known form of matter forms only a small fraction of the total energy density of the universe. Also, a mysterious dark energy dominates the universe and causes acceleration in the rate of expansion. These findings raise new questions concerning the ultimate constitution of matter in the universe.

COUPLED QUINTESSENCE AND THE COINCIDENCE PROBLEM

2003 ◽  
Vol 18 (12) ◽  
pp. 831-842 ◽  
Author(s):  
G. MANGANO ◽  
G. MIELE ◽  
V. PETTORINO
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Phenomenological Model ◽  
Coincidence Problem ◽  
Strongly Coupled ◽  
Coexisting Phases ◽  
The Universe ◽  
Universe Evolution

We consider a model of interacting cosmological constant/quintessence, where dark matter and dark energy behave as, respectively, two coexisting phases of a fluid, a thermally excited Bose component and a condensate, respectively. In a simple phenomenological model for the dark components interaction we find that their energy density evolution is strongly coupled during the universe evolution. This feature provides a possible way out for the coincidence problem affecting many quintessence models.

The scalar field models of Tsallis holographic dark energy with Granda-Oliveros cut-off in modified gravity

2021 ◽  
Author(s):  
Anirudh Pradhan ◽  
Gunjan Varshney ◽  
Umesh Kumar Sharma
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Holographic Dark Energy ◽  
Scalar Fields ◽  
Accelerated Expansion ◽  
Model Parameters ◽  
Frw Universe ◽  
Dark Energy Density ◽  
Eos Parameter ◽  
Expansion Of The Universe

This research explores the Tsallis holographic quintessence, k-essence, and tachyon model of dark energy in the modified f(R, T) gravity framework with Granda-Oliveros cutoff. We have analyzed the energy density through ρΛ = (αH<sup>2</sup> + βH)<sup>-δ+2</sup>. We study the correspondence between the quintessence, k-essence, and tachyon energy density with the Tsallis holographic dark energy density in a flat FRW Universe. The reconstruction is performed for the different values of Tsallis parameter δ in the region of ωΛ > -1 for the EoS parameter. This correspondence allows reconstructing the potentials and the dynamics for the scalar fields models, if we set some constraints for the model parameters, which describe the accelerated expansion of the Universe.

scholarly journals A new parametrization for dark energy density and future deceleration

2018 ◽  
Vol 33 (20) ◽  
pp. 1850113 ◽  
Author(s):  
Abdulla Al Mamon
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Present Model ◽  
Background Radiation ◽  
Cosmic Acceleration ◽  
Model Parameters ◽  
Acoustic Oscillations ◽  
Dark Energy Density ◽  
Evolution Of The Universe ◽  
The Universe

In this work, we have proposed a general dark energy density parametrization to study the evolution of the universe. We have also constrained the model parameters using the combination of Type Ia supernova (SNIa), baryonic acoustic oscillations (BAO), cosmic microwave background radiation (CMB) and observational [Formula: see text] datasets. For the [Formula: see text] dataset, we have used the direct observations of the Hubble rate, from the radial BAO size and the cosmic chronometer methods. Our result indicates that the [Formula: see text] dataset does not favor the [Formula: see text]CDM model at more than [Formula: see text] confidence level. Furthermore, we have also measured the percentage deviation in the evolution of the normalized Hubble parameter for the present model compared to a [Formula: see text]CDM model, and the corresponding deviation is found to be 4–5% at low redshifts [Formula: see text]. Finally, we have also investigated whether the deceleration parameter [Formula: see text] may have more than one transition during the evolution of the universe. The present model shows a transient accelerating phase, in which the universe was decelerated in the past and is presently accelerating, but will return to a decelerating phase in the near future. This result is in great contrast to the [Formula: see text]CDM scenario, which predicts that the cosmic acceleration must remain forever.

scholarly journals QUANTUM EFFECTS AND SUPERQUINTESSENCE IN THE NEW AGE OF PRECISION COSMOLOGY

2004 ◽  
Vol 13 (10) ◽  
pp. 2255-2259 ◽  
Author(s):  
E. GUNZIG ◽  
ALBERTO SAA
Keyword(s):  
Experimental Data ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Classical Approach ◽  
Constant Ratio ◽  
Energy Component ◽  
Dark Energy Component ◽  
Type Ia ◽  
The Universe

Recent observations of Type Ia supernova at high redshifts establish that the dark energy component of the universe has (a probably constant) ratio between pressure and energy density [Formula: see text]. The conventional quintessence models for dark energy are restricted to the range -1≤w<0, with the cosmological constant corresponding to w=-1. Conformally coupled quintessence models are the simplest ones compatible with the marginally allowed superaccelerated regime (w<-1). However, they are known to be plagued with anisotropic singularities. We argue here that the extension of the classical approach to the semiclassical one, with the inclusion of quantum counterterms necessary to ensure the renormalization, can eliminate the anisotropic singularities preserving the isotropic behavior of conformally coupled superquintessence models. Hence, besides of having other interesting properties, they are consistent candidates to describe the superaccelerated phases of the universe compatible with the present experimental data.

Sign in / Sign up

Export Citation Format

Share Document