Seminars

Winter term 2019/20


 

Quantum phase-field: from de Broglie–Bohm double solution program to doublon networks

Abstract: We study different variants of linear and non-linear field equations, so-called ‘phase-field’ equations, in application to the de Broglie–Bohm double solution program. This defines a framework in which elementary particles are described by peaked non-linear wave solutions moving by the quidance of a linear pilot wave. First, we consider the phase-field order parameter as a phase for the pilot wave, second as the pilot wave, third as a moving soliton which describes the particle. In the last case, we intoduce a superwave which amplitude is responsible for the particle moving in accordance to the de Broglie–Bohm theory. Lax pairs for the coupled problems are found in order to discover the phase-field equations and to draw analogies to the de Broglie–Bohm double solution program. Finally, doublons in 1+1 dimensions are constructed as self similar solutions of a non-linear phase-field equation. The doublons set the frame for a Schrödinger type linear wave equation determining the energetics of the coupled system. Applying a conservation constraint and using general symmetry considerations the doublons are arranged as a network in 1+1+2 dimensions where nodes are interpreted as elementary particles.

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Quantum creation of a universe-antiuniverse pair

Abstract: The creation of two universes, one contracting and another expanding, filled with matter can also be interpreted as the creation of two expanding universes, one of them filled with matter and the other filled with antimatter, forming a universe-antiuniverse pair. In that case, the total amount of matter and antimatter in the two universes is completely balanced, restoring the (apparent) matter-antimatter asymmetry observed in each single universe. Furthermore, the creation of universes in pairs would entail observational consequences, perhaps distinguishable, in the properties of the CMB of a universe like ours, making testable the whole multiverse proposal.

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Spatial curvature of cosmic structures

Abstract: Curvature of spatial hyper-surfaces is usually considered in the context of globally homogeneous cosmological models, however it can also play a non-negligible role below the scale of homogeneity. Relativistic Lagrangian perturbations allow us to get insight into mildly non-linear stages of structure formation, substantially exceeding the standard Eulerian regime. In my talk, I will mainly focus on the spatial curvature estimates utilizing the Relativistic Zel'dovich approximation which is the first order solution to Einstein equations in Lagrangian form. Several theoretical and numerical results will be presented including the value of scalar curvature and averaged scalar curvature at the turnaround epoch for a wide set of initial conditions. Potential observational consequences will be put into perspective.

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Quantum black hole structure with the Event Horizon Telescope, an overview of S. Gidding's paper

Abstract: We will review the ideas presented in and motivating the paper “Searching for quantum black hole structure with the Event Horizon Telescope” (Giddings, arXiv:1904.05287) and give a brief overview of possible perturbations for the EHT image presented in “Event Horizon Telescope Observations as Probes for Quantum Structure of Astrophysical Black Holes” (Giddings and Psaltis, arXiv:1606.07814).

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On the factor ordering problem in Quantum Cosmology

Abstract: Choosing the three metric as a configuration variable and applying the Dirac quantization method to general relativity leads to Quantum Geometrodynamics. The main equations of the theory are the Wheeler–DeWitt equation and the quantized version of the diffeomorphism constraints. Apart from technical issues (the Wheeler–DeWitt equation is ill-defined) the canonical quantization reveals some conceptual problems. These are most prominently the problem of time, the Hilbert space problem and the factor ordering problem. All of these problems are in fact intimately connected.

The symmetry reduction to spatially homogeneous cosmological models, the so called minisuperspace models, provides us with mechanical system analogues of full general relativity. Hence the application of Dirac quantization yields quantum mechanical analogues of Quantum Geometrodynamics. This allows us, among other things, to address the problems encountered in the full theory in a simplified setup.

In this talk I will introduce a generalized mechanical system endowed with the main features of a typical minisuperspace model. We study the geometry of this model and pave the way for the canonical quantization of the system. Our main focus will be on the factor ordering problem.

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On the construction of diffeomorphism-invariant observables

Abstract: We describe a method of construction of gauge-invariant operators (Dirac observables or “evolving constants of motion”) from the knowledge of the eigenstates of the gauge generator of time-reparametrisation invariant mechanical systems. These invariant operators evolve unitarily with respect to an arbitrarily chosen time variable. We emphasise that the dynamics is relational, both in the classical and quantum theories. In this framework, we show how the “emergent WKB time” often employed in quantum cosmology arises from a weak-coupling expansion of invariant transition amplitudes, and we illustrate an example of singularity avoidance in a vacuum Bianchi I (Kasner) model.

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Quantum gravitational computations in de Sitter

Abstract: Inflation is an extremely efficient particle collider. Particles up to Hubble energies (roughly 1014 GeV) can be excited, giving us the chance to explore a vast particle spectrum. A common feature of all the inflationary models is that they predict at least 2 massless particles: The so-called comoving curvature perturbation ζ and the graviton field. The corresponding primordial power spectra as well as the non-gaussian correlators of these fields are a central topic of study nowadays in cosmology. In the current talk, some issues related to quantum loop corrections to these tree level results will be discussed. In particular, the focus will be mostly on the interaction (computations performed at 1-loop order) between gravitons and scalar fields in an exact de Sitter background.

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Date Time Speaker Topic Room
October 8, 2019 12:00 Leonardo Chataignier
(Universität zu Köln)
Conference report Konferenzraum 1 (Neubau)
October 15 12:00 Ingo Steinbach
(Ruhr-Universität Bochum)
Quantum phase-field: from de Broglie–Bohm double solution program to doublon networks Konferenzraum 1 (Neubau)
October 22 12:00 Salvador Robles-Pérez
(Estación Ecológica de Biocosmología de Medellín (Spain))
Quantum creation of a universe-antiuniverse pair Konferenzraum 1 (Neubau)
November 5 12:00
Literature seminar: Quantum information in quantum gravity Konferenzraum 1 (Neubau)
November 19 12:00 Jan J. Ostrowski
(Narodowe Centrum Badań Jądrowych, Warsaw)
Spatial curvature of cosmic structures Konferenzraum 1 (Neubau)
November 26 12:00 Alexander Hermanns
(Universität zu Köln)
Quantum black hole structure with the Event Horizon Telescope, an overview of S. Giddings' paper Konferenzraum 1 (Neubau)
December 3 12:00 Nick Kwidzinski
(Universität zu Köln)
On the factor ordering problem in Quantum Cosmology Konferenzraum 1 (Neubau)
December 10 12:00 Leonardo Chataignier
(Universität zu Köln)
On the construction of diffeomorphism-invariant observables Konferenzraum (Altbau)
December 17 12:00 Claus Kiefer
(Universität zu Köln)
Conference Report and Beyond Konferenzraum 1 (Neubau)
January 21, 2019 12:00 Vasilis Fragkos
(Universiteit Utrecht)
Quantum gravitational computations in de Sitter Konferenzraum 1 (Neubau)

 


Past seminars


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