POST-INFLATIONARY COSMOLOGICAL MODEL BASED ON THE SEVEN-DIMENSIONAL SUPERGRAVITY

1995 ◽  
Vol 04 (02) ◽  
pp. 279-289
Author(s):  
JÚLIO CÉSAR FABRIS ◽  
RICHARD KERNER ◽  
JOËL TOSSA
Keyword(s):  
Cartesian Product ◽  
Scalar Fields ◽  
Big Bang ◽  
Classical Solutions ◽  
Internal Space ◽  
Supergravity Theory ◽  
Potential Term ◽  
Walker Metric ◽  
Stable Solutions ◽  
Nontrivial Coupling

We study classical solutions of the bosonic sector of seven-dimensional supergravity theory. This study is three-fold: first, we look for power law solutions in a space which is the Cartesian product of a four-dimensional Robertson-Walker metric and a compact internal space; next, for the same geometric configuration, we sketch the phase diagram of all possible stable solutions; finally, we consider the evolution of scalar fluctuations on the background of the exact solutions found here. We observe that in spite of the presence of a potential term and a nontrivial coupling of three scalar fields, no inflationary scenario can emerge from such theory, and that all stable solutions display a big-bang type singularity. We conclude that the supersymmetric theories are well suited to describe the post-inflationary behavior of the Universe emerging from the inflationary phase before it enters the pure radiation stage.

scholarly journals Dynamical gravastars from the interaction between scalar fields and matter

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
Alejandro Cabo Montes de Oca ◽  
Duvier Suarez Fontanella ◽  
David Valls-Gabaud
Keyword(s):  
Scalar Field ◽  
Yukawa Potential ◽  
Direct Interaction ◽  
Scalar Fields ◽  
Classical Solutions ◽  
Internal Space ◽  
De Sitter ◽  
Matter Interaction ◽  
Klein Gordon ◽  
Trapping Forces

AbstractGravastars are configurations of compact singularity-free gravitational objects which are interesting alternatives to classical solutions in the strong gravitational field regime. Although there are no static star-like solutions of the Einstein–Klein–Gordon equations for real scalar fields, we show that dynamical gravastars solutions arise through the direct interaction of a scalar field with matter. Two configurations presented here show that, within the internal zone, the scalar field plays a role similar to a cosmological constant, while it decays at large distances as the Yukawa potential. Like classical gravastars, these solutions exhibit small values of the temporal metric component near a transitional radial value, although this behaviour is not determined by the de Sitter nature of the internal space-time, but rather by a slowly-varying scalar field. The scalar field-matter interaction is able to define trapping forces that rigorously confine the polytropic gases to the interior of a sphere. At the surface of these spheres, pressures generated by the field-matter interaction play the role of “walls” preventing the matter from flowing out. These solutions predict a stronger scattering of the accreting matter with respect to Schwarzschild black holes.

scholarly journals New AdS4 vacua in dyonic ISO(7) gauged supergravity

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Nikolay Bobev ◽  
Thomas Fischbacher ◽  
Fridrik Freyr Gautason ◽  
Krzysztof Pilch
Keyword(s):  
Scalar Fields ◽  
Global Symmetry ◽  
Supergravity Theory

Abstract We identify 219 AdS4 solutions in four-dimensional dyonically gauged ISO(7) $$ \mathcal{N} $$ N = 8 supergravity and present some of their properties. One of the new solutions preserves $$ \mathcal{N} $$ N = 1 supersymmetry and provides a rare explicit example of an AdS4 vacuum dual to a 3d SCFT with no continuous global symmetry. There are also two new non-supersymmetric solutions for which all 70 scalar fields in the supergravity theory have masses above the BF bound. All of these AdS4 solutions can be uplifted to massive type IIA supergravity. Motivated by this we present the low lying operator spectra of the dual 3d CFTs for all known supersymmetric AdS4 solutions in the theory and organize them into superconformal multiplets.

CLASSICAL INSTABILITY OF THE EINSTEIN-GAUSS-BONNET GRAVITY THEORY WITH COMPACTIFIED HIGHER DIMENSIONS

1991 ◽  
Vol 06 (25) ◽  
pp. 4517-4555 ◽  
Author(s):  
LESZEK M. SOKOŁOWSKI ◽  
ZDZISŁAW A. GOLDA ◽  
MARCO LITTERIO ◽  
LUCA AMENDOLA
Keyword(s):  
Scalar Fields ◽  
Gravity Theory ◽  
Effective Theory ◽  
Internal Space ◽  
Bonnet Gravity ◽  
Four Dimensions ◽  
Effective Gravity ◽  
Tensor Theory ◽  
Exciting System ◽  
Bonnet Term

The energy spectrum and stability of the effective theory resulting from the Einstein-Gauss-Bonnet gravity theory with compactified internal space are investigated. The internal space can evolve in its volume and/or shape, giving rise to a system of scalar fields in the external space-time. The resulting scalar-tensor theory of gravity has physically unacceptable properties. First of all, the scalar fields’ energy is indefinite and unbounded from below, and thereby the gravitational and scalar fields form a self-exciting system. In contradistinction to the case of multidimensional Einstein gravity, this inherent instability of the effective theory cannot be removed by field redefinitions in the process of dimensional reduction (e.g. by a conformal rescaling of the metric in four dimensions, as is done in the former case). To get a viable effective gravity theory one should discard either the geometric scalar fields or the Gauss-Bonnet term from the Lagrangian of the multidimensional theory. It is argued that it is the Gauss-Bonnet term that should be discarded.

scholarly journals The Ambiguity in the Definition and Behavior of the Gravitational and Cosmological `Coupling Constants’ in the Theory of Induced Gravity

Symmetry ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 81 ◽  
Author(s):  
Farkhat Zaripov
Keyword(s):  
Gravitational Interaction ◽  
Scalar Fields ◽  
Coupling Constants ◽  
De Sitter ◽  
Induced Gravity ◽  
Mean Values ◽  
Gravitational And Cosmological Constants ◽  
Centrally Symmetric ◽  
Walker Metric ◽  
Cosmological Constants

This work is the extension of author`s research, where the modified theory of induced gravity (MTIG) is proposed. The theory describes two systems (stages): Einstein (ES) and “restructuring” (RS). We consider equations with quadratic potential that are symmetric with respect to scale transformations. The solutions of the equations obtained for the case of spaces defined by the Friedman-Robertson-Walker metric, as well as for a centrally symmetric space are investigated. In our model arise effective gravitational and cosmological “constants”, which are defined by the “mean square” of the scalar fields. In obtained solutions the values of such parameters as “Hubble parameter”, gravitational and cosmological “constants” in the RS stage fluctuate near monotonically evolving mean values. These parameters are matched with observational data, described as phenomena of dark energy and dark matter. The MTIG equations for the case of a centrally symmetric gravitational field, in addition to the Schwarzschild-de Sitter solutions, contain solutions that lead to the new physical effects at large distances from the center. The Schwarzschild-Sitter solution becomes unstable and enters the oscillatory regime. For distances greater than a certain critical value, the following effects can appear: deviation from General relativity and Newton’s law of gravitational interaction, antigravity.

Dynamical properties of scaling solutions in teleparallel dark energy cosmologies with nonminimal coupling

2017 ◽  
Vol 26 (09) ◽  
pp. 1750103 ◽  
Author(s):  
Mihai Marciu
Keyword(s):  
Dark Energy ◽  
Power Law ◽  
Scalar Fields ◽  
Teleparallel Gravity ◽  
Inverse Power ◽  
Coupling Coefficients ◽  
Potential Term ◽  
Inverse Power Law ◽  
The Stability ◽  
The Impact

The dynamical aspects of scaling solutions for the dark energy component in the theoretical framework of teleparallel gravity are considered, where dark energy is represented by a scalar field nonminimally coupled with the torsion and with a boundary term, where the boundary coupling term represents the divergence of the torsion vector. The behavior and stability of the scaling solutions are studied for scalar fields endowed with inverse power law potentials and with exponential potentials. It is shown that for scalar fields endowed with inverse power-law potentials, the stability conditions are not affected by the coupling coefficients. For the scalar fields endowed with exponential potentials, two cases are studied: at first, we have considered an infinitesimal deviation from the scaling solution in the corresponding Klein–Gordon equation, and the impact of distinct coupling coefficients on the stability of the solution are analyzed. Secondly, the potential-free case is considered where the dominance of the coupling terms over the potential term is analyzed, discussing the validity of the corresponding particular solution.

FINITE TEMPERATURE EFFECTIVE POTENTIAL IN A KALUZA-KLEIN UNIVERSE

1990 ◽  
Vol 05 (02) ◽  
pp. 353-361 ◽  
Author(s):  
PINAKI ROY
Keyword(s):  
Low Temperature ◽  
Effective Potential ◽  
Finite Temperature ◽  
Scalar Fields ◽  
Walker Metric ◽  
The One ◽  
Kaluza Klein

We evaluate the finite temperature one-loop effective potential for scalar fields in Kaluza-Klein universe consisting of the product of a space with open Robertson-Walker metric and the N sphere SN. The one-loop effective potential has been computed in both high and low temperature limits.

scholarly journals Turbulence in the Ocean, Atmosphere, Galaxy, and Universe

1996 ◽  
Vol 49 (5) ◽  
pp. 299-315 ◽  
Author(s):  
Carl H. Gibson
Keyword(s):  
Scalar Fields ◽  
Reynolds Numbers ◽  
Big Bang ◽  
Galactic Halos ◽  
Ocean Atmosphere ◽  
Turbulence Velocity ◽  
Galaxy Masses ◽  
Higher Order Spectra ◽  
Fossil Turbulence ◽  
The Big Bang

Flows in natural bodies of fluid often become turbulent, with eddy-like motions dominated by inertial-vortex forces. Buoyancy, Coriolis, viscous, self-gravitational, electromagnetic, and other force constraints produce a complex phase space of wave-like hydrodynamic states that interact with turbulence eddies, masquerade as turbulence, and preserve information about previous hydrodynamic states as fossil turbulence. Evidence from the ocean, atmosphere, galaxy and universe are compared with universal similarity hypotheses of Kolmogorov (1941, 1962) for turbulence velocity u, and extensions to scalar fields θ like temperature mixed by turbulence. Universal u and θ spectra of natural flows can be inferred from laboratory and computer simulations with satisfactory accuracy, but higher order spectra and the intermittency constant u of the third Kolmogorov hypothesis (1962) require measurements at the much larger Reynolds numbers found only in nature. Information about previous hydrodynamic states is preserved by Schwarz viscous and turbulence lengths and masses of self-gravitating condensates (rarely by the classical Jeans length and mass), as it is by Ozmidov, Hopfinger and Fernando scales in hydrophysical fields of the ocean and atmosphere. Viscous-gravitational formation occurred 104-105 y after the Big Bang for supercluster, cluster, and then galaxy masses of the plasma, producing the first turbulence. Condensation after plasma neutralization of the H-4He gas was to a primordial fog of sub-solar particles that persists today in galactic halos as dark matter. These gradually formed all stars, star clusters, etc (humans!) within.

scholarly journals Singularities in Inflationary Cosmological Models

Universe ◽  
2021 ◽  
Vol 7 (12) ◽  
pp. 491
Author(s):  
Leonardo Fernández-Jambrina
Keyword(s):  
Scalar Field ◽  
Field Potential ◽  
Fractional Power ◽  
Scalar Fields ◽  
Big Bang ◽  
Cosmological Models ◽  
Accelerated Expansion ◽  
Type Iv ◽  
Big Crunch ◽  
Expansion Of The Universe

Due to the accelerated expansion of the universe, the possibilities for the formation of singularities has changed from the classical Big Bang and Big Crunch singularities to include a number of new scenarios. In recent papers it has been shown that such singularities may appear in inflationary cosmological models with a fractional power scalar field potential. In this paper we enlarge the analysis of singularities in scalar field cosmological models by the use of generalised power expansions of their Hubble scalars and their scalar fields in order to describe all possible models leading to a singularity, finding other possible cases. Unless a negative scalar field potential is considered, all singularities are weak and of type IV.

scholarly journals A transition between bouncing hyper-inflation to ΛCDM from diffusive scalar fields

2018 ◽  
Vol 33 (20) ◽  
pp. 1850119 ◽  
Author(s):  
David Benisty ◽  
Eduardo I. Guendelman
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Numerical Solutions ◽  
Diffusion Constant ◽  
Scalar Fields ◽  
Big Bang ◽  
Energy Tensor ◽  
Stress Energy ◽  
Two Measures ◽  
The Universe

We consider the history of the universe from a possible big bang or a bounce into a late period of a unified interacting dark energy–dark matter model. The model is based on the Two Measures Theories (TMT) which introduces a metric independent volume element and this allows us to construct a unification of dark energy and dark matter. A generalization of the Two Measures Theories gives a diffusive nonconservative stress-energy–momentum tensor in addition to the conserved stress-energy tensor which appear in Einstein equations. These leads to a formulation of interacting DE–DM dust models in the form of a diffusive-type interacting Unified Dark Energy and Dark Matter scenario. The deviation from [Formula: see text]CDM is determined by the diffusion constant [Formula: see text]. For [Formula: see text] the model is indistinguishable from [Formula: see text]CDM. Numerical solutions of the theories show that in some [Formula: see text] the evolution of the early universe is governed by Stiff equation of state or the universe bounces to hyper-inflation. But all of those solutions have a final transition to [Formula: see text]CDM as a stable fixed point for the late universe.

scholarly journals Cosmology from quantum potential in a system of oscillating branes

2016 ◽  
Vol 31 (01) ◽  
pp. 1650004 ◽  
Author(s):  
Alireza Sepehri
Keyword(s):  
Generalized Uncertainty Principle ◽  
Scalar Fields ◽  
Big Bang ◽  
Fundamental String ◽  
Extra Energy ◽  
Age Of The Universe ◽  
The Big Bang ◽  
M Theory ◽  
Derivatives Of ◽  
The Universe

Recently, some authors proposed a new mechanism which gets rid of the Big Bang singularity and shows that the age of the universe is infinite. In this paper, we will confirm their results and predict that the universe may expand and contract many N fundamental strings decay to N M0–anti-M0-branes. Then, M0-branes join each other and build a M8-anti-M8 system. This system is unstable, broken and two anti-M4-branes, a compactified M4-brane, a M3-brane in addition to one M0-brane are produced. The M3-brane wraps around the compactified M4-brane and both of them oscillate between two anti-M4-branes. Our universe is located on the M3-brane and interacts with other branes by exchanging the M0-brane and some scalars in transverse directions. By wrapping of M3-brane, the contraction epoch of universe starts and some higher order of derivatives of scalar fields in the relevant action of branes are produced which are responsible for generating the generalized uncertainty principle (GUP). By oscillating the compactified M4-M3-brane and approaching one of anti-M4-branes, one end of M3-brane glues to the anti-M4-brane and other end remains sticking and wrapping around M4-brane. Then, by getting away of the M4-M3 system, M4 rolls, wrapped M3 opens and expansion epoch of universe begins. By closing the M4 to anti-M4, the mass of some scalars become negative and they make a transition to tachyonic phase. To remove these states, M4 rebounds, rolls and M3 wraps around it again. At this stage, expansion branch ends and universe enters a contraction epoch again. This process is repeated many times and universe expands and contracts due to oscillation of branes. We obtain the scale factor of universe in this system and find that its values only at t [Formula: see text] shrinks to zero. Thus, in our method, the Big Bang is replaced by the fundamental string and the age of universe is predicted to be infinite. Also, when tachyonic states disappear at the beginning of expansion branch, some extra energy is produced and leads to an increase in the velocity of opening of M3. In these conditions, our universe, which is located on this brane, expands very fast and experiences an inflation epoch. Finally, by reducing the fields in 11-dimensional M-theory to the fields in four-dimensional universe, we show that our theory matches with quantum field theory prescriptions.

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