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.

scholarly journals The Large Number Hypothesis and Einstein's Theory of Gravitation

1985 ◽  
Vol 38 (4) ◽  
pp. 547 ◽  
Author(s):  
Yun-Kau Lau
Keyword(s):  
Cosmological Model ◽  
Cosmological Constant ◽  
Matter Density ◽  
Time Dependent ◽  
Field Equations ◽  
Large Number Hypothesis ◽  
Theory Of Gravitation ◽  
The Mean ◽  
Limiting Case ◽  
The Universe

In an attempt to reconcile the large number hypothesis (LNH) with Einstein's theory of gravitation, a tentative generalization of Einstein's field equations with time-dependent cosmological and gravitational constants is proposed. A cosmological model consistent with the LNH is deduced. The coupling formula of the cosmological constant with matter is found, and as a consequence, the time-dependent formulae of the cosmological constant and the mean matter density of the Universe at the present epoch are then found. Einstein's theory of gravitation, whether with a zero or nonzero cosmological constant, becomes a limiting case of the new generalized field equations after the early epoch.

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.

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.

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.

QUANTUM CORRECTIONS HELP EINSTEIN GRAVITY EXIT GRACIOUSLY

1991 ◽  
Vol 06 (10) ◽  
pp. 861-867 ◽  
Author(s):  
J. PÉREZ-MERCADER
Keyword(s):  
Initial Period ◽  
Einstein Gravity ◽  
Bubble Nucleation ◽  
Time Dependent ◽  
Quantum Corrections ◽  
Exponential Potential ◽  
Exit Problem ◽  
Conformal Equivalence ◽  
The Universe ◽  
Natural Way

We exploit the conformal equivalence between the 1-loop corrected Einstein gravity coupled to a scalar field, and linear Einstein gravity with an exponential potential, to show how the Graceful Exit Problem is solved in the context of this theory in a natural and simple way. What emerges is a scenario with a chaotic initial period followed by an era of old inflation. The resulting bubble nucleation rate is time-dependent in such a way that the second inflationary period, helped by the chaotic period, brings the Universe out of its inflationary era in a self-regulated and natural way.

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 Emergence of a cosmological constant in anisotropic fluid cosmology

2021 ◽  
pp. 2150156
Author(s):  
M. Cadoni ◽  
A. P. Sanna
Keyword(s):  
Cosmological Constant ◽  
Large Scale ◽  
Spatial Scales ◽  
Time Dependent ◽  
Anisotropic Fluid ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Coincidence Problem ◽  
Order Of Magnitude ◽  
Natural Way

In this paper, we investigate anisotropic fluid cosmology in a situation where the space–time metric back-reacts in a local, time-dependent way to the presence of inhomogeneities. We derive exact solutions to the Einstein field equations describing Friedmann–Lemaítre–Robertson–Walker (FLRW) large-scale cosmological evolution in the presence of local inhomogeneities and time-dependent backreaction. We use our derivation to tackle the cosmological constant problem. A cosmological constant emerges by averaging the backreaction term on spatial scales of the order of 100 Mpc, at which our universe begins to appear homogeneous and isotropic. We find that the order of magnitude of the “emerged” cosmological constant agrees with astrophysical observations and is related in a natural way to baryonic matter density. Thus, there is no coincidence problem in our framework.

scholarly journals CPTM symmetry, closed time paths and cosmological constant problem in the formalism of extended manifold

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
S. Bondarenko
Keyword(s):  
Cosmological Constant ◽  
Classical Solution ◽  
Vacuum Energy ◽  
Condensed Matter ◽  
Scalar Fields ◽  
Einstein Equations ◽  
Cosmological Constant Problem ◽  
Classical Level ◽  
Extended Space ◽  
Charge Parity

AbstractThe problem of the cosmological constant is considered in the formalism of an extended space-time consisting of the extended classical solution of Einstein equations. The different regions of the extended manifold are proposed to be related by the charge, parity, time and mass (CPTM) reversal symmetry applied with respect to the metric fields of the manifolds. There are interactions between the points of the extended manifold provided by scalar fields present separately in the different patches of the extended solution. The value of the constant is obtained equal to zero at the classical level due the mutual contribution of the fields in the vacuum energy, it’s non-zero value is due the quantum interactions between the fields. There are few possible scenario for the actions of the fields are discussed. Each from the obtained variants is similar to the closed time path approach of non-equilibrium condensed matter physics and among these possibilities for the closed paths, there is a variant of the action equivalent to the formalism of Keldysh. Accordingly, we consider and shortly discuss the application of the proposed formalism to the problem of smallness of the cosmological constant and singularities problem.

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