DILATON INDUCED QUANTUM INFLATION-COMPACTIFICATION AND POSSIBILITY OF TRANSITION TO CLASSICAL ERA

1994 ◽  
Vol 09 (13) ◽  
pp. 1141-1150 ◽  
Author(s):  
E.I. GUENDELMAN ◽  
A.B. KAGANOVICH
Keyword(s):  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Cosmic Time ◽  
Higher Dimensions ◽  
Classical Description ◽  
Negative Cosmological Constant ◽  
Inflationary Phase ◽  
Superstring Theories

In many interesting models, including superstring theories, a vacuum with negative cosmological constant is predicted. For quantum cosmology (in higher dimensions) in the presence of coherent dilaton excitations and a negative cosmological constant, the role of cosmic time can be understood and we can then predict the existence of a “quantum inflationary phase” for some dimensions and a simultaneous “quantum deflationary phase” for the remaining dimensions. We discuss qualitatively how it may be possible to exit from this inflation-compactification era and give an example which involves a transition to a phase with zero cosmological constant which allows a classical description at late times.

COSMIC TIME IN QUANTUM COSMOLOGY: INFLATION-COMPACTIFICATION AS A QUANTUM EFFECT

1993 ◽  
Vol 02 (02) ◽  
pp. 221-247 ◽  
Author(s):  
E.I. GUENDELMAN ◽  
A.B. KAGANOVICH
Keyword(s):  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Quantum Effect ◽  
Cosmic Time ◽  
Expectation Values ◽  
Cosmological Singularity ◽  
Inflationary Phase ◽  
Definition Of ◽  
The Universe ◽  
Kaluza Klein

We consider 1+D-dimensional, toroidally compact Kaluza-Klein theories. In the context of the minisuperspace approach of quantum cosmology, we solve the Wheeler-DeWitt equation in the presence of a negative cosmological constant and dust. Then, it is found that the quantum effects stabilize the volume of the Universe, so that there can be an avoidance of the cosmological singularity. Although cosmic time does not appear explicitly in the Wheeler-DeWitt equation, we find that a cosmic time dependence appears for the expectation values of certain variables. This result is obtained when proper care of some subtle points concerning the definition of averages in this model is taken. The stabilization of the volume, when there is anisotropy in the evolution of the Universe (which turns out to be quantized), is consistent with another effect we find: the existence of a “quantum inflationary phase” for some dimensions and simultaneously the existence of a “quantum deflationary contraction” for the rest.

scholarly journals Global monopole metric in 2 + 1 dimensions

2019 ◽  
Vol 16 (01) ◽  
pp. 1950006
Author(s):  
S. Habib Mazharimousavi ◽  
M. Halilsoy
Keyword(s):  
Exact Solution ◽  
Cosmological Constant ◽  
Electric Charge ◽  
Radial Distance ◽  
Series Solutions ◽  
Global Monopole ◽  
Negative Cosmological Constant ◽  
Consistent Manner ◽  
Positive Integers

In order to obtain the geometry of a global monopole without cosmological constant and electric charge in [Formula: see text] dimensions, we make use of the broken [Formula: see text] symmetry. In the absence of an exact solution, we determine the series solutions for both the metric and monopole functions in a consistent manner that satisfies all equations in appropriate powers. The new expansion elements are of the form [Formula: see text] for the radial distance [Formula: see text] and positive integers [Formula: see text] and [Formula: see text] constrained by [Formula: see text]. To the lowest order of expansion, we find that in analogy with the negative cosmological constant the geometry of the global monopole acts repulsively, i.e. in the absence of a cosmological constant the global monopole plays at large distances the role of a negative cosmological constant.

EARLY HOMOGENEOUS UNIVERSE WITH VARIABLE COSMOLOGICAL CONSTANT: KINEMATICS TESTS

2007 ◽  
Vol 22 (13) ◽  
pp. 2415-2431 ◽  
Author(s):  
C. P. SINGH
Keyword(s):  
Cosmological Constant ◽  
Cosmic Time ◽  
Field Equations ◽  
Variable Cosmological Constant ◽  
Angular Diameter Distance ◽  
Proper Distance ◽  
Inflationary Phase ◽  
Homogeneous Universe ◽  
Gamma Law ◽  
The Look

A spatially homogeneous cosmological model with flat geometry filled with perfect fluid is studied in the presence of a variable cosmological "constant." Einstein's field equations are solved by using the "gamma-law" equation of state p = (γ-1)ρ, where the adiabatic parameter γ, varies with cosmic time. The functional form of γ, which is assumed to be the function of scale factor R as proposed by Carvalho, is used to describe the early evolution of universe with variable cosmological "constant." A unified description of early universe is given in which an inflationary phase is followed by radiation-dominated phase. It has been observed that the solutions are compatible with the result of recent observations. Exact expressions for the look-back time, proper distance, luminosity distance and angular diameter distance versus redshift are derived and their meaning are discussed in detail. The various physical aspects of the models are also discussed.

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.

“Stationary” Schrödinger equation in quantum cosmology

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040040
Author(s):  
N. Gorobey ◽  
A. Lukyanenko ◽  
A. Shavrin
Keyword(s):  
Energy Density ◽  
Quantum Cosmology ◽  
Quantum Dynamics ◽  
Harmonic Approximation ◽  
Cosmic Time ◽  
Positive Functional ◽  
The Universe ◽  
Principle Of Extremum ◽  
Extremum Conditions

The conditional principle of extremum in quantum cosmology is formulated for a positive functional of the energy density of space, in which gravitational constraints serve as additional conditions. The extremum conditions determine the discrete spectrum of the “stationary” state of the universe with the corresponding values of the energy density of space. A dynamic interpretation of solutions is proposed, in which the quantum number of the energy density plays the role of cosmic time. In the self-consistent harmonic approximation, the quantum dynamics of the anisotropic model of the Bianchi IX universe is considered.

scholarly journals Bootstrapped Newtonian Cosmology and the Cosmological Constant Problem

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 358
Author(s):  
Roberto Casadio ◽  
Andrea Giusti
Keyword(s):  
Black Holes ◽  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Quantum Physics ◽  
Gravitational Interaction ◽  
Newtonian Gravity ◽  
Cosmological Constant Problem ◽  
Newtonian Cosmology ◽  
Natural Solution ◽  
The Impact

Bootstrapped Newtonian gravity was developed with the purpose of estimating the impact of quantum physics in the nonlinear regime of the gravitational interaction, akin to corpuscular models of black holes and inflation. In this work, we set the ground for extending the bootstrapped Newtonian picture to cosmological spaces. We further discuss how such models of quantum cosmology can lead to a natural solution to the cosmological constant problem.

scholarly journals The role of mergers and interactions in driving the evolution of dwarf galaxies over cosmic time

2020 ◽  
Vol 500 (4) ◽  
pp. 4937-4957 ◽  
Author(s):  
G Martin ◽  
R A Jackson ◽  
S Kaviraj ◽  
H Choi ◽  
J E G Devriendt ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Large Fraction ◽  
Structural Evolution ◽  
Cosmic Time ◽  
Stellar Mass ◽  
High Mass ◽  
Key Drivers ◽  
Mass Assembly

ABSTRACT Dwarf galaxies (M⋆ < 109 M⊙) are key drivers of mass assembly in high-mass galaxies, but relatively little is understood about the assembly of dwarf galaxies themselves. Using the NewHorizon cosmological simulation (∼40 pc spatial resolution), we investigate how mergers and fly-bys drive the mass assembly and structural evolution of around 1000 field and group dwarfs up to z = 0.5. We find that, while dwarf galaxies often exhibit disturbed morphologies (5 and 20 per cent are disturbed at z = 1 and z = 3 respectively), only a small proportion of the morphological disturbances seen in dwarf galaxies are driven by mergers at any redshift (for 109 M⊙, mergers drive under 20 per cent morphological disturbances). They are instead primarily the result of interactions that do not end in a merger (e.g. fly-bys). Given the large fraction of apparently morphologically disturbed dwarf galaxies which are not, in fact, merging, this finding is particularly important to future studies identifying dwarf mergers and post-mergers morphologically at intermediate and high redshifts. Dwarfs typically undergo one major and one minor merger between z = 5 and z = 0.5, accounting for 10 per cent of their total stellar mass. Mergers can also drive moderate star formation enhancements at lower redshifts (3 or 4 times at z = 1), but this accounts for only a few per cent of stellar mass in the dwarf regime given their infrequency. Non-merger interactions drive significantly smaller star formation enhancements (around two times), but their preponderance relative to mergers means they account for around 10 per cent of stellar mass formed in the dwarf regime.

scholarly journals Coherence Effects in Multiple Medium-Induced Radiation

Proceedings ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 11
Author(s):  
Fabio Dominguez ◽  
Jose Guilherme Milhano ◽  
Carlos A. Salgado ◽  
Konrad Tywoniuk ◽  
Victor Vila
Keyword(s):  
Time Scales ◽  
Survival Probability ◽  
Jet Quenching ◽  
Close Correspondence ◽  
Gluon Emission ◽  
Classical Description ◽  
Theoretical Support ◽  
Coherence Effects ◽  
Hard Gluon

In the first part of this work we study the color coherence phenomenon by considering the well-known quark-antiquark antenna with an in-medium hard gluon emission and an extra very soft emission outside it—double antenna. By discussing the coherence effects in terms of the survival probability, we generalize previous studies of the antenna radiation to the case of more than two emitters. After providing support to the jet quenching picture with effective emitters in the QCD cascade, we present a novel setup of an antenna splitting inside the medium taking into account the finite formation time of the dipole, which turns out to be an important scale. We read into the role of coherence and the relevant time scales which control the scenario, while also providing theoretical support for vacuum-like emissions early in the medium. Finally, by mapping the spectrum of in-medium splittings through the corresponding kinematical Lund diagram, we appreciate regimes of a close correspondence to a semi-classical description.

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