The Universe emerging from a vacuum in loop–string cosmology

Mielczarek, Jakub; Szydłowski, Marek

doi:10.1088/1475-7516/2008/08/014

Cited by 3 publications

(2 citation statements)

References 36 publications

(62 reference statements)

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“…A phenomenological study based on exporting the non-perturbative quantum gravitational effects as understood in LQC to these models reveals that this problem can be successfully resolved both in the Einstein and the Jordan frame without any fine tuning of the initial conditions [197]. Similar results have been derived in the presence of a positive potential [198]. Thus, modified FLRW dynamics in LQC alleviates a major problem of the pre-big-bang scenarios and provides a clear insight on the form of the required non-perturbative terms from higher order effective actions in the string cosmologies.…”

Section: E Summary Of Other Applicationssupporting

confidence: 53%

Loop quantum cosmology: a status report

Ashtekar¹,

Singh²

2011

Class. Quantum Grav.

1,057

1,741

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Loop quantum cosmology (LQC) is the result of applying principles of loop quantum gravity (LQG) to cosmological settings. The distinguishing feature of LQC is the prominent role played by the quantum geometry effects of LQG. In particular, quantum geometry creates a brand new repulsive force which is totally negligible at low space-time curvature but rises very rapidly in the Planck regime, overwhelming the classical gravitational attraction. In cosmological models, while Einstein's equations hold to an excellent degree of approximation at low curvature, they undergo major modifications in the Planck regime: For matter satisfying the usual energy conditions any time a curvature invariant grows to the Planck scale, quantum geometry effects dilute it, thereby resolving singularities of general relativity. Quantum geometry corrections become more sophisticated as the models become richer. In particular, in anisotropic models there are significant changes in the dynamics of shear potentials which tame their singular behavior in striking contrast to older results on anisotropies in bouncing models. Once singularities are resolved, the conceptual paradigm of cosmology changes and one has to revisit many of the standard issues -e.g., the 'horizon problem'-from a new perspective. Such conceptual issues as well as potential observational consequences of the new Planck scale physics are being explored, especially within the inflationary paradigm. These considerations have given rise to a burst of activity in LQC in recent years, with contributions from quantum gravity experts, mathematical physicists and cosmologists.The goal of this article is to provide an overview of the current state of the art in LQC for three sets of audiences: young researchers interested in entering this area; the quantum gravity community in general; and, cosmologists who wish to apply LQC to probe modifications in the standard paradigm of the early universe. An effort has been made to streamline the material so that each of these communities can read only the sections they are most interested in, without a loss of continuity. * Electronic address: ashtekar@gravity.psu.edu † Electronic address: psingh@phys.lsu.eduAs before, C H and the symplectic structure are insensitive to the choice ofq ab but they do

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Section: E Summary Of Other Applicationssupporting

confidence: 53%

Loop quantum cosmology: a status report

Ashtekar¹,

Singh²

2011

Class. Quantum Grav.

1,057

1,741

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“…The gravitationally bound quantum systems cannot be considered within the only approach, which may be a manifestationm of the general pattern of a future theory [25], wherein one succeeds in a transition to the next stage of solving the gravity quantization problem.…”

Section: Discussionmentioning

confidence: 99%

Quantization of Gravitationally Bound Systems

Fil'chenkov

Laptev

2021

Universe

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Some of the approaches to quantization in gravity theory concerning gravitationally bound systems are considered. Grades of quantization applicable to these systems have been classified in terms of quantum mechanics, quantum field theory, and quantum geometrodynamics. Energy levels for the graviatom, Lemaître’s atom, quantum gravitational collapse have been calculated, and relationships for the masses of bound system components, as well as Universe’s birth probabilities, are presented to exemplify the properties of gravitationally bound systems. Objects and processes in them have been analyzed to construct quantum models of compact astrophysical objects and the early Universe.

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Multi-fluid potential in the loop cosmology

Mielczarek¹

2009

Physics Letters B

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The scalar field can behave like a fluid with equation of state $p_{\phi}=w\rho_{\phi}$, where $w \in [-1,1]$. In this Letter we derive a class of the scalar field potentials for which $w=$ const. Scalar field with such a potential can mimic ordinary matter, radiation, cosmic strings, etc. We perform our calculations in the framework of the loop cosmology with holonomy corrections. We solve the model analytically for the whole parameter space. Subsequently, we perform similar consideration for the model with a phantom field ($w<-1$). We show that scalar field is monotonic function in both cases. This indicates that it can be treated as a well-defined internal time for these models. Moreover we perform preliminary studies of the scalar field perturbations with this potential. We indicate that non-Gaussian features are present admitting for the possible observational constraints of the model.Comment: 6 pages, 6 figures, new section on perturbations added. Version to appear in PL

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The Universe emerging from a vacuum in loop–string cosmology

Cited by 3 publications

References 36 publications

Loop quantum cosmology: a status report

Loop quantum cosmology: a status report

Quantization of Gravitationally Bound Systems

Multi-fluid potential in the loop cosmology

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