scholarly journals ACCELERATING UNIVERSE AS WINDOW FOR EXTRA DIMENSIONS

2006 ◽  
Vol 21 (31) ◽  
pp. 6491-6511 ◽  
Author(s):  
D. PANIGRAHI ◽  
S. CHATTERJEE ◽  
Y. Z. ZHANG
Keyword(s):  
Equations Of State ◽  
Equations Of Motion ◽  
Relative Magnitude ◽  
Matter Field ◽  
Smooth Transition ◽  
Accelerating Universe ◽  
De Sitter ◽  
Fifth Dimension ◽  
Higher Dimensional ◽  
New Interpretation

Homogeneous cosmological solutions are obtained in five-dimensional (5D) space–time assuming equations of state p = kρ and p1 = γρ where p is the isotropic 3-pressure and p1, that for the fifth dimension. Using different values for the constants k and γ many known solutions are rediscovered. Further the current acceleration of the universe has led us to investigate higher dimensional gravity theory, which is able to explain acceleration from a theoretical viewpoint without the need of introducing dark energy by hand. We also extend a recent work of Mohammedi where using a special form of the extra dimensional scale factor a new interpretation of the higher dimensional equations of motion is given and the concept of an effective 4D pressure is introduced. Interestingly the 5D matter field remains regular while the effective negative pressure is responsible for the inflation. Relaxing the assumptions of two equations of state we also present a class of solutions which provide early deceleration followed by a late acceleration in a unified manner. Relevant to point out that in this case our cosmology apparently mimics the well-known quintessence scenario fuelled by a generalized Chaplygin-type of fluid where a smooth transition from a dust dominated model to a de Sitter-like one takes place. Depending on the relative magnitude of the different constants appearing in our solutions we show that some of the cases are amenable to the desirable property of dimensional reduction.

scholarly journals The third way to 3D gravity

2015 ◽  
Vol 24 (12) ◽  
pp. 1544015 ◽  
Author(s):  
Eric Bergshoeff ◽  
Wout Merbis ◽  
Alasdair J. Routh ◽  
Paul K. Townsend
Keyword(s):  
Equations Of Motion ◽  
Massive Gravity ◽  
De Sitter ◽  
Gravitational Field Equation ◽  
Third Way ◽  
Metric Tensor ◽  
The Third ◽  
Higher Dimensional ◽  
Conservation Condition ◽  
3D Gravity

Consistency of Einstein’s gravitational field equation [Formula: see text] imposes a “conservation condition” on the [Formula: see text]-tensor that is satisfied by (i) matter stress tensors, as a consequence of the matter equations of motion and (ii) identically by certain other tensors, such as the metric tensor. However, there is a third way, overlooked until now because it implies a “nongeometrical” action: one not constructed from the metric and its derivatives alone. The new possibility is exemplified by the 3D “minimal massive gravity” model, which resolves the “bulk versus boundary” unitarity problem of topologically massive gravity with Anti-de Sitter asymptotics. Although all known examples of the third way are in three spacetime dimensions, the idea is general and could, in principle, apply to higher dimensional theories.

scholarly journals Black hole perturbations of massive and partially massless spin-2 fields in (anti) de Sitter spacetime

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Rachel A. Rosen ◽  
Luca Santoni
Keyword(s):  
Black Hole ◽  
Explicit Form ◽  
Equations Of Motion ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Sitter Spacetime ◽  
Black Hole Background ◽  
Massless Spin ◽  
Higher Dimensional ◽  
Massless Fields

Abstract We provide a systematic and comprehensive derivation of the linearized dynamics of massive and partially massless spin-2 particles in a Schwarzschild (anti) de Sitter black hole background, in four and higher spacetime dimensions. In particular, we show how to obtain the quadratic actions for the propagating modes and recast the resulting equations of motion in a Schrödinger-like form. In the case of partially massless fields in Schwarzschild de Sitter spacetime, we study the isospectrality between modes of different parity. In particular, we prove isospectrality analytically for modes with multipole number L = 1 in four spacetime dimensions, providing the explicit form of the underlying symmetry. We show that isospectrality between partially massless modes of different parity is broken in higher-dimensional Schwarzschild de Sitter spacetimes.

scholarly journals Accelerating universe as a result of an adjustment mechanism

2015 ◽  
Vol 24 (12) ◽  
pp. 1544018 ◽  
Author(s):  
Prado Martín-Moruno ◽  
Nelson J. Nunes
Keyword(s):  
Critical Point ◽  
Vacuum Energy ◽  
Equations Of Motion ◽  
Accelerating Universe ◽  
De Sitter ◽  
Material Content ◽  
Adjustment Mechanism ◽  
General Scalar ◽  
Second Order Equations ◽  
Matter Fields

In this essay, we propose that the theory of gravity’s vacuum is described by a de Sitter geometry. Under this assumption, we consider an adjustment mechanism able to screen any value of the vacuum energy of the matter fields. We discuss the most general scalar–tensor cosmological models with second-order equations of motion that have a fixed de Sitter critical point for any kind of material content. These models give rise to interesting cosmological evolutions that we shall discuss.

scholarly journals ELEMENTARY PARTICLES AND SPIN REPRESENTATIONS

2004 ◽  
Vol 19 (05) ◽  
pp. 357-362 ◽  
Author(s):  
PAOLO MARANER
Keyword(s):  
Matter Field ◽  
Elementary Particles ◽  
Spacetime Symmetries ◽  
Spin Representation ◽  
Dimensional Spacetime ◽  
Higher Dimensional ◽  
Spin Representations ◽  
Theoretical Considerations ◽  
Unified Description

We emphasize that the group-theoretical considerations leading to SO (10) unification of electroweak and strong matter field components naturally extend to spacetime components, providing a truly unified description of all generation degrees of freedoms in terms of a single chiral spin representation of one of the groups SO (13,1), SO (9,5), SO (7,7) or SO (3,11). The realization of these groups as higher-dimensional spacetime symmetries produces unification of all fundamental fermions is a single spacetime spinor.

scholarly journals HIGHER DIMENSIONAL INHOMOGENEOUS DUST COLLAPSE AND COSMIC CENSORSHIP

2002 ◽  
Vol 17 (20) ◽  
pp. 2747-2747
Author(s):  
A. BEESHAM
Keyword(s):  
Black Holes ◽  
Cosmic Censorship ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Naked Singularities ◽  
Singularity Theorems ◽  
Sitter Spacetime ◽  
Higher Dimensional ◽  
Cosmic Censorship Hypothesis ◽  
Strong Curvature

The singularity theorems of general relativity predict that gravitational collapse finally ends up in a spacetime singularity1. The cosmic censorship hypothesis (CCH) states that such a singularity is covered by an event horizon2. Despite much effort, there is no rigorous formulation or proof of the CCH. In view of this, examples that appear to violate the CCH and lead to naked singularities, in which non-spacelike curves can emerge, rather than black holes, are important to shed more light on the issue. We have studied several collapse scenarios which can lead to both situations3. In the case of the Vaidya-de Sitter spacetime4, we have shown that the naked singularities that arise are of the strong curvature type. Both types of singularities can also arise in higher dimensional Vaidya and Tolman-Bondi spacetimes, but black holes are favoured in some sense by the higher dimensions. The charged Vaidya-de Sitter spacetime also exhibits both types of singularities5.

Charged gravastars in f(R,T,RμνTμν) gravity

2021 ◽  
pp. 2150084
Author(s):  
Z. Yousaf ◽  
M. Z. Bhatti
Keyword(s):  
Perfect Fluid ◽  
Energy Momentum Tensor ◽  
Equations Of State ◽  
Mathematical Formulation ◽  
Momentum Tensor ◽  
Spherically Symmetric ◽  
De Sitter ◽  
The Stability ◽  
Physical Features ◽  
Modified Theory

We explore the aspects of the electromagnetism on the stability of gravastar in a particular modified theory, i.e. [Formula: see text] where [Formula: see text], [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of energy–momentum tensor. We assume a spherically symmetric static metric coupled comprising of perfect fluid in the presence of electric charge. The purpose of this paper is to extend the results of [S. Ghosh, F. Rahaman, B. K. Guha and S. Ray, Phys. Lett. B 767 (2017) 380.] to highlight the effects of [Formula: see text] gravity in the formation of charged gravastars. We demonstrated the mathematical formulation, utilizing different equations of state, for the three respective regions (i.e. inner, shell, exterior) of the gravastar. We have matched smoothly the interior de Sitter and the exterior Reissner–Nordström metric at the hypersurface. At the end we extracted few conclusions by working on the physical features of the charged gravastar, mathematically and graphically.

Symmetry

2021 ◽  
pp. 52-64
Author(s):  
Adrian P Sutton
Keyword(s):  
Physical Properties ◽  
Equations Of Motion ◽  
Topological Defects ◽  
Phase Changes ◽  
Broken Symmetry ◽  
Broken Symmetries ◽  
Higher Dimensional ◽  
Continuous Symmetries ◽  
Dimensional Crystal ◽  
Deep Sense

Symmetry arises not only in the invariance of an object to certain operations, but also in invariance of the equations governing motion of particles. Noether’s theorem connects continuous symmetries of equations of motion to conservation laws. The concept of broken symmetry arises in phase changes and topological defects, such as dislocations and disclinations. The principle of symmetry compensation reveals a deep sense in which symmetry is never destroyed – broken symmetries relate variants of an object displaying reduced symmetry. Symmetry plays a fundamental role in characterising the physical properties of crystals through Neumann’s principle. The concept of quasiperiodicity is introduced and it is shown how it is related to periodicity in a higher dimensional crystal.

String inspired cosmological models through Lagrangian invariance

2020 ◽  
Vol 17 (06) ◽  
pp. 2050085
Author(s):  
José Antonio Belinchón ◽  
Danae Polychroni
Keyword(s):  
Perfect Fluid ◽  
Power Law ◽  
Matter Field ◽  
Scale Factor ◽  
Cosmological Models ◽  
De Sitter ◽  
Text Field ◽  
Duality Property ◽  
Constant Potential ◽  
Variable Potential

We study a string inspired cosmological with variable potential through the Lagrangian invariance method in order to determine the form of the potential. We have studied four cases by combining the different fields, that is, the dilaton [Formula: see text] the potential [Formula: see text] the [Formula: see text]-field and the matter field (a perfect fluid). In all the studied cases, we found that the potential can only take two possible forms: [Formula: see text] and [Formula: see text] where [Formula: see text] and [Formula: see text] are numerical constants. We conclude that when we take into account the Kalb–Ramond field, i.e. the [Formula: see text]-field, then it is only possible to get a constant potential, [Formula: see text] Nevertheless, if this field is not considered, then we get two possible solutions for the potential: [Formula: see text] and [Formula: see text] In all the cases, if the potential is constant, [Formula: see text] then we get a de Sitter like solution for the scale factor of the metric, [Formula: see text], which verifies the [Formula: see text]-duality property, while if the potential varies, then we get a power-law solution for the scale factor, [Formula: see text] [Formula: see text]

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