scholarly journals Brane world scenarios and the cosmological constant

2001 ◽  
Vol 597 (1-3) ◽  
pp. 263-278 ◽  
Author(s):  
S.P. de Alwis
Keyword(s):  
Cosmological Constant ◽  
Brane World

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.

The possibility of a stable flat dark energy-dominated Swiss-cheese brane-world universe

2020 ◽  
Vol 17 (05) ◽  
pp. 2050075
Author(s):  
Nasr Ahmed ◽  
Kazuharu Bamba ◽  
F. Salama
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Cosmological Models ◽  
Brane World ◽  
Fine Tuning ◽  
Energy Conditions ◽  
Late Time ◽  
Swiss Cheese ◽  
Black Strings ◽  
The Stability

In this paper, we study the possibility of obtaining a stable flat dark energy-dominated universe in a good agreement with observations in the framework of Swiss-cheese brane-world cosmology. Two different brane-world cosmologies with black strings have been introduced for any cosmological constant [Formula: see text] using two empirical forms of the scale factor. In both models, we have performed a fine-tuning between the brane tension and the cosmological constant so that the Equation of state (EoS) parameter [Formula: see text] for the current epoch, where the redshift [Formula: see text]. We then used these fine–tuned values to calculate and plot all parameters and energy conditions. The deceleration–acceleration cosmic transition is allowed in both models, and the jerk parameter [Formula: see text] at late-times. Both solutions predict a future dark energy-dominated universe in which [Formula: see text] with no crossing to the phantom divide line. While the pressure in the first solution is always negative, the second solution predicts a better behavior of cosmic pressure where the pressure is negative only in the late-time accelerating era but positive in the early-time decelerating era. Such a positive-to-negative transition in the evolution of pressure helps to explain the cosmic deceleration–acceleration transition. Since black strings have been proved to be unstable by some authors, this instability can actually reflect doubts on the stability of cosmological models with black strings (Swiss-cheese type brane-worlds cosmological models). For this reason, we have carefully investigated the stability through energy conditions and sound speed. Because of the presence of quadratic energy terms in Swiss-cheese type brane-world cosmology, we have tested the new nonlinear energy conditions in addition to the classical energy conditions. We have also found that a negative tension brane is not allowed in both models of the current work as the energy density will no longer be well defined.

Is the Massive Graviton a Viable Possibility?

2003 ◽  
Vol 18 (supp01) ◽  
pp. 329-339
Author(s):  
Antonios Papazoglou
Keyword(s):  
Cosmological Constant ◽  
Brane World ◽  
Massive Graviton ◽  
Curved Space ◽  
Negative Cosmological Constant ◽  
World Theory ◽  
Six Dimensions

In this talk we discuss the scenario of multigravity according to which the gravity we observe in intermediate scales (1 mm < r < 1026 cm ) is mediated by both a massless graviton and one or more of ultralight spin-2 state. We present how this can be realized in a five dimensional brane-world theory with flat branes and the complications associated with the extra polarizations of the massive gravitons (van Dam-Veltman-Zakharov discontinuity) and the ghost radions corresponding to the fluctuations of the negative tension branes present in these models. We then show how we can construct models of AdS4 branes instead with exclusively positive tension and demonstrate how the van Dam-Veltman-Zakharov no-go theorem can be circumvented in curved space. These models, although they are consistent, face phenomenological problems related to the presence of a remnant negative cosmological constant on the branes. We finally present how we can obtain the same constructions in six dimensions with flat positive tensions branes only, in a manner that they are both theoretically consistent and phenomenologically acceptable. The latter come in two copies each and offer the first problem-free realization of the multigravity scenario.

scholarly journals Vacuum Expectation Value Profiles of the Bulk Scalar Field in the Generalized Randall-Sundrum Model

2015 ◽  
Vol 2015 ◽  
pp. 1-10
Author(s):  
A. Tofighi ◽  
M. Moazzen ◽  
A. Farokhtabar
Keyword(s):  
Scalar Field ◽  
Boundary Conditions ◽  
Cosmological Constant ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Brane World ◽  
Dirichlet Boundary Conditions ◽  
World Model ◽  
Expectation Value ◽  
Bulk Scalar Field

In the generalized Randall-Sundrum warped brane-world model the cosmological constant induced on the visible brane can be positive or negative. In this paper we investigate profiles of vacuum expectation value of the bulk scalar field under general Dirichlet and Neumann boundary conditions in the generalized warped brane-world model. We show that the VEV profiles generally depend on the value of the brane cosmological constant. We find that the VEV profiles of the bulk scalar field for a visible brane with negative cosmological constant and positive tension are quite distinct from those of Randall-Sundrum model. In addition we show that the VEV profiles for a visible brane with large positive cosmological constant are also different from those of the Randall-Sundrum model. We also verify that Goldberger and Wise mechanism can work under nonzero Dirichlet boundary conditions in the generalized Randall-Sundrum model.

scholarly journals A comment on self-tuning and vanishing cosmological constant in the brane world

2000 ◽  
Vol 481 (2-4) ◽  
pp. 360-364 ◽  
Author(s):  
Stefan Förste ◽  
Zygmunt Lalak ◽  
Stéphane Lavignac ◽  
Hans Peter Nilles
Keyword(s):  
Cosmological Constant ◽  
Brane World ◽  
Self Tuning

scholarly journals A VARYING-e BRANE WORLD COSMOLOGY

2002 ◽  
Vol 17 (03) ◽  
pp. 175-184 ◽  
Author(s):  
DONAM YOUM
Keyword(s):  
Cosmological Model ◽  
Cosmological Constant ◽  
Electric Charge ◽  
Brane World ◽  
Speed Of Light ◽  
Cosmological Constant Problem ◽  
System Of Units ◽  
Flatness Problem

We study a varying electric charge brane world cosmology in the RS2 model obtained from a varying-speed-of-light brane world cosmology by redefining the system of units. We elaborate conditions under which the flatness problem and the cosmological constant problem can be resolved by such cosmological model.

scholarly journals THE COSMOLOGICAL CONSTANT PROBLEM AND INFLATION IN THE STRING LANDSCAPE

2009 ◽  
Vol 24 (10) ◽  
pp. 1925-1962 ◽  
Author(s):  
QING-GUO HUANG ◽  
S.-H. HENRY TYE
Keyword(s):  
Cosmological Constant ◽  
Planck Scale ◽  
Brane World ◽  
Road Map ◽  
The Standard Model ◽  
Long Lifetime ◽  
String Landscape ◽  
Quantum Treatment ◽  
The Universe ◽  
Nucleation Bubble

An earlier paper points out that a quantum treatment of the string landscape is necessary. It suggests that the wave function of the universe is mobile in the landscape until the universe reaches a meta-stable site with its cosmological constant Λ0 smaller than the critical value Λc, where Λc is estimated to be exponentially small compared to the Planck scale. Since this site has an exponentially long lifetime, it may well be today's universe. We investigate specific scenarios based on this quantum diffusion property of the cosmic landscape and find a plausible scenario for the early universe. In the last fast tunneling to the Λ0(<Λc) site in this scenario, all energies are stored in the nucleation bubble walls, which are released to radiation only after bubble collisions and thermalization. So the Λ0 site is chosen even if Λ0 plus radiation is larger than Λc, as long as the radiation does not destabilize the Λ0 vacuum. A consequence is that inflation must happen before this last fast tunneling, so the inflationary scenario that emerges naturally is extended brane inflation, where the brane motion includes a combination of rolling, fast tunnelings, slow-roll, hopping and percolation in the landscape. We point out that, in the brane world, radiation during nucleosynthesis are mostly on the standard model branes (brane radiation, as opposed to radiation in the bulk). This distinction may lead to interesting dynamics. We consider this paper as a road map for future investigations.

scholarly journals Origin of a small cosmological constant in a brane world

2002 ◽  
Vol 66 (12) ◽  
Author(s):  
Kazuo Ghoroku ◽  
Masanobu Yahiro
Keyword(s):  
Cosmological Constant ◽  
Brane World

scholarly journals THE NATURE OF THE COSMOLOGICAL CONSTANT PROBLEM

2009 ◽  
Vol 24 (08n09) ◽  
pp. 1545-1548 ◽  
Author(s):  
M. D. MAIA ◽  
A. J. S. CAPISTRANO ◽  
E. M. MONTE
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
Energy Density ◽  
Cosmological Constant ◽  
Ground State ◽  
Vacuum Energy ◽  
Dimensional Space ◽  
Brane World ◽  
Vacuum Energy Density ◽  
Cosmological Constant Problem

General relativity postulates the Minkowski space-time as the standard (flat) geometry against which we compare all curved space-times and also as the gravitational ground state where particles, quantum fields and their vacua are defined. On the other hand, experimental evidences tell that there exists a non-zero cosmological constant, which implies in a deSitter ground state, which not compatible with the assumed Minkowski structure. Such inconsistency is an evidence of the missing standard of curvature in Riemann's geometry, which in general relativity manifests itself in the form of the cosmological constant problem. We show how the lack of a curvature standard in Riemann's geometry can be fixed by Nash's theorem on metric perturbations. The resulting higher dimensional gravitational theory is more general than general relativity, similar to brane-world gravity, but where the propagation of the gravitational field along the extra dimensions is a mathematical necessity, rather than a postulate. After a brief introduction to Nash's theorem, we show that the vacuum energy density must remain confined to four-dimensional space-times, but the cosmological constant resulting from the contracted Bianchi identity represents a gravitational term which is not confined. In this case, the comparison between the vacuum energy and the cosmological constant in general relativity does not make sense. Instead, the geometrical fix provided by Nash's theorem suggests that the vacuum energy density contributes to the perturbations of the gravitational field.

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