scholarly journals ON WEYL COSMOLOGY IN FIVE DIMENSIONS AND THE COSMOLOGICAL CONSTANT

2009 ◽  
Vol 24 (08n09) ◽  
pp. 1505-1509 ◽  
Author(s):  
JOSE EDGAR MADRIZ AGUILAR ◽  
CARLOS ROMERO
Keyword(s):  
Cosmological Constant ◽  
Energy Momentum Tensor ◽  
Constant Term ◽  
Momentum Tensor ◽  
Five Dimensions ◽  
Four Dimensions ◽  
Riemannian Spacetime ◽  
Matter Theory ◽  
Induced Matter ◽  
Weyl Scalar

In this talk notes we expose the possibility to induce the cosmological constant from extra dimensions from a geometrical framework where our four-dimensional Riemannian spacetime is embedded into a five-dimensional Weyl integrable space. In particular following the approach of the induced matter theory (IMT) we show that when we go down from five to four dimensions we may recover the induced energy momentum tensor of the IMT plus a cosmological constant term that is determined by the presence of the Weyl scalar field on the bulk.

Supersymmetric quantum field theory (QFT): Introduction

2021 ◽  
pp. 656-669
Author(s):  
Jean Zinn-Justin
Keyword(s):  
Cosmological Constant ◽  
Particle Physics ◽  
Vector Fields ◽  
Hadron Collider ◽  
Large Mass ◽  
Momentum Tensor ◽  
Fine Tuning ◽  
Four Dimensions ◽  
New Feature ◽  
The Masses

Supersymmetry has been proposed, in particular as a principle to solve the so-called fine-tuning problem in particle physics by relating the masses of scalar particles (like Higgs fields) to those of fermions, which can be protected against ‘large’ mass renormalization by chiral symmetry. However, supersymmetry is, at best, an approximate symmetry broken at a scale beyond the reach of a large hadron collider (LHC), because the possible supersymmetric partners of known particles have not been discovered yet (2020) and thus, if they exist, must be much heavier. Exact supersymmetry would also have implied the vanishing of the vacuum energy and thus, of the cosmological constant. The discovery of dark energy has a natural interpretation as resulting from a very small cosmological constant. However, a naive model based on broken supersymmetry would still predict 60 orders of magnitude too large a value compared to 120 orders of magnitude otherwise. Gauging supersymmetry leads naturally to a unification with gravity, because the commutators of supersymmetry currents involve the energy momentum tensor. First, examples of supersymmetric theories involving scalar superfields, simple generalizations of supersymmetric quantum mechanics (QM) are described. The new feature of supersymmetry in higher dimensions is the combination of supersymmetry with spin, since fermions have spins. In four dimensions, theories with chiral scalar fields and vector fields are constructed.

THE EMBEDDING OF THE SPACETIME IN FIVE DIMENSIONS

2002 ◽  
Vol 17 (29) ◽  
pp. 4287-4295
Author(s):  
C. ROMERO
Keyword(s):  
Differential Geometry ◽  
Geometrical Structure ◽  
Embedding Theorems ◽  
Five Dimensions ◽  
Matter Theory ◽  
Klein Theory ◽  
Induced Matter ◽  
Kaluza Klein

We briefly review the problem of embedding the spacetime in five dimensions and discuss the geometrical structure of a non-compactified version of Kaluza-Klein theory, known as induced-matter theory. We also highlight the importance of the embedding theorems of differential geometry in the context of embedding theories and present new results which may be considered as extensions of the Campbell-Magaard theorem.

Gravity, stability and cosmological models

2017 ◽  
Vol 26 (12) ◽  
pp. 1743026
Author(s):  
Asher Yahalom
Keyword(s):  
Stability Analysis ◽  
Cosmological Model ◽  
Cosmological Constant ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Lorentzian Metric ◽  
Standard Cosmological Model ◽  
Flat Spacetimes ◽  
Stable Solutions ◽  
The Universe

Stability analysis plays a major rule in our understanding of nature. For example it was shown that among empty flat spacetimes only those with a Lorentzian metric are stable [A. Yahalom, Found Phys. 38 (2008) 489–497; Int. J. Mod. Phys. D 18(4) (2009) 2155–2158]. However, the universe is not empty and the energy momentum tensor is metric dependent an thus effects stability. In this essay we concentrate on simple perturbations of the standard cosmological model with and without cosmological constant which is based on a uniform mass distribution. The results suggest that while Euclidean, open or closed section models are valid solutions, the choice of stable solutions is limited. In particular, the popular Lambda-CDM model is unstable.

scholarly journals GÖDEL SOLUTION IN f(R, T) GRAVITY

2013 ◽  
Vol 28 (32) ◽  
pp. 1350141 ◽  
Author(s):  
A. F. SANTOS
Keyword(s):  
Cosmological Constant ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Modified Theories Of Gravity ◽  
Curvature Scalar ◽  
Theories Of Gravity ◽  
Modified Theory ◽  
Gödel Universe

In this paper, we study Gödel universe in the framework of f(R, T) modified theories of gravity, where R is the curvature scalar and T the trace of the energy–momentum tensor. We demonstrate that Gödel solution occurs in this modified theory and still we suggest a path to understanding the smallness of the cosmological constant.

scholarly journals Quasilocal conservation laws in cosmology: A first look

2020 ◽  
Vol 29 (14) ◽  
pp. 2043029
Author(s):  
Marius Oltean ◽  
Hossein Bazrafshan Moghaddam ◽  
Richard J. Epp
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Conservation Laws ◽  
Perfect Fluid ◽  
Vacuum Energy ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Stress Energy ◽  
Fluid Matter ◽  
Stress Energy Momentum Tensor

Quasilocal definitions of stress-energy–momentum—that is, in the form of boundary densities (in lieu of local volume densities) — have proven generally very useful in formulating and applying conservation laws in general relativity. In this Essay, we take a basic look into applying these to cosmology, specifically using the Brown–York quasilocal stress-energy–momentum tensor for matter and gravity combined. We compute this tensor and present some simple results for a flat FLRW spacetime with a perfect fluid matter source. We emphasize the importance of the vacuum energy, which is almost universally underappreciated (and usually “subtracted”), and discuss the quasilocal interpretation of the cosmological constant.

scholarly journals Nonconservative traceless type gravity

2019 ◽  
Vol 28 (15) ◽  
pp. 1950175 ◽  
Author(s):  
Mahamadou Daouda ◽  
J. C. Fabris ◽  
A. M. Oliveira ◽  
F. Smirnov ◽  
H. E. S. Velten
Keyword(s):  
Cosmological Constant ◽  
Type Theory ◽  
Energy Momentum Tensor ◽  
Coupling Parameter ◽  
Momentum Tensor ◽  
Gravity Theory ◽  
Field Equations ◽  
Cosmological Constant Problem ◽  
Interesting Approach ◽  
Mimetic Gravity

Extensions of the gravity theory in order to obtain traceless field equations have been widely considered in the literature. The leading example of such class of theories is the unimodular gravity, but there are other possibilities like the mimetic gravity and the Rastall gravity with a coupling parameter [Formula: see text]. The unimodular gravity proposal is a very interesting approach in order to address the cosmological constant problem. When coupled to matter, such theories may imply that the energy–momentum tensor is not divergence free anymore. In this paper, a unimodular type theory will be developed by evading the conservation [Formula: see text]. The cosmological consequences of the later, both at background as well as for scalar and tensor perturbations, are explored. Possible further extensions of this approach are discussed as well as its connection with the traditional unimodular gravity.

scholarly journals Energy-Momentum Tensor and Parameters in Cosmological Model

2020 ◽  
Author(s):  
Ying-Qiu Gu
Keyword(s):  
Cosmological Model ◽  
Cosmological Constant ◽  
Energy Momentum Tensor ◽  
Equations Of State ◽  
Mass Density ◽  
Big Bang ◽  
Momentum Tensor ◽  
Ideal Gas ◽  
Dimensional Sphere ◽  
The Universe

In cosmology, the cosmic curvature $K$ and the cosmological constant $\Lambda$ are two most important parameters, whose values have strong influence on the behavior of the universe. By analyzing the energy-momentum tensor and equations of state of ideal gas, scalar, spinor and vector potential in detail, we find that the total mass density of all matter is always positive, and the initial total pressure is negative. Under these conditions, by qualitatively analyzing the global behavior of the dynamical equation of cosmological model, we get the following results: (i) $K= 1$, namely, the global spatial structure of the universe should be a 3-dimensional sphere $S^3$. (ii) $0\le\Lambda < 10 ^ {-24} {\rm ly} ^ {-2}$, the cosmological constant should be zero or an infinitesimal. (iii) $a(t)>0$, the initial singularity of the universe is unreachable, and the evolution of universe should be cyclic in time. This means that the initial Big Bang is impossible at all. Since the matter components considered are quite complete and the proof is very elementary and strict, these logical conclusions should be quite reliable. Obviously, these conclusions will be much helpful to correct some popular misconceptions and bring great convenience to further research other problems in cosmology such as property of dark matter and dark energy.

scholarly journals Warping wormholes with dust: a metric construction of the Python’s Lunch

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Ning Bao ◽  
Aidan Chatwin-Davies ◽  
Grant N. Remmen
Keyword(s):  
General Relativity ◽  
Mutual Information ◽  
Cosmological Constant ◽  
Cross Sections ◽  
Energy Momentum Tensor ◽  
Local Maximum ◽  
Momentum Tensor ◽  
Positive Energy ◽  
De Sitter ◽  
New Class

Abstract We show how wormholes in three spacetime dimensions can be customizably warped using pressureless matter. In particular, we exhibit a large new class of solutions in (2 + 1)-dimensional general relativity with energy-momentum tensor describing a negative cosmological constant and positive-energy dust. From this class of solutions, we construct wormhole geometries and study their geometric and holographic properties, including Ryu- Takayanagi surfaces, entanglement wedge cross sections, mutual information, and outer entropy. Finally, we construct a Python’s Lunch geometry: a wormhole in asymptotically anti-de Sitter space with a local maximum in size near its middle.

scholarly journals Wormholes in Einstein-Born-Infeld Gravity

2018 ◽  
Vol 168 ◽  
pp. 09003 ◽  
Author(s):  
Jin Young Kim ◽  
Mu-In Park
Keyword(s):  
Cosmological Constant ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Conventional Approach ◽  
New Approach ◽  
The Stability

We introduce a new approach to construct wormholes without introducing exotic matters in Einstein-Born-Infeld gravity with a cosmological constant. Contary to the conventional approach, the throat is located at the place where the solutions can be joined smoothly. The metric and its derivatives are continuous so that the exotic matters are not needed there. The exoticity of the energy-momentum tensor is not essential to sustain the wormhole. We also present a method to check the stability of wormholes in the new approach.

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