MIRROR BRANES

2005 ◽  
Vol 20 (30) ◽  
pp. 2283-2294 ◽  
Author(s):  
YURI SHTANOV ◽  
ALEXANDER VIZNYUK
Keyword(s):  
Cosmological Constant ◽  
Scalar Curvature ◽  
Vacuum Energy ◽  
Vacuum Solution ◽  
Matter Content ◽  
Brane Model ◽  
Gravitational Forces ◽  
Dimensional Gravity ◽  
The One ◽  
Reasonable Model

The Randall–Sundrum two-brane model admits the flat-brane Lorentz-invariant vacuum solution only if the branes have exactly opposite tensions. We pay attention to this condition and propose a generalization of this model in which two branes are described by actions of the same form and with the same matter content but with opposite signs. In this way, the relation between their tensions (which are their vacuum energy densities) is naturally accounted for. We study a simple example of such a model in detail. It represents the Randall–Sundrum model supplemented by the Einstein scalar-curvature terms in the actions for the branes. We show that this model is tachyon-free for sufficiently large negative values of the brane cosmological constant, that gravitational forces on the branes are of opposite signs, and that physically most reasonable model of this type is the one where the five-dimensional gravity is localized around the visible brane. The massive gravitational modes in this model have ghost-like character, and we discuss the significance of this fact for the quantum instability of the vacuum on the visible brane.

scholarly journals EXPONENTIAL LAGRANGIAN FOR THE GRAVITATIONAL FIELD AND THE PROBLEM OF VACUUM ENERGY

2008 ◽  
Vol 23 (08) ◽  
pp. 1286-1289 ◽  
Author(s):  
ORCHIDEA MARIA LECIAN ◽  
GIOVANNI MONTANI
Keyword(s):  
Gravitational Field ◽  
Cosmological Constant ◽  
Lagrangian Density ◽  
Vacuum Energy ◽  
The Other ◽  
Present Value ◽  
Other Hand ◽  
Free Parameters ◽  
The One

We will analyze two particular features of an exponential gravitational Lagrangian. On the one hand, while this choice of the Lagrangian density allows for two free parameters, only one scale, the cosmological constant, arises as fundamental when the proper Einsteinian limit is to be recovered. On the other hand, the vacuum energy arising from f(R) theories such that f(0) ≠ 0 needs a cancellation mechanism, by which the present value of the cosmological constant can be recast.

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.

scholarly journals TIME, VACUUM ENERGY, AND THE COSMOLOGICAL CONSTANT

2009 ◽  
Vol 18 (14) ◽  
pp. 2265-2268 ◽  
Author(s):  
VIQAR HUSAIN
Keyword(s):  
Quantum Gravity ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Cosmological Constant Problem ◽  
Problem Of Time ◽  
The Relationship

We describe a link between the cosmological constant problem and the problem of time in quantum gravity. This arises from examining the relationship between the cosmological constant and vacuum energy in light of nonperturbative formulations of quantum gravity.

Water retention in Australian soils. 2.* Prediction using particle size, bulk density, and other properties

Soil Research ◽  
1996 ◽  
Vol 34 (5) ◽  
pp. 679 ◽  
Author(s):  
Z Paydar ◽  
HP Cresswell
Keyword(s):  
Particle Size ◽  
Bulk Density ◽  
Soil Water ◽  
Multiple Regression ◽  
Empirical Relationship ◽  
Organic Matter Content ◽  
Matter Content ◽  
Point Method ◽  
Eastern Australia ◽  
The One

Different approaches were investigated for estimating the parameters in the Campbell soil water characteristic (SWC) equation from soil attributes such as particle size distribution (PSD), bulk density, and organic matter content. Predicted soil water characteristics were compared with measured values for soils of the wheatbelt of south-eastern Australia. A method of prediction is proposed incorporating an empirical relationship for estimating the slope of the SWC from the slope of the cumulative PSD. A power-law form is assumed for both the SWC and PSD functions. One measured SWC point is then used to locate and thus define the SWC curve. When SWC points predicted with this 'one-point' method were compared with measured values, the mean absolute value of the difference between each measured and predicted SWC point was 0.016 m3/m3 for the Geeves data and 0.027 m3/m3 for the Forrest data. Eight sets of predictive equations, previously developed using multiple regression analysis, were also evaluated. Whilst the equations predicted the slope of the SWC curves reasonably well, predictions of the air entry potential were poor. Although less accurate, the equations developed by multiple regression are less demanding in data requirement compared with alternative SWC prediction methods. The one-point method gave better predictions than the multiple regression approach but was less accurate than the 'two-point' method proposed in the first paper in this series. The one-point method should be considered where PSD data and 1 measured SWC point are available. In most other circumstances it will be more accurate and cost-effective to measure 2 SWC points to define the soil water characteristic function (the two-point method).* Part I, Aust. J. Soil Res., 1996, 34, 195–212.

scholarly journals The nature of the gravitational vacuum

2019 ◽  
Vol 28 (14) ◽  
pp. 1944005
Author(s):  
Samir D. Mathur
Keyword(s):  
Black Hole ◽  
String Theory ◽  
Cosmological Constant ◽  
Mass Formula ◽  
Vacuum Energy ◽  
Planck Scale ◽  
Cosmological Constant Problem ◽  
Horizon Radius ◽  
Number Formula ◽  
Gravitational Vacuum

The vacuum must contain virtual fluctuations of black hole microstates for each mass [Formula: see text]. We observe that the expected suppression for [Formula: see text] is counteracted by the large number [Formula: see text] of such states. From string theory, we learn that these microstates are extended objects that are resistant to compression. We argue that recognizing this ‘virtual extended compression-resistant’ component of the gravitational vacuum is crucial for understanding gravitational physics. Remarkably, such virtual excitations have no significant effect for observable systems like stars, but they resolve two important problems: (a) gravitational collapse is halted outside the horizon radius, removing the information paradox, (b) spacetime acquires a ‘stiffness’ against the curving effects of vacuum energy; this ameliorates the cosmological constant problem posed by the existence of a planck scale [Formula: see text].

scholarly journals Vacuum Energy Decay from a q-Bubble

Physics ◽  
2019 ◽  
Vol 1 (3) ◽  
pp. 321-338 ◽  
Author(s):  
Frans R. Klinkhamer ◽  
Osvaldo P. Santillán ◽  
Grigory E. Volovik ◽  
Albert Zhou
Keyword(s):  
Cosmological Constant ◽  
Time Evolution ◽  
Gravitational Collapse ◽  
Vacuum Energy ◽  
Finite Size ◽  
Energy Scale ◽  
Gravitational Energy ◽  
Numerical Results ◽  
Field Energy ◽  
Spherical Bubble

We consider a finite-size spherical bubble with a nonequilibrium value of the q-field, where the bubble is immersed in an infinite vacuum with the constant equilibrium value q 0 for the q-field (this q 0 has already cancelled an initial cosmological constant). Numerical results are presented for the time evolution of such a q-bubble with gravity turned off and with gravity turned on. For small enough bubbles and a q-field energy scale sufficiently below the gravitational energy scale E Planck , the vacuum energy of the q-bubble is found to disperse completely. For large enough bubbles and a finite value of E Planck , the vacuum energy of the q-bubble disperses only partially and there occurs gravitational collapse near the bubble center.

scholarly journals Gravitational Theory Without the Cosmological Constant Problem

1997 ◽  
Vol 12 (32) ◽  
pp. 2421-2424 ◽  
Author(s):  
E. I. Guendelman ◽  
A. B. Kaganovich
Keyword(s):  
Cosmological Constant ◽  
Degrees Of Freedom ◽  
Vacuum Energy ◽  
Dimensional Space ◽  
Realistic Model ◽  
Gravitational Theory ◽  
Space Time ◽  
Higher Dimensional Space Time ◽  
Higher Dimensional ◽  
Dimensional Space Time

We develop a gravitational theory where the measure of integration in the action principle is not necessarily [Formula: see text] but it is determined dynamically through additional degrees of freedom. This theory is based on the demand that such measure respects the principle of "non-gravitating vacuum energy" which states that the Lagrangian density L can be changed to L + const. without affecting the dynamics. Formulating the theory in the first-order formalism we get as a consequence of the variational principle a constraint that enforces the vanishing of the cosmological constant. The most realistic model that implements these ideas is realized in a six or higher dimensional space–time. The compactification of extra dimensions into a sphere gives the possibility of generating scalar masses and potentials, gauge fields and fermionic masses. It turns out that the remaining four-dimensional space–time must have effective zero cosmological constant.

scholarly journals COSMOLOGICAL CONSTANT PROBING SHAPE MODULI THROUGH LARGE EXTRA DIMENSIONS

2006 ◽  
Vol 21 (15) ◽  
pp. 3095-3109 ◽  
Author(s):  
SATOSHI MATSUDA ◽  
SHIGENORI SEKI
Keyword(s):  
Cosmological Constant ◽  
Extra Dimensions ◽  
Vacuum Energy ◽  
Large Extra Dimensions ◽  
Casimir Energy ◽  
Wilkinson Microwave Anisotropy Probe ◽  
Extra Space ◽  
Kaluza Klein

We consider a compactification of extra dimensions and numerically calculate Casimir energy which is provided by the mass of Kaluza–Klein modes. For the extra space we consider a torus with shape moduli and show that the corresponding vacuum energy is represented as a function of the moduli parameter of the extra dimensions. By assuming that the Casimir energy may be identified with cosmological constant, we evaluate the size of extra dimensions in terms of the recent data given by the Wilkinson Microwave Anisotropy Probe (WMAP) measurement and the supernovae observations. We suggest that the observed cosmological constant may probe the shape moduli of the extra space by the study of the Casimir energy of the compactified extra dimensions.

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