## Seminars

### Summer term 2013

Date | Time | Speaker | Topic | Room |
---|---|---|---|---|

April 9 | 12:00 | Alberto Favaro
(Köln) |
Fresnel versus Kummer surfaces: geometrical optics in dispersionless linear (meta)materials and vacuum | R 215 |

April 16 | 12:00 | Ulrich Feindt
(Bonn) |
Investigating anisotropies in the local universe with the Supernova Factory | R 215 |

April 23 | 12:00 | Suman Ghosh
(Trivandrum, India) |
Entanglement entropy and near Planck-size black holes | R 215 |

April 30 | 12:00 | Manuel Krämer
(Köln) |
Overview of the Planck 2013 results | R 215 |

May 7 | 12:00 | Matias Dahl
(Aalto U, Finland) |
Classification of electromagnetic media from the behaviour of phase velocity | R 215 |

May 14 | 12:00 | Magdalena Zych
(Wien) |
Quantum Mass–Energy Equivalence Principle | R 215 |

May 28 | 12:00 | Nicolas Boulanger
(Mons, Belgium) |
A brief introduction to higher-spin gauge theory | R 215 |

June 4 | 17:45 | Ilkka Mäkinen
(Jyväskylä, Finland) |
An introduction to loop quantum gravity | Konferenzraum Theorie |

June 5 | 15:15 | Sebastian Schuster
(Köln/Bonn) |
Diplomkolloquium: „Ein Ansatz zur Untersuchung der Quantengeometrodynamik im starken Kopplungslimes der Gravitation“ | Konferenzraum I
Phys. Institut, Bonn |

June 18 | 12:00 | Daniel Becker
(Mainz) |
Asymptotic Safety and Black Hole Thermodynamics | R 215 |

July 16 | 12:00 | › Bachelorkolloquium (Jan Manousakis)
› Bericht von der GR20-Tagung in Warschau |
R 215 |

## Past seminars

Winter term 2012/13

Summer term 2012

Winter term 2011/12

Summer term 2011

Winter term 2010/11

Summer term 2010

Winter term 2009/10

Summer term 2009

Winter term 2008/09

Summer term 2008

Winter term 2007/08

Summer term 2007

Winter term 2006/07

Summer term 2006

Summer term 2005

Winter term 2004/05

Summer term 2004

Winter term 2003/04

Summer term 2003

Ulrich Feindt (Bonn)

Our Local Group of galaxies appears to be moving relative to the Cosmic Microwave Background with a velocity of 627 ± 22 km/s, with the source of the peculiar motion still unidentified. While this has been studied mostly using galaxies in the past, the weight of SNe Ia has increased recently with the continuously improving statistics of available low-redshift SNe. In particular, SNe allow to extend the distance up to which the velocity field can be probed. This talk will present results from an analysis of coherent peculiar velocities in the nearby Universe (0.015 < z < 0.1) using 117 SNe Ia measured by the Nearby Supernova Factory, as well the world literature SN data. We find evidence that the peculiar velocity field continues to point into the direction of the CMB dipole up to a redshift of 0.06 and is conistent with zero beyond that. Hence we can constrain the contribution of the Shapley Concentration, i.e. the largest bound structure in the nearby Universe, as the source of the cosmic attraction as well as large scale dark flows caused by pre-inflationary inhomogeneities.

Close

**Investigating anisotropies in the local universe with the Supernova Factory**Our Local Group of galaxies appears to be moving relative to the Cosmic Microwave Background with a velocity of 627 ± 22 km/s, with the source of the peculiar motion still unidentified. While this has been studied mostly using galaxies in the past, the weight of SNe Ia has increased recently with the continuously improving statistics of available low-redshift SNe. In particular, SNe allow to extend the distance up to which the velocity field can be probed. This talk will present results from an analysis of coherent peculiar velocities in the nearby Universe (0.015 < z < 0.1) using 117 SNe Ia measured by the Nearby Supernova Factory, as well the world literature SN data. We find evidence that the peculiar velocity field continues to point into the direction of the CMB dipole up to a redshift of 0.06 and is conistent with zero beyond that. Hence we can constrain the contribution of the Shapley Concentration, i.e. the largest bound structure in the nearby Universe, as the source of the cosmic attraction as well as large scale dark flows caused by pre-inflationary inhomogeneities.

Close

Matias Dahl (Aalto University, Finland)

If we are given an electromagnetic medium tensor we can compute the speed of a propagating signal. For example, in a homogeneous medium we can compute the phase velocity using plane waves. A less well understood question is the converse: If we know the behaviour of phase velocity in all possible directions for an unknown medium, how much can we say about the anisotropic structure of that medium? In this talk we describe a number of results on this question in the setting of linear, local, and non-dissipative (skewon-free) media. In particular, we discuss the classification of medium tensors where wave propagation is determined by one or two Lorentz null cones.

Close

**Classification of electromagnetic media from the behaviour of phase velocity**If we are given an electromagnetic medium tensor we can compute the speed of a propagating signal. For example, in a homogeneous medium we can compute the phase velocity using plane waves. A less well understood question is the converse: If we know the behaviour of phase velocity in all possible directions for an unknown medium, how much can we say about the anisotropic structure of that medium? In this talk we describe a number of results on this question in the setting of linear, local, and non-dissipative (skewon-free) media. In particular, we discuss the classification of medium tensors where wave propagation is determined by one or two Lorentz null cones.

Close

Magdalena Zych (Wien)

Mass-energy equivalence principle is considered an important consequence of General Relativity. I will reverse the usual approach and take the validity of the mass-energy equivalence principle as a postulate within the non-relativistic mechanics. In the classical case this yields special and general relativistic time dilation effects (to lowest order) and Nordtvedt’s quantitative version of the Schiff’s conjecture – a relation between the violations of the universality of free fall and deviations from the gravitational redshift. However, these results do not necessarily extend to quantum mechanics. Various semiclassical extensions of the mass-energy equivalence principle will be presented that correspond to theories in which the free fall and/or the time dilation effects are modified in the presence of quantum effects. These theories in general violate Schiff’s conjecture, yet, in the scenario considered by Nordtvedt, they all agree with the classical result. I will explain this apparent “paradox” and derive a quantum version of the Nordtvedt’s relation from a fully quantum extension of the mass–energy equivalence principle. In the end I briefly discuss experimental scenarios that allow distinguishing between these various formulations of the mass-energy equivalence principle.

Close

**Quantum Mass–Energy Equivalence Principle**Mass-energy equivalence principle is considered an important consequence of General Relativity. I will reverse the usual approach and take the validity of the mass-energy equivalence principle as a postulate within the non-relativistic mechanics. In the classical case this yields special and general relativistic time dilation effects (to lowest order) and Nordtvedt’s quantitative version of the Schiff’s conjecture – a relation between the violations of the universality of free fall and deviations from the gravitational redshift. However, these results do not necessarily extend to quantum mechanics. Various semiclassical extensions of the mass-energy equivalence principle will be presented that correspond to theories in which the free fall and/or the time dilation effects are modified in the presence of quantum effects. These theories in general violate Schiff’s conjecture, yet, in the scenario considered by Nordtvedt, they all agree with the classical result. I will explain this apparent “paradox” and derive a quantum version of the Nordtvedt’s relation from a fully quantum extension of the mass–energy equivalence principle. In the end I briefly discuss experimental scenarios that allow distinguishing between these various formulations of the mass-energy equivalence principle.

Close

Nicolas Boulanger (Mons, Belgium)

We would like to explain the basic mechanisms underlying fully interacting higher-spin theory, aiming at giving a flavor of Vasiliev’s equations. We will start from the linearised theory, explain the Fradkin-Vasiliev procedure for cubic interactions and arrive at Vasiliev’s equations if time allows.

Close

**A brief introduction to higher-spin gauge theory**We would like to explain the basic mechanisms underlying fully interacting higher-spin theory, aiming at giving a flavor of Vasiliev’s equations. We will start from the linearised theory, explain the Fradkin-Vasiliev procedure for cubic interactions and arrive at Vasiliev’s equations if time allows.

Close

Ilkka Mäkinen (Jyväskylä, Finland)

Loop quantum gravity is a background independent proposal for a quantum theory of gravity. I will give an introduction to the theory, focusing on its canonical formulation. After giving arguments in favour of a background independent approach to quantum gravity, I will describe how loop quantum gravity results from a canonical quantization of general relativity written in the Ashtekar variables. I show that discreteness of geometry at the Planck scale is a basic prediction of the theory, and briefly discuss some of the physical implications of this result. If I have time, I will conclude by sketching the elements of the more recent covariant formulation of loop quantum gravity.

Close

**An introduction to loop quantum gravity**Loop quantum gravity is a background independent proposal for a quantum theory of gravity. I will give an introduction to the theory, focusing on its canonical formulation. After giving arguments in favour of a background independent approach to quantum gravity, I will describe how loop quantum gravity results from a canonical quantization of general relativity written in the Ashtekar variables. I show that discreteness of geometry at the Planck scale is a basic prediction of the theory, and briefly discuss some of the physical implications of this result. If I have time, I will conclude by sketching the elements of the more recent covariant formulation of loop quantum gravity.

Close

Daniel Becker (Mainz)

The goal of the Asymptotic Safety program consists in finding a nonperturbatively renormalizable quantum field theory of gravity and analyzing its properties. The ideas, the motivation and the concepts of Asymptotic Safety will be explained in the first part of this talk. Then, we focus on Quantum Einstein Gravity in case spacetime has boundaries and consider a specific example of a renormalization group calculation including scale dependent boundary terms. In the third part I show the impact of these results on black hole thermodynamics.

Close

**Asymptotic Safety and Black Hole Thermodynamics**The goal of the Asymptotic Safety program consists in finding a nonperturbatively renormalizable quantum field theory of gravity and analyzing its properties. The ideas, the motivation and the concepts of Asymptotic Safety will be explained in the first part of this talk. Then, we focus on Quantum Einstein Gravity in case spacetime has boundaries and consider a specific example of a renormalization group calculation including scale dependent boundary terms. In the third part I show the impact of these results on black hole thermodynamics.

Close