scholarly journals New type scalar fields for cosmic acceleration

2007 ◽  
Vol 68 ◽  
pp. 012017
Author(s):  
A Kehagias ◽  
S Pakis
Keyword(s):  
Scalar Fields ◽  
Cosmic Acceleration ◽  
New Type

scholarly journals Late-time cosmic acceleration: ABCD of dark energy and modified theories of gravity

2016 ◽  
Vol 25 (12) ◽  
pp. 1630031 ◽  
Author(s):  
M. Sami ◽  
R. Myrzakulov
Keyword(s):  
Dark Energy ◽  
Scalar Fields ◽  
Massive Gravity ◽  
Cosmic Acceleration ◽  
Modified Theories Of Gravity ◽  
Late Time ◽  
Cosmological Constant Problem ◽  
Chameleon Mechanism ◽  
Theories Of Gravity ◽  
Basic Ideas

We briefly review the problems and prospects of the standard lore of dark energy. We have shown that scalar fields, in principle, cannot address the cosmological constant problem. Indeed, a fundamental scalar field is faced with a similar problem dubbed naturalness. In order to keep the discussion pedagogical, aimed at a wider audience, we have avoided technical complications in several places and resorted to heuristic arguments based on physical perceptions. We presented underlying ideas of modified theories based upon chameleon mechanism and Vainshtein screening. We have given a lucid illustration of recently investigated ghost-free nonlinear massive gravity. Again, we have sacrificed rigor and confined to the basic ideas that led to the formulation of the theory. The review ends with a brief discussion on the difficulties of the theory applied to cosmology.

scholarly journals Coupled scalar fields in the late Universe: the mechanical approach and the late cosmic acceleration

2016 ◽  
Vol 2016 (09) ◽  
pp. 045-045 ◽  
Author(s):  
Alvina Burgazli ◽  
Alexander Zhuk ◽  
João Morais ◽  
Mariam Bouhmadi-López ◽  
K. Sravan Kumar
Keyword(s):  
Scalar Fields ◽  
Cosmic Acceleration ◽  
Mechanical Approach

scholarly journals Dynamical dark energy: Scalar fields and running vacuum

2017 ◽  
Vol 32 (09) ◽  
pp. 1750054 ◽  
Author(s):  
Joan Solà ◽  
Adrià Gómez-Valent ◽  
Javier de Cruz Pérez
Keyword(s):  
Dark Energy ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
Field Approach ◽  
Hubble Rate ◽  
Representative Model ◽  
Cosmological Data ◽  
Energy Scalar ◽  
Dynamical Dark Energy ◽  
Better Than

Recent analyses in the literature suggest that the concordance [Formula: see text]CDM model with rigid cosmological term, [Formula: see text] may not be the best description of the cosmic acceleration. The class of “running vacuum models”, in which [Formula: see text] evolves with the Hubble rate, has been shown to fit the string of SNIa + BAO + H(z) + LSS + CMB data significantly better than the [Formula: see text]CDM. Here, we provide further evidence on the time-evolving nature of the dark energy (DE) by fitting the same cosmological data in terms of scalar fields. As a representative model, we use the original Peebles and Ratra potential, [Formula: see text]. We find clear signs of dynamical DE at [Formula: see text] c.l., thus reconfirming through a nontrivial scalar field approach the strong hints formerly found with other models and parametrizations.

Coexistence of early-time inflation and late-time acceleration with scalar fields in theory of F(G,T) gravity

2018 ◽  
Vol 27 (08) ◽  
pp. 1850078 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Scalar Field ◽  
Source Term ◽  
Friedmann Equation ◽  
Early Time ◽  
Scalar Fields ◽  
Momentum Tensor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Late Time Acceleration ◽  
The Universe

In this study, we discuss coexistence of the early-time inflation and the late-time acceleration of the universe in the context of the theory of [Formula: see text] gravity with scalar field which is minimally coupled with the gravity, where [Formula: see text] is the gauss bonnet invariant and [Formula: see text] is the trace of energy–momentum tensor (EMT). We reconstruct the Friedmann equation (FE) and then search for the real value of a particular model [Formula: see text], where [Formula: see text] and [Formula: see text] are real constants. A Gauss–Bonnet system (GBS) for viable cosmologies arising from the matter-source term [Formula: see text] and the scalar field, is obtained. We find that the case [Formula: see text] together with [Formula: see text] in the system gives the late-time cosmic acceleration while the source term [Formula: see text] acts as a quintessence type of dark energy. On the other hand, the general entropy expression of the universe is obtained by making use of the first law of thermodynamics (FLT) method. After theoretically analyzing the inflation in the entropy frame, we find a new condition [Formula: see text] with [Formula: see text] in the system. Then, from the observational analysis of inflation, the spectral index parameter and the scalar-tensor ratio are calculated under the new condition. In brief, we obtain a viable cosmological system arising from some modifications such as the scalar field and the source term, which can unify the early inflation and the late-time cosmic acceleration besides the deceleration regions of the universe.

scholarly journals Interacting dark matter and cosmic acceleration

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
Víctor H. Cárdenas ◽  
Samuel Lepe
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Constant ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
Recent Proposal ◽  
Small Coupling

AbstractWe study the effect of an explicit interaction between two scalar fields components describing dark matter in the context of a recent proposal framework for interaction. We find that, even assuming a very small coupling, it is sufficient to explain the observational effects of a cosmological constant, and also overcome the problems of the $$\Lambda $$ Λ CDM model without assuming an exotic dark energy.

Tsallis holographic dark energy in Bianchi type-III spacetime with scalar fields

2019 ◽  
Vol 34 (37) ◽  
pp. 1950310 ◽  
Author(s):  
Murat Korunur
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Bianchi Type ◽  
Holographic Dark Energy ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Acceleration Phase ◽  
Eos Parameter ◽  
Type Iii

In this paper, we study one of the new dark energy models named Tsallis holographic dark energy (THDE) model considering the Bianchi type-III spacetime model. Considering deceleration parameter, transition from deceleration to acceleration phase happens at [Formula: see text]. The equation of state (EoS) parameter has been found using the Granda–Oliveros (GO) scale. It is found that for [Formula: see text] values, EoS parameter behaves like the quintessence era; for [Formula: see text], EoS parameter behaves like the phantom dark energy and approaches [Formula: see text]CDM model at late-time cosmic acceleration phase. Also, we reconstructed a correspondence between THDE model and some well-known scalar fields, such as tachyon, quintessence and [Formula: see text]-essence. In addition, we evaluated equation of state parameter, kinetic energy and scalar potential versus time.

scholarly journals Non-Locality and Late-Time Cosmic Acceleration from an Ultraviolet Complete Theory †

Universe ◽  
2018 ◽  
Vol 4 (8) ◽  
pp. 82 ◽  
Author(s):  
Gaurav Narain ◽  
Tianjun Li
Keyword(s):  
Dark Energy ◽  
Local Treatment ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Scale Invariant ◽  
Higher Derivative ◽  
Local Gravity ◽  
Non Local ◽  
Non Locality

A local phenomenological model that reduces to a non-local gravitational theory giving dark energy is proposed. The non-local gravity action is known to fit the data as well as Λ-CDM thereby demanding a more fundamental local treatment. It is seen that the scale-invariant higher-derivative scalar-tensor theory of gravity, which is known to be ultraviolet perturbative renormalizable to all loops and where ghosts become innocuous, generates non-locality at low energies. The local action comprises of two real scalar fields coupled non-minimally with the higher-derivative gravity action. When one of the scalar acquiring the Vacuum Expectation Value (VEV) induces Einstein–Hilbert gravity, generates mass for fields, and gets decoupled from system, it leaves behind a residual theory which in turn leads to a non-local gravity generating dark energy effects.

scholarly journals Out of the swampland with multifield quintessence?

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Michele Cicoli ◽  
Giuseppe Dibitetto ◽  
Francisco G. Pedro
Keyword(s):  
Initial Conditions ◽  
Functional Dependence ◽  
Scalar Potential ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Kinetic Coupling ◽  
Current State ◽  
The Stability ◽  
Promising Avenue

Abstract Multifield models with a curved field space have already been shown to be able to provide viable quintessence models for steep potentials that satisfy swampland bounds. The simplest dynamical systems of this type are obtained by coupling Einstein gravity to two scalar fields with a curved field space. In this paper we study the stability properties of the non-trivial fixed points of this dynamical system for a general functional dependence of the kinetic coupling function and the scalar potential. We find the existence of non-geodesic trajectories with a sharp turning rate in field space which can give rise to late-time cosmic acceleration with no need for flat potentials. In particular, we discuss the properties of the phase diagram of the system and the corresponding time evolution when varying the functional dependence of the kinetic coupling. Interestingly, upon properly tuning the initial conditions of the field values, we find trajectories that can describe the current state of the universe. This could represent a promising avenue to build viable quintessence models out of the swampland if they could be consistently embedded in explicit string constructions.

Locally rotationally symmetric Bianchi type-I string cosmological models in f(R) theory of gravity

2018 ◽  
Vol 15 (09) ◽  
pp. 1850156 ◽  
Author(s):  
Y. Aditya ◽  
D. R. K. Reddy
Keyword(s):  
Bianchi Type ◽  
Scalar Fields ◽  
Cosmological Models ◽  
Cosmic Acceleration ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Locally Rotationally Symmetric ◽  
Rotationally Symmetric ◽  
Theory Of Gravity

This study deals with spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi type-I universe with cosmic string source in the framework of [Formula: see text] theory of gravity [S. Capozziello, S. Carloni and A. Troisi, Quintessence without scalar fields, Recent Res. Dev. Astron. Astrophys. 1 (2003), 625; S. Nojiri and S. D. Odintsov, Modified gravity with negative and positive powers of curvature: Unification of inflation and cosmic acceleration, Phys. Rev. D 68 (2003) 123512]. Solving the field equations using (i) relation between metric potentials, (ii) power law relation between [Formula: see text] and average scale factor [Formula: see text] and (iii) equations of state for string models we have presented Takabayasi [T. Takabayasi, Quantum Mechanics Determinism, Causality, and Particles (Springer, Berlin, 1976)], Nambu [P. S. Letelier, String cosmologies, Phys. Rev. D 28 (1983) 2414–2419] and Reddy [D. R. K. Reddy, A string cosmological model in a scalar–Tensor theory of gravitation, Astrophys. Space Sci. 286 (2003) 359–363] string cosmological models. The dynamical parameters of our models are determined and their physical behavior is discussed. The most interesting result about the models is that the anisotropic effects are wiped out at late times.

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