Cosmological reconstruction and stability in F(T,TG) gravity

2018 ◽  
Vol 27 (02) ◽  
pp. 1850001
Author(s):  
M. Sharif ◽  
Kanwal Nazir
Keyword(s):  
Dark Matter ◽  
Power Law ◽  
Cold Dark Matter ◽  
Universe Model ◽  
De Sitter ◽  
Field Equations ◽  
Torsion Scalar ◽  
Reconstruction Scheme ◽  
Homogeneous Universe ◽  
Stable Solutions

This study investigates the reconstruction scheme and stability of some well-known cosmological models in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] represent the torsion scalar and Gauss–Bonnet invariant torsion term, respectively. For this purpose, we consider isotropic homogeneous universe model and develop the corresponding field equations. It is found that we can reproduce cosmological evolution for power-law, de Sitter solutions, phantom/nonphantom era and [Formula: see text] cold dark matter by applying reconstruction scheme in this gravity. Finally, we discuss stability of the reconstructed power-law and de Sitter solutions as well as two well-known [Formula: see text] models. It is concluded that all these models provide stable solutions for suitable choices of the constants except power-law solutions.

scholarly journals Cold dark matter: Bose-Einstein condensation of gluons in Anti-de Sitter space time

2021 ◽  
Author(s):  
Gilles Cohen-Tannoudji ◽  
Jean-Pierre Gazeau
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Standard Model ◽  
Cosmological Constant ◽  
Cold Dark Matter ◽  
Hidden Variables ◽  
Einstein Condensation ◽  
De Sitter ◽  
Bose Einstein ◽  
The Universe

In the same way as the realization of some of the famous gedanken experiments imagined by the founding fathers of quantum mechanics has recently led to the current renewal of the interpretation of quantum physics, it seems that the most recent progresses of observational astrophysics can be interpreted as the realization of some cosmological gedanken experiments such as the removal from the universe of the whole visible matter or the cosmic time travel leading to a new cosmological standard model. This standard model involves two dark components of the universe, dark energy and dark matter. Whereas dark energy is usually associated with the positive cosmological constant, we propose to explain dark matter as a pure QCD effect. This effect is due to the trace anomaly viewed as a negative cosmological constant accompanying baryonic matter at the hadronization transition from the quark gluon plasma phase to the colorless hadronic phase. Our approach not only yields a ratio Dark/Visible equal to 11/2 but also provides gluons and (anti-)quarks with an extra mass of vibrational nature. Currently observed dark matter is thus interpreted as a gluon Bose Einstein condensate that is a relic of the quark period. Such an interpretation would comfort the idea that, apart from the violation of the matter/antimatter symmetry satisfying the Sakharov’s conditions, the reconciliation of particle physics and cosmology needs not the recourse to any ad hoc fields, particles or hidden variables.

scholarly journals Extended General Relativity for a Curved Universe

2021 ◽  
Author(s):  
Mohammed B. Al-Fadhli
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Early Universe ◽  
Cold Dark Matter ◽  
Positive Curvature ◽  
Boundary Term ◽  
Radius Of Curvature ◽  
Field Equations ◽  
Extended Field ◽  
Background Curvature

The recent Planck Legacy release revealed the presence of an enhanced lensing amplitude in the cosmic microwave background (CMB). Notably, this amplitude is higher than that estimated by the lambda cold dark matter model (ΛCDM), which endorses the positive curvature of the early Universe with a confidence level greater than 99%. Although General Relativity (GR) performs accurately in the local/present Universe where spacetime is almost flat, its lost boundary term, incompatibility with quantum mechanics and the necessity of dark matter and dark energy might indicate its incompleteness. By utilising the Einstein–Hilbert action, this study presents extended field equations considering the pre-existing/background curvature and the boundary contribution. The extended field equations consist of Einstein field equations with a conformal transformation feature in addition to the boundary term, which could remove singularities from the theory and facilitate its quantisation. The extended equations have been utilised to derive the evolution of the Universe with reference to the scale factor of the early Universe and its radius of curvature.

scholarly journals Interacting quintessence in light of generalized uncertainty principle: cosmological perturbations and dynamics

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Andronikos Paliathanasis ◽  
Genly Leon ◽  
Wompherdeiki Khyllep ◽  
Jibitesh Dutta ◽  
Supriya Pan
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Uncertainty Principle ◽  
Generalized Uncertainty Principle ◽  
Background Level ◽  
De Sitter ◽  
Field Equations ◽  
General Behaviour ◽  
Wide Range ◽  
Coupling Parameters

AbstractWe consider a cosmological scenario endowed with an interaction between the universe’s dark components – dark matter and dark energy. Specifically, we assume the dark matter component to be a pressure-less fluid, while the dark energy component is a quintessence scalar field with Lagrangian function modified by the quadratic Generalized Uncertainty Principle. The latter modification introduces new higher-order terms of fourth-derivative due to quantum corrections in the scalar field’s equation of motion. Then, we investigate asymptotic dynamics and general behaviour of solutions of the field equations for some interacting models of special interests in the literature. At the background level, the present interacting model exhibits the matter-dominated and de Sitter solutions which are absent in the corresponding quintessence model. Furthermore, to boost the background analysis, we study cosmological linear perturbations in the Newtonian gauge where we show how perturbations are modified by quantum corrected terms from the quadratic Generalized Uncertainty Principle. Depending on the coupling parameters, scalar perturbations show a wide range of behavior.

scholarly journals Phase transition and geometrical thermodynamics of energy-dependent dilatonic BTZ black holes with power-law electrodynamics

2020 ◽  
Vol 2020 (3) ◽  
Author(s):  
M Dehghani ◽  
M Badpa
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Power Law ◽  
Scalar Potential ◽  
Standard Form ◽  
Three Dimensional ◽  
Nonlinear Electrodynamics ◽  
De Sitter ◽  
Field Equations ◽  
Energy Dependent

Abstract The coupled scalar, electromagnetic, and gravitational field equations of Einstein–dilaton gravity theory have been solved in a three-dimensional energy-dependent spacetime and in the presence of power-law nonlinear electrodynamics. The scalar potential is written as the linear combination of two exponential functions, and two families of three-dimensional dilatonic black hole solutions have been introduced which indicate the impacts of rainbow functions on the spacetime geometry. Through consideration of curvature scalars, it has been found that the asymptotic behavior of the solutions is neither flat nor anti-de Sitter. It has been illustrated that, with a suitable choice of parameters, the solutions can produce the two-horizon, extreme and naked singularity black holes. By calculating the black hole charge, mass, entropy, temperature, and electric potential, it has been proved that they fulfill the standard form of the first law of black hole thermodynamics. The thermodynamic stability of the black holes has been analyzed by utilizing the canonical and grand canonical ensembles and noting the signature of the black hole heat capacity and Gibbs free energy of the black holes. The points of type-1, type-2, and Hawking–Page phase transitions and the ranges at which the black holes are locally or globally stable have been determined. The geometrical thermodynamics of the black holes has been studied by use of different thermodynamic metrics, and the results of different approaches have been compared.

scholarly journals Probing the Origins of Voids in the Distribution of Galaxies

2005 ◽  
Vol 22 (2) ◽  
pp. 166-173 ◽  
Author(s):  
Louise M. Ord ◽  
Martin Kunz ◽  
Hugues Mathis ◽  
Joseph Silk
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
External Source ◽  
Scientific Meeting ◽  
Acoustic Oscillations ◽  
De Sitter ◽  
Matter Distribution ◽  
Microwave Background ◽  
Sitter Background ◽  
Dark Matter Distribution

AbstractIf the voids that we see today in the distribution of galaxies existed at recombination, they will leave an imprint on the cosmic microwave background (CMB). On the other hand, if these voids formed much later, their effect on the CMB will be negligible and will not be observed with the current generation of experiments. In this paper, presented at the 2004 Annual Scientific Meeting of the Astronomical Society of Australia, we discuss our ongoing investigations into voids of primordial origin. We show that if voids in the cold dark matter distribution existed at the epoch of decoupling, they could contribute significantly to the apparent rise in CMB power on small scales detected by the Cosmic Background Imager (CBI) Deep Field. Here we present our improved method for predicting the effects of primordial voids on the CMB in which we treat a void as an external source in the cold dark matter (CDM) distribution employing a Boltzmann solver. Our improved predictions include the effects of a cosmological constant (Λ) and acoustic oscillations generated by voids at early times. We find that models with relatively large voids on the last scattering surface predict too much CMB power in an Einstein–de Sitter background cosmology but could be consistent with the current CMB observations in a ΛCDM universe.

scholarly journals SOLVING THE INVERSE PROBLEM WITH INHOMOGENEOUS UNIVERSES

2011 ◽  
Vol 01 ◽  
pp. 234-239
Author(s):  
CHUL-MOON YOO ◽  
TOMOHIRO KAI ◽  
KEN-ICHI NAKAO
Keyword(s):  
Inverse Problem ◽  
Dark Matter ◽  
Cold Dark Matter ◽  
Big Bang ◽  
Universe Model ◽  
Cosmological Redshift ◽  
Λcdm Model ◽  
The Big Bang ◽  
The Universe ◽  
Dust Universe

We construct the Lemaître-Tolman-Bondi (LTB) dust universe whose distance-redshift relation is equivalent to that in the concordance Λ cold dark matter (ΛCDM) cosmological model. In our model, the density distribution and velocity field are not homogeneous, whereas the big-bang time is uniform, which implies that the universe is homogeneous at its beginning. We also study the temporal variation of the cosmological redshift and show that, by the observation of this quantity, we can distinguish our LTB universe model from the concordance ΛCDM model, even if their redshift-distance relations are equivalent to each other.

Inflationary dynamics in f(𝒢) gravity

2017 ◽  
Vol 26 (04) ◽  
pp. 1750030 ◽  
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Power Spectrum ◽  
Universe Model ◽  
De Sitter ◽  
Slow Roll ◽  
Homogeneous Universe ◽  
Text Model ◽  
Flow Functions ◽  
Hubble Flow

This paper investigates inflationary dynamics for isotropic and homogeneous universe model in the background of [Formula: see text] gravity. We construct Hubble-flow functions, slow-roll parameters, amplitude of scalar power spectrum, spectral index and tensor–scalar ratio for a particular form of equation of state which describes quasi-de Sitter expansion. The dynamics of inflationary epoch is analyzed for scalar field as well as fluid cosmology with viable power-law [Formula: see text] model. We obtain different potential functions that correspond to chaotic inflation and Starobinsky type models. The graphical behavior of these parameters shows compatible results with observational Planck 2015 data in this gravity.

scholarly journals Thermodynamic constraints on matter creation models

2020 ◽  
Vol 80 (11) ◽  
Author(s):  
R. Valentim ◽  
J. F. Jesus
Keyword(s):  
Dark Matter ◽  
Event Horizon ◽  
Thermodynamic Equilibrium ◽  
Cold Dark Matter ◽  
Apparent Horizon ◽  
Total Entropy ◽  
De Sitter ◽  
Derivatives Of ◽  
The Universe ◽  
Entropy Of The Universe

AbstractEntropy is a fundamental concept from Thermodynamics and it can be used to study models on context of Creation Cold Dark Matter (CCDM). From conditions on the first ($$\dot{S}\ge 0$$ S ˙ ≥ 0 ) (throughout the present work we will use dots to indicate time derivatives and dashes to indicate derivatives with respect to scale factor) and second order ($$\ddot{S}<0$$ S ¨ < 0 ) time derivatives of total entropy in the initial expansion of Sitter through the radiation and matter eras until the end of Sitter expansion, it is possible to estimate the intervals of parameters. The total entropy ($$S_{t}$$ S t ) is calculated as sum of the entropy at all eras ($$S_{\gamma }$$ S γ and $$S_{m}$$ S m ) plus the entropy of the event horizon ($$S_h$$ S h ). This term derives from the Holographic Principle where it suggests that all information is contained on the observable horizon. The main feature of this method for these models are that thermodynamic equilibrium is reached in a final de Sitter era. Total entropy of the universe is calculated with three terms: apparent horizon ($$S_{h}$$ S h ), entropy of matter ($$S_{m}$$ S m ) and entropy of radiation ($$S_{\gamma }$$ S γ ). This analysis allows to estimate intervals of parameters of CCDM models.

scholarly journals Cold Dark Matter: A Gluonic Bose–Einstein Condensate in Anti-de Sitter Space Time

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 402
Author(s):  
Gilles Cohen-Tannoudji ◽  
Jean-Pierre Gazeau
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Standard Model ◽  
Cold Dark Matter ◽  
Hidden Variables ◽  
Einstein Condensate ◽  
De Sitter ◽  
Bose Einstein Condensate ◽  
Bose Einstein ◽  
The Universe

In the same way as the realization of some of the famous gedanken experiments imagined by the founding fathers of quantum mechanics has recently led to the current renewal of the interpretation of quantum physics, it seems that the most recent progress of observational astrophysics can be interpreted as the realization of some cosmological gedanken experiments such as the removal from the universe of the whole visible matter or the cosmic time travel leading to a new cosmological standard model. This standard model involves two dark components of the universe, dark energy and dark matter. Whereas dark energy is usually associated with the cosmological constant, we propose explaining dark matter as a pure QCD effect, namely a gluonic Bose–Einstein condensate, following the transition from the quark gluon plasma phase to the colorless hadronic phase. Our approach not only allows us to assume a Dark/Visible ratio equal to 11/2 but also provides gluons (and di-gluons, viewed as quasi-particles) with an extra mass of vibrational nature. Such an interpretation would support the idea that, apart from the violation of the matter/antimatter symmetry satisfying the Sakharov’s conditions, the reconciliation of particle physics and cosmology needs not the recourse to any ad hoc fields, particles or hidden variables.

scholarly journals Galaxy Formation in a Universe Dominated by Cold Dark Matter

1987 ◽  
Vol 117 ◽  
pp. 360-360
Author(s):  
Edmund Bertschinger
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Globular Clusters ◽  
Cold Dark Matter ◽  
Mass Function ◽  
Spherical Approximation ◽  
De Sitter ◽  
Density Peaks ◽  
Lower Amplitude ◽  
Baryonic Mass

ABSTRACT The mass spectrum of bound baryonic systems (galaxies and globular clusters) is computed as a function of redshift in an Einstein-de Sitter (Ω=1) universe dominated by weakly interacting, cold dark matter. Baryons are assumed to fall into primordial density peaks in the cold particle distribution when the mass in the peaks exceeds the baryon Jeans mass. The distribution of peaks is computed using Gaussian statistics. As the universe expands the baryonic mass attached to a given peak increases because of infall (treated in a spherical approximation), and new peaks of lower amplitude become nonlinear. Globular clusters form first (by z∼40 if the galaxies represent a biased mass distribution). The remaining gas may be reheated to ∼10000 K if a few percent of globular cluster (or Pop. III) stars are very massive. Reheating increases the baryon Jeans mass and delays galaxy formation until z≲10. The present method reproduces the shape (but not the amplitude) of the Schechter galaxy mass function when merging of substructure is included in an approximate fashion.

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