EFFECTIVE 3-BRANE BRANS–DICKE COSMOLOGY

2008 ◽  
Vol 23 (06) ◽  
pp. 401-415 ◽  
Author(s):  
AHMAD RAMI EL-NABULSI
Keyword(s):  
Cosmological Constant ◽  
Scalar Fields ◽  
Brane Cosmology ◽  
High Energies ◽  
Effective Cosmological Constant ◽  
String Theories

A Brans–Dicke brane cosmology with two scalar fields inspired from string theories and phenomenological effective cosmological constant is investigated and some features are described in some details, in particular the low and high energies limit.

EFFECTIVE COSMOLOGICAL CONSTANT IN BRANE COSMOLOGY

2006 ◽  
Vol 15 (06) ◽  
pp. 895-903
Author(s):  
SEN HU ◽  
JING-RONG WANG
Keyword(s):  
Cosmological Constant ◽  
Vacuum Energy ◽  
Brane World ◽  
Reflection Symmetry ◽  
Brane Cosmology ◽  
Effective Cosmological Constant ◽  
Dimensional Gravity ◽  
Bulk Cosmological Constant ◽  
Dimension One

We consider a brane-world of co-dimension one without reflection symmetry. Through it, we give a possible explanation of the great discrepancy between the vacuum energy and the observed cosmological constant without contradiction to the knowledge we have about our Universe. We also show the gravity observed will be standard four-dimensional gravity as long as the discrepancy of the bulk cosmological constant at different sides of the brane is small enough.

GENERATING Λ FROM THE VACUUM

1999 ◽  
Vol 14 (33) ◽  
pp. 2269-2275 ◽  
Author(s):  
VARUN SAHNI
Keyword(s):  
Cosmological Constant ◽  
Vacuum Energy ◽  
Particle Production ◽  
Particle Creation ◽  
Scalar Fields ◽  
Momentum Tensor ◽  
Inflationary Universe ◽  
Static Universe ◽  
Effective Cosmological Constant ◽  
Close Relationship

The close relationship between the cosmological constant and the vacuum has been emphasized in the past by Zeldovich amongst others. We briefly discuss different approaches to the cosmological constant issue including the possibility that Λ could be generated by vacuum polarization in a static universe. Fresh possibilities occur in an expanding universe. An inflationary universe generically leads to particle creation from the vacuum, the nature and extent of particle production depending upon the mass of the field and its coupling to gravity. For ultra-light, non-minimally coupled scalar fields, particle production can be large and the resulting vacuum energy–momentum tensor will have the form of an effective cosmological constant. The inflationary scenario therefore, could give rise to a universe that is both flat andΛ-dominated, in agreement with observations.

scholarly journals Symmetry and unification from soft theorems and unitarity

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Clifford Cheung ◽  
Zander Moss
Keyword(s):  
Symmetry Algebra ◽  
Scalar Fields ◽  
Particle Interactions ◽  
Massive Scalar ◽  
Coset Space ◽  
Dimensional Theory ◽  
Finite Spectrum ◽  
Physical Constraints ◽  
High Energies ◽  
Zero Condition

Abstract We argue that symmetry and unification can emerge as byproducts of certain physical constraints on dynamical scattering. To accomplish this we parameterize a general Lorentz invariant, four-dimensional theory of massless and massive scalar fields coupled via arbitrary local interactions. Assuming perturbative unitarity and an Adler zero condition, we prove that any finite spectrum of massless and massive modes will necessarily unify at high energies into multiplets of a linearized symmetry. Certain generators of the symmetry algebra can be derived explicitly in terms of the spectrum and three-particle interactions. Furthermore, our assumptions imply that the coset space is symmetric.

scholarly journals de Sitter in non-supersymmetric string theories: no-go theorems and brane-worlds

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Ivano Basile ◽  
Stefano Lanza
Keyword(s):  
Flux Compactifications ◽  
Cosmological Constant ◽  
Dimensional Reduction ◽  
Brane World ◽  
De Sitter ◽  
Top Down ◽  
Brane Worlds ◽  
Concrete Realization ◽  
String Models ◽  
String Theories

Abstract We study de Sitter configurations in ten-dimensional string models where supersymmetry is either absent or broken at the string scale. To this end, we derive expressions for the cosmological constant in general warped flux compactifications with localized sources, which yield no-go theorems that extend previous works on supersymmetric cases. We frame our results within a dimensional reduction and connect them to a number of Swampland conjectures, corroborating them further in the absence of supersymmetry. Furthermore, we construct a top-down string embedding of de Sitter brane-world cosmologies within unstable anti-de Sitter landscapes, providing a concrete realization of a recently revisited proposal.

scholarly journals An effective cosmological constant from an entropic formulation of gravity

2020 ◽  
Vol 29 (09) ◽  
pp. 2050064
Author(s):  
I. Díaz-Saldaña ◽  
J. C. López-Domínguez ◽  
M. Sabido
Keyword(s):  
Cosmological Constant ◽  
Apparent Horizon ◽  
Friedmann Equation ◽  
Scale Factor ◽  
Late Time ◽  
Frw Universe ◽  
Equation Solving ◽  
Effective Cosmological Constant ◽  
Time Regime ◽  
Modified Entropy

In this work, we study a Friedmann–Robertson–Walker (FRW) universe derived from a modified entropy–area relationship. By applying the first law of thermodynamics to the so-called apparent horizon and a modified entropy–area relationship, we obtain a modified Friedmann equation. Solving this model for a perfect fluid with vanishing cosmological constant, we find that for early times, the scale factor is the same as that of an FRW universe. In the late-time regime, although the cosmological constant is zero, the asymptotic behavior of the scale factor is exponential, and therefore, we can identify an effective cosmological constant. The origin of the effective cosmological constant can be traced to the modifications of the entropy–area relation.

scholarly journals Brane cosmology and the self-tuning of the cosmological constant

2019 ◽  
Vol 2019 (10) ◽  
pp. 007-007 ◽  
Author(s):  
A. Amariti ◽  
C. Charmousis ◽  
D. Forcella ◽  
E. Kiritsis ◽  
F. Nitti
Keyword(s):  
Cosmological Constant ◽  
The Self ◽  
Brane Cosmology ◽  
Self Tuning

scholarly journals Extremal Cosmological Black Holes in Horndeski Gravity and the Anti-Evaporation Regime

Universe ◽  
2020 ◽  
Vol 6 (11) ◽  
pp. 210
Author(s):  
Ismael Ayuso ◽  
Diego Sáez-Chillón Gómez
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Cosmological Constant ◽  
Linear Order ◽  
Scalar Tensor Theory ◽  
De Sitter ◽  
Tensor Theory ◽  
Effective Cosmological Constant ◽  
Cosmological Black Holes ◽  
Extremal Black Holes

Extremal cosmological black holes are analysed in the framework of the most general second order scalar-tensor theory, the so-called Horndeski gravity. Such extremal black holes are a particular case of Schwarzschild-De Sitter black holes that arises when the black hole horizon and the cosmological one coincide. Such metric is induced by a particular value of the effective cosmological constant and is known as Nariai spacetime. The existence of this type of solutions is studied when considering the Horndeski Lagrangian and its stability is analysed, where the so-called anti-evaporation regime is studied. Contrary to other frameworks, the radius of the horizon remains stable for some cases of the Horndeski Lagrangian when considering perturbations at linear order.

scholarly journals Dark Energy as a Cosmological Consequence of Existence of the Dirac Scalar Field in Nature

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
O. V. Babourova ◽  
B. N. Frolov
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Early Universe ◽  
Large Time ◽  
Field Equations ◽  
Conformal Theory ◽  
Effective Cosmological Constant ◽  
Theory Of Gravitation ◽  
Cosmological Consequence

The solution of the field equations of the conformal theory of gravitation with Dirac scalar field in Cartan-Weyl spacetime at the very early Universe is obtained. In this theory dark energy (described by an effective cosmological constant) is a function of the Dirac scalar field β. This solution describes the exponential decreasing of β at the inflation stage and has a limit to a constant value of the dark energy at large time. This can give a way to solving the fundamental cosmological constant problem as a consequence of the fields dynamics in the early Universe.

scholarly journals ON DETERMINATION OF THE GEOMETRIC COSMOLOGICAL CONSTANT FROM THE OPERA EXPERIMENT OF SUPERLUMINAL NEUTRINOS

2012 ◽  
Vol 27 (11) ◽  
pp. 1250041 ◽  
Author(s):  
MU-LIN YAN ◽  
SEN HU ◽  
WEI HUANG ◽  
NENG-CHAO XIAO
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Fundamental Constant ◽  
Zero Point ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Point Energy ◽  
Sitter Spacetime ◽  
Effective Cosmological Constant

The recent OPERA experiment of superluminal neutrinos has deep consequences in cosmology. In cosmology a fundamental constant is the cosmological constant. From observations one can estimate the effective cosmological constant Λ eff which is the sum of the quantum zero point energy Λ dark energy and the geometric cosmological constant Λ. The OPERA experiment can be applied to determine the geometric cosmological constant Λ. It is the first study to distinguish the contributions of Λ and Λ dark energy from each other by experiment. The determination is based on an explanation of the OPERA experiment in the framework of Special Relativity with de Sitter spacetime symmetry.

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