Weekend Seminar
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The Bonn-Cologne Graduate School of Physics and Astronomy is organizing a weekend seminar at the Physikzentrum Bad Honnef. As in the previous events  we will have a mixture of workshops, evening talks, excursions, etc.

There is no fee, but you will be required to pay your own drinks, and you will also need to cover your travel costs. Lodging will be paid, and as there are evening events it is advisable to stay overnight in the Physikzentrum. We are limited to 90 participants, so early registration is recommended.

Date & Venue

Friday, May 17th to sunday, May 19th 2019 at the Physikzentrum Bad Honnef 


The number of participants is limited to 90, and due to the overwhelming amount of applications we have closed down registration..


Here is a sketch of the program, and a list of the available topics below. 


  Breakfast Breakfast

Workshop B1-B3

[B1] C. Porciani (Bonn) - The large-scale structure of the Universe: from the mystery of dark energy to galaxy formation

[B2] A. Altland (Cologne) - Disorder and Chaos in Quantum Matter

[B3] T. Bollenbach (Cologne) - Biological physics and systems biology 

Workshop C1-C3

[C1] S. Stellmer (Bonn) - Quantum metrology at the University of Bonn: from fundamental physics to applications

[C2] M. Disertori (HCM Bonn) - 
A model for liquid crystals in two and three dimensions;
M. Lager (HCM Bonn) -

Random Band Matrices and supersymmetry


12:00   12:30 Lunch

12:15 Closing

12:30 Lunch



15:30 Welcome Note

Socializing Events


Workshop A1-A3

[A1] S. Walch, A. Klepitko, E. Borchert (Cologne) - Star formation and feedback in the multi-phase interstellar medium

[A2] J. Dingfelder (Bonn) - Flavor physics at a new e+e- machine - A look into physics analysis and detector development for Belle II

[A3] AG van Loosdrecht  (Cologne) - Advanced ultrafast spectroscopy on Quantum Materials


18:00 Dinner
19:00 19:15 Dinner


Evening Talk

  Friday, 17th Saturday, 18th Sunday, 19th

Details on the Workshops:

[A1] Theoretical Astrophysics Cologne

S. Walch
Star formation and feedback in the multi-phase interstellar medium

Star formation takes place in the densest and coldest parts of the interstellar medium (ISM), in dark molecular clouds. These are swept up by multiple supernova explosions on scales of several hundred parsec. While condensing out of the warm ISM, the clouds are continuously fed with fresh gas. Thus, the turbulent substructure and magnetic field properties are imprinted during cloud formation. The formation of dense clouds from the multi-phase ISM, the onset of star formation, and the evolution of the molecular clouds under the impact of stellar feedback from newly born massive stars is studied in high-resolution simulations within my work group. In this talk I will give an overview of the physics and chemistry involved in molecular cloud formation and evolution. After the onset of star formation, the latter is governed by stellar feedback from newly born massive stars. The detailed cloud substructure determines the clouds' vulnerability to stellar feedback processes, in particular to ionizing radiation. Moreover, the ionization state of the gas can be highly variable on scales of tens of parsec due to small-scale turbulent motions within the star-forming clouds, which shield and release the ionizing radiation. This leads to a flickering of the young HII regions on the scale of ~10 pc. On scales of several 100 pc and time scales of tens of Mega-years, the combined feedback from star clusters leads to a reduced star formation rate, such that long depletion time scales are observed.

Andre Klepitko
Radiation pressure: effective computing through tree based ray-tracing

Radiation Pressure has been put forward as an important feedback mechanism throughout many scales, where its global impact is not yet fully understood. For the purpose of investigating into the nature of radiation pressure, we have developed a novel method for its computation in AMR grid code simulations. The general approach makes use of tree based inverse ray tracing, rendering the computational effort inexpensive. The luminosity is split into two parts, a streaming and a trapped part, where only the streaming part is allowed to propagate, while the trapped radiation remains stationary. Each cell is considered a source of radiation according to their thermal and chemical properties. By iteration we approach a global equilibrium in an infinite speed of light approximation including reprocessed radiation. This method is used to study the effects of radiation pressure on the collapse of a massive core, and the impact of massive stars on their environment forming within the core.

Elisabeth Borchert
The effect of numerical resolution on synthetic CO observations of molecular clouds

CO is the most observed molecule of molecular clouds, as it is very bright and emission occurs at radio frequencies, making it observable using ground-based telescopes. It is commonly used to determine the mass in molecular hydrogen (H_2) of an observed region using the X_CO factor (which relates the H_2 mass to the CO luminosity). We present synthetic CO observations of two molecular clouds from the SILCC-Zoom simulations using the radiative transfer code RADMC-3D. In these synthetic observations we are studying the effect of the finite resolution of the SILCC-Zoom simulations on the cloud composition, such as the H2 mass, observable CO area and CO luminosity. Using CO emission maps, we determine the X_CO factor for different times, resolution levels, line of sights and clouds. We find that the X_CO factor changes with time and resolution by a factor of 2-5

Workshop A2

Jochen Dingfelder (Bonn)
Flavor physics at a new e+e- machine - A look into physics analysis and detector development for Belle II

Belle II has a broad physics program, ranging from precision studies of the CKM mechanism and rare decays to hadron spectroscopy and dark matter searches. The Bonn group has been involved in the development of the pixel detector for Belle II and the preparation of analyses related to some of the current hot topics in flavor physics, the measurement of the CKM matrix element|Vub| and studies of semileptonic B decays to tau leptons. Hints of potentially interesting deviations are seen by both the e+e- B factories and LHCb. Already with the first 1-2 years of data taking, Belle II can make signicant progress in the study of these so-called flavor anomalies.
After a general introduction to the Belle II experiment and its physics program, there will be two more contributions, one on the development and operation of the pixel detector and the other illustrating how a physics analysis of semileptonic B decays is done with Belle II.

Workshop A3

Robin Bernhardt, Anuja Sahasrabudhe (Optical Condensed Matter Science, Cologne)

Advanced ultrafast spectroscopy on Quantum Materials

In the last decades, new classes of materials with extraordinary optical, electrical and magnetic behavior emerged. This includes topological insulators, semiconducting 2D materials, spin liquids and many more. Ultrafast spectroscopy allows access to their interesting physical properties on ultrashort timescales, allowing to study the dynamics of various excitations in the solid state materials. In the AG van Loosdrecht, we use different powerful advanced transient optical methods to get access to the excitation dynamics and other fascinating properties of quantum materials like Majorana fermions. The presentations will highlight part of the underlying theory as well as current results of our measurements and the potential application of semiconducting TMDCs, BiSbTeSe 2 and α-RuCl 3 . We will also give an overview over some of our setups, especially (time-resolved) Raman-spectroscopy, Photoluminescene and Transient Grating.

Workshop B1

Christiano Porciani (Argelander Institut für Astronomie, Bonn)
Title The large-scale structure of the Universe: from the mystery of dark energy to galaxy formation


Workshop B2

Alexander Altland (Theoretical physics, Cologne)

 Disorder and Chaos in Quantum Matter


The inevitable presence of imperfections and disorder in quantum matter can be looked at from two different perspectives: first, while disorder may have a detrimental effect on the observability of physical quantities, rather more often it leads to novel phenomena, including some which would not exist without it —  the integer quantum Hall effect being a classic example. Second, the averaging over disorder or other statistically distributed system parameters is a potent source of universality. Disordered systems are often simpler than their idealized clean counterparts, and they let the fundamental principles truly important to the physics at hand stand out. 

Both principles are strongly represented in the work our our group. In this talk I will illustrate them on two recent examples, the physics of disordered topological insulators, and that of the Sachdev-Ye-Kitaev model, a paradigmatic model of many body quantum chaos which is currently discussed in the context of holographic quantum matter.


Workshop B3

Tobias Bollenbach, Gabriela Petrungaro, Sakshi Khaiwal, Bor Kavcic, Janina Müller, Gerrit Ansmann (Cologne)

Biological physics and systems biology

We will introduce several current topics in the fields of biological physics and systems biology. Our recent experimental and theoretical work focuses on the effects of antibiotics on bacteria. Antibiotic resistance is an increasingly serious concern. At the same time, this phenomenon provides a rare opportunity to observe evolution in real time in the laboratory. The most challenging open questions in this field include how resistance evolution can be predicted and how this worrying process can be slowed or perhaps even entirely circumvented. Here, a promising approach is combining multiple antibiotics. We use empirical laws of bacterial growth to develop predictive theoretical models of such drug interactions and compare them to precise measurements of growth in two-dimensional antibiotic landscapes. Finally, we investigate how multiple different species interact with each other in polymicrobial infections using experiments together with the toolbox of dynamical systems theory.


Workshop C1

Simon Stellmer (Bonn, Quantum metrology group)
Quantum metrology at the University of Bonn: from fundamental physics to applications

The quantum metrology research group has recently been established at the University of Bonn. Quite generally, we aim to perform precision measurements that take advantage of quantum phenomena for improved sensitivity. The presentation will touch upon three research topics. At first, I will elaborate on the permanent electric dipole moment (EDM) as a promising candidate to search for physics beyond the standard model. We employ ultracold atoms of mercury to measure the atomic EDM of mercury, and hope to improve current limits by orders of magnitude. Next, I will give a broad introduction to optical clocks. I will present the current state of the art, along with the challenges of transportability and uptime. We are currently developing optical clocks with reduced performance, but 100% uptime and small footprint, which could find broad applications. Degenerate quantum gases and quantum simulations of alkaline-earth metal atoms will be at the focus of the third part of my presentation. I will explain the unique properties of these elements, introduce novel techniques such as narrow-line cooling, and mention some of the applications. Further, I will present the current status of our work.


Workshop C2

Margherita Disertori (Hausdorff Center for Mathematics)
A model for liquid crystals in two and three dimensions


Mareike Lager (Hausdorff Center for Mathematics)
Random Band Matrices and supersymmetry 

In 1949, L. Onsager proposed a statistical theory for a system of elongated molecules interacting via repulsive short-range forces. Onsager's theory predicted the existence at intermediate densities of a nematic liquid crystal phase, in which the distribution of orientations of the particles is anisotropic, while the distribution of the particles in space is homogeneous and does not exhibit the periodic variation of densities that characterizes solid crystals (periodicity in all space dimensions). I will introduce a toymodel for this problem consisting of long rods (in two dimensions) and anisotropic plates (in three dimensions). The rods/plates interact via purely hard core interactions and have a finite number of allowed orientations. For this model I will review some results/conjectures and the main technical tools. This is a joint work with A. Giuliani and I. Jauslin

The ensemble of Random Band Matrices is a model for conducting properties in disordered materials. It is assumed that it behaves similarly as the Anderson Model. We consider the ensemble on a two and three dimensional lattice, in the limit of infinite volume and fixed but large band width. For this model, we discuss rigorous results on the averaged density of states. The main steps of the proof are a supersymmetric dual representation, a saddle point analysis and a suitable cluster expansion. This is a joint work with M. Disertori.


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