(n+1)-dimensional spherically symmetric expanding structures in R2-gravity

2015 ◽  
Vol 30 (20) ◽  
pp. 1550098
Author(s):  
Esmaeil Ebrahimi
Keyword(s):  
Energy Condition ◽  
Naked Singularity ◽  
Ricci Scalar ◽  
Spherically Symmetric ◽  
Higher Dimensional ◽  
Inflationary Phase ◽  
Acceleration Of The Universe ◽  
Scalar Constant ◽  
The Universe ◽  
Basic Constraint

In this work, we consider higher-dimensional structures in [Formula: see text]-gravity in an expanding background. We assume a Ricci scalar constant background and use this assumption as the basic constraint to find solutions. Two classes of solutions are presented in which every one includes naked singularity and wormhole geometries. Both classes of solutions show inflationary phase of expansion favored by recent acceleration of the universe. Traversability of the wormhole solutions is discussed. The possibility of satisfying or violating the weak energy condition (WEC) for wormholes is explored. For one class of solutions, particular choices of constants result in wormholes which satisfy the WEC all over the spacetime.

scholarly journals Hamiltonian formalism for nonlocal gravity models

2022 ◽  
Author(s):  
Pawan Joshi ◽  
Utkarsh Kumar ◽  
Sukanta Panda
Keyword(s):  
Ricci Tensor ◽  
Degrees Of Freedom ◽  
Hamiltonian Formalism ◽  
Riemann Tensor ◽  
Ricci Scalar ◽  
Gravity Models ◽  
Lagrangian Formalism ◽  
Acceleration Of The Universe ◽  
Nonlocal Action ◽  
The Universe

Nonlocal gravity models are constructed to explain the current acceleration of the universe. These models are inspired by the infrared correction appearing in Einstein–Hilbert action. Here, we develop the Hamiltonian formalism of a nonlocal model by considering only terms to quadratic order in Riemann tensor, Ricci tensor and Ricci scalar. We show how to count degrees of freedom using Hamiltonian formalism including Ricci tensor and Ricci scalar terms. In this model, we have also worked out with a choice of a nonlocal action which has only two degrees of freedom equivalent to GR. Finally, we find the existence of additional constraints in Hamiltonian required to remove the ghosts in our full action. We also compare our results with that of obtained using Lagrangian formalism.

scholarly journals SPATIAL RICCI SCALAR DARK ENERGY MODEL

2011 ◽  
Vol 26 (02) ◽  
pp. 317-329 ◽  
Author(s):  
RONG-JIA YANG ◽  
ZONG-HONG ZHU ◽  
FENGQUAN WU
Keyword(s):  
Dark Energy ◽  
Power Spectra ◽  
Ricci Scalar ◽  
Temperature Anisotropy ◽  
Microwave Background ◽  
Cosmic Microwave Background Temperature ◽  
Acceleration Of The Universe ◽  
Background Temperature ◽  
Best Fit ◽  
The Universe

Inspired by the holographic principle, we suggest that the density of dark energy is proportional to the spatial Ricci scalar curvature (SRDE). Such a model is phenomenologically viable. The best fit values of its parameters at 68% confidence level are found to be Ωm 0= 0.259±0.016 and α = 0.261±0.0122, constrained from the Union+CFA3 sample of 397 SNIa and the BAO measurement. We find that the equation of state of SRDE crosses -1 at z ≃ -0.14. The present value of the deceleration parameter q(z) for SRDE is found to be qz = 0~-0.85. The phase transition from deceleration to acceleration of the Universe for SRDE occurs at the redshift zq = 0~0.4. After studying the perturbation of each component of the Universe, we show that the matter power spectra and cosmic microwave background temperature anisotropy are slightly affected by SRDE, compared with ΛCDM.

HIGHER DIMENSIONAL CHARGED NULL FLUID COLLAPSE AND COSMIC CENSORSHIP

2002 ◽  
Vol 11 (02) ◽  
pp. 237-244 ◽  
Author(s):  
S. G. GHOSH ◽  
R. V. SARAYKAR
Keyword(s):  
Black Holes ◽  
Energy Condition ◽  
Cosmic Censorship ◽  
Final Outcome ◽  
Spherically Symmetric ◽  
Curvature Singularity ◽  
Naked Singularities ◽  
Dimensional Spacetime ◽  
Higher Dimensional ◽  
Strong Curvature

We analyze here the spherically symmetric collapse of a charged null fluid in a higher dimensional spacetime. Both naked singularities and black holes are shown to be developing as final outcome of the collapse. A relationship between weak energy condition and occurrence of strong curvature singularity is pointed out.

scholarly journals Cosmological inflation driven by a scalar torsion function

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
T. M. Guimarães ◽  
R. de C. Lima ◽  
S. H. Pereira
Keyword(s):  
Initial Conditions ◽  
Small Deviation ◽  
Torsion Function ◽  
Scalar Spectral Index ◽  
Inflationary Phase ◽  
The Standard Model ◽  
Cosmological Inflation ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Viable Model

AbstractA viable model for inflation driven by a torsion function in a Friedmann background is presented. The scalar spectral index in the interval $$0.92\lesssim n_{s}\lesssim 0.97$$ 0.92 ≲ n s ≲ 0.97 is obtained in order to satisfy the initial conditions for inflation. The post inflationary phase is also studied, and the analytical solutions obtained for scale factor and energy density generalizes that ones for a matter dominated universe, indicating just a small deviation from the standard model evolution. The same kind of torsion function used also describes satisfactorily the recent acceleration of the universe, which could indicate a possible unification of different phases, apart form specific constants

scholarly journals An Analysis for Conservative and Non-conservative f(R, T) Gravity Models

2021 ◽  
pp. 1-11
Author(s):  
Diyadin Can ◽  
Ertan Güdekli
Keyword(s):  
Energy Condition ◽  
Hubble Constant ◽  
Momentum Tensor ◽  
Cosmic Acceleration ◽  
Gravity Models ◽  
Energy Conditions ◽  
Theory Of Relativity ◽  
General Theory Of Relativity ◽  
Acceleration Of The Universe ◽  
The Universe

As it is known that General Theory of Relativity does not explain the current acceleration of the universe, so there are many attempts to generalize this theory in order to explain the cosmic acceleration without introducing some dark components such as the Dark Energy. Because of the crowd of models in literature, a need to check the models according to some criteria arises. In this study, we analyze two classes of models by means of energy condition restrictions and illustrate the analysis of those classes by graphical simulations. We consider the conservative and non-conservative cases of two classes of  models to perform the analysis. The results of the viability of the classes are discussed and it is found that the value of the Hubble constant has no effect on the viability of the models. Focusing on some general classes for the models, we restrict them by means of the so-called energy conditions the energy-momentum tensor on physical grounds. Besides, we find numerical values for coefficients of those classes of models.

scholarly journals Nature of Singularity in Einstein-Massless Scalar Theory

1997 ◽  
Vol 06 (03) ◽  
pp. 357-361 ◽  
Author(s):  
K. S. Virbhadra ◽  
S. Jhingan ◽  
P. S. Joshi
Keyword(s):  
Exact Solution ◽  
Energy Condition ◽  
Naked Singularity ◽  
Weak Energy Condition ◽  
Massless Scalar ◽  
Spherically Symmetric ◽  
Scalar Theory ◽  
Scalar Equations

We study the static and spherically symmetric exact solution of the Einstein-massless scalar equations given by Janis, Newman and Winicour. We find that this solution satisfies the weak energy condition and has strong globally naked singularity.

scholarly journals CosMIn: THE SOLUTION TO THE COSMOLOGICAL CONSTANT PROBLEM

2013 ◽  
Vol 22 (12) ◽  
pp. 1342001 ◽  
Author(s):  
HAMSA PADMANABHAN ◽  
T. PADMANABHAN
Keyword(s):  
Cosmological Constant ◽  
Theoretical Physics ◽  
Cosmological Constant Problem ◽  
Holy Grail ◽  
Cosmic Evolution ◽  
Inflationary Phase ◽  
Acceleration Of The Universe ◽  
Hubble Radius ◽  
Theoretical Considerations ◽  
The Universe

The current acceleration of the universe can be modeled in terms of a cosmological constant Λ. We show that the extremely small value of [Formula: see text], the holy grail of theoretical physics, can be understood in terms of a new, dimensionless, conserved number Cosmic Mode Index (CosMIn), which counts the number of modes crossing the Hubble radius during the three phases of evolution of the universe. Theoretical considerations suggest that N ≈ 4π. This single postulate leads us to the correct, observed numerical value of the cosmological constant! This approach also provides a unified picture of cosmic evolution relating the early inflationary phase to the late accelerating phase.

IS THE COSMIC NO HAIR CONJECTURE TRUE IN THE EINSTEIN–MAXWELL-DILATON SYSTEM?

2001 ◽  
Vol 16 (09) ◽  
pp. 1501-1530 ◽  
Author(s):  
KENGO MAEDA ◽  
MAKOTO NARITA ◽  
SHINGO SUZUKI ◽  
TAKASHI TORII
Keyword(s):  
Energy Condition ◽  
Dominant Energy Condition ◽  
Spherically Symmetric ◽  
De Sitter ◽  
Field Equations ◽  
Positive Cosmological Constant ◽  
Null Infinity ◽  
Asymptotic Structure ◽  
The Universe ◽  
Matter Fields

We investigate the gravitational collapsing phenomenon in the spherically symmetric Einstein–Maxwell-dilaton system with a positive cosmological constant. As a preparation, we first study some general properties of the horizons in asymptotically de Sitter space–time and prove that the area of the horizons does not decrease and has an upper bound if the matter fields satisfy the dominant energy condition. By using these results, we analytically show that once gravitational collapse occurs from any initial data on a null hypersurface, the system of field equations breaks down inevitably in the domain of outer communications or the boundary, i.e. the black hole event horizon provided that a future null infinity ℐ+ exists, or the asymptotic structure at ℐ+ is broken and the universe will recollapse. In order to clarify which history does the universe trace, we perform a numerical simulation. Then, the dilaton field diverges faster than the logarithmic function almost uniformly and the asymptotic structure would be broken. This implies that the cosmic no hair conjecture is violated in the generalized theory of gravity.

scholarly journals LARGE SCALE ANISOTROPY DUE TO PRE-INFLATIONARY PHASE OF COSMIC EVOLUTION

2012 ◽  
Vol 27 (04) ◽  
pp. 1250014 ◽  
Author(s):  
PAVAN K. ALURI ◽  
PANKAJ JAIN
Keyword(s):  
Large Scale ◽  
Cosmological Evolution ◽  
Cosmic Evolution ◽  
Cosmological Observations ◽  
Inflationary Phase ◽  
The Universe ◽  
Dipole Modulation

We show that perturbations generated during the anisotropic pre-inflationary stage of cosmic evolution may affect cosmological observations today for a certain range of parameters. Due to the anisotropic nature of the universe during such early times, it might explain some of the observed signals of large scale anisotropy. In particular, we argue that the alignment of CMB quadrupole and octopole may be explained by the Sachs–Wolfe effect due to the large scale anisotropic modes from very early times of cosmological evolution. We also comment on how the observed dipole modulation of CMB power may be explained within this framework.

scholarly journals Chameleon field and the late time acceleration of the Universe

Pramana ◽  
2010 ◽  
Vol 74 (3) ◽  
pp. 481-489 ◽  
Author(s):  
Narayan Banerjee ◽  
Sudipta Das ◽  
Koyel Ganguly
Keyword(s):  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe
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