scholarly journals Scalar field assisted f(R) gravity inflation

2018 ◽  
Vol 15 (08) ◽  
pp. 1850137 ◽  
Author(s):  
K. Kleidis ◽  
V. K. Oikonomou
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Field Potential ◽  
Cosmological Evolution ◽  
De Sitter ◽  
Array Data ◽  
The One ◽  
Canonical Scalar Field

In this paper, we investigate the inflationary dynamics of an [Formula: see text] gravity in the presence of a canonical scalar field. We specifically choose the cosmological evolution to be a quasi-de Sitter evolution and also the [Formula: see text] gravity is assumed to be a modified version of the [Formula: see text] gravity. We investigate which scalar field potential can produce the quasi-de Sitter evolution for the choice of the [Formula: see text] gravity we made, and also we study in detail the inflationary dynamics of the resulting theory. As we demonstrate, the spectral index is identical to the one corresponding to the ordinary [Formula: see text] gravity, while the scalar-to-tensor ratio is found to be smaller than the [Formula: see text] inflation one consequently, compatibility with both the Planck 2015 and BICEP2/Keck-Array data is achieved.

scholarly journals Dynamics of scalar potentials in theory of gravity

2019 ◽  
Vol 97 (8) ◽  
pp. 880-894
Author(s):  
M. Zubair ◽  
Farzana Kousar ◽  
Saira Waheed
Keyword(s):  
Scalar Field ◽  
Field Potential ◽  
Graphical Analysis ◽  
Chaplygin Gas ◽  
Field Potentials ◽  
De Sitter ◽  
Field Equations ◽  
Barotropic Fluid ◽  
First Case ◽  
De Sitter Universe

In this paper, we explore the nature of scalar field potential in [Formula: see text] gravity using a well-motivated reconstruction scheme for flat Friedmann–Robertson–Walker (FRW) geometry. The beauty of this scheme lies in the assumption that the Hubble parameter can be expressed in terms of scalar field and vice versa. Firstly, we develop field equations in this gravity and present some general explicit forms of scalar field potential via this technique. In the first case, we take the de Sitter universe model and construct some field potentials by taking different cases for the coupling function. In the second case, we derive some field potentials using the power law model in the presence of different matter sources like barotropic fluid, cosmological constant, and Chaplygin gas for some coupling functions. From graphical analysis, it is concluded that using some specific values of the involved parameters, the reconstructed scalar field potentials are cosmologically viable in both cases.

scholarly journals α-Attractors and reheating in a nonminimal inflationary model

2020 ◽  
Vol 29 (10) ◽  
pp. 2050077
Author(s):  
R. Shojaee ◽  
K. Nozari ◽  
F. Darabi
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Parameter Space ◽  
Model Potential ◽  
Index Formula ◽  
Inflationary Model ◽  
Scalar Spectral Index ◽  
Canonical Scalar Field

We study [Formula: see text]-attractor models with both E-model and T-model potential in an extended Nonminimal Derivative (NMD) inflation where a canonical scalar field and its derivatives are nonminimally coupled to gravity. We calculate the evolution of perturbations during this regime. Then by adopting inflation potentials of the model we show that in the large [Formula: see text] and small [Formula: see text] limit, the value of the scalar spectral index [Formula: see text] and tensor-to-scalar ratio [Formula: see text] are universal. Next, we study reheating after inflation in this formalism. We obtain some constraints on the model’s parameter space by adopting the results with Planck 2018.

The entropy evolution of a Schwarzschild–(Anti) de Sitter black hole

2020 ◽  
Vol 29 (07) ◽  
pp. 2050048
Author(s):  
Xin-Yang Wang ◽  
Yi-Ru Wang ◽  
Wen-Biao Liu
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Scalar Field ◽  
Hawking Radiation ◽  
Dynamical Variable ◽  
De Sitter ◽  
The One ◽  
Definition Of ◽  
Spherically Symmetry ◽  
Interior Volume

Based on the definition of the interior volume of spherically symmetry black holes, the interior volume of Schwarzschild–(Anti) de Sitter black holes is calculated. It is shown that with the cosmological constant ([Formula: see text]) increasing, the changing behaviors of both the position of the largest hypersurface and the interior volume for the Schwarzschild–Anti de Sitter black hole are the same as the Schwarzschild–de Sitter black hole. Considering a scalar field in the interior volume and Hawking radiation with only energy, the evolution relation between the scalar field entropy and Bekenstein–Hawking entropy is constructed. The results show that the scalar field entropy is approximately proportional to Bekenstein–Hawking entropy during Hawking radiation. Meanwhile, the proportionality coefficient is also regarded as a constant approximately with the increasing [Formula: see text]. Furthermore, considering [Formula: see text] as a dynamical variable, the modified Stefan–Boltzmann law is proposed which can be used to describe the variation of both the mass and [Formula: see text] under Hawking radiation. Using this modified law, the evolution relation between the two types of entropy is also constructed. The results show that the coefficient for Schwarzschild–de Sitter black holes is closer to a constant than the one for Schwarzschild–Anti de Sitter black holes during the evaporation process. Moreover, we find that for Hawking radiation carrying only energy, the evolution relation is a special case compared with the situation that the mass and [Formula: see text] are both considered as dynamical variables.

scholarly journals WHAT IF THE INFLATON IS A SPINOR CONDENSATE?

2009 ◽  
Vol 18 (14) ◽  
pp. 2173-2179 ◽  
Author(s):  
S. SHANKARANARAYANAN
Keyword(s):  
Scalar Field ◽  
Gravitational Wave ◽  
Spectral Index ◽  
Spinor Condensate ◽  
Slow Roll ◽  
Scalar Spectral Index ◽  
The Future ◽  
Wmap Data ◽  
Elementary Field ◽  
Canonical Scalar Field

In the usual cosmological inflationary scenarios, the scalar field — the inflaton — is usually assumed to be an elementary field. In this essay, we ask: What are the observational signatures if the scalar field is a spinor condensate? And is there a way to distinguish between the canonical scalar field and the spinor-condensate-driven models? In the homogeneous and isotropic background, we show that — although the dark-spinor (Elko) condensate leads to an acceleration equation identical to that of the canonical-scalar-field-driven inflation — the dynamics of the two models are different. In the slow-roll limit, we show that the model predicts a running of the scalar spectral index consistent with the WMAP data. We show that the consistency relations between the spinor condensate and the canonical-scalar-field-driven model are different, which we will be able to test using the future CMB and gravitational wave missions.

SOLITONS IN TWO-DIMENSIONAL ANTI-DE SITTER SPACE

2010 ◽  
Vol 25 (02n03) ◽  
pp. 289-299
Author(s):  
TONNIS TER VELDHUIS
Keyword(s):  
Field Theory ◽  
Scalar Field ◽  
Soliton Solution ◽  
Quantum Correction ◽  
Soliton Solutions ◽  
Two Dimensional ◽  
De Sitter ◽  
Fluctuation Spectrum ◽  
Background Space ◽  
The One

Soliton solutions in a scalar field theory defined on an AdS1+1 background space-time are investigated. An analytic soliton solution is obtained in a polynomial model, and the classical soliton mass is calculated. The fluctuation spectrum around the soliton solution is determined, and the one-loop quantum correction to the soliton mass is computed in the semi-classical approximation.

scholarly journals Dimensional reduction and (Anti) de Sitter bounds

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Tom Rudelius
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Dimensional Reduction ◽  
Energy Condition ◽  
Field Potential ◽  
Limited Range ◽  
Mass Scale ◽  
Accelerated Expansion ◽  
De Sitter ◽  
Expansion Of The Universe

Abstract Dimensional reduction has proven to be a surprisingly powerful tool for delineating the boundary between the string landscape and the swampland. Bounds from the Weak Gravity Conjecture and the Repulsive Force Conjecture, for instance, are exactly preserved under dimensional reduction. Motivated by its success in these cases, we apply a similar dimensional reduction analysis to bounds on the gradient of the scalar field potential V and the mass scale m of a tower of light particles in terms of the cosmological constant Λ, which ideally may pin down ambiguous O(1) constants appearing in the de Sitter Conjecture and the (Anti) de Sitter Distance Conjecture, respectively. We find that this analysis distinguishes the bounds $$ \left|\nabla V\right|/V\ge \sqrt{4/\left(d-2\right)} $$ ∇ V / V ≥ 4 / d − 2 , m ≲ |Λ|1/2, and m ≲ |Λ|1/d in d-dimensional Planck units. The first of these bounds is equivalent to the strong energy condition in Einstein-dilaton gravity and precludes accelerated expansion of the universe. It is almost certainly violated in our universe, though it may apply in asymptotic limits of scalar field space. The second bound cannot be satisfied in our universe, though it is saturated in supersymmetric AdS vacua with well-understood uplifts to 10d/11d supergravity. The third bound likely has a limited range of validity in quantum gravity as well, so it may or may not apply to our universe. However, if it does apply, it suggests a possible relation between the cosmological constant and the neutrino mass, which (by the see-saw mechanism) may further provide a relation between the cosmological constant problem and the hierarchy problem. We also work out the conditions for eternal inflation in general spacetime dimensions, and we comment on the behavior of these conditions under dimensional reduction.

scholarly journals ONE-LOOP QUANTUM COSMOLOGICAL CORRECTION TO THE GRAVITATIONAL CONSTANT USING THE KINK SOLUTION IN DE SITTER UNIVERSE

2010 ◽  
Vol 25 (35) ◽  
pp. 2955-2971
Author(s):  
F. DARABI ◽  
S. JALALZADEH
Keyword(s):  
Field Theory ◽  
Scalar Field ◽  
Cosmological Model ◽  
Gravitational Constant ◽  
Invariance Property ◽  
De Sitter ◽  
Scalar Field Theory ◽  
Shape Invariance ◽  
The One ◽  
De Sitter Universe

In this paper, we show the equivalence between a classical static scalar field theory and the (closed) de Sitter cosmological model whose potential represents shape invariance property. Based on this equivalence, we calculate the one-loop quantum cosmological correction to the ground state energy of the kink-like solution in the (closed) de Sitter cosmological model in which the fluctuation potential V′′ has a shape invariance property. It is shown that this type of correction, which yields a renormalized mass in the case of scalar field theory, may be interpreted as a renormalized gravitational constant in the case of (closed) de Sitter cosmological model.

scholarly journals WARPED GEOMETRY OF BRANE WORLDS

2002 ◽  
Vol 17 (29) ◽  
pp. 4297-4305 ◽  
Author(s):  
GARY FELDER
Keyword(s):  
Scalar Field ◽  
Three Dimensional ◽  
Field Potential ◽  
Brane World ◽  
Phase Portraits ◽  
Warp Factor ◽  
De Sitter ◽  
Dynamical Equations ◽  
Dimensional Dependence ◽  
Finite Distance

We study the dynamical equations for extra-dimensional dependence of a warp factor and a bulk scalar in 5D brane world scenarios with 3+1 de Sitter slices. We show that these equations are similar to the equations for 4D scalar field cosmology, but with the sign of the scalar field potential reversed. We construct three dimensional phase portraits for this system for a variety of potentials. We show that for many potentials there will be an unavoidable singularity occuring a finite distance from the brane. This singularity can be shielded by the addition of a second brane. The properties of these branes will generally fix the inter-brane separation and effective 4D cosmological constants, thus providing a possible mechanism for stabilizing the braneworld. Some of these results were previously known for some models, but we bring together a variety of results and show how they can all be easily seen using phase portraits.

scholarly journals A NATURAL RENORMALIZATION OF THE ONE-LOOP EFFECTIVE ACTION FOR SCALAR FIELD IN CURVED SPACETIME

2005 ◽  
Vol 14 (02) ◽  
pp. 219-223 ◽  
Author(s):  
MOHAMMAD VAHID TAKOOK
Keyword(s):  
Scalar Field ◽  
Effective Action ◽  
Minkowski Spacetime ◽  
De Sitter ◽  
Renormalization Procedure ◽  
Negative Norm ◽  
Curved Space ◽  
Loop Approximation ◽  
The One ◽  
Infrared Divergences

It has been shown that the negative norm states necessarily appear in a covariant quantization of the free minimally coupled scalar field in de Sitter space.1,2 In this process, ultraviolet and infrared divergences have been automatically eliminated.3 A natural renormalization of the one-loop interacting quantum field in Minkowski spacetime (λϕ4 theory) has been achieved through the consideration of the negative norm states.4 The one-loop effective action for scalar field in a general curved space-time has been calculated by this method, and a natural renormalization procedure in the one-loop approximation has been established.

A GEOMETRIC WAY TO OBTAIN DE-SITTER SUBSPACES PERPENDICULAR TO A FINITE SIZE EXTRA-DIMENSION IN CURVED 5D UNIVERSES

2004 ◽  
Vol 19 (20) ◽  
pp. 3377-3394 ◽  
Author(s):  
E. GUENDELMAN ◽  
H. RUCHVARGER
Keyword(s):  
Scalar Field ◽  
Extra Dimension ◽  
Special Form ◽  
Separation Of Variables ◽  
Field Potential ◽  
Finite Size ◽  
Flat Space ◽  
Space Time ◽  
De Sitter ◽  
Geodesic Lines

We define curved five-dimensional (5D) space–time from the embedding of 5D surfaces in a 6D flat space. Demanding that the 6D coordinates satisfy a separation of variables form and that the 5D metric is diagonal, we obtain that each curved 5D surface contains 4D hyperboloid de-Sitter subspaces with maximally symmetry SO (4,1). Therefore, we define a very special form for the curved 5D surface where the extra-dimension is perpendicular to the 4D hyperboloid de-Sitter spaces. By relating to a minimally coupled scalar field with a potential which depends on the extra-dimension only, the curved 5D surface's form is satisfied. A mechanism by means of which the extra-dimension can be of a finite size, is found. The borders of the finite extra-dimension are obtained when the scalar field potential goes to infinity for certain finite values of the scalar field. The geodesic lines' equations show that a particle cannot cross such borders.

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