scholarly journals What ξ ? Cosmological constraints on the non-minimal coupling constant

2017 ◽  
Vol 768 ◽  
pp. 218-227 ◽  
Author(s):  
Orest Hrycyna
Keyword(s):  
Coupling Constant ◽  
Minimal Coupling ◽  
Cosmological Constraints

Gravitational collapse in f(R) theories of gravity with non-minimal coupling

2019 ◽  
Vol 34 (03) ◽  
pp. 1950025 ◽  
Author(s):  
H. Nazar ◽  
G. Abbas
Keyword(s):  
Perfect Fluid ◽  
Gravitational Collapse ◽  
Spherically Symmetric ◽  
Coupling Constant ◽  
Minimal Coupling ◽  
Apparent Horizons ◽  
Exterior Regions ◽  
Theories Of Gravity ◽  
Minimal Curvature ◽  
Zero Coupling

The purpose of this paper is to discuss the perfect fluid gravitational collapse in modified f(R) metric gravity theories with non-minimal curvature coupled to matter. For this inference, we investigate the effects on self-gravitating implosion with spherically symmetric non-static geometry in the presence of extra force [Formula: see text], that express the cosmic expansion with dark source constraints. Matching conditions are given in which we have taken the insertion of non-static interior and static exterior regions along with cosmological constant. We have investigated the apparent horizons with effective results and along with their physical interpretation. It is analyzed that the extra component of dark source material reduces the gravitating implosion, hence slowing the rate of collapse. This study also reflects the contribution towards the perfect fluid for the generalization in f(R) gravity with zero coupling constant [Formula: see text].

INFLATION AND COMPACT HYPERBOLIC EXTRA DIMENSIONS

2012 ◽  
Vol 10 ◽  
pp. 69-76
Author(s):  
YOONBAI KIM ◽  
SEONG CHAN PARK
Keyword(s):  
Extra Dimension ◽  
Extra Dimensions ◽  
Gravitational Perturbation ◽  
Coupling Constant ◽  
Coupling Term ◽  
Minimal Coupling ◽  
Slow Roll ◽  
Cosmological Observations ◽  
Cosmological Inflation ◽  
Natural Scale

We propose a scenario of cosmological inflation, called "hyperbolic inflation", based on compact hyperbolic extra dimensions and a non-minimal coupling term (ξϕ2 R) with a simple inflaton potential (λϕ4) in Ref. 1. The non-minimal coupling term ensures the presence of the slow-roll inflation potential and the large compact hyperbolic extra dimension provides an explanation to the seemingly unnatural smallness of the non-minimal coupling constant (λ/ξ2 ~ 10-10). The natural scale of inflation of the order of 1013 GeV is singled out fitting the current cosmological observations and predicts a sizable gravitational perturbation, r ≃ 3 × 10-3.

scholarly journals The non-minimal coupling constant and the primordial de Sitter state

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
Orest Hrycyna
Keyword(s):  
Scalar Field ◽  
Potential Functions ◽  
Constant Parameter ◽  
Coupling Constant ◽  
De Sitter ◽  
Dimensional Theory ◽  
Minimal Coupling ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Friedmann Robertson Walker

AbstractDynamical systems methods are used to investigate dynamics of a flat Friedmann–Robertson–Walker cosmological model with the non-minimally coupled scalar field and a potential function. Performed analysis distinguishes the value of non-minimal coupling constant parameter $$\xi =\frac{3}{16}$$ ξ = 3 16 , which is the conformal coupling in five dimensional theory of gravity. It is shown that for a monomial potential functions at infinite values of the scalar field there exist generic de Sitter and Einstein–de Sitter states. The de Sitter state is unstable with respect to expansion of the Universe for potential functions which do not change faster than linearly. This leads to a generic cosmological evolution without the initial singularity.

THE PHASE-SPACE VIEW OF INFLATION I: THE NON-MINIMALLY COUPLED SCALAR FIELD

1990 ◽  
Vol 05 (20) ◽  
pp. 3861-3886 ◽  
Author(s):  
LUCA AMENDOLA ◽  
MARCO LITTERIO ◽  
FRANCO OCCHIONERO
Keyword(s):  
Phase Space ◽  
Scalar Field ◽  
Cosmological Model ◽  
Analytical Form ◽  
Point Of View ◽  
Coupling Constant ◽  
Minimal Coupling ◽  
Vacuum States ◽  
Forbidden Region ◽  
Phase Space Portrait

The Phase Space portrait of a cosmological model with a scalar field coupled to curvature is discussed in detail, analytically and numerically, for any value of the coupling constant ξ and any power law (ϕ2n) potential. The results, particularly intuitive from the graphical point of view, generalize previous studies on the phase space with minimal coupling (ξ = 0) and quadratic or quartic potentials to the entire parameter space (ξ, n). We find global inflationary attractors, often in analytical form, with or without the correct Friedmannian limit. If the coupling constant is negative, escaping regions may occur, while, if it is positive, a forbidden region cuts out a large part of the phase space. Semiclassical instability of vacuum states and singularity-free trajectories are also discussed.

Exchange-Correlation Energy Densities and Response Potentials: Connection Between Two Definitions and Analytical Model for the Strong-Coupling Limit of a Stretched Bond

2019 ◽  
Author(s):  
S. Giarrusso ◽  
Paola Gori-Giorgi
Keyword(s):  
Density Functional Theory ◽  
Strong Coupling ◽  
Density Functional ◽  
Correlation Energy ◽  
Order Term ◽  
Strong Coupling Limit ◽  
Local Form ◽  
Coupling Constant ◽  
Functional Theory ◽  
Exchange Correlation

We analyze in depth two widely used definitions (from the theory of conditional probablity amplitudes and from the adiabatic connection formalism) of the exchange-correlation energy density and of the response potential of Kohn-Sham density functional theory. We introduce a local form of the coupling-constant-dependent Hohenberg-Kohn functional, showing that the difference between the two definitions is due to a corresponding local first-order term in the coupling constant, which disappears globally (when integrated over all space), but not locally. We also design an analytic representation for the response potential in the strong-coupling limit of density functional theory for a model single stretched bond.<br>

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Function Calculations

2019 ◽  
Author(s):  
Xianghai Sheng ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Density Functional Theory ◽  
Exchange Coupling ◽  
Density Functional ◽  
Spin Crossover ◽  
Coupling Constants ◽  
Spin Projection ◽  
Coupling Constant ◽  
Projection Model ◽  
Functional Theory

This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Project model provides an affordable and practical approach for effectively correcting spin-contamination errors in molecular exchange coupling constant and spin crossover gap calculations.

Sign in / Sign up

Export Citation Format

Share Document