scholarly journals CLOSING THE UNIVERSE BY RELAXING THE COSMOLOGICAL CONSTANT

1994 ◽  
Vol 09 (30) ◽  
pp. 2755-2760 ◽  
Author(s):  
JORGE L. LOPEZ ◽  
D. V. NANOPOULOS
Keyword(s):  
Higgs Boson ◽  
String Theory ◽  
Cosmological Constant ◽  
Parameter Space ◽  
Vacuum Energy ◽  
Positive Contribution ◽  
Negative Contribution ◽  
Cosmological Observations ◽  
The Universe

We consider a string-inspired no-scale SU (5) × U (1) supergravity model. In this model there is a negative contribution to the vacuum energy, which may be suitably canceled by a positive contribution typically present in string theory. One may then end up with a vacuum energy which brings many cosmological observations into better agreement with theoretical expectations, and a fixed value for the present abundance of neutralinos. We delineate the regions of parameter space allowed in this scenario, and study the ensuing predictions for the sparticle and Higgs-boson masses in this model.

scholarly journals WHY THERE IS SOMETHING SO CLOSE TO NOTHING: TOWARDS A FUNDAMENTAL THEORY OF THE COSMOLOGICAL CONSTANT

2007 ◽  
Vol 22 (10) ◽  
pp. 1797-1818 ◽  
Author(s):  
VISHNU JEJJALA ◽  
DJORDJE MINIC
Keyword(s):  
Quantum Theory ◽  
String Theory ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Uncertainty Relation ◽  
Space Time ◽  
Large Size ◽  
Minkowski Space Time ◽  
The Universe ◽  
Canonical Quantum

The cosmological constant problem is turned around to argue for a new foundational physics postulate underlying a consistent quantum theory of gravity and matter, such as string theory. This postulate is a quantum equivalence principle which demands a consistent gauging of the geometric structure of canonical quantum theory. We argue that string theory can be formulated to accommodate such a principle, and that in such a theory the observed cosmological constant is a fluctuation about a zero value. This fluctuation arises from an uncertainty relation involving the cosmological constant and the effective volume of space–time. The measured, small vacuum energy is dynamically tied to the large "size" of the universe, thus violating naive decoupling between small and large scales. The numerical value is related to the scale of cosmological supersymmetry breaking, supersymmetry being needed for a nonperturbative stability of local Minkowski space–time regions in the classical regime.

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].

BLACK HOLE QUANTIZATION, THERMODYNAMICS AND COSMOLOGICAL CONSTANT

2004 ◽  
Vol 13 (05) ◽  
pp. 885-898
Author(s):  
LI XIANG
Keyword(s):  
Black Hole ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Planck Scale ◽  
Additional Term ◽  
Logarithmic Correction ◽  
De Sitter ◽  
Horizon Area ◽  
Constant Distance ◽  
The Universe

Bekenstein argues that the horizon area of a black hole has a constant distance spectrum. We investigate the effects of such a discrete spectrum on the thermodynamics of a Schwarzchild black hole (SBH) and a Schwarzchild–de Sitter black hole (SdBH), in terms of the time-energy uncertainty relation and Stefan–Boltzman law. For the massive SBH, a negative and logarithmic correction to the Bekenstein–Hawking entropy is obtained, as well as other authors by using other methods. As to the minimal hole near the Planck scale, its entropy is no longer proportional to the horizon area, but is of order of the mass of the hole. This is similar to an excited stringy state. The vanishing heat capacity of such a minimal black hole implies that it may be a remnant as the ground state of the evaporating hole. The properties of a SdBH are similar to the SBH, except for an additional term of square area associated with the cosmological constant. In order to maintain the validity of the Bekenstein–Hawking formula, the cosmological constant is strongly limited by the size of the biggest black hole in the universe. A relation associated with the cosmological constant, Planck area and the Stefan–Boltzman constant is obtained. The cosmological constant is not only related to the vacuum energy, but is also related to the thermodynamics.

scholarly journals ON THE COSMOLOGICAL CONSTANT PROBLEM

1996 ◽  
Vol 05 (04) ◽  
pp. 433-440 ◽  
Author(s):  
DHURJATI PRASAD DATTA
Keyword(s):  
Cosmological Constant ◽  
Mechanical Model ◽  
Vacuum Energy ◽  
Quantum Mechanical ◽  
Cosmological Constant Problem ◽  
Molecular Physics ◽  
Simple Quantum ◽  
Time Formalism ◽  
Oppenheimer Approximation ◽  
The Universe

A simple quantum mechanical model of a closed interacting system is studied following the intrinsic time formalism developed recently, on the basis of the modified Born-Oppenheimer approximation. Apart from shedding further insights into the recent results on a possible nongravitating vacuum energy in the universe, the study also offers potentially interesting possibilities even in atomic/molecular physics.

PROBLEMS OF COSMOLOGICAL CONSTANT, DARK ENERGY AND POSSIBLE ADJUSTMENT MECHANISM

2005 ◽  
Vol 20 (11) ◽  
pp. 2403-2414 ◽  
Author(s):  
A. D. DOLGOV
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Astronomical Data ◽  
Adjustment Mechanism ◽  
State Of Matter ◽  
The Universe ◽  
Constant Dark

Vacuum and dark energy energy problems are reviewed. Cosmology with non-zero vacuum energy is discussed. The astronomical data which indicate that the universe is filled with an anti-gravitating state of matter are described. The mechanisms which may lead to cancellation of almost infinite vacuum energy down to the astronomically observed value are enumerated with an emphasis to dynamical adjustment.

scholarly journals Hybrid inflation and waterfall field in string theory from D7-branes

2022 ◽  
Vol 2022 (1) ◽  
Author(s):  
Ignatios Antoniadis ◽  
Osmin Lacombe ◽  
George K. Leontaris
Keyword(s):  
String Theory ◽  
Flux Compactifications ◽  
Saddle Point ◽  
Present State ◽  
Global Minimum ◽  
Vacuum Energy ◽  
De Sitter ◽  
Hybrid Inflation ◽  
De Sitter Vacuum ◽  
The Universe

Abstract We present an explicit string realisation of a cosmological inflationary scenario we proposed recently within the framework of type IIB flux compactifications in the presence of three magnetised D7-brane stacks. Inflation takes place around a metastable de Sitter vacuum. The inflaton is identified with the volume modulus and has a potential with a very shallow minimum near the maximum. Inflation ends due to the presence of “waterfall” fields that drive the evolution of the Universe from a nearby saddle point towards a global minimum with tuneable vacuum energy describing the present state of our Universe.

Quantifying uncertainty in future projections of ice loss from the Filchner-Ronne basin, Antarctica

2021 ◽  
Author(s):  
Emily Hill ◽  
Sebastian Rosier ◽  
Hilmar Gudmundsson ◽  
Matthew Collins
Keyword(s):  
Sea Level ◽  
Parameter Space ◽  
Climate Warming ◽  
Input Parameter ◽  
Ice Sheet ◽  
Training Sample ◽  
Positive Contribution ◽  
Ice Shelf ◽  
Ice Streams ◽  
Negative Contribution

<p>The future of the Antarctic Ice Sheet under climate warming is one of the largest sources of uncertainty for changes in global mean sea level (GMSL). Accelerated ice loss in recent decades has been concentrated in regions where warm circumpolar deep water forces high rates of sub-shelf melt. It is unclear how ice shelves currently surrounded by cold ocean waters with low melt rates will respond to changes in ocean conditions in future. For example, previous studies have shown that if warm water were to infiltrate beneath the Filchner-Ronne ice shelf, it could drastically increase sub-shelf melt rates. However, the inland ice-sheet response to climate-ocean changes remains uncertain. Here, we set out to quantify uncertainties in projections of GMSL from the Filchner-Ronne region of Antarctica over the next two centuries. To do this we take a large random sample from a probabilistic input parameter space and evaluate these parameter sets in the ice-sheet model Úa under four RCP forcing scenarios. We then use this training sample to generate a statistical surrogate model to capture the parameter to projection relationship from our ice-sheet model. Finally, we use sensitivity analysis to identify which parameters drive the majority of uncertainty in our projections.</p><p>Our results suggest that accumulation expected with warming is capable of suppressing increases in ice discharge associated with increased ocean-driven sub-shelf melt rates. This could allow the Filcher-Ronne basin to have a negative contribution to GMSL. However, parameters controlling mass accumulation and sub-shelf melting are highly uncertain. Crucially, there is potential within our input parameter space for major collapse and retreat of ice streams feeding the Filchner-Ronne ice shelf and a positive contribution to sea level rise. Further improvements in the representation of accumulation and sub-shelf melt under climate warming in ice-sheet models will help determine the sign of GMSL projections from this region of the ice sheet.</p>

scholarly journals Cosmological consequences of a variable cosmological constant model

2016 ◽  
Vol 26 (07) ◽  
pp. 1750060 ◽  
Author(s):  
Hemza Azri ◽  
A. Bounames
Keyword(s):  
Cosmological Constant ◽  
Vacuum Energy ◽  
Gravitational Constant ◽  
Scale Factor ◽  
Accelerated Expansion ◽  
Variable Cosmological Constant ◽  
Age Of The Universe ◽  
Two Phases ◽  
Limiting Case ◽  
The Universe

We derive a model of dark energy which evolves with time via the scale factor. The equation-of-state is studied as a function of a parameter [Formula: see text] introduced in this model as [Formula: see text]. In addition to the recent accelerated expansion, the model predicts another decelerated phase. These two phases are studied via the parameter [Formula: see text]. The age of the universe is found to be almost consistent with the observation. In the limiting case, the cosmological constant model, we find that vacuum energy gravitates with a tiny gravitational constant which evolves with the scale factor, rather than with Newton’s constant. This enables degravitation of the vacuum energy which in turn produces the tiny observed curvature, rather than a 120 orders of magnitude larger value.

scholarly journals INFLATION INDUCED BY VACUUM ENERGY AND GRACEFUL EXIT FROM IT

2001 ◽  
Vol 16 (40) ◽  
pp. 2545-2555 ◽  
Author(s):  
E. PAPANTONOPOULOS ◽  
I. PAPPA
Keyword(s):  
Cosmological Constant ◽  
Vacuum Energy ◽  
Einstein Equations ◽  
Time Dependent ◽  
Brane Cosmology ◽  
Fast Growing ◽  
Early Epoch ◽  
The Universe ◽  
Natural Way

Motivated by brane cosmology, we solve the Einstein equations with a time-dependent cosmological constant. Assuming that at an early epoch the vacuum energy scales as 1/log t, we show that the universe passes from a fast growing phase (inflation) to an expanding phase in a natural way.

Brane cosmological constant in two-brane warped geometry model

2014 ◽  
Vol 29 (20) ◽  
pp. 1450093
Author(s):  
Sayantani Lahiri ◽  
Soumitra SenGupta
Keyword(s):  
Cosmological Constant ◽  
Hubble Parameter ◽  
Vacuum Energy ◽  
Hubble Constant ◽  
Time Dependent ◽  
Time Varying ◽  
Constant Modulus ◽  
Expanding Universe ◽  
Geometry Model ◽  
The Universe

In the backdrop of generalized Randall–Sundrum braneworld scenario, we look for the possible origin of an effective four-dimensional cosmological constant (Ω vis ) on the visible three-brane due to the effects of bulk curvature and the modulus field that can either be a constant or a time-dependent quantity. In case of constant modulus field, the induced Ω vis leads to an exponentially expanding universe and the presence of vacuum energy densities on either of the three-branes as well as a nonvanishing bulk curvature [Formula: see text] are essential to generate an effective Ω vis . The Hubble constant turns out to be equal to the visible brane cosmological constant which agrees with the present result. In an alternative scenario, a time-dependent modulus field is found to be capable of decelerating the universe. The Hubble parameter, in this case is determined for a slowly time-varying modulus field.

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