scholarly journals Influence of the cosmological constant in closed-universe models containing matter and radiation

1970 ◽  
Vol 66 (2) ◽  
pp. 202-216 ◽  
Author(s):  
A. Agnese ◽  
M. La Camera ◽  
A. Wataghin
Keyword(s):  
Cosmological Constant ◽  
Closed Universe ◽  
Universe Models

WEYL-DIRAC QUINTESSENCE AND DARK MATTER

2002 ◽  
Vol 17 (29) ◽  
pp. 4229-4237 ◽  
Author(s):  
MARK ISRAELIT
Keyword(s):  
Dark Matter ◽  
Cosmological Constant ◽  
Gauge Function ◽  
Accelerated Expansion ◽  
Closed Universe ◽  
Dirac Theory ◽  
Free Model ◽  
Classical Singularity ◽  
Dirac Gauge ◽  
The Universe

In the Integrable Weyl-Dirac theory we consider a spatially closed universe undergoing at present accelerated expansion, having a non-vanishing cosmological constant, and filled with luminous- and dark matter. During the dust-dominated period, dark matter and the quintessence pressure, the latter giving rise to acceleration: both are created by the Dirac gauge function. The behavior of F-R-W models is considered in appropriate gauges, and plausible scenarios are obtained. The outcome of the present paper, together with results of a previous work, provide a geometrically based, classical, singularity-free model of the universe. This has originated from a pure geometric Weyl-Dirac entity, passed a prematter period, the radiation-dominated era, and continues its development in the present dust period.

scholarly journals De sitter magnetic black hole dipole with a supersymmetric horizon

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
Davide Astesiano ◽  
S.L. Cacciatori
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Scalar Field ◽  
Cosmological Constant ◽  
The Other ◽  
Gauge Fields ◽  
Positive Pressure ◽  
Closed Universe ◽  
De Sitter ◽  
Extremal Black Holes

Abstract We find a new non BPS solution in N = 2 D = 4 gauged supergravity coupled to U(1) gauge fields and matter. It consists in a closed universe with two extremal black holes of equal size, surrounding two singularities. They have opposite magnetic charges (and no electric charges), but stay in static equilibrium thanks to the positive pressure of a cosmological constant. The geometry is perfectly symmetric under the exchange of the black holes and the flip of the sign of the charges. However the scalar field is non constant and non symmetric, with different values at the horizons, which depend on a real modulus. Remarkably we show that it satisfies the attractor mechanism and the entropy indeed depends only on the magnetic charges. At one of the horizons the solution becomes $$ \frac{1}{2} $$ 1 2 -BPS supersymmetric, while at the other one there is no supersymmetry, but the entropy remains independent from the scalar modulus.

SIMULATIONS OF FOUR-DIMENSIONAL SIMPLICIAL QUANTUM GRAVITY AS DYNAMICAL TRIANGULATION

1992 ◽  
Vol 07 (12) ◽  
pp. 1039-1061 ◽  
Author(s):  
M.E. AGISHTEIN ◽  
A.A. MIGDAL
Keyword(s):  
Phase Transition ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Order Phase Transition ◽  
Transition Point ◽  
Second Order ◽  
Closed Universe ◽  
Statistical Limit ◽  
Dynamical Triangulation ◽  
Second Order Phase Transition

Four-Dimensional Simplicial Quantum Gravity is simulated using the dynamical triangulation approach. We studied simplicial manifolds of spherical topology and found the critical line for the cosmological constant as a function of the gravitational one, separating the phases of opened and closed Universe. When the bare cosmological constant approaches this line from above, the four-volume grows: we reached about 5×104 simplexes, which proved to be sufficient for the statistical limit of infinite volume. However, for the genuine continuum theory of gravity, the parameters of the lattice model should be further adjusted to reach the second order phase transition point, where the correlation length grows to infinity. We varied the gravitational constant, and we found the first order phase transition, similar to the one found in three-dimensional model, except in 4D the fluctuations are rather large at the transition point, so that this is close to the second order phase transition. The average curvature in cutoff units is large and positive in one phase (gravity), and small negative in another (antigravity). We studied the fractal geometry of both phases, using the heavy particle propagator to define the geodesic map, as well as with the old approach using the shortest lattice paths. The heavy propagator geodesic appeared to be much smoother, so that the scaling laws were found, corresponding to finite fractal dimensions: D+~2.3 in the gravity phase and D−~4.6 in the antigravity phase. Similar, but somewhat lower numbers were obtained from the heat kernel singularity. The influence of the αR2 terms in 2, 3 and 4 dimensions is discussed.

scholarly journals CLOSED INFLATIONARY UNIVERSE MODELS IN BRANE WORLD COSMOLOGY

2005 ◽  
Vol 14 (05) ◽  
pp. 861-872 ◽  
Author(s):  
SERGIO DEL CAMPO ◽  
RAMÓN HERRERA ◽  
JOEL SAAVEDRA
Keyword(s):  
General Relativity ◽  
Scalar Field ◽  
Brane World ◽  
Inflationary Universe ◽  
Closed Universe ◽  
Cosmological Context ◽  
The One ◽  
Universe Models ◽  
Einstein’S General Relativity

In this article we study closed inflationary universe models proposed by Linde in a brane world cosmological context. In this scenario we determine and characterize the existence of a closed universe, in presence of one self-interacting scalar field with an inflationary stage. We have found that our model, which takes into account a Brane World Cosmology, is less restrictive than the one that uses standard Einstein's General Relativity cosmology.

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