| Date |
Time |
Speaker |
Topic |
Room |
| April 21, 2020 |
11:30 |
Ali Lezeik
(Universität zu Köln)
|
Bryce DeWitt, Quantum Theory of Gravity I: The Canonical Theory, 1967. doi:10.1103/PhysRev.160.1113
|
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| April 28 |
11:30 |
Christina Koliofoti
(Universität zu Köln)
|
Volume average regularisation of the Wheeler–DeWitt equation
|
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Volume average regularisation of the Wheeler–DeWitt equation
Abstract:
One of the most important canonical approaches to quantum gravity is through the Wheeler–DeWitt equation. However, the theory, being a second order differential equation of a functional, produces delta functions and derivates of delta functions which lead to infinities. Thus a regularization of this term is needed. In this presentation I will discuss the approach of Justin C. Feng for the regularization of the Wheeler–DeWitt equation, the volume average regularization (arxiv.org/abs/1802.08576v3). For this I will go through some mathematical basics of functional calculus as well as some ground work to arrive to the Wheeler–DeWitt equation. The main idea of the paper will be discussed, which is performing an integral average of the second functional derivative part of the Wheeler–DeWitt equation over a finite volume. This is justified when we consider quantum general relativity as a low-energy effective field theory of the full theory of quantum gravity. That regularization will lead to an approximate solution of the Wheeler–DeWitt equation for the low-curvature, long-distance limit.
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| May 5 |
11:30 |
Nick Kwidzinski
(Universität zu Köln)
|
Singularity avoidance in Wheeler–DeWitt quantum cosmology
|
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| May 12 |
11:30 |
Sandeep Suresh
(Universität zu Köln)
|
Commutation relations for currents of RC space, Sugawara Model, Schwinger disease and Anomalies
|
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| May 19 |
11:30 |
Group members
(Universität zu Köln)
|
Progress report
|
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| May 26 |
11:30 |
Tejinder Pal Singh
(Tata Institute, Mumbai)
|
The theory of spontaneous quantum gravity
|
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The theory of spontaneous quantum gravity
Abstract:
Starting from classical general relativity coupled to matter, we raise the
canonical variables to the status of operators. These matrix-valued
dynamical variables obey a Lagrangian dynamics invariant under global
unitary transformations, and there is no distinction between space-time and
matter degrees of freedom. This deterministic matrix dynamics is assumed to
hold at the Planck scale, and the Hamiltonian of the theory is not
restricted to be self-adjoint. When this dynamics is
coarse-grained over time scales much larger than Planck time, there emerge
quantum commutation relations, and a theory of quantum general relativity.
If a very large number of degrees of freedom get entangled, the emergent
theory reduces to classical general relativity on a Riemannian space-time
manifold. The unentangled d.o.f. obey the rules of quantum field theory on a
classical background. This matrix dynamics provides a dynamical explanation
for the quantum-to-classical transition, and makes predictions for
black-hole entropy and dark energy. In our theory, quantum indeterminism is
shown to be a consequence of
coarse-graining the underlying deterministic matrix dynamics.
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| Jun 2 |
11:30 |
Leonardo Chataignier
(Universität zu Köln)
|
Relational observables, reference frames and conditional probabilities
|
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Relational observables, reference frames and conditional probabilities
Abstract:
We discuss the construction of relational observables in time-reparametrisation invariant quantum mechanics and we argue that their physical interpretation can be understood in terms of conditional probabilities, which are defined from the solutions of the quantum constraint equation in a generalisation of the Page-Wootters formalism. In this regard, we show how conditional expectation values of worldline tensor fields are related to quantum averages of suitably defined relational observables. We also comment on how the dynamics of these observables can be related to a notion of quantum reference frames. Based on https://arxiv.org/abs/2006.05526 .
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| Jun 9 |
11:30 |
Tatevik Vardanyan
(Universität zu Köln)
|
Inflation in a closed model of universe
|
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| Jun 23 |
11:30 |
Tim Schmitz
(Universität zu Köln)
|
Quantum Oppenheimer–Snyder model
|
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Quantum Oppenheimer–Snyder model
Abstract:
We construct two reduced quantum theories for the Oppenheimer–Snyder
model, respectively taking the point of view of the comoving and the
exterior stationary observer, using affine coherent states
quantization. Investigations of the quantum corrected dynamics reveal
that both observers can see a bounce, although for the exterior
observer certain quantization ambiguities have to be chosen correctly.
The minimal radius for this bounce as seen from the stationary
observer is then shown to always be outside of the photon sphere.
Possible avenues to lower this minimal radius and reclaim black holes
as an intermediate state in the collapse are discussed. We demonstrate
further that switching between the observers at the level of the
quantum theories can be achieved by modifying the commutation relations.
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| Jun 30 |
11:30 |
Nick Kwidzinski
(Universität zu Köln; disputation)
|
Quantum Fate of Singularities in Anisotropic Cosmological Models
|
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| Jul 7 |
11:30 |
Alexander Kamenshchik
(Università di Bologna)
|
Exact solutions in General Relativity, Kasner universes and singularities
|
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Exact solutions in General Relativity, Kasner universes and singularities
Abstract:
We find exact static solutions of the Einstein equations in the
spacetime with plane symmetry, where an infinite slab with finite
thickness and homogeneous energy (mass) density is present. In the first
solution the pressure is isotropic, while in the second solution the
tangential components of the pressure are equal to zero. In both cases the
pressure vanishes at the boundaries of the slab. Outside the slab these
solutions are matched with the Rindler spacetime and with the
Weyl-Levi-Civita spacetime, which represent special cases of the Kasner
solution. We construct also the third solution of this type. We also show
that there are solutions that can be matched with general anisotropic
Kasner spacetime outside the slab. In any case, it is impossible to avoid
the presence of the Kasner type singularities in contrast to the
well-known case of spherical symmetry, where by matching the internal
Schwarzschild solution with the external one, the singularity in the
center of coordinates can be eliminated.
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| Jul 21 |
11:30 |
Manuel Krämer
(Katholieke Universiteit Leuven)
|
Quantum cosmology of Starobinsky inflation revisited
|
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Quantum cosmology of Starobinsky inflation revisited
Abstract:
In this talk, I will present the canonical quantization of a minisuperspace model of Starobinsky inflation in the Einstein frame formulation. The resulting Wheeler–DeWitt equation is solved using a Born–Oppenheimer approximation and I will discuss the implications of the quantization for the evolution of the universe in this model.
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| Sept 8 |
12:00 |
Group members
(Universität zu Köln)
|
Progress report
|
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| Sept 15 |
11:30 |
Sandeep Suresh
(Universität zu Köln)
|
Sugawara construction for spin currents and quantum corrections to spin current algebra due to U(1) gauge fields
|
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| Sept 22 |
11:30 |
Tatevik Vardanyan
(Universität zu Köln; master colloquium)
|
Quantum-gravitational effects for inflationary scalar perturbations in a model for a closed universe
|
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| Sept 29 |
11:30 |
Leonardo Chataignier
(Universität zu Köln)
|
Unitarity of quantum-gravitational corrections to primordial fluctuations in the Born–Oppenheimer approach
|
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Unitarity of quantum-gravitational corrections to primordial fluctuations in the Born–Oppenheimer approach
Abstract:
We revisit the calculation of quantum-gravitational corrections to the power spectra of scalar and tensor perturbations in the Born-Oppenheimer approach to quantum gravity. We focus on the issue of the definition of the inner product of the theory and the unitarity of the corrections to the dynamics of the cosmological perturbations. We argue that the correction terms are unitary, provided the inner product is defined in a suitable way, which can be related to a notion of gauge-fixing the time variable and the use of conditional probabilities in quantum cosmology. We compare the corrections obtained within this framework to earlier results in the literature and we conclude with some remarks on the physical interpretation of the correction terms.
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