| 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) |
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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| October 22 |
12:00 |
Salvador Robles-Pérez
(Estación Ecológica de Biocosmología de Medellín (Spain))
|
Quantum creation of a universe-antiuniverse pair
|
Konferenzraum 1 (Neubau) |
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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| 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) |
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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| 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) |
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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| December 3 |
12:00 |
Nick Kwidzinski
(Universität zu Köln)
|
On the factor ordering problem in Quantum Cosmology
|
Konferenzraum 1 (Neubau) |
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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| December 10 |
12:00 |
Leonardo Chataignier
(Universität zu Köln)
|
On the construction of diffeomorphism-invariant observables
|
Konferenzraum (Altbau) |
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.
Close
| December 17 |
12:00 |
Claus Kiefer
(Universität zu Köln)
|
Conference Report and Beyond
|
Konferenzraum 1 (Neubau) |
| January 14, 2019 |
12:00 |
Yi-Fan Wang
(Universität zu Köln)
|
Towards a classical correspondence of wave packets in quantum cosmology
|
Konferenzraum 1 (Neubau) |
Quantum gravitational computations in de Sitter
Abstract:
In Wheeler–DeWitt quantum cosmology, a classical universe can
emerge from a realistic wave function at a suitable scale. It has been
argued that such wave functions are strongly peaked around classical
solutions; in other words, the ridgeline of a physical wave packet
corresponds to a classical solution.
We give quantitative descriptions of the ridge-line of a wave packet.
With explicit examples of wave packets, it is shown that ridgelines can
deviate from classical trajectories at classical scales. Possible
interpretations are discussed.
Close
| January 21 |
12:00 |
Vasilis Fragkos
(Universiteit Utrecht)
|
Quantum gravitational computations in de Sitter
|
Konferenzraum 1 (Neubau) |
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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| January 28 |
12:00 |
Artur Miroszewski
(Narodowe Centrum Badań Jądrowych, Warsaw)
|
Perturbations on a quantum cosmological spacetime
|
Konferenzraum 1 (Neubau) |
Perturbations on a quantum cosmological spacetime
Abstract:
With the use of canonical General Relativity and coherent state
quantisation procedure one obtains a quantum model of spacetime. For
cosmological spacetimes such models produce singularity avoidance
scenarios, resulting in a smooth evolution of the universe undergoing
the Big Bounce. Introducing quantum perturbations to the quantum
cosmological spacetime allows to consider interesting observables such
as primordial amplitude spectra, and to study how they are influenced by
genuinely quantum properties of the cosmological background. Discussed
theoretical effects may in principle probe the quantum era of the
universe and should be further developed.
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