COSMOLOGICAL SOLUTIONS AND THEIR EFFECTIVE PROPERTIES OF MATTER IN KALUZA-KLEIN THEORY

1994 ◽  
Vol 03 (03) ◽  
pp. 627-637 ◽  
Author(s):  
HONGYA LIU ◽  
PAUL S. WESSON
Keyword(s):  
Globular Clusters ◽  
Effective Properties ◽  
Plane Waves ◽  
Big Bang ◽  
Field Equations ◽  
Fifth Dimension ◽  
Cosmological Solutions ◽  
Klein Theory ◽  
The Universe ◽  
Kaluza Klein

We derive a “wave-like” class of exact cosmological solutions of the apparently empty 5D Kaluza-Klein field equations. Here by “wave-like” we mean that the solutions look like plane waves propagating in the fifth dimension. In the interpretation that the fifth dimension in Kaluza-Klein theory may induce matter in four dimensions, we then calculate the effective energy density ρ and pressure p, and study in detail the case for which the equation of state is p=γρ (where γ is an arbitrary constant). We show that for both the matter-dominated (γ=0) and radiation-dominated (γ=1/3) eras of the universe, the 4D spacetime defined by hypersurfaces of the 5D metrics are just the same as those of the standard Friedmann-Robertson-Walker models of general relativity. However, in our models the big bang is like a shock wave propagating along the fifth dimension, and different observers can measure different ages for the universe. This property may be tested using the spread in ages of astrophysical objects such as globular clusters.

scholarly journals A 5D NONCOMPACT KALUZA–KLEIN COSMOLOGY IN THE PRESENCE OF NULL PERFECT FLUID

2010 ◽  
Vol 19 (11) ◽  
pp. 1823-1830 ◽  
Author(s):  
HOSSEIN FARAJOLLAHI ◽  
HAMED AMIRI
Keyword(s):  
Perfect Fluid ◽  
Observational Data ◽  
Field Equations ◽  
Fifth Dimension ◽  
Frw Model ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Kaluza Klein

For the description of the early inflation and acceleration expansion of the universe that are compatible with observational data, the 5D noncompact Kaluza–Klein cosmology is investigated. It is proposed that the 5D space is filled with a null perfect fluid, resulting in a perfect fluid in a 4D universe, plus one along the fifth dimension. By analyzing the reduced field equations for the flat FRW model, we show the early inflationary behavior and the current acceleration of the universe.

PHYSICAL ASPECTS OF SOLITONS IN (4+1) GRAVITY

1995 ◽  
Vol 04 (05) ◽  
pp. 639-659 ◽  
Author(s):  
ANDREW BILLYARD ◽  
PAUL S. WESSON ◽  
DIMITRI KALLIGAS
Keyword(s):  
Physical Properties ◽  
Extra Dimension ◽  
Dimensional Case ◽  
Schwarzschild Solution ◽  
Circular Orbits ◽  
Know How ◽  
Fifth Dimension ◽  
Klein Theory ◽  
Limiting Case ◽  
Kaluza Klein

The augmentation of general relativity’s spacetime by one or more dimensions is described by Kaluza-Klein theory and is within testable limits. Should an extra dimension be observable and significant, it would be beneficial to know how physical properties would differ from “conventional” relativity. In examining the class of five-dimensional solutions analogous to the four-dimensional Schwarzschild solution, we examine where the origin to the system is located and note that it can differ from the four-dimensional case. Furthermore, we study circular orbits and find that the 5D case is much richer; photons can have stable circular orbits in some instances, and stable orbits can exist right to the new origin in others. Finally, we derive both gravitational and inertial masses and find that they do not generally agree, although they can in a limiting case. For all three examinations, it is possible to obtain the four-dimensional results in one limiting case, that of the Schwarzschild solution plus a flat fifth dimension, and that the differences between 4D and 5D occur when the fifth dimension obtains any sort of significance.

Alternative cosmological theories

2019 ◽  
pp. 119-161
Author(s):  
Helge Kragh
Keyword(s):  
Standard Model ◽  
Cosmic Time ◽  
Big Bang ◽  
Field Equations ◽  
Static Universe ◽  
The Standard Model ◽  
Scientific Nature ◽  
Big Bang Model ◽  
The Universe ◽  
Alternative Theories

Since about 1970 the broadly accepted theory of the universe has been the standard hot big-bang model. However, there is and has always been alternative theories which challenge one or more features of the standard model or, more radically, question the scientific nature of cosmology. Is the universe governed by Einstein’s field equations? Is it really in a state of expansion? Did it begin with a big bang? The chapter discusses various alternative or heterodox theories in the period from about 1930 to 1980, among them the idea of a static universe and the conception that our universe evolves cyclically in infinite cosmic time. While some of these theories have been abandoned long ago, others still live on and are cultivated by a minority of cosmologists and other scientists.

Kaluza–Klein dark energy model in the form of wet dark fluid in f(R, T) gravity

2014 ◽  
Vol 92 (9) ◽  
Author(s):  
P.K. SAHOO ◽  
B. Mishra
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Wet Dark Fluid ◽  
Dark Fluid ◽  
The Universe ◽  
Kaluza Klein

A five dimensional Kaluza-Klein space time is considered with wet dark fluid (WDF) source in the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor proposed by Harko et al. (Phys. Rev. D \textbf{84}, 024020, (2011)). A new equation of state in the form of WDF has been used for dark energy (DE) component of the universe. It is modeled on the equation of state p=\omega(\rho-\rho^*) which can be describing a liquid, for example water. The exact solutions to the corresponding field equations are obtained for power law and exponential law of the volumetric expansion. The geometrical and physical parameters for both the models are studied. The model obtained here may represent the inflationary era in the early universe and the very late time of the universe. This model obtained here shows that even in the presence of wet dark fluid, the universe indicates accelerated expansion of the universe.

scholarly journals FIVE-DIMENSIONAL KALUZA–KLEIN THEORY WITH A SOURCE

2004 ◽  
Vol 19 (29) ◽  
pp. 5043-5050 ◽  
Author(s):  
YONGGE MA ◽  
JUN WU
Keyword(s):  
Electromagnetic Field ◽  
Test Particle ◽  
Dimensional Reduction ◽  
Dimensional Space ◽  
Space Time ◽  
Fifth Dimension ◽  
Klein Theory ◽  
Dimensional Space Time ◽  
Kaluza Klein

A free test particle in five-dimensional Kaluza–Klein space–time will show its electricity in the reduced four-dimensional space–time when it moves along the fifth dimension. In the light of this observation, we study the coupling of a five-dimensional dust field with the Kaluza–Klein gravity. It turns out that the dust field can curve the five-dimensional space–time in such a way that it provides exactly the source of the electromagnetic field in the four-dimensional space–time after the dimensional reduction.

The early universe in a generalized theory of gravitation

1982 ◽  
Vol 60 (5) ◽  
pp. 659-663 ◽  
Author(s):  
J. W. Moffat ◽  
D. Vincent
Keyword(s):  
Early Universe ◽  
Initial Conditions ◽  
Big Bang ◽  
Field Equations ◽  
Anisotropic Solution ◽  
Plane Symmetric ◽  
Frw Model ◽  
Theory Of Gravitation ◽  
The Big Bang ◽  
The Universe

The standard Friedmann–Robertson–Walker (FRW) big-bang model of the universe requires special initial conditions: the early universe is highly homogeneous and isotropic even though there exist causally disconnected regions (horizon problem). A plane symmetric (anisotropic) solution of a system of field equations in a generalized theory of gravitation, predicts the beginning of the universe as a vacuum instability at a specific fundamental time (which can be associated with the Planck time (tp)), after which matter is created as the universe begins to expand. At a time t = tc there is a singular expansion, the anisotropy vanishes, and the physical horizon becomes infinite. Thereafter the solution of the field equations goes over into the FRW model. Thus the special initial conditions of the FRW model at the big-bang singularity t = tc are predicted by the theory.

Kaluza–Klein dark energy model in the form of wet dark fluid in f(R, T) gravity

2014 ◽  
Vol 92 (9) ◽  
pp. 1062-1067 ◽  
Author(s):  
P. K. Sahoo ◽  
B. Mishra
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Wet Dark Fluid ◽  
Dark Fluid ◽  
The Universe ◽  
Kaluza Klein

In this paper, we have investigated the five-dimensional Kaluza–Klein space time with wet dark fluid (WDF), which is a candidate for dark energy (DE), in the framework of f(R, T) gravity. R and T denote the Ricci scalar and the trace of the energy–momentum tensor, respectively (Harko et al. Phys. Rev. D, 84, 024020 (2011)). We have used equation of state in the form of WDF for the DE component of the universe. It is modeled on the equation of state p = ω(ρ – ρ*). With the help of the power law and exponential law of volumetric expansion, we have derived the exact solutions of the corresponding field equations. The geometrical and physical parameters for both the models are studied. The model obtained here may represent the inflationary era in the early universe and very late time of the universe. It is concluded that the model obtained here shows that even in the presence of WDF, the universe indicates accelerated expansion of the universe.

ROLE OF EXTRA DIMENSION IN ACCELERATED EXPANSION

2008 ◽  
Vol 23 (06) ◽  
pp. 909-917 ◽  
Author(s):  
K. D. PUROHIT ◽  
YOGESH BHATT
Keyword(s):  
Cosmological Model ◽  
Extra Dimension ◽  
Accelerated Expansion ◽  
Field Equations ◽  
Four Dimensions ◽  
Scale Factors ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Kaluza Klein

A five-dimensional FRW-type Kaluza–Klein cosmological model is taken to study the role of extra dimension in the expansion of the universe. Relation between scale factors corresponding to conventional four dimensions and the extra dimension has been established. Field equations are solved in order to find out the effect of pressure corresponding to these scale factors. Conditions for accelerated expansion are derived.

scholarly journals Light Elements in the Universe

2021 ◽  
Vol 8 ◽  
Author(s):  
Sofia Randich ◽  
Laura Magrini
Keyword(s):  
Globular Clusters ◽  
Light Element ◽  
Big Bang ◽  
Stellar Structure ◽  
Age Dating ◽  
Sequence Evolution ◽  
Light Elements ◽  
Chemical Enrichment ◽  
Star Formation Histories ◽  
The Universe

Due to their production sites, as well as to how they are processed and destroyed in stars, the light elements are excellent tools to investigate a number of crucial issues in modern astrophysics: from stellar structure and non-standard processes at work in stellar interiors to age dating of stars; from pre-main sequence evolution to the star formation histories of young clusters and associations and to multiple populations in globular clusters; from Big Bang nucleosynthesis to the formation and chemical enrichment history of the Milky Way Galaxy and its populations, just to cite some relevant examples. In this paper, we focus on lithium, beryllium, and boron (LiBeB) and on carbon, nitrogen, and oxygen (CNO). LiBeB are rare elements, with negligible abundances with respect to hydrogen; on the contrary, CNO are among the most abundant elements in the Universe, after H and He. Pioneering observations of light-element surface abundances in stars started almost 70 years ago and huge progress has been achieved since then. Indeed, for different reasons, precise measurements of LiBeB and CNO are difficult, even in our Sun; however, the advent of state-of-the-art ground- and space-based instrumentation has allowed the determination of high-quality abundances in stars of different type, belonging to different Galactic populations, from metal-poor halo stars to young stars in the solar vicinity and from massive stars to cool dwarfs and giants. Noticeably, the recent large spectroscopic surveys performed with multifiber spectrographs have yielded detailed and homogeneous information on the abundances of Li and CNO for statistically significant samples of stars; this has allowed us to obtain new results and insights and, at the same time, raise new questions and challenges. A complete understanding of the light-element patterns and evolution in the Universe has not been still achieved. Perspectives for further progress will open up soon thanks to the new generation instrumentation that is under development and will come online in the coming years.

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