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 Brane cosmology and the self-tuning of the cosmological constant in the presence of bulk black holes

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
P. Betzios ◽  
O. Papadoulaki
Keyword(s):  
Black Hole ◽  
Cosmological Constant ◽  
Static Solution ◽  
Brane World ◽  
De Sitter ◽  
Brane Cosmology ◽  
Brane Worlds ◽  
Higher Dimensional ◽  
Self Tuning ◽  
Hole Geometry

Abstract Motivated by the holographic self-tuning proposal of the cosmological constant, we generalize and study the cosmology of brane-worlds embedded in a higher-dimensional bulk black hole geometry. We describe the equations and matching conditions in the case of flat, spherical and hyperbolic slicing of the bulk geometry and find the conditions for the existence of a static solution. We solve the equations that govern dynamical geometries in the probe brane limit and we describe in detail the resulting brane-world cosmologies. Of particular interest are the properties of solutions when the brane-world approaches the black hole horizon. In this case the geometry induced on the brane is that of de Sitter, whose entropy and temperature is related to those of the higher dimensional bulk black hole.

scholarly journals BLACK HOLES IN THE PRESENCE OF COSMOLOGICAL CONSTANT AND LARGE-N BRANE WORLD

2009 ◽  
Vol 24 (26) ◽  
pp. 2107-2118 ◽  
Author(s):  
MINGXING LUO ◽  
SIBO ZHENG
Keyword(s):  
Cosmological Constant ◽  
Higher Dimensions ◽  
Brane World ◽  
Gauge Fields ◽  
Brane Worlds ◽  
Gravitational Theories ◽  
Large N ◽  
Gauge Gravity ◽  
Gravity Duality ◽  
Constant Dilaton

Gravitational theories including negative cosmological constant, dilaton and gauge fields are explored in higher dimensions, in which black hole solutions are shown to exist and their asymptotic behaviors are obtained. Based on these solutions, effective Randall–Sundrum brane worlds are constructed. In the framework of gauge/gravity duality, effects from cosmological constant on the spectra of standard model fields on the branes are perturbatively calculated.

scholarly journals Dimensional reduction and (Anti) de Sitter bounds

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Tom Rudelius
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Dimensional Reduction ◽  
Energy Condition ◽  
Field Potential ◽  
Limited Range ◽  
Mass Scale ◽  
Accelerated Expansion ◽  
De Sitter ◽  
Expansion Of The Universe

Abstract Dimensional reduction has proven to be a surprisingly powerful tool for delineating the boundary between the string landscape and the swampland. Bounds from the Weak Gravity Conjecture and the Repulsive Force Conjecture, for instance, are exactly preserved under dimensional reduction. Motivated by its success in these cases, we apply a similar dimensional reduction analysis to bounds on the gradient of the scalar field potential V and the mass scale m of a tower of light particles in terms of the cosmological constant Λ, which ideally may pin down ambiguous O(1) constants appearing in the de Sitter Conjecture and the (Anti) de Sitter Distance Conjecture, respectively. We find that this analysis distinguishes the bounds $$ \left|\nabla V\right|/V\ge \sqrt{4/\left(d-2\right)} $$ ∇ V / V ≥ 4 / d − 2 , m ≲ |Λ|1/2, and m ≲ |Λ|1/d in d-dimensional Planck units. The first of these bounds is equivalent to the strong energy condition in Einstein-dilaton gravity and precludes accelerated expansion of the universe. It is almost certainly violated in our universe, though it may apply in asymptotic limits of scalar field space. The second bound cannot be satisfied in our universe, though it is saturated in supersymmetric AdS vacua with well-understood uplifts to 10d/11d supergravity. The third bound likely has a limited range of validity in quantum gravity as well, so it may or may not apply to our universe. However, if it does apply, it suggests a possible relation between the cosmological constant and the neutrino mass, which (by the see-saw mechanism) may further provide a relation between the cosmological constant problem and the hierarchy problem. We also work out the conditions for eternal inflation in general spacetime dimensions, and we comment on the behavior of these conditions under dimensional reduction.

scholarly journals LOCALIZATION OF GRAVITY IN BRANE WORLD COSMOLOGIES

2003 ◽  
Vol 18 (14) ◽  
pp. 983-992 ◽  
Author(s):  
PARAMPREET SINGH ◽  
NARESH DADHICH
Keyword(s):  
Cosmological Constant ◽  
Bound State ◽  
Cosmological Models ◽  
Brane World ◽  
Fine Tuning ◽  
Expanding Universe ◽  
De Sitter ◽  
Positive Cosmological Constant ◽  
Zero Mass ◽  
Bulk Parameters

The most remarkable and interesting feature of brane world scenario is the use of bulk's curvature to localize gravity on the brane, albeit with fine tuning of the brane and bulk parameters. For FRW expanding universe on the brane, it is a moving hypersurface in Schwarzschild anti de Sitter bulk spacetime. We show that zero mass gravitons have bound state on the brane for suitable values of brane and bulk parameters. There occur various cases giving rise to different cosmological models, in particular we discuss a model with positive cosmological constant on the brane.

scholarly journals STATE OF THE UNIFICATION ADDRESS

2001 ◽  
Vol 16 (supp01a) ◽  
pp. 77-91 ◽  
Author(s):  
M. J. DUFF
Keyword(s):  
String Theory ◽  
Cosmological Constant ◽  
Brane World ◽  
Brane Worlds ◽  
Self Tuning ◽  
M Theory

After reviewing how M-theory subsumes string theory, I report broadly on some new and interesting developments, focusing on the "brane world": circumventing no-go theorems for supersymmetric brane-worlds, complementarity of the Maldacena and Randall-Sundrum pictures; self-tuning of the cosmological constant. I conclude with the top ten unsolved problems.

scholarly journals VACUUM POLARIZATION IN AN ANTI-DE SITTER SPACE AS AN ORIGIN FOR A COSMOLOGICAL CONSTANT IN A BRANE WORLD

2005 ◽  
Vol 20 (10) ◽  
pp. 733-743 ◽  
Author(s):  
LI-XIN LI
Keyword(s):  
Cosmological Constant ◽  
Vacuum Polarization ◽  
Mass Density ◽  
De Sitter Space ◽  
Brane World ◽  
Curvature Radius ◽  
De Sitter ◽  
Cosmological Observations ◽  
Near Future ◽  
Planck Energy

We show that the vacuum polarization of quantum fields in an anti-de Sitter space can naturally give rise to a small but nonzero cosmological constant in a brane world living in it. To explain the extremely small ratio of mass density in the cosmological constant to the Planck mass density in our universe (≈10-123) as suggested by cosmological observations, all we need is a four-dimensional brane world (our universe) living in a five-dimensional anti-de Sitter space with a curvature radius r0~10-3 cm and a fundamental Planck energy M P ~109 GeV , and a scalar field with a mass [Formula: see text]. Probing gravity down to a scale ~10-3 cm, which is attainable in the near future, will provide a test of the model.

scholarly journals SCALAR FIELD IN A MINIMALLY COUPLED BRANE WORLD: NO-HAIR AND OTHER NO-GO THEOREMS

2004 ◽  
Vol 13 (04) ◽  
pp. 593-606 ◽  
Author(s):  
K. A. BRONNIKOV ◽  
S. B. FADEEV ◽  
A. V. MICHTCHENKO
Keyword(s):  
Scalar Field ◽  
Strong Field ◽  
Scalar Fields ◽  
Brane World ◽  
Einstein Equations ◽  
De Sitter ◽  
Brane Worlds ◽  
Traversable Wormholes ◽  
Tensor Formula ◽  
Causal Structures

In the brane-world framework, we consider static, spherically symmetric configurations of a scalar field with the Lagrangian (∂ϕ)2/2-V(ϕ), confined on the brane. We use the 4D Einstein equations on the brane obtained by Shiromizu et al., containing the conventional stress tensor [Formula: see text], the tensor [Formula: see text] which is quadratic in [Formula: see text], and [Formula: see text] describing interaction with the bulk. For models under study, the tensor [Formula: see text] has zero divergence, allowing one to consider [Formula: see text]. Such a brane, whose 4D gravity is decoupled from the bulk geometry, may be called minimally coupled. Assuming [Formula: see text], we try to extend to brane worlds some theorems valid for scalar fields in general relativity (GR). Thus, the list of possible global causal structures in all models under consideration is shown to be the same as is known for vacuum with a cosmological constant in GR: Minkowski, Schwarzschild, (anti-) de Sitter and Schwarzschild–(anti-)de Sitter. A no-hair theorem, saying that, given a potential V≥0, asymptotically flat black holes cannot have nontrivial external scalar fields, is proved under certain restrictions. Some objects, forbidden in GR, are allowed on the brane, e.g, traversable wormholes supported by a scalar field, but only at the expense of enormous matter densities in the strong field region.

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.

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