scholarly journals K-essence model from the mechanical approach point of view: coupled scalar field and the late cosmic acceleration

2016 ◽  
Vol 2016 (07) ◽  
pp. 050-050 ◽  
Author(s):  
Mariam Bouhmadi-López ◽  
K. Sravan Kumar ◽  
João Marto ◽  
João Morais ◽  
Alexander Zhuk
Keyword(s):  
Scalar Field ◽  
Point Of View ◽  
Cosmic Acceleration ◽  
Mechanical Approach

Bouncing scenario in Brans–Dicke theory

2020 ◽  
Vol 17 (04) ◽  
pp. 2050056
Author(s):  
Sunil Kumar Tripathy ◽  
Subingya Pandey ◽  
Alaka Priyadarsini Sendha ◽  
Dipanjali Behera
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Linear Equation ◽  
Scale Factor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Dark Fluid

A bouncing scenario is studied in the framework of generalized Brans–Dicke theory. In order to have a dark energy (DE) driven late time cosmic acceleration, we have considered a unified dark fluid simulated by a linear equation of state (EoS). The evolutionary behavior of the DE equation of parameter derived from the unified dark fluid has been discussed. The effect of the bouncing scale factor on the Brans–Dicke parameter, self-interacting potential and the Brans–Dicke scalar field is investigated.

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.

scholarly journals Accelerating universe and the time-dependent fine-structure constant

2009 ◽  
Vol 5 (H15) ◽  
pp. 302-302
Author(s):  
Yasunori Fujii
Keyword(s):  
Fine Structure ◽  
Scalar Field ◽  
Structure Constant ◽  
Theoretical Background ◽  
Point Of View ◽  
Fine Structure Constant ◽  
Time Variability ◽  
Accelerating Universe ◽  
Tensor Theory ◽  
The Right

I start with assuming a gravitational scalar field as the dark-energy supposed to be responsible for the accelerating universe. Also from the point of view of unification, a scalar field implies a time-variability of certain “constants” in Nature. In this context I once derived a relation for the time-variability of the fine-structure constant α: Δα/α =ζ Ƶ(α/π) Δσ, where ζ and Ƶ are the constants of the order one, while σ on the right-hand side is the scalar field in action in the accelerating universe. I use the reduced Planckian units with c=ℏ =MP(=(8π G)−1/2)=1. I then compared the dynamics of the accelerating universe, on one hand, and Δα/α derived from the analyses of QSO absorption lines, Oklo phenomenon, also different atomic clocks in the laboratories, on the other hand. I am here going to discuss the theoretical background of the relation, based on the scalar-tensor theory invented first by Jordan in 1955.

scholarly journals Dynamical system analysis of dark energy models in scalar coupled Metric-Torsion theories

2017 ◽  
Vol 26 (13) ◽  
pp. 1750149 ◽  
Author(s):  
Arshdeep Singh Bhatia ◽  
Sourav Sur
Keyword(s):  
Dark Energy ◽  
Phase Space ◽  
Scalar Field ◽  
System Analysis ◽  
Coupling Parameter ◽  
Cosmological Parameters ◽  
Direct Interaction ◽  
Cosmic Acceleration ◽  
Energy Models ◽  
Space Dynamics

We study the phase-space dynamics of cosmological models in the theoretical formulations of nonminimal metric-torsion couplings with a scalar field, and investigate in particular the critical points (CPs) which yield stable solutions exhibiting cosmic acceleration driven by the dark energy (DE). The latter is so defined that it effectively has no direct interaction with the cosmological fluid, although in an equivalent scalar–tensor cosmological setup, the scalar field interacts with the fluid (which we consider to be the pressureless dust). Determining the conditions for the existence of the stable CPs, we check their physical viability in both Einstein and Jordan frames. We also verify that in either of these frames, the evolution of the universe at the corresponding stable points matches with that given by the respective exact solutions we have found in an earlier work [S. Sur and A. S. Bhatia, arXiv:1611.00654 [gr-qc]]. We not only examine the regions of physical relevance in the phase-space when the coupling parameter is varied, but also demonstrate the evolution profiles of the cosmological parameters of interest along fiducial trajectories in the effectively noninteracting scenarios, in both Einstein and Jordan frames.

Cosmic aspects of chameleon Brans–Dicke gravity with parameterized deceleration parameters

2020 ◽  
Vol 17 (08) ◽  
pp. 2050115
Author(s):  
Abdul Jawad ◽  
Asma Aslam
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Vital Role ◽  
Cosmic Acceleration ◽  
Minimal Coupling ◽  
Frw Universe ◽  
Equation Of State Parameter

We investigate the chameleon Brans–Dicke gravity with new holographic dark energy which includes a non-minimal coupling between matter and scalar field. We use parameterized forms of deceleration parameter for flat FRW universe, which play a vital role to describe the nature of cosmic acceleration. We explore the cosmological parameters like Hubble parameter, equation of state parameter as well as its plane and stability of the obtained solution. The results of cosmological parameter and plane are consistent with observational data.

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 COSMIC ACCELERATION IN A MODEL OF SCALAR–TENSOR GRAVITATION

2008 ◽  
Vol 17 (11) ◽  
pp. 2007-2015 ◽  
Author(s):  
SANIL UNNIKRISHNAN ◽  
T. R. SESHADRI
Keyword(s):  
Scalar Field ◽  
Cosmic Acceleration ◽  
Accelerated Expansion ◽  
Observational Constraints ◽  
Gravitational Coupling ◽  
Effective Equation ◽  
Expansion Phase ◽  
Tensor Theory ◽  
Theory Of Gravitation ◽  
Cosmological Consequence

In this paper we consider a model of the scalar–tensor theory of gravitation, in which the scalar field ϕ determines the gravitational coupling G and has a Lagrangian of the form [Formula: see text]. We study the cosmological consequence of this theory in the matter-dominated era and show that it leads to a transition from an initial decelerated expansion to an accelerated expansion phase at the present epoch. Using observational constraints, we see that the effective equation of state today for the scalar field turns out to be pϕ = wϕρϕ, with wϕ = -0.88, and that the transition to an accelerated phase happened at a redshift of about 0.3.

scholarly journals Approximation methods in modified gravity models

2018 ◽  
Vol 27 (15) ◽  
pp. 1848004 ◽  
Author(s):  
Baojiu Li
Keyword(s):  
Modified Gravity ◽  
Large Scale ◽  
A Priori ◽  
Point Of View ◽  
Cosmic Acceleration ◽  
Gravity Models ◽  
Approximation Methods ◽  
Theoretical Point ◽  
Speed Up ◽  
Efficiency And Reliability

We review some of the commonly used approximation methods to predict large-scale structure formation in modified gravity (MG) models for the cosmic acceleration. These methods are developed to speed up the often slow [Formula: see text]-body simulations in these models, or directly make approximate predictions of relevant physical quantities. In both cases, they are orders of magnitude more efficient than full simulations, making it possible to explore and delineate the large cosmological parameter space. On the other hand, there is a wide variation of their accuracies and ranges of validity, and these are usually not known a priori and must be validated against simulations. Therefore, a combination of full simulations and approximation methods will offer both efficiency and reliability. The approximation methods are also important from a theoretical point of view, since they can often offer useful insight into the nonlinear physics in MG models and inspire new algorithms for simulations.

scholarly journals Quantum Mechanical 4-dimensional Non-polarizing Beamsplitter

2021 ◽  
Author(s):  
Artem Kryvobok ◽  
Alan Kathman
Keyword(s):  
Quantum Computing ◽  
Scalar Field ◽  
Experimental Evidence ◽  
Vector Fields ◽  
Matrix Representation ◽  
Point Of View ◽  
Quantum Mechanical ◽  
Simple Experiment ◽  
Canonical Commutation Relations ◽  
Classical Fields

Abstract The effects of a beamsplitter are frequently described mathematically as a matrix acting on a two input ports vector. This might be comprehensive for a scalar field but certainly insufficient in case of photons which are vector fields. In this paper we discuss theoretical grounds to define elements of a 4x4 matrix to more accurately represent the beamsplitter, fully accounting for transverse polarization modes. We also provide experimental evidence confirming this matrix representation. From scientific point of view the paper addresses a non-trivial equivalence between the classical fields Fresnel formalism and the canonical commutation relations of the quantized photonic fields. That the formalism can be readily verified with a simple experiment provides further benefit. The beamsplitter expression derived can be applied in the field of quantum computing.

scholarly journals Two-dimensional Analysis of Cracks Propagation in Structures of Concrete

2013 ◽  
Vol 3 (3) ◽  
pp. 429-432
Author(s):  
D. Benarbia ◽  
M. Benguediab ◽  
S. Benguediab
Keyword(s):  
Point Of View ◽  
Two Dimensional ◽  
The Finite Element Method ◽  
Fracture Criteria ◽  
Development Processes ◽  
Mechanical Approach ◽  
Indirect Tensile ◽  
Cracks Propagation ◽  
Phenomenological Point

In this article we present a numerical simulation that allows describing and studying the damage of concrete works subjected to various stress types. In this study, the propagation of cracks in the concrete is analyzed as of their appearance, which requires having a thorough knowledge of the mechanical behavior of the material. The mechanical approach which leads to better understanding of fracture phenomena and can give satisfactory results, is that of the elastic linear mechanics of failure. The interest in this study is focused in the development processes of the cracks from a phenomenological point of view. The analysis is carried out by using fracture criteria while being based on the determination of the critical stress intensity factors, for each case of the several elaborate tests of indirect tensile per bending and Brazilian Disc. The analysis is carried out in a two-dimensional medium by the finite element method by using the ABAQUS software. The results obtained are compared with experimental data obtained analytically from other authors.

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