| Date |
Time |
Speaker |
Topic |
Room |
| March 15 |
12:00 |
Nick Kwindzinski
|
Classical and quantum cosmology of Born-Infeld type models
|
Konferenzraum 1 (Neubau) |
Classical and quantum cosmology of Born-Infeld type models
Abstract: In this master colloquium we are going to explore the cosmology of Born-Infeld type models. We
will first review the classical cosmology of these models and extend the discussion with a particular focus on the
singularities occurring in the models with an inverse square potential. Afterwards we shall study the quantum cosmology
in which we employ the framework of quantum geometrodynamics. The quantization of these models is quite challenging since
the Hamiltonian constraints contain square roots over the phase space variables. We work around this problem by using canonical
transformations. By doing so we derive the Wheeler-DeWitt equations for the constant and inverse square potential and analyze their solutions.
For a general potential the Wheeler-DeWitt equation can be brought into the form of a difference equation. We derive these
difference equations and discuss the form of their solutions.
Close
| March 22 |
12:00 |
Oleg Zaslavskii (Kharkov University)
|
High energy particle collisions near black holes and super-Penrose process
|
Konferenzraum 1 (Neubau) |
| April 12 |
12:00 |
Maxim Eingorn
|
First-order cosmological perturbations produced by point-like masses: all scales covered
|
Konferenzraum 1 (Neubau) |
First-order cosmological perturbations produced by point-like masses: all scales covered
Abstract:
In the framework of the concordance cosmological model the first-order scalar and vector
perturbations of the homogeneous background are derived without any supplementary
approximations in addition to the weak gravitational field limit. The sources of these
perturbations (inhomogeneities) are presented in the discrete form of a system of separate point-like gravitating masses. The obtained expressions for the metric corrections are valid at all (sub-horizon and super-horizon) scales and converge in all points except the locations of the sources,
and their average values are zero (thus, first-order backreaction effects are absent). Both the
Minkowski background limit and the Newtonian cosmological approximation are reached under
certain well-defined conditions. An important feature of the velocity-independent part of the
scalar perturbation is revealed: up to an additive constant it represents a sum of Yukawa
potentials produced by inhomogeneities with the same finite time-dependent Yukawa interaction
range. The suggesting itself connection between this range and the homogeneity scale is briefly
discussed along with other possible physical implications.
Close
| April 19 |
12:00 |
Jonnathan Onody
|
The Pais-Uhlenbeck Oscillator and its Application in Quantum Cosmology
|
Konferenzraum 1 (Neubau) |
The Pais-Uhlenbeck Oscillator and its Application in Quantum Cosmology
Abstract:
The Pais-Uhlenbeck oscillator, a simple model for theories with higher
order derivatives, is discussed classically and quantum-mechanically.
Then, tensorial perturbations in Einstein plus Conformal Gravity for a
flat Friedmann universe are investigated. The quantization scheme of the
Pais-Uhlenbeck oscillator is applied and it is shown that the evolution
of perturbations may be connected to the case of conformal coupling of
scalar field to a closed Friedmann universe, which is dealt with before.
Close
| April 19 |
12:45 |
Nick Kwidzinski
|
The classical har monic chain: solution via Laplace transforms and continued fractions
|
Konferenzraum 1 (Neubau) |
The classical harmonic chain: solution via Laplace transforms and continued fractions
Abstract: The harmonic chain is a classical many-particle system which can be
solved exactly for arbitrary number of particles (at least in simple cases, such as equal masses and spring constants). A nice
feature of the harmonic chain is that the final result for the displacements of the individual particles can be easily
understood -- therefore, this example fits well into a course of classical mechanics for undergraduates.
Here we show how to calculate the displacements by solving equations of motion for the Laplace transforms
of the displacements. This leads to a continued fraction representation of the Laplace transforms which can be evaluated
analytically. The inverse Laplace transform finally gives the displacements which generically have the form of Bessel functions. We also comment on the similarities between this
approach and the Green function method for quantum many-particle systems.
Close
| April 26 |
12:00 |
Silvia De Bianchi (Universitat Autònoma de Barcelona)
|
Why is the world four-dimensional? Hermann Weyl's 1955 argument and the
topology of causation
|
Konferenzraum 1 (Neubau) |
Why is the world four-dimensional? Hermann Weyl's 1955 argument and the
topology of causation
Abstract: Hermann Weyl asked the question of the dimensionality of the world
in the manuscript of a lecture entitled "Why is the world four-dimensional?" (1955).
In this talk, I shall spell out Weyl's argument and its main features. After rejecting
any theological explanation of the dimensionality of the world, Weyl evaluates the fact
that the Riemannian manifold is not bound to the special dimensionality 4, and as far
as this metrical structure goes, any other dimension would do just as well.
However, in Weyl's view, the question of the four-dimensionality of the world will rest
unanswered if we do not introduce a possible explanation by appealing to what he calls
a "topology of causation". I will clarify why Weyl thought that a solution to the question
of the dimensionality of the world could come from topology and which kind of implications
Weyl's approach have in recent history and philosophy of physics.
Close
| May 3 |
12:00 |
Anupam Mazumdar (Lancaster University)
|
Construction of Asymptotically Free Theory of Gravity
|
Konferenzraum 1 (Neubau) |
Construction of Asymptotically Free Theory of Gravity
Holes
Abstract: I will discuss how to construct infinite derivative theory of Gravity which can be made Ghost Free and also
Singularity Free (from Cosmological and Blackhole type singularities). I will also discuss quantum aspects of the problem
and how one can obtain a finite theory in the ultraviolet, and discuss similar construction around deSitter and Anti-deSitter
backgrounds.
Close
| May 10 |
12:00 |
Swastik Bhattacharya (Trivandrum, India)
|
Fluctuations and Transport Phenomena in Horizon-Fluids for Black
Holes
|
Konferenzraum 1 (Neubau) |
Fluctuations and Transport Phenomena in Horizon-Fluids for Black
Holes
Abstract: It is well-known that the Black Hole horizon obeys the equation of motion
for a viscous fluid. A statistical model of this fluid can help us obtain some insight into the
thorny problems of the microscopic Black Hole degrees of freedom and Black Hole entropy. In
this talk, we shall take this fluid to be of a physical origin and construct a Theory of
Fluctuations for it. In particular, I shall show that the Langevin equation governing the energy transported
from outside into the horizon-fluid corresponds to the Raychaudhuri equation for the null
congruences on the Black Hole horizon. We shall also briefly outline a method, that uses the Kubo formula
to compute the coefficient of Bulk Viscosity of the Horizon fluid. We shall show that this comes out to
be negative due to the teleological nat ure of the Black Hole event horizon.Finally, I shall
briefly outline how it is possible to have a statistical mechanical understanding of the negative specific heat of
Black Holes in a similar manner.
Close
| May 24 |
12:00 |
Branislav Nikolic
|
Conformal (Weyl rescaling) symmetry: scales vanish without a trace!
|
Konferenzraum 1 (Neubau) |
Conformal (Weyl rescaling) symmetry: scales vanish without a trace!
Abstract: In this pedagogical talk, I will demonstrate on an example of a non-minimally coupled scalar field
that conformal (local Weyl) rescaling symmetry implies vanishing of
the scale (i.e. 3-volume, determinant of the 3-metric, or 'intrinsic time') and
the trace of the extrinsic curvature, making them arbitrary. This will be done in 3+1 decomposed variables,
which are further decomposed to their scale and conformally invariant part. The decomposition turns out to be quite a
useful tool, since it manifestly reveals conditions for conformal invariance, and simplifies the investigation, providing a deeper insight
into the structure of the theory with respect to scale and conformal degrees of freedom. The decomposed variables are
called 'unimodular-conformal' variables and may be used as canonical variables for more elegant and clear
Hamiltonian formulations and quantization procedures in other theories as well.
Close
| May 31 |
12:00 |
Sinan Zeissner and Mathias Becker (Dortmund)
|
Integrated Information Theory - Is the Universe Conscious?
|
Konferenzraum 1 (Neubau) |
Integrated Information Theory - Is the Universe Conscious?
Abstract: Integrated Information Theory (IIT) is an information-theoretic model of consciousness
advocated by neuroscientists such as Guilio Tononi and Christof Koch which aims at a quantative
understanding of the conditions which are necessary for consciousness to arise.
The talk introduces the concept of IIT and outlines the problems faced when IIT is applied to
quantum systems.
Close
| June 7 |
12:00 |
Naresh Dadhich (Pune, India)
|
On 1/r gravitational potential in pure Lovelock gravity
|
Konferenzraum 1 (Neubau) |
On 1/r gravitational potential in pure Lovelock gravity
Abstract: Gravitational potential for Einstein gravity goes as 1/r(d - 3) while
for Lovelock gravity it goes as 1/rα where α = (d - 2N - 1)/N. For Einstein it
goes as 1/r only in d = 4 in contrast for Lovelock it does so for in all dimensions,
dN = 3N + 1. This means gravitational field is the same in dimensions, 4, 7, 10, ...
corresponding to N = 1, 2, 3, ... . We will discuss some implications of this interesting
Lovelock property.
Close
| June 21 |
12:00 |
Sebastian Schuster (Wellington, New Zealand)
|
Particle Sparsity in the Hawking Effect
|
Konferenzraum 1 (Neubau) |
Particle Sparsity in the Hawking Effect
Abstract: Although known since the 1970s, the sparsity of particles emitted in black
hole evaporation remains under-appreciated. In this talk, I will present
ways to quantify this aspect of black hole physics under a range of
different assumptions: Different black hole configurations, different
particle species and different approximations to the full effect. It will
become apparent that super-radiation can and should be distinguished from
the Hawking flux. Parts of the calculations will be demonstrated both
semi-analytically and numerically, showing that this effect is essential to
the Hawking process and is there to stay. Therefore, it leads to several
interesting and important physical intricacies in the realm of black hole
physics, of which I will discuss some and link others to future work.
Close
| July 5 |
12:00 |
Marcel Reginatto (Braunschweig)
|
Hybrid model of a black hole
|
Konferenzraum 1 (Neubau) |
Hybrid model of a black hole
Abstract: Hybrid theories describe systems with interacting classical and quantum
subsystems. In this talk, I will consider a particular hybrid theory that is
formulated in terms of ensembles on configuration space. The approach is
very general and it satisfies a number of consistency requirements. After a
brief overview, I will discuss the coupling of a classical gravitational
field to a quantum field. This leads to a formalism that differs from the
standard approach of semiclassical gravity. There are two ways of looking at
the theory that results: as a consistent hybrid theory in its own right, or
as an approximation to a fully quantized theory, one which may provide clues
that can help in the search for a full quantum theory of gravity. I will
focus on the application of the hybrid theory to black holes ? in
particular, the example of a CGHS black hole interacting with a quantized
scalar field.
Close
| July 12 |
12:00 |
Przemyslaw Malkiewicz (Paris)
|
What is dynamics in quantum gravity?
|
Konferenzraum 1 (Neubau) |
What is dynamics in quantum gravity?
Abstract: I will discuss the reduced phase space quantization
of canonical relativity. I will show how the choice of the so
called internal clock determines the properties of the resultant
quantum theory. It turns out that by changing a clock the quantum
dynamics of a given system may be almost unboundedly altered.
Nevertheless, there exist important statements about the dynamics
of a given quantum system that are independent of the employed clock.
For illustration I will use simple cosmological models. I will
conclude with a discussion of how the obtained result could be
reconciled with the usual quantum mechanics based on the deterministic
evolution of wavefunctions.
Close
| July 12 |
17:30 |
Ratindranath Akhoury
|
Unitary S matrices with long range correlations: Gauge invariance,
entanglement and black holes
|
Konferenzraum 1 (Neubau) |
| July 15 |
14:00 |
Jens Boos
|
Symplectic boundary degrees of freedom in Poincar\'e gauge theory of gravity
|
Konferenzraum 1 (Neubau) |
Symplectic boundary degrees of freedom in Poincar\'e gauge theory of gravity
Abstract: The symplectic potential lies at heart of Hamiltonian mechanics since it induces a Poisson bracket on phase space
in a geometric fashion. In this talk, we will consider a gravitational system whose spatial part is
bipartite by means of a closed, spacelike hypersurface S. Gravitation is described using Poincar\'e
gauge theory. We derive the most general symplectic potential and show that it is not gauge-invariant.
The talk is closed by a motivation as to why symplectic boundary degrees of freedom can potentially
ameliorate the spoiled gauge invariance; if time permits, analogies to the Yang--Mills theory and
General Relativity in the metric formulation will be presented. This talk is based on work by
Donnelly and Freidel [1].
[1] W. Donnelly and L. Freidel, ``Local subsystems in gauge theory and gravity,'' arXiv:1601.04744 [hep-th]
Close
| July 19 |
12:30 |
Claus Kiefer
|
Conference reports
|
Konferenzraum 1 (Neubau) |
| July 26 |
12:00 |
Tim Schmitz
|
Bachelor Colloquium: Closed timelike curves in the Gödel universe |
Konferenzraum 1 (Neubau) |
