scholarly journals Positive cosmological constant in loop quantum cosmology

2012 ◽  
Vol 85 (6) ◽  
Author(s):  
Tomasz Pawłowski ◽  
Abhay Ashtekar
Keyword(s):  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Loop Quantum Cosmology ◽  
Positive Cosmological Constant

scholarly journals The Effect of a Positive Cosmological Constant on the Bounce of Loop Quantum Cosmology

Mathematics ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 186
Author(s):  
Mercedes Martín-Benito ◽  
Rita B. Neves
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Quantum Dynamics ◽  
Solvable Model ◽  
Massless Scalar ◽  
Loop Quantum Cosmology ◽  
Massless Scalar Field ◽  
Positive Cosmological Constant ◽  
Semiclassical States

We provide an analytical solution to the quantum dynamics of a flat Friedmann-Lemaître- Robertson-Walker model with a massless scalar field in the presence of a small and positive cosmological constant, in the context of Loop Quantum Cosmology. We use a perturbative treatment with respect to the model without a cosmological constant, which is exactly solvable. Our solution is approximate, but it is precisely valid at the high curvature regime where quantum gravity corrections are important. We compute explicitly the evolution of the expectation value of the volume. For semiclassical states characterized by a Gaussian spectral profile, the introduction of a positive cosmological constant displaces the bounce of the solvable model to lower volumes and to higher values of the scalar field. These displacements are state dependent, and in particular, they depend on the peak of the Gaussian profile, which measures the momentum of the scalar field. Moreover, for those semiclassical states, the bounce remains symmetric, as in the vanishing cosmological constant case. However, we show that the behavior of the volume is more intricate for generic states, leading in general to a non-symmetric bounce.

scholarly journals Universe’s memory and spontaneous coherence in loop quantum cosmology

2016 ◽  
Vol 25 (08) ◽  
pp. 1642013 ◽  
Author(s):  
Tomasz Pawłowski
Keyword(s):  
Cosmological Constant ◽  
Present State ◽  
Quantum Cosmology ◽  
A Priori ◽  
Loop Quantum Cosmology ◽  
Positive Cosmological Constant ◽  
Isotropic Universe ◽  
Constant Of Motion ◽  
Universe Evolution

The quantum bounce a priori connects several (semi)classical epochs of universe evolution, however determining if and how well the semiclassicality is preserved in this transition is highly nontrivial. We review the present state of knowledge in that regards in the isotropic sector of loop quantum cosmology (LQC). This knowledge is next extended by studies of an isotropic universe admitting positive cosmological constant (featuring an infinite chain of large universe epochs). It is also shown, that such universe always admits a semiclassical epoch thanks to spontaneous coherence, provided it is semiclassical in certain constant of motion playing the role of energy.

scholarly journals Asymptotically equivalent functions and ultrafilters applied to noncommutative quantum cosmology

2019 ◽  
Vol 65 (5 Sept-Oct) ◽  
pp. 519
Author(s):  
J.A. Astorga-Moreno ◽  
E.A. Mena Barboza ◽  
And M.A. García-Aspeitia
Keyword(s):  
Dynamical System ◽  
Cosmological Constant ◽  
Commutation Relation ◽  
Quantum Cosmology ◽  
Positive Cosmological Constant ◽  
Classical Approximation ◽  
Noncommutative Quantum

Using the semi-classical approximation to the Wheeler-DeWitt equation obtained via Arnowitt-Deser-Misner (ADM) formalism in the Friedmann-Lemaitre-Robertson-Walker (FLRW) model coupled to a scalar eld and positive cosmological constant, and in the Kantowski-Sachs (KS) Universe, we introduced a deformation on the commutation relation for the minisuperspace variables and find an explicit semiclassical expression equivalent, in an adequate limit, to the solution with the aid of asymptotically equal functions and the theory of Ultralters, oering a suggestive alternative to sketch the behavior of the dynamical system involved without the need to solve it numerically.

scholarly journals High-order quantum back-reaction and quantum cosmology with a positive cosmological constant

2011 ◽  
Vol 84 (4) ◽  
Author(s):  
Martin Bojowald ◽  
David Brizuela ◽  
Hector H. Hernández ◽  
Michael J. Koop ◽  
Hugo A. Morales-Técotl
Keyword(s):  
Cosmological Constant ◽  
Quantum Cosmology ◽  
High Order ◽  
Back Reaction ◽  
Positive Cosmological Constant

scholarly journals CAUSAL LOOP QUANTUM COSMOLOGY IN MOMENTUM SPACE

2009 ◽  
Vol 18 (01) ◽  
pp. 83-93
Author(s):  
ALI SHOJAI ◽  
FATIMAH SHOJAI
Keyword(s):  
Cosmological Constant ◽  
Momentum Space ◽  
Quantum Cosmology ◽  
Cosmological Solution ◽  
Dynamical Variable ◽  
Loop Quantum Cosmology ◽  
Causal Interpretation ◽  
Causal Loop ◽  
Bohmian Trajectories

We shall show that it is possible to make a causal interpretation of loop quantum cosmology using the momentum as the dynamical variable. We shall show that one can derive Bohmian trajectories. For a sample cosmological solution with cosmological constant, the trajectory is plotted.

scholarly journals On the Geometry of No-Boundary Instantons in Loop Quantum Cosmology

Universe ◽  
2019 ◽  
Vol 5 (1) ◽  
pp. 22 ◽  
Author(s):  
Suddhasattwa Brahma ◽  
Dong-han Yeom
Keyword(s):  
Cosmological Constant ◽  
Path Integral ◽  
Quantum Cosmology ◽  
Einstein Gravity ◽  
Peculiar Feature ◽  
Loop Quantum Cosmology ◽  
Quantum Geometry

We study the geometry of Euclidean instantons in loop quantum cosmology (LQC) such as those relevant for the no-boundary proposal. Confining ourselves to the simplest case of a cosmological constant in minisuperspace cosmologies, we analyze solutions of the semiclassical (Euclidean) path integral in LQC. We find that the geometry of LQC instantons have the peculiar feature of an infinite tail which distinguishes them from Einstein gravity. Moreover, due to quantum-geometry corrections, the small-a behaviour of these instantons seem to naturally favor a closing-off of the geometry in a regular fashion, as was originally proposed for the no-boundary wavefunction.

scholarly journals No smooth beginning for spacetime

2019 ◽  
Vol 28 (02) ◽  
pp. 1930005 ◽  
Author(s):  
Jean-Luc Lehners
Keyword(s):  
Cosmological Constant ◽  
Gravitational Wave ◽  
Path Integral ◽  
Quantum Cosmology ◽  
Path Integrals ◽  
Mathematical Tool ◽  
Positive Cosmological Constant ◽  
Quantum Amplitude ◽  
The Universe

In this paper, I will review an obstruction for theories of the beginning of the universe which can be formulated as semiclassical path integrals. Hartle and Hawking’s no boundary proposal and Vilenkin’s tunneling proposal are examples of such theories. Each may be formulated as the quantum amplitude for obtaining a final 3-geometry by integrating over 4-geometries. The result is obtained using a new mathematical tool — Picard–Lefschetz theory — for defining the semiclassical path integral for gravity. The Lorentzian path integral for quantum cosmology with a positive cosmological constant is mathematically meaningful in this approach, but the Euclidean version is not. Framed in this way, the resulting framework and predictions are unique. Unfortunately, the outcome is that primordial gravitational wave fluctuations are unsuppressed.

scholarly journals Discretization parameter and operator ordering in loop quantum cosmology with the cosmological constant

2011 ◽  
Vol 83 (10) ◽  
Author(s):  
Tomo Tanaka ◽  
Fumitoshi Amemiya ◽  
Masahiro Shimano ◽  
Tomohiro Harada ◽  
Takashi Tamaki
Keyword(s):  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Loop Quantum Cosmology ◽  
Discretization Parameter ◽  
Operator Ordering

scholarly journals Neutral signature gauged supergravity solutions

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
J. Gutowski ◽  
W. A. Sabra
Keyword(s):  
Cosmological Constant ◽  
Geometric Structure ◽  
Base Space ◽  
Killing Spinor ◽  
Positive Cosmological Constant ◽  
3 Dimensional

Abstract We classify all supersymmetric solutions of minimal D = 4 gauged supergravity with (2) signature and a positive cosmological constant which admit exactly one Killing spinor. This classification produces a geometric structure which is more general than that found for previous classifications of N = 2 supersymmetric solutions of this theory. We illustrate how the N = 2 solutions which consist of a fibration over a 3-dimensional Lorentzian Gauduchon-Tod base space can be written in terms of this more generic geometric structure.

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