scholarly journals Brane world solutions of perfect fluid in the background of a bulk containing dust or a cosmological constant

2008 ◽  
Vol 14 (4) ◽  
pp. 355-361
Author(s):  
T. Bandyopadhyay ◽  
S. Chakraborty ◽  
A. Banerjee
2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Ivano Basile ◽  
Stefano Lanza

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.


2020 ◽  
Vol 17 (05) ◽  
pp. 2050075
Author(s):  
Nasr Ahmed ◽  
Kazuharu Bamba ◽  
F. Salama

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.


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

2003 ◽  
Vol 18 (supp01) ◽  
pp. 329-339
Author(s):  
Antonios Papazoglou

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.


2015 ◽  
Vol 2015 ◽  
pp. 1-10
Author(s):  
A. Tofighi ◽  
M. Moazzen ◽  
A. Farokhtabar

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.


2013 ◽  
Vol 22 (02) ◽  
pp. 1350009 ◽  
Author(s):  
LI ZOU ◽  
FANG-YU LI ◽  
HAO WEN

Exact solutions of the Einstein–Maxwell equations for spherically symmetric charged perfect fluid have been broadly studied so far. However, the cases with a nonzero cosmological constant are seldom focused. In the present paper, the Tolman–Oppenheimer–Volkoff (TOV) equations have been generalized from the neutral case of hydrostatic equilibrium to the charged case of hydroelectrostatic equilibrium, and base on it, for the first time we find a series of new exact solutions of Einstein–Maxwell's equations with a nonzero cosmological constant for static charged perfect fluid spheres. Moreover, two special TOV equations and two classical constant density interior solutions are also given.


2000 ◽  
Vol 481 (2-4) ◽  
pp. 360-364 ◽  
Author(s):  
Stefan Förste ◽  
Zygmunt Lalak ◽  
Stéphane Lavignac ◽  
Hans Peter Nilles

2009 ◽  
Vol 24 (08n09) ◽  
pp. 1602-1605
Author(s):  
JIŘÍ KOVÁŘ ◽  
PETR SLANÝ ◽  
ZDENĔK STUCHLÍK

Results of our recent studies concerning possible effects of Λ > 0 for equilibrium positions of spinning test particles and stationary configurations of perfect-fluid tori are presented.


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