Past activities

The Bethe Forum on "Geometries and Special Functions for Physics and Mathematics" invited both physicists and mathematicians to the bctp. The organizers were Claude Duhr (Bonn), Herbert Gangl (Durham), Albrecht Klemm and Florian Loebbert (both Bonn).

Further information is available on the homepage.

The first experimental observation of gravitational waves in 2016 has brought new interest to this fascinating research area. This school elucidated the theoretical background of gravitational wave physics and the novel connections to the methods of scattering amplitude computations. Lecturers for this school were Jan-Willem van Holten from Leiden University and Ricardo Monteiro from Queen Mary University of London.

Further information is available on the homepage.

The Bethe Forum "Axions", originally planned for 2020, took place on October 10-14, 2022. The Forum was organized by S. Pokorski (Warsaw), H. P. Nilles (Bonn), T. Gherghetta (Minneapolis) and E. Dudas (Palaiseau).

Further information is available on the homepage.

The Bethe Forum "Multihadron Dynamics in a Box - A.D. 2022", postponed from February 21-25, 2022, took place in the bctp as a follow-up event of the conference "Lattice2022" in Bonn. The organizers were M. Mai (Bonn), U.-G. Meißner (Bonn / Jülich), A. Rusetsky and C. Urbach (both Bonn).

For more information please see the event webpage.

June's Bethe Colloquium took place on Thursday, June 30, at 4:15 p.m. as an online meeting. The talk was held within the program of the Bethe Forum "Machine Learning: Where to Apply in Theoretical Physics", June 27 - July 1, 2022, in the bctp.

• Koji Hashimoto (Kyoto University)
• Deep learning and quantum gravity
• Online meeting

Abstract: Formulating quantum gravity is one of the final goals of fundamental physics. Recent progress in string theory brought a concrete formulation called AdS/CFT correspondence, in which a gravitational spacetime emerges from lower-dimensional non gravitational-quantum systems, but we still lack understanding how the correspondence works. At this end, I discuss similarities between quantum gravity and deep learning architecture, by regarding the neural network as a discretized spacetime. The application of machine learning in physics has been successful in some subjects, which I will review, and I use it to implement the AdS/CFT framework into a deep learning architecture, and show the emergence of a curved spacetime as a neural network, from a given teacher data of quantum systems.

The Bethe Forum "Machine Learning: Where to Apply in Theoretical Physics", initially planned for June 2020, was rescheduled to June 27 - July 1, 2022. The Forum was organized by F. Rühle (Boston), J. Halverson (Boston) and H. P. Nilles (Bonn).
For further information please visit the event webpage.

The Bethe Forum "Modular Flavor Symmetries", initially planned for May 2020, took place on May 2 - 6, 2022.
The organizers were: M. Ratz (Irvine), F. Feruglio (Padua), T. Kobayashi (Sapporo) and H. P. Nilles (Bonn).
For further information please visit the event webpage.

The second Bethe Colloquium of the summer term 2022 took place on Thursday, May 5, at 4:15 pm in Lecture Hall I, Physics Institute. This talk was held within the program of the Bethe Forum "Modular Flavor Symmetries", May 2-6, 2022, in the bctp.

• Mu-Chun Chen (University of California, Irvine)
• NoTORIous Neutrinos
• Lecture Hall I, Physics Institute

Abstract: The discovery of non-zero neutrino masses has provided arguably the most compelling evidence for Physics beyond the Standard Model. Their observed small masses hint at Physics at a very high energy scale, and thus offer a unique window into the theory that underlies the Standard Model of Particle Physics. In this talk, I will describe how the pattern of neutrino masses may be closely connected to the intricate mathematics of modular symmetries.

The first Bethe Colloquium in the summer term 2022 was held on Thursday, April 21, at 4:15 pm in Lecture Hall I, Physics Institute.

• Gudrun Hiller (Dortmund)
• The same, yet not the same: how to crack a paradigm
• Lecture Hall I, Physics Institute

Abstract: The behavior of matter is ruled by the standard model of particle physics -- really? Old puzzles and new evidences from precision measurements are lurking and pose challenges to standard theory. Deviations in processes as rare as one in a billion suggest that electrons and muons are more different than thought: they should behave the same according to the standard model, yet, recent data from the Large Hadron Collider in Geneva finds them to behave differently. If taken at face value, this anomaly heralds a very loud breakdown of the standard model, and requires out-of-the-box new physics. Intriguingly, cracking this with leptoquarks, i.e., new particles which share features from quarks and leptons alike, also open doors into the notorious and longstanding flavor puzzle.

This talk reports on the rise of the anomalies in flavor physics, rare decays of beauty quarks and further cracks in the building.

The Bethe Forum "Inflation", initially planned for March 2020, took place in the bctp on April 4-8, 2022.Organizers: M. Peloso (Padua), M. Drees (Bonn), H. P. Nilles (Bonn) and I. Zavala (Swansea).
For further information please visit the event webpage.

The Spring Meeting of the IRN Terascale took place in the bctp on March 28-30, 2022. For more information please see the event webpage.

The first Bethe Colloquium in 2022 took place on Thursday, January 27, at 4:15 p.m.

• Zvi Bern (Los Angeles)
• From Quantum Scattering Amplitudes to Gravitational Waves
• Zoom meeting

Abstract: The remarkable detection of gravitational waves by the LIGO/Virgo collaboration has opened a new window into the cosmos. In this colloquium we explain how particle theorists can help out with calculations directly relevant for gravitational-wave emission from compact astrophysical objects. The past decade has seen enormous advances in our ability to compute quantum scattering amplitudes making seemingly impossible calculations tractable. These advances include ideas such as the duality between color and kinematics, double-copy relations, generalized unitarity, and improved integration methods. After introducing these concepts, we explain how these ideas are transferred to produce new state-of-the-art calculations for the binary black hole inspiral problem.

The MadGraph / FeynRules meeting 2021, hosted by the bctp on November 15-17, 2021, brought together experts and developers of FeynRules and MadGraph_aMC@NLO, with the aim of summarising the state-of-the-art as well as to plan future developments.

More information is available on the event webpage.

The EU funds the project EXOTIC (Emergent Complexity from Strong Interactions) by Ulf-G. Meißner (HISKP, Bonn University / FZ Jülich) with an ERC Advanced Grant starting in autumn 2021.

Further information is available on the Bonn University webpage.

The last Bethe Colloquium in the summer term 2021 was scheduled for Thursday, July 8, at 4:15 pm.

• Timo Weigand (DESY, Hamburg)
• The Swampland Program in Quantum Gravity: From Conjectures to Theorems
• Zoom meeting

Abstract: Which effective field theory can be coupled to gravity in a consistent quantum theory? This fundamental question has triggered considerable recent interest within the so-called Swampland Program. A growing web of conjectured criteria aims to distinguish the Swampland of effective quantum field theories without an ultra-violet completion with gravity from the Landscape of consistent low-energy approximations to quantum gravity. Within the computational framework of string theory, these conjectures can be rigorously tested. I will describe progress in this direction, focusing on two central conjectures, the Weak Gravity Conjecture and the Swampland Distance Conjecture. Its refinement, the Emergent String Conjecture, explains how and why the Weak Gravity Conjecture holds at least in suitable weak coupling limits, thanks to asymptotic properties of the moduli space of string compactifications and the (quasi-)modularity the elliptic genus of asymptotically tensionless emergent strings. I will focus on compactifications to four dimensions with minimal N=1 supersymmetry.

June's Bethe Colloquium took place on Thursday, June 24, at 4:15 pm.

• Frank Krauss (Durham University)
• Introducing JUNE - an open-source epidemiological simulation
• Zoom meeting

Abstract: We constructed a detailed digital twin of the UK population, with supreme social and geographical granularity, representing 55 million residents in England and Wales and tracing their daily movements and activities. The spread of the infection is propagated through the virtual population through simulated social contacts. The progress of the disease in infected individuals and their trajectory through the healthcare system is modelled based on public health data. We resolve the spatio-temporal development of the disease spread through the population in great detail and are able to find non-trivial correlations of infection and fatality rares with a variety of societal factors. Our model has been proven in the midst of the current crisis and is currently being used by NHS-England’s COVID-19 response team to inform their strategic and operational planning.

Jim Halverson (Northeastern University, Boston) gave a preliminary lecture to the postponed Bethe Forum "Machine Learning: Where to Apply in Theoretical Physics" as a Zoom meeting on June 8, 2021.

Title: Recent Results at the Intersection of Machine Learning and Theoretical Physics.

More information is available on the event webpage.

May's Bethe Colloquium took place on Thursday, May 27, at 4:15 pm.

• Claude Duhr (CERN)
• The Mathematics of Precision Physics
• Zoom meeting

Abstract: Precise predictions for observables in perturbative Quantum Field Theory require the evaluation of multi-loop scattering amplitudes and integrals. We review recent advances in understanding the mathematics underlying perturbative higher-order computations and how they have led to new results for precision collider observables.

David Shih (NHETC, Rutgers University) gave a Lecture Series on "Machine Learning in High Energy Physics" on May 25 - 29, 2021, as a Zoom meeting.

Topics included
- Introduction to Machine Learning and Neural Networks
- Classifiers - Jet Tagging
- Generative Modeling - Fast Simulation
- Anomaly Detection - Model-independent Searches for New Physics

For more information please visit the event webpage.

Two preliminary lectures to the postponed Bethe Forum "Modular Flavor Symmetries" have taken place as a Zoom meeting on May 3 - 4, 2021. The speakers were Gui-Jun Ding (Hefei, CUST) and Saúl Ramos-Sánchez (Mexico).

More information, the slides and recordings of the lectures are available on the event webpage.

The first Bethe Colloquium of the summer term 2021 took place on Thursday, April 22, at 4:15 pm.

• Richard Dawid (Stockholm University)
• The Current Status of Non-Empirical Confirmation
• Zoom meeting

Abstract: Non-empirical and meta-empirical confirmation were initially proposed as concepts for understanding the degree of trust many theoretical physicists have developed in empirically unconfirmed theories such as string theory. In recent years, the analysis has broadened. The basic arguments of meta-empirical theory assessment are now taken to play an implicit but central background role in all confirmation, be it empirical or non-empirical. To the extent confirmation is about generating trust in a scientific theory, meta-empirical theory assessment must be involved. This perspective contributes to a clearer understanding of the continuities between empirical and non-empirical confirmation. It also allows for a more nuanced appraisal of research contexts where both forms of confirmation happen side by side. In the talk, I will present the rationale behind the described view and illustrate it with examples from high energy physics and cosmology.

A record of the Bethe Colloquium is available here.

Three preliminary lectures to the postponed Bethe Forum "Inflation" have taken place on March 22 - 24, 2021, as a Zoom-meeting. The speakers were: Anthony Challinor (Cambridge), Arthur Hebecker (Heidelberg) and Lorenzo Sorbo (UMass Amherst).

For more information please see the event webpage.

Claude Duhr (CERN) gave a Lecture Series on "New Approaches to Feynman Integrals" on March 15 - 19, 2021, as a Zoom meeting. .

Abstract: Feynman integrals are the backbone of all higher-order calculations in perturbative quantum field theory. They are not only of formal interest, but they are also key to performing precise calculations for experiments. In these lecture we review some recent developments in the understanding of the mathematics underlying Feynman integrals. We focus in particular on tools inspired from modern number theory and the theory of motivic periods, which have been instrumental in some of the most advanced computations for experiments in collider physics.

For more information please visit the event webpage.

The Lecture Series on "Modular Forms in String Compactifications" by Thorsten Schimannek (Wien) was held as a Zoom meeting on February 22 - 26, 2021.

Topics included were:
- Basics of modular forms, Jacobi forms and string compactifications
- Symmetries of string theories on tori
- Modularity from Calabi-Yau compactifications
- Jacobi forms and swampland conjectures

For more information please visit the event webpage.

The last Bethe Colloquium in the winter term 2020/21 took place Thursday, February 4, at 4:15 pm.

• Gerald V. Dunne (University of Connecticut)
• Decoding the Path Integral: Resurgent Asymptotics and Extreme Quantum Field Theory
• ZOOM meeting

Abstract: There are several important conceptual and computational questions concerning path integrals, which have recently been approached from new perspectives motivated by "resurgent asymptotics", a novel mathematical formalism that seeks to unify perturbative and non-perturbative physics. I will review the basic ideas behind the connections between resurgent asymptotics and physics, ranging from differential equations to phase transitions and QFT. I will also discuss the reconstruction problem: how to optimally reconstruct non-perturbative information from a finite amount of perturbative information.

The first Bethe Colloquium in 2021 was held on Thursday, January 21, at 4:15 pm.

• Simone Montangero (Università di Padova)
• Tensor network algorithms for high-dimensional quantum many-body systems
• ZOOM webinar

Abstract: We review some recent results on the development of efficient unconstrained tree tensor network algorithms and their application to high-dimensional many-body quantum systems and machine learning problems in High Energy Physics. In particular, we present results on topological two-dimensional systems, two dimensional Rydberg atom systems, and two and three-dimensional lattice gauge theories in presence of fermonic matter. Finally, we present their application to LHCb event classification and to the study of open many-body quantum systems, specifically to the computation of the entanglement of formation in critical many-body quantum systems at finite temperature, resulting in the generalization of the Calabrese-Cardy formula to open systems.

[1] T. Felser, P. Silvi, M. Collura, and S. Montangero, Phys. Rev. X 10, 041040 (2020).
[2] P. Silvi, F. Tschirsich, M. Gerster, J. Jünemann, D. Jaschke, M. Rizzi, and S. Montangero, SciPost Phys. Lect. Notes 8, 8 (2019).
[3] T. Felser, S. Notarnicola, and S. Montangero, http://arxiv.org/abs/2011.08200
[4] L. Arceci, P. Silvi, and S. Montangero, http://arxiv.org/abs/2011.01247
[5] M. Trenti, L. Sestini, A. Gianelle, D. Zuliani, T. Felser, D. Lucchesi, and S. Montangero, http://arxiv.org/abs/2004.13747

The Colloquium of the Kenneth G. Wilson Award was held as a Bethe Colloquium on Thursday, November 12, at 4:15 pm.

• Phiala Shanahan (MIT)
• From quarks to nuclei: computing the structure of matter
• ZOOM webinar

Abstract: Our understanding of the structure of matter, encapsulated in the Standard Model of particle physics, is that protons, neutrons, and nuclei emerge dynamically from the interactions of underlying quark and gluon degrees of freedom. In this colloquium, I will give a broad introduction and overview of the numerical lattice field theory approach to studying this structure from first principles, before focusing on some specific examples of recent progress in this field. In particular, I will describe how lattice calculations have given us new insights into the structure of the proton, including recent predictions of the contributions of gluons to its pressure and shear distributions, which will be measurable for the first time at the planned Electron-Ion Collider. I will also discuss how studies of light nuclei are beginning to reveal how the complexities of nuclear structure and reactions arise from the Standard Model, and how this work can provide important theory insights for searches for new physics, such as through dark matter direct detection experiments. Finally, I will explain how provably exact machine learning algorithms are providing new possibilities in this field.

Martin Winkler (Stockholm) gave a Lecture Series on "Cosmic Rays and Indirect Dark Matter Detection".

Topics included were:
- Galactic and extragalactic sources of cosmic rays
- Fermi acceleration
- Propagation of cosmic rays
- Indirect matter detection: Postirons, antiprotons and antinuclei
- Suggested dark matter signals in cosmic rays

More information is available on the event webpage.

The second Bethe Colloquium in June took place as a ZOOM meeting on Thursday, 18th, at 4:15 pm.

• Ferruccio Feruglio (University of Padova)
• Modular Flavour Symmetries
• ZOOM meeting

Abstract: The hope of relating fermion masses and mixing angles to some fundamental underlying principle has lead the scientific community to explore a vast variety of possible symmetry patterns and their origin. Such effort, which will be briefly reviewed in this talk, has revealed that realistic candidate symmetries should be substantially broken, thus raising the problem of a correct description and interpretation of the symmetry breaking sector. In this talk I will discuss an approach to the flavour puzzle where the role of flavour symmetry is played by modular invariance, ubiquitous in string theory and in condense matter systems. I will explain why modular invariance is, in a sense, always a broken symmetry and how we can naturally interpret its symmetry breaking sector as arising from the the simplest compactifications of extra dimensions, as realized in string theory. I will describe some models of neutrino masses and mixing angles, stressing the remarkable and unique properties of modular invariance in this context.

The first Bethe Colloquium in the summer term 2020 was scheduled as a ZOOM meeting on Thursday, June 4th.

• Fabian Ruehle (CERN, Geneva)
• Machine Learning in Theoretical Physics
• ZOOM meeting

Abstract: Machine Learning has become an integrable part of our daily lives. Owing to its versatile and universal nature, it is also increasingly utilized in Science. I will first provide an overview of different machine learning techniques and how they are applied in Physics. After that, I will discuss example applications from my own field of research. In a first application, we use deep neural networks to solve the differential geometry problem of finding (complex Kahler) metrics with vanishing Ricci tensor, leading to so-called Calabi-Yau metrics. In a second example, we use Reinforcement Learning to solve the combinatorial problem of finding integer solutions to a coupled system of polynomial equations. We demonstrate that the Reinforcement Learning algorithm discovers human-derived strategies, but also finds new, more efficient ones. Lastly, we adopt a recent development from the field of natural language processing, called the Reformer Neural Network, to study knot theory.

Raphael Flauger (UC San Diego) gave a Lecture Series on the "Cosmic Microwave Background" from February 10 - 14 in the Bethe Center for Theoretical Physics in Bonn.

Abstract: The cosmic microwave background (CMB) is one of the pillars of modern cosmology. Its existence firmly establishes that our universe was once filled with a hot and dense plasma, and the statistical properties of the CMB anisotropies teach us a great deal about the history and composition of our universe.

These lectures provide an introduction to the physics underlying the spectrum of the CMB as well as its anisotropies. In addition to an introduction to the underlying theory, they will provide a short introduction to the analysis of the data from current CMB experiments and will give an outlook what we may hope to learn from future precision measurements of CMB polarization.

More information is available on the event webpage.

The first Bethe Colloquium in 2020 was scheduled for Thursday, January 9th, at 4:15 pm in Hörsaal I.

• Herbert Spohn (TU München)
• Hydrodynamics of integrable many-body systems
• Hörsaal I, Physikalisches Institut

Abstract: Integrable many-body systems have an extensive number of conservation laws. This implies that conventional hydrodynamics, based on mass, momentum, and energy, has to be rewritten. Surprisingly, on large space-time scales the two particle phase shift is the only microscopic information retained (except for Bose, Fermi, classical). For the purpose of the talk I will mainly focus on the classical Toda lattice.

December's Bethe Colloquium took place on Thursday, December 5th, 2019, at 5:15 pm in Hörsaal I.

• Uwe-Jens Wiese (University of Bern)
• Quantum Simulation of Abelian and non-Abelian Gauge Theories
• Hörsaal I, Physikalisches Institut

Abstract: Strongly coupled gauge theories play an important role in different areas of physics. Quantum Chromodynamics is the non-Abelian SU(2) gauge theory that describes the strong interactions between quarks and gluons in particle physics. Some strongly correlated electron systems in condensed matter physics are described by Abelian U(1) gauge theories, and the toric code, a quantum information storage device, is an Abelian Z(2) gauge theory. Many non-trivial aspects of gauge theories are accessible to accurate numerical simulations on classical computers. However, at high fermion density or in out-of-equilibrium situations such simulations suffer from notorious sign problems that prevent the importance sampling underlying Monte Carlo calculations. Quantum simulators are accurately controllable quantum devices that mimic other quantum systems. They do not suffer from sign problems, because their hardware is intrinsically quantum mechanical. For example, trapped ions that follow a laser-driven stroboscopic discrete time evolution through a sequence of quantum gate operations, have been used as a digital quantum simulator for particle-anti-particle pair creation. Analog quantum simulators, on the other hand, follow the continuous time-evolution of a tunable model Hamiltonian. Using ultra-cold atoms in optical lattices, analog quantum simulators have been designed for Abelian and non-Abelian gauge theories. Their experimental realization is a challenge for the foreseeable future, which holds the promise to access the real-time dynamics of string breaking, the out-of-equilibrium decay of a false vacuum, or the evolution af a chiral condensate after a quench, from first principles. Quantum link models which realize gauge theories including QCD, not with classical fields but with discrete quantum degrees of freedom, are ideally suited for implementation in ultracold quantum matter. For example, the nuclear spin of alkaline-earth atoms can be used to embody the SU(3) color degrees of freedom of quarks and gluons. SU(3) quantum spin ladders are closely related condensed matter systems which can be quantum simulated in a similar manner.

November's Bethe Colloquium took place on Thursday, November 21st, 2019, at 4:15 pm in Hörsaal I.

• Dieter Zeppenfeld (Karlsruher Institut für Technologie - KIT, TP)
• Diboson production at the LHC
• Hörsaal I, Physikalisches Institut

Abstract: Diboson production processes provide a rich testing ground for SM predictions at the LHC. The talk will discuss recent progress in vector boson pair production from quark-antiquark annihilation as well as vector boson scattering processes. Both put stringent constraints on extensions of the SM as parameterized by effective field theories.

The first Bethe Colloquium of the winter term 2019/20 took place on Thursday, October 24th, 2019, at 4:15 pm in Hörsaal I.

• Riccardo Barbieri (SNS,Pisa)
• Standard Model or Standard Theory
• Hörsaal I, Physikalisches Institut

Abstract: The impressive extension of successful tests of the Standard Model of elementary particles suggests to promote it to a / the Standard Theory. After arguing why this may be premature, I discuss the potential of precision measurements in the next decade or so to search for possible Beyond the Standard Model effects, crucial to try to answer the question of the title.

Fabian Ruehle (CERN, Geneva) gave a Lecture Series on "Machine Learning and its Applications" from October 7 - 11, 2019, in the Bethe Center for Theoretical Physics in Bonn.

Abstract: Machine Learning techniques, in particular neural networks, have become an integral part of our lives. Due to their versatile nature, they are applied in the private and academic sector with tremendous success. In these lectures, I will first review the basic building blocks of neural networks and how they are trained. I will then discuss popular neural network architectures and how they are used in unsupervised, semi-supervised and supervised machine learning. I will also introduce other common machine learning techniques and present example applications to problems in Physics (ranging from Astrophysics and Cosmology to Particle Physics, Mathematical Physics and String Theory). In the exercises, I will use the techniques introduced in the lectures to solve simple problems in real time.

For more information please check the event webpage.

From September 9 - 13, 2019, the Bethe Forum "Multihadron Dynamics in a Box" took place in the Bethe Center for Theoretical Physics in Bonn. The Forum was organized by M. Mai (Washington, DC), U.-G. Meißner (Bonn / Jülich), A. Rusetsky and C. Urbach (both Bonn).

For more information please see the event webpage.

Recent years have witnessed a growing interest in the study of three-particle systems in lattice QCD. Substantial progress has been achieved both in the development of the methods that enable one to extract infinite-volume observables from lattice data produced on finite-size lattices, as well as in Monte-Carlo calculations of the three-particle systems, but important recent developments in the two-particle sector have also been addressed, since these questions are inherently related to each other.
In particular, the following questions were discussed:

• What is the best strategy in the analysis of data in the three-particle sector?
• 
  
• What are the quantities to extract form the finite-volume sector?
• 
  
• How the further progress in the field looks like after the derivation of the quantization condition (analysis of the data on the Roper resonance, three-particle decay matrix elements, etc.)?
• 
  
• What are the present status and immediate perspectives of lattice simulations in the three-particle sector? For example, can one expect the calculation of the excited levels in the three-particle sector? Are the calculations in many-body (four and more) systems feasible in a forseeable future?

From July 15th to 19th, the Bethe Forum on "Number Theoretic Methods in Quantum Physics" took place in the Bethe Center for Theoretical Physics in Bonn. The Bethe Forum was organized by H. Jockers (PI Bonn, bctp), A. Klemm (PI Bonn, bctp), H. Monien (PI Bonn, bctp), G. Oberdieck (HIM Bonn) and D. Zagier (MPIfM, Bonn).

For more information please see the event webpage.

The last Bethe Colloquium of summer term 2019 was scheduled for Thursday, July 4th, 2019, at 4:15 pm in Hörsaal I.

• Yuval Grossman (Cornell University, LEPP)
• Neutrinos as the key to the universe as we know it
• Hörsaal I, Physikalisches Institut

Abstract: There are three open questions in physics which seem unrelated: Why is there only matter around us? How do neutrinos acquire their tiny masses? Why do all particles in nature have integer electric charges? It turns out that these open questions are related. In this talk I will explain these open questions, the connection between them, and describe the ongoing theoretical and experimental efforts in understanding them.

As a major outcome of the work on nuclear lattice effective field theory in the DFG-funded project CRC 110 "Symmetries and the emergence of Structure in QCD", a monograph was just published by Timo A. Lähde (associated scientist) and by Ulf-G. Meißner in the Springer Lecture Notes in Physics Series as volume 957 (May 2019).

Members of the DFG Research Unit 2239 got together for a final meeting at the bctp. The goal of the DFG Research Unit 2239 was to provide theoretical calculations, numerical tools and analyses for the systematic study of new physics phenomena in the context of the LHC. Results have been discussed in regular meetings.

Further information about the Research Unit and the program of the meeting can be found here.

June's Bethe Colloquium took place on Thursday, June 6th, 2019, at 4:15 pm in Hörsaal I.

• Corinna Kollath (HISKP, Bonn)
• Unconventional dynamics of ultracool bosons in optical lattices
• Hörsaal I, Physikalisches Institut

Abstract: Atomic gases cooled to Nanokelvin temperatures are a new exciting tool to study a broad range of quantum phenomena. In particular, an outstanding degree of control over the fundamental parameters, such as interaction strength, spin composition, or dimensionality has been achieved. This has facilitated access to strongly correlated quantum many body physics in exceptionally clean samples. For example, artificial periodic structures for the atomic gas can be created using laser light to mimic condensed matter systems. Further, the outstanding tunability of cold gases allows to rapidly change the system parameters or to induce a coupling to an environment and to observe the subsequent quantum evolution. This ability poses new challenges for the understanding of quantum dynamics in correlated many-body systems. I will report on recent progress on investigating bosonic gases in optical lattices coupled to dissipative light fields described by Markovian Master equations. In particular, we point out different dynamical regimes: The first one is an algebraic decay of correlations which is followed by a stretched exponential decay. We analyze the origin of this unconventional dynamics. The algebraic behavior is related to the continuum spectrum of the bosonic gas and we develop a classical diffusion equation description for the dynamics. In contrast, the stretched exponential dynamics can be traced back to the existence of rare states with increasingly long time scales.

The second Bethe Colloquium of the current term took place on Thursday, May 9th, 2019, at 4:15 pm in Hörsaal I.

• Lance Dixon (SLAC, Stanford)
• Particle Scattering and Number Theory
• Hörsaal I, Physikalisches Institut

Abstract: From the softest of interactions of a magnetic field with an electron, to the most violent collisions at the Large Hadron Collider, precision quantum field theory produces numbers and functions with interesting number-theoretic properties. In many examples a co-action principle holds, an invariance under a "cosmic" Galois group. I will provide several arenas in which this principle can be seen at work, including perhaps the richest set of theoretical data, scattering amplitudes in planar N=4 super-Yang-Mills theory.

The first Bethe Colloquium in summer term 2019 was scheduled for Thursday, April 25th, 2019, (4:15 pm) in Hörsaal I.

• Hirosi Ooguri (Caltech, Pasadena/IPMU Tokyo/ACP Aspen)
• Constraints on Quantum Gravity
• Hörsaal I, Physikalisches Institut

Abstract: Superstring theory is our best candidate for the ultimate unification of general relativity and quantum mechanics. Although predictions of the theory are typically at extremely high energy and out of reach of current experiments and observations, several non-trivial constraints on its low energy effective theory have been found. Because of the unusual ultraviolet behavior of gravitational theory, the standard argument for separation of scales may not work for gravity, leading to robust low energy predictions of consistency requirements at high energy. In this colloquium talk, I will start by explaining why the unification of general relativity and quantum mechanics has been difficult. After introducing the holographic principle as our guide to the unification, I will discuss its use in finding constraints on symmetry in quantum gravity. I will also discuss other conjectures onlow energy effective theories, collectively called swampland conditions, with various levels of rigors. They include the weak gravity conjecture, which gives a lower bound on Coulomb-type forces relative to the gravitational force, and the distance conjecture, which is about structure of the space of scalar fields. I will discuss consequences of the conjectures.

On Thursday, April 2019, members of the bctp celebrated the 10th anniversary of the bctp with a little party. We were delighted to welcome a former member, Ms Dagmar Fassbender, who presented director Hans Peter Nilles with a birthday cake for the bctp.

A special lecture series took place from March 25th to 27th, 2019, in Seminar room bctp 1 (2.019) in the bctp, Wegelerstr. 10, 53115 Bonn.

• Lorenzo Ubaldi, (SISSA, Trieste)
• Dark photon dark matter from inflation
• 
  
• Monday, 25th, to Wednesday, 27th March, 9 - 10 a.m.

Abstract: In a series of three one-hour blackboard lectures I plan to introduce pedagogically a new non-thermal mechanism for dark matter production, which I explored recently with my collaborators. First, I will review some basics of inflation driven by a scalar field. Second, I will couple the scalar field to an abelian gauge field (the dark photon), consider the dynamics of the system, and show that it leads to the production of a significant energy density of the dark photon. Third, I will follow the evolution of this energy density through the expansion of the Universe.

From March 11th to March 14th, 2019, the yearly workshop "Beyond the Standard Model" took place at the Physikzentrum Bad Honnef, organized by Jan Plefka (Berlin). The workshop focused on recent developments in the theory of fundamental particles, the physics of the early universe, and mathematical physics. Introductory pedagogical lectures each morning were followed by shorter talks by the participants.
For more information see the webpage.

Iosif Bena, (IPhT, CEA Saclay), held a Lecture Series on "Black Holes in String Theory" from 25th February to 1st March, 2019, in the Bethe Center for Theoretical Physics, Bonn.

For more information please check the event webpage.

The first Bethe Colloquium in 2019 took place on Thursday, January 17th, 2019, (4:15 pm) in Hörsaal I.

• Gleb Arutyunov (Hamburg University, II. Institute for Theoretical Physics)
• R-matrix Quantization of the Ruijsenaars-Schneider Models
• Hörsaal I, Physikalisches Institut

Abstract: I describe an algebraic scheme for quantizing the Ruijsenaars-Schneider models in the R-matrix formalism. It is based on a special parametrization of the cotangent bundle over GL(n,C). In new variables the standard symplectic structure is described by a classical (Frobenius) r-matrix and by a new dynamical \bar{r}-matrix. Quantizing these r-matrices, I will exhibit the quantum L-operator algebra and construct its particular representation corresponding to the Ruijsenaars-Schneider system. I will also indicate a couple of open problems.

December's Bethe Colloquium took place on Thursday, 13th December, 2018, (4:15 pm) in Hörsaal I.

• Gabriela Barenboim (Valencia)
• A nu hope
• Hörsaal I, Physikalisches Institut

Abstract: Massive neutrinos who were the last addition to the Standard Model, and arguably the first piece of evidence of the physics that hides behind it, can become an ideal tool to test the way we understand and describe Nature: local relativistic quantum field theory. I will show that used as tools neutrinos have the potential not only to chalenge the building we live in (SM), but also threaten the construction system. A fact that should not be underestimated.

The first Bethe Colloquium in the winter term took place on Thursday, October 11th, 2018, (4:15 pm) in Hörsaal I.

• Dmitri Kharzeev (Stony Brook)
• Chiral matter: from quarks to quantum materials
• Hörsaal I, Physikalisches Institut

Abstract: Chirality is an ubiquitous concept in modern science, from particle physics to biology. In quantum physics, chirality is linked to the topology of gauge fields due to the quantum chiral anomaly. While the quantum anomaly is usually associated with the short-distance behavior, recently it has been realized that it affects also the macroscopic behavior of fluids with chiral fermions. In particular, the local imbalance between left- and right-handed fermions in the presence of magnetic field induces the non-dissipative transport of electric charge ("the Chiral Magnetic Effect"). In heavy ion collisions, there is an ongoing search for this effect at Relativistic Heavy Ion Collider, with a dedicated isobar run completed in June of 2018. Recently, the Chiral Magnetic Effecht has been discovered in ZrTe5 and other materials possessing chiral quasi-particles. This observation opens a path towards applications in microelectronic devices and quantum computers.

July's Bethe Colloquium took place on Thursday, July 12th, 2018, (4:15 pm) in Hörsaal I, within the program of the ongoing Bethe Forum.

• Stuart Raby (Ohio State University, Columbus, USA)
• String Theory Challenges in Particle Physics and Cosmology
• Hörsaal I, Physikalisches Institut

Abstract: In this talk I will attempt to summarize some of the major particle physics and cosmological constraints on string theory model building.

From July 9th to 13th, a Bethe Forum on "String Theory Challenges in Particle Physics and Cosmology" took place in the Bethe Center for Theoretical Physics.
The Forum was organized by Michael Ratz (Irvine), Gabriele Honecker (Mainz), Hans Peter Nilles (Bonn) and Sakura Schäfer-Nameki (Oxford).

More information is available on the event webpage.

June's Bethe Colloquium took place on Thursday, June 21st, 2018, (4:15 pm) in Hörsaal I:

• Ruth Durrer (Geneva)
• Testing General Relativity with the Large Scale Structure of the Universe
• Hörsaal I, Physikalisches Institut

Abstract: In the measured distribution of galaxies we see not only the density fluctuations of the matter distribution but also effects from peculiar velocities and from perturbation of the spacetime metric. I shall discuss how these enter the observations of the galaxy distribution and how they may be extracted. I shall show that they can help us to test Einstein's equations of General Relativity in cosmology.

The Bethe Forum on "Grand Unification in the Real World" followed the 21st International Conference "Planck 2018 - From the Planck Scale to the Electroweak Scale" and took place from May 28th to June 1st, 2018,in the Bethe Center for Theoretical Physics, Bonn. The Forum was open to master and phd students as well as junior and senior scientists.
The organizers were Stuart Raby (Columbus), Lara Anderson (Blacksburg, Kaladi S. Babu (Stillwater) and Herbert Dreiner (Bonn).

More information is available on the event webpage.

The 21st International Conference "Planck 2018 - From the Planck Scale to the Electroweak scale" took place from May 21st to May 25th, 2018, at Universität Bonn.

The conference was organized by the Bethe Center for Theoretical Physics (bctp) of the Universität Bonn for a network consisting of several European research groups: Bonn, CERN, Trieste, Madrid, Oxford, Padua, Paris and Warsaw.
More information is available here.

The conference was followed by an accompanying Bethe Forum Program.

A special lecture series took place at three afternoons in May, 2018, in Seminar room bctp 1 (2.019) in the bctp, Wegelerstr. 10, 53115 Bonn.

• Sach Mukherjee (DZNE, Bonn)
• Machine Learning in Three Lectures
• 
  
• 1. Wednesday, 9th May, 2 - 3 p.m.
• 2. Thursday, 17th May, 3:30 - 4.30 p.m.
• 3. Friday, 18th May, 2 - 3 p.m.

Abstract: In recent decades, machine learning (ML) has developed into a major new approach to a wide variety of scientific and technological questions. Conceptually, ML places an emphasis on near-automatically building models using data and on empirical performance with respect to specific goals. These lectures provided a self-contained introduction to the main ideas in ML, including some key tasks, problem classes and methods as well as insight into unifying themes and the broader conceptual approach.

The slides are available here: Talk 1, Talk 2, Talk 3.

The second Bethe Colloquium of the summer term 2018 took place on Thursday, May 3rd (4:15 pm) in Hörsaal I:

• Hitoshi Murayama (Berkeley / Tokyo)
• New Developments on Spontaneous Symmetry Breaking: universal theme to all physics
• Hörsaal I, Physikalisches Institut

Abstract: The concept of spontaneous symmetry breaking was developed by a group of outstanding physicists including both condensed matter and particle physicists. Every textbook on Quantum Field Theory quotes the Goldstone's theorem, which states that there are dim (G/H) gapless excitations when the symmetry group G of the Hamiltonian is spontaneously broken with only its subgroup H respected by the ground state. Its has been known for more than half a century that this "theorem" doesn't work in a simple piece of magnet on the fridge. I discuss how the "theorem" is generalized when applied to systems without Lorentz invariance, and a deep mathematical structure behind it called pre-sympletic structure on homogeneous spaces. I will also discuss applications of the newly developed framework to spacetime symmetries, skyrmions, etc.

The first Bethe Colloquium in the summer term took place on Thursday, April 19th (4:15 pm) in Hörsaal I:

• Johannes Henn (Mainz University)
• From the Motion of Planets to Elementary Particles
• Hörsaal I, Physikalisches Institut

Abstract: Planetary orbits, energy levels of atoms, and elementary particle interactions are all governed by the same hidden symmetry principles. I will describe these symmetries and how they help simplify calculations. In particular, I will focus on recent progress for scattering amplitudes in quantum field theory.

Kyriakos Papadodimas (CERN, Geneva) held the Lecture Series on "Black Holes and Quantum Information" from March 19th to 23rd, 2018, in the Bethe Center for Theoretical Physics, Bonn.

Details can be found on the event webpage.

From February 19th to 23rd, 2018, the Bethe Forum on "Scattering Amplitudes in Gauge Theory, Gravity and Beyond" took place in the Bethe Center for Theoretical Physics in Bonn.
The Forum was organized by Jan Plefka (HU Berlin), Hans Jockers and Albrecht Klemm (both Bonn).

More information is available on the webpage.

The second Bethe Colloquium in 2018 was scheduled for Thursday, January 18th (4:15 pm) in Hörsaal I:

• Catharina Stroppel (University of Bonn, Mathematical Institute)
• Quantum cohomology of Grassmannians via R-matrices and integrable systems
• Hörsaal I, Physikalisches Institut

Abstract: In this talk I want to give an elementary description of the quantum cohomology rings of Grassmannians. The main idea is to connect it with a concrete model of particle configurations on a circle. The model allows to describe the case of an arbitrary Grassmannian from the case of a point using certain creation operators. As a consequence we obtain a proof of an isomorphism theorem going back to Witten between these rings and certain WZNW-fusion rings. Connections to R-matrices and equivariant quantum cohomology might be mentioned.

The first Bethe Colloquium in 2018 took place on Thursday, January 11th (4:15 pm) in Hörsaal I:

• Luis Ibáñez (IFT, UAM Madrid)
• Swampland Constraints on SM Physics and the Cosmological Constant
• Hörsaal I, Physikalisches Institut

Abstract: The swampland is the space of field theories which cannot be embedded into a consistent theory of quantum gravity. Recently substantial effort has been dedicated to understand this swampland in terms of black-hole physics and string theory. One of the leading ideas is the weak gravity conjecture and different generalisations and extensions. In one of them Ooguri and Vafa have conjectured that no consistent theory of quantum gravity can contain AdS non-SUSY, stable minima. Appplying this criterium to the SM and its compactifications to 3 and 2 dimensions, one can derive strong con-straints on neutrino masses and the cosmological constant. The lightest neutrino mass is predicted to be lighter than the cosmological constant scale. This bound, for fixed Yukawa couplings, implies that values of the Electro-Weak scale above 1 TeV would be in the swampland and would not count as possible consistent theories. This would bring a new perspective into the issue of the EW hierarchy.

November's Bethe Colloquium took place on Thursday, November 9th (4:15 pm) in Hörsaal I:

• Michael Kramer (Max Planck Institute for Radio Astronomy)
• Precision fundamental physics with astronomy
• Hörsaal I, Physikalisches Institut

Abstract: The Universe is vast. And even though we live on a tiny planet among billions of stars in a galaxy that is one of very many, we are curious enough to seek to understand its beginning and the fundamental laws that govern it: Curiosity-driven research in its purest form - and of fundamental importance. Einstein himself said that "he had no special talent" but "that he was only passionately curious". This "slight" understatement mocks the fact that his theory of general relativity (GR) represents our best understanding of gravity - by far. But whether it is also our last word, at least on macroscopic scales, remains to be seen. Radio astronomy provides a unique tool for making appropriate experiments to test gravity and to explore fundamental physics with high precision. I will present some of these tests related to radio pulsars and compare them with observations using gravitational wave detectors or experiments to image the black hole in the center of the Milky Way.

October's Bethe Colloquium took place on Thursday, October 26th (4:15 pm) in Hörsaal I:

• Marc Knecht (Marseille, CPT)
• The anomalous magnetic moment of the muon: a precision probe of the standard model
• Hörsaal I, Physikalisches Institut

Abstract: Despite dedicated searches at colliders like the LHC, hints for physics beyond the standard model remain at best indirect. They come either from the cosmic frontier, where, for instance, the nature of dark matter still eludes our understanding, or from the flavour sector. In particular, recent measurements at LHCb of B meson decays into neutral-current channels with a pair of charged leptons have attracted attention by showing some deviation with respect to the predictions of the standard model. Although definite statements can hardly be made at this stage, they point towards some kind of violation of lepton-flavour universality, the channels with an electron-positron pair looking more standard-model-like than the channels with a pair of charged muons. If confirmed, these observations would begin to compose a coherent picture when combined with another persistent discrepancy: for about fifteen years, there is a deviation, at the level of 3.5 standard deviations, between the experimental measurement, at a relative precision of 0.54 ppm, of the anomalous magnetic moment of the muon, and its evaluation within the standard model. The purpose of this talk is to review the theoretical aspects which build up the standard-model prediction for the anomalous magnetic moment of the muon, and to present the prospects to improve upon it, in view of upcoming experiments, at FNAL and at J-PARC, which aim at measuring it at a relative precision of 0.14 ppm in the near future.

The 9th Bethe Center Workshop "Computational Sciences and Reality" took place on October 2 - 6, 2017 in Physikzentrum Bad Honnef, Hauptstr. 5, 53604 Bad Honnef.

The organizers were Markus Gabriel (Bonn), Tom Luu (Jülich), Ulf-G. Meißner (Bonn/Jülich) and Carsten Urbach (Bonn).

More information and the program are available here.

July's Bethe Colloquium will take place on Thursday, July 6th (4:15 pm) in Hörsaal I:

• Zoltan Fodor (Bergische Universität Wuppertal)
• The Origin of Mass of the Visible Universe
• Hörsaal I, Physikalisches Institut

Abstract: More than 99% of the mass of the visible universe is made up of protons and neutrons. Both particles are much heavier than their quark and gluon constituents. The existence and stability of atoms rely on the fact that the mass difference between the neutron and the proton is about 0.14%. A slightly smaller or larger value would have led to a dramatically different universe. I show how theoretical breakthroughs and high-performance computing resources have transitioned to a point where these masses, their differences and similar physics observables can be calculated accurately on space-time lattices directly from Quantum Chromodynamics, the strongly interacting theory of quarks and gluons. 

The Lecture Series on "Conformal Field Theories, Trace Anomalies and Their Applications" by Stefan Theisen (Max Planck Institute for Gravitational Physics, Germany) took place from 3rd to 7th July, 2017, in the Bethe Center for Theoretical Physics in Bonn.

For more information see the webpage.

A second Bethe Colloquium in June took place on Thursday, June 22nd (4:15 pm) in Hörsaal I:

• Fernando Quevedo (ICTP, Trieste / DAMTP, Cambridge)
• On String Theory, Particle Physics and Cosmology
• Hörsaal I, Physikalisches Institut

Abstract: An overview is presented on the efforts and challenges for string theory to make contact with particle physics and cosmology. 

From May 29th to June 2nd, the Bethe Forum on "SUSY breakdown confronting LHC and other data" took place in the Bethe Center for Theoretical Physics in Bonn.
The Bethe Forum was organized by Xerxes Tata (Hawaii), Manuel Drees (Bonn), Hans Peter Nilles (Bonn), and Stefan Pokorski (Warsaw).

More information as well as the talks are available on the webpage.

June's Bethe Colloquium took place on Thursday, June 1st
(4:15 pm) in Seminar room 1, Bethe Center for Theoretical Physics:

• Joseph D. Lykken (Fermilab)
• Supersymmetry and the Real World
• Note the unusual room:
  Seminar room 1, Bethe Center for Theoretical Physics
  Wegelerstr. 10, 2nd floor

Abstract: Supersymmetry has proven to be one of the most powerful ideas in gaining a better theoretical understanding of how quantum physics meshes with gravity and other fundamental forces. However it remains to be seen if supersymmetry is actually realized in the real world. This is a challenge for experiments, as well as for theorists exploring different mechanisms for how a universe born supersymmetric can evolve to the complexity that we see around us.  

May's Bethe Colloquium took place on Thursday, May 4th
(4:15 pm) in Hörsaal I:

• Richard Neher (Biozentrum, University of Basel)
• Rapid adaptation and the predictability of next year's flu
• Hörsaal I, Physikalisches Institut

Abstract: Evolution is simple if adaptive mutations, that is evolutionary innovations, appear and spread one at a time. However, in large microbial populations many mutations arise simultaneously resulting in a complex dynamics of competing variants. I will discuss recent insights into universal properties of such rapidly adapting populations which has surprising parallels to the physics of front propagation and disordered systems. Not only do these models describe observations, but they also allow to predict which variants in the population are likely to be successful. When applied to seasonal influenza virus, such predictions can anticipate virus variants of future seasons and help to optimize the influenza vaccine.  

From 3rd to 7th April, 2017, the bctp hosted the Bethe Forum on "Discrete Symmetries". The Bethe Forum was organized by Steve King (Southampton), Stefan Antusch (Basel), Hans Peter Nilles (Bonn), and Andreas Trautner (Bonn).

More information and the talks are available on the webpage.

From March 20th to March 23rd, 2017, the yearly workshop "Beyond the Standard Model" took place at the Physikzentrum Bad Honnef. The workshop focused on recent developments in the theory of fundamental particles, the physics of the early universe, and mathematical physics. There have been four introductory pedagogical lectures as well as shorter talks by the participants.
The topics and speakers of the pedagogical lectures were:

• G. Arutyunov (Hamburg): Quantum Integrable Models in the AdS/CFT correspondence
• D. Berman (London): An introduction to double and exceptional field theory
• A. Nielsen (Hannover): Gravitational Waves and Black Holes
• J. Wells (Ann Arbor): Particle Physics - Quo Vadis?

For more information and see the webpage.

The Lecture Series on "Neutrinos" took place from 6th to 10th March, 2017, in the Bethe Center for Theoretical Physics in Bonn. The lectures were held by Alexei Smirnov (Max Planck Institute for Nuclear Physics, Heidelberg, Germany).

Topics included were

• Masses, mixing and oscillations
• Flavor transformations in matter
• Phenomenology of neutrinos from various sources
• Mass hierarchy and CP-violation
• Beyond the 3-neutrino paradigm
• Neutrino masses: towards the underlying physics

For more information see the webpage.

The first Bethe Colloquium in 2017 took place on Thursday, January 19th
(4:15 pm) in Hörsaal I:

• James Wells (University of Michigan, Ann Arbor / DESY, Hamburg)
• The theoretical physics ecosystem behind the Higgs boson discovery
• Hörsaal I, Physikalisches Institut

Abstract: A simplified history of the Higgs boson has Peter Higgs positing it in the mid-1960s followed by a long wait while experimentalists progressively turned up collider energies until it appeared several decades later. However, in order for both the hypothesis and the experimental discovery to occur, a vast and complex theory ecosystem, across multiple subfields, had to thrive in the years before Higgs's hypothesis and in the years that followed, builing up to its discovery. In the process I describe how important the discovery of the Higgs boson has been to particle physics and what it means for the future. I also provide a response to Anderson's recent statement in Nature: "Maybe the Higgs boson (of particle physics) is fictitious!"  

The Bethe Forum "Beyond the standard Higgs-system" took place from November 28th to December 2nd, 2016, in the Bethe Center for Theoretical Physics in Bonn. The organizers were Sabine Kraml (Grenoble), Hans Peter Nilles (Bonn), Tilman Plehn (Heidelberg) and Veronica Sanz (Sussex).

More information is available here.

November's 2nd Bethe Colloquium took place on November 21th
(2:15 pm) in Hörsaal I:

• Joachim Schultze (LIMES Institut, Bonn)
• Genomic Research goes Computational
• Hörsaal I, Physikalisches Institut

Abstract: The life and medical sciences have seen a revolution in the last decade. Initiated in the 1990s with the Human Genome Project, genomic research has significantly accelerated since 2007 when next generation sequencing (NGS) technologies were introduced. NGS is seen as the single most important driver of innovation in the life sciences in the next 10 to 25 years. The number of human genomes sequenced by 2015 already reached 300,000 and in the same year US-president Barack Obama announced a US-based project sequencing 1 million American citizens. A few weeks ago, the pharma company Astra Zeneca announced to sequence even 2 million human beings. At the same time the Beijing Genome Center is on its way sequencing all species existing in China. All these advances have triggered three main developments: first, biology becomes more and more computational. Mathematics and informatics play an ever-increasing role in genomic research and therefore in the life sciences. This biological data avalanche without computation and meaningful algorithms - even including deep learning algorithms - would be meaningless. Second, biology becomes quantitative. Indeed, genomic technologies allow the generation of truly quantitative data. And third, data-driven hypothesis generation and machine learning-based decision making slowly but steadily replaces classical approaches based on thoughts, postulates and speculation. I will give an overview of these developments and will also bring them into the perspective of our own goals applying genomics to questions in neurodegeneration and immunology.  

November's Bethe Colloquium took place on November 14th
(2:15 pm) in Hörsaal I:

• Markus Gabriel (Institut für Philosophie, Bonn)
• What is Metaphysics and Why Does it Matter?
• Hörsaal I, Physikalisches Institut

Abstract: As a first approximation metaphysics is a discipline which deals with absolutely everything which exists. There are many names for this extraordinary totality: the world as a whole, reality, cosmos, nature, the universe. Yet, how could we possibly ever know enough in order to figure out what the fundamental structure of such an extraordinary object or domain of objects is? In my presentation, I will introduce some contemporary philosophical arguments in central fields of theoretical philosophy such as metaphysics, metametaphysics and epistemology. In particular, my aim is to raise questions concerning the limits of both science and metaphysics. In this context, I will also deal with the recently much-discussed question whether the universe is or could be a simulation and how anyone could ever come to believe that it might be.

October's Bethe Colloquium took place on October 27th
(4:15 pm) in Hörsaal I:

• Peter Scholze (Mathematical Institute Bonn)
• Hyperbolic 3-manifolds and Galois representations
• Hörsaal I, Physikalisches Institut

Abstract: A large part of modern number theory deals with the relation between algebraic objects and analytic objects, as in the famous Shimura-Taniyama-Weil conjecture relating elliptic curves with modular forms, whose proof by Wiles, completed by Taylor, et. al., lead to the solution of Fermat's Last Theorem. I will try to explain the general Langlands conjectures underlying this picture, and describe some recent results, in particular in the situation mentioned in the title.

We are happy to announce the 8th Bethe Center Workshop "Particle Physics meets Cosmology" on October 10 - 14, 2016 in Physikzentrum Bad Honnef, Hauptstr. 5, 53604 Bad Honnef. The organizers are Hans Peter Nilles (co-chair), Cristiano Porciani (co-chair), Matthias Bartelmann, Wilfried Buchmüller, Arthur Hebecker, Bruno Leibundgut, Thomas Konstandin and Jochen Weller. The workshop is jointly organized by Transregio 33 - The Dark Universe (Bonn, Heidelberg, München) and SFB 676 Particle, Strings and the Early Universe (Hamburg).

More information and the application form are available here.

The goal of the DFG Research Unit 2239 is to provide theoretical calculations, numerical tools and analyses for the systematic study of new physics phenomena in the context of the LHC. Results are being discussed in regular meetings. This upcoming meeting will be focusing on Higgs physics and dark matter at the LHC as well as on the interpretation of exciting new data.

Further information about the Research Unit and the program of the meeting can be found here:
http://web.physik.rwth-aachen.de/service/wiki/bin/view/Kraemer/NewPhysicsattheLHC

July's Bethe Colloquium took place on July 17th
(2:30 pm) in Hörsaal I:

• Xenia de la Ossa (Oxford) and Eric Zaslow (Evanston)
• 25 Years of Mirror Symmetry, 20 Years of Homological Mirror Symmetry
• Hörsaal I, Physikalisches Institut
• Part 1 by Xenia de la Ossa at 2:30pm, part 2 by Eric Zaslow at 4:15pm
• Coffee break at 3:45pm

Part 1: Reflections on Mirror Symmetry (Xenia de la Ossa, Oxford)
I will give a review of the history of mirror symmetry. This has had many ramifications, but its prime utility in physics is that it permits the evaluation of path integrals without recourse to perturbation theory. I will make reference also to a possible impact on arithmetic, and return to the origins of the subject with a consideration of the moduli space of the vacuum state of the heterotic string.

Part 2: HMS, Hopefully Made Simple (Eric Zaslow, Evanston)
I will try to explain a few ideas which make Homological Mirror Symmetry tractable and intuitive in a few simple examples.

The Bethe Forum on "Mirror Symmetry" took place from 4th to 8th July, 2016, in the Bethe Center for Theoretical Physics. The organizers were Daniel Huybrechts (Bonn), Hans Jockers (Bonn) and Albrecht Klemm (Bonn).

Further information can be found here.

As in the previous years, the Bonner Schüerakademie Physik/Astronomie took place from 11th to 15th July, 2016, in the Bethe Center for Theoretical Physics.
Students from upper secondary schools and future university students took part in this event. The 19 participants enjoyed a varied program of scientific talks, guided laboratory tours, visits and experiments.

Further information can be found here.

The Bethe Forum on "Dark matter beyond Supersymmetry" took place from 13th to 17th June, 2016, in the Bethe Center for Theoretical Physics. The organizers are Oleg Lebedev (Helsinki), Lars Bergström (Stockholm), Manuel Drees (Bonn) and Alejandro Ibarra (TUM, Munich).

Further information, the registration form and updates on the program can be found here.

June's 2nd Bethe Colloquium took place on June 16nd
(4:15 pm) in Hörsaal I:

• Gabrijela Zaharijas (Nova Gorica)
• Dark Matter search with the Fermi Large Area Telescope
• Hörsaal I, Physikalisches Institut

Abstract: High energy gamma-rays are one of the most promising tools to constrain or reveal the nature of dark matter. During the almost eight years of the Fermi satellite mission, the data from its Large Area Telescope (LAT) were used to set constraints on the dark matter cross section to various particle channels which now cut well into the theoretically motivated region of the parameter space. In this talk I will describe methods used to search for evidence of dark matter with the LAT, and review the status of the searches. Special attention will be given to the latest indications of the origin of the unaccounted gamma-ray excess at few GeV in the Fermi-LAT data in the region around the Galactic Center, which steered lots of attention as it was shown to be consistent with putative signals of WIMP dark matter particles. Finally I will discuss projections of the expected sensitivities with continued LAT data taking.

The Bethe Forum on "Model Building in the 13 TeV Era" took place from May 30th to to June 3rd, 2016, in the Bethe Center for Theoretical Physics. The organizers are Rolf Kappl (Bonn), Herbert K. Dreiner (Bonn), Christophe Grojean (DESY, Hamburg) and Martin Winkler (Bonn).

Further information, the registration form and updates on the program can be found here.

June's Bethe Colloquium took place on June 2nd
(4:15 pm) in Hörsaal I:

• Gilad Perez (Weizmann Institute, Rehovot)
• Probing the atomic Higgs force
• Hörsaal I, Physikalisches Institut

Abstract: After the discovery of the Higgs particle at the LHC, the Higgs mechanism is expected to account for the masses of the fundamental particles. We argue that, while this is true for the electroweak gauge bosons, we are still in the dark regarding the origin of the charged fermions masses, in particular those of electron, up and down quark. It motivates us to propose a non-collider approach to probe Higgs boson couplings to these matter constituents via precision measurement of isotope shifts in atomic clock transitions. We present an experimental method which competes with and potentially surpasses the LHC in bounding the Higgs-to-light-fermion couplings. Better knowledge of the latter is an important test of the Standard Model and could lead to an alternative understanding of the flavor puzzle (the fact that the fermion masses span five orders of magnitude in scale). We will then discuss how to translate the above (potential) fantastic sensitivity to constrain the presence of heavy new particles that are well beyond the reach of near future accelerators.

The goal of the DFG Research Unit 2239 is to provide theoretical calculations, numerical tools and analyses for the systematic study of new physics phenomena in the context of the LHC. Results are being discussed in regular meetings. This upcoming meeting will be focusing on Higgs physics and dark matter at the LHC as well as on the interpretation of exciting new data.

Further information about the Research Unit and the program of the meeting can be found here:
http://web.physik.rwth-aachen.de/service/wiki/bin/view/Kraemer/NewPhysicsattheLHC

April's Bethe Colloquium took place on April 21st
(4:15 pm) in Hörsaal I:

• Hans-Thomas Janka (MPI for Astrophysics, Garching)
• Supernova Simulations in Three Dimensions: Models Confronting Observations
• Hörsaal I, Physikalisches Institut

Abstract: Recently the first self-consistent three-dimensional computer simulations of supernova explosions of massive stars have become possible and reveal new, stunning phenomena like a dipolar emission asymmetry of electron neutrinos and antineutrinos. They lend support to the viability of the neutrino-driven explosion mechanism in principle, although stars above ten solar masses are hard to explode and might suggest still missing physics. The violent hydrodynamical instabilities that facilitate the onset of the explosion lead to kicks and spins of the newly formed neutron stars and to supernova asymmetries whose observations can help to decipher the physics of the central engine.

The lecture course will start with a discussion of the Brout-Englert-Higgs mechanism of electroweak symmetry breaking and its relation to the quantum structure of the vacuum. Possible realisations of electroweak symmetry breaking within the Standard Model of particle physics, extended Higgs sectors and composite Higgs models will be presented, and their phenomenology will be highlighted. Our present knowledge about the signal that has been discovered at about 125 GeV will be summarised, and possible interpretations will be discussed. Prospects for the upcoming runs of the LHC and possible future colliders will be sketched. In this context also possible implications of the excess that was recently observed by ATLAS and CMS at about 750 GeV in searches in the two-photon channel will be discussed.
You will find further information here.

The Bethe Forum on "Axions and the Low Energy Frontier" took place from 7th to 18th March, 2016, in the Bethe Center for Theoretical Physics. The organizers are Klaus Desch (Bonn), Axel Lindner (DESY, Hamburg), Hans Peter Nilles (Bonn), Georg Raffelt (MPI, Munich). You will find further information here.

We are happy to announce the Lecture Series on "Supersymmetric Grand Unified Theories" from 15th to 19th February, 2016, in the Bethe Center for Theoretical Physics in Bonn. The lectures will be held by Stuart Raby (Ohio State University, Columbus, Ohio, USA).

Topics included

• GUT model building in space-time dimensions
• Examples of complete 4D SUSY GUTs
• Orbifold GUTs
• Embedding orbifold GUTs into the heterotic string
• Testing SUSY GUTs at the LHC

Further information and the registration can be found here.

January's Bethe Colloquium took place on January 28th
(4:15 pm) in Hörsaal I:

• Marc Vanderhaeghen (Johannes Gutenberg University Mainz)
• Precision hadron physics
• Hörsaal I, Physikalisches Institut

Abstract: To answer physics questions at both the highest and lowest energy scales, hadron physics plays a central and connecting role. In many questions at the forefront of particle physics, atomic physics, and nuclear astrophysics, the progress is limited by a missing quantitative knowledge of the strong interaction in the non-perturbative domain of Quantum Chromo Dynamics (QCD). On the other hand, precision measurement e.g. in atomic and particle physics lead to new insights on the structure of hadrons, as well as to the question how hadrons emerge out of their constituent quarks and gluons.
In this talk, I will survey several examples of this fruitful interplay. In the field of particle physics, the most precise measurement worldwide of the weak mixing angle in electron-proton scattering will open a window on searches for new physics. Furthermore, I will illustrate how measurements and theoretical calculations will lead to an improved knowledge of the anomalous magnetic moment of the muon. In the interplay with atomic physics, new measurement campaigns of nucleon form factors and polarizabilities, combined with more refined theoretical analyses, will allow to importantly improve on the limiting factors in the interpretation of high precision tests of the Lamb shift in muonic atoms and to shed light on the proton radius puzzle. In the interplay with nuclear astrophysics, measurements in nuclear systems will allow to study the nuclear equation of state, and address important questions in astrophysics, such as the detailed structure of neutron stars.

December's Bethe Colloquium took place on December 3rd
(4:15 pm) in Hörsaal I:

• Andreas Weiler (Technische Universität München)
• Naturalness' last stand
• Hörsaal I, Physikalisches Institut

Abstract: With the discovery of the Higgs boson, the Standard Model of particle physics celebrated a great triumph. It also brought the naturalness puzzle sharper into focus: What keeps the Higgs mass so light? Will supersymmetry soon be found or should we consider a cosmological solution? Run 2 of the LHC is about to tackle this and a multitude of urgent questions. We will review what I consider as the most interesting lessons learned and open issues, and outline the main directions for future progress.

The goal of the DFG Research Unit 2239 is to provide theoretical calculations, numerical tools and analyses for the systematic study of new physics phenomena in the context of the LHC. Results are being discussed in regular meetings. This upcoming meeting will be focusing on Higgs physics and dark matter at the LHC as well as on the interpretation of exciting new data.

Further information about the Research Unit and the program of the meeting can be found here:
http://web.physik.rwth-aachen.de/service/wiki/bin/view/Kraemer/NewPhysicsattheLHC

November's Bethe Colloquium took place on November 19th (4:15 pm) in Hörsaal I:

• Christof Wetterich (Universität Heidelberg)
• Big Bang or freeze?
• Hörsaal I, Physikalisches Institut

Abstract: If the sizes of atoms are allowed to vary, the geometry of our Universe can be described by different pictures, with distances between galaxies shrinking, expanding or static. Motivated by quantum gravity we discuss a unified picture where both inflation and a present dynamical dark energy arise from the same scalar field. The history of the Universe undergoes a crossover from a „past fixed point“ where all particles are massless, to a „future fixed point“ where spontaneous breaking of the exact scale invariance generates the particle masses. The cosmological solution can be extrapolated to the infinite past in physical time - the Universe has no beginning and no physical singularity. This is seen most easily in a frame where particle masses and the Planck mass are field-dependent and increase with time. In this „freeze frame“ the Universe shrinks and heats up during radiation and matter domination. In the equivalent, but singular Einstein frame cosmic history finds the familiar big bang description. The big-bang-singularity turns out to be an artifact of an unsuitable choice of „field-coordinates“. We discuss a simple model which is compatible with all present cosmological observations. It could be tested by the observation of huge lumps in the cosmic neutrino background, the detection of early dark energy , or rather large primordial graviton fluctuations generated during inflation.

The members of the Research Unit "New Physics at the LHC" pursue theoretical calculations and analyses of new physics scenarios at the LHC which address the hierarchy problem, the origin of dark matter, or both.
A meeting of the Research Unit took place on Wednesday, 28th October, in the bctp. A further meeting in the bctp is scheduled for Wednesday, 25th November.

Details about the work of the Research Unit and the program of the meeting can be found here.

October's Bethe Colloquium took place on October 22nd (4:15 pm) in Hörsaal I:

• Jan Louis (Universität Hamburg)
• String Theory - Status and Perspectives
• Hörsaal I, Physikalisches Institut

Abstract: After a brief introduction to string theory we discuss its relevance for particle physics, cosmology and mathematics.

On Saturday, 10th October, 2015, the seminar room on the Bethe Center for Theoretical Physics was filled to the rafters with young DPG members for the re-inauguration of the jDPG Bonn. The inaugural event exceeded the expectations of the organizing team. After a meeting with an interesting talk by Dr. Michael Geffert (AIfA, Bonn), lively discussion and the exchange of ideas about future events of the Bonn group, the organizers are looking forward to a range of excursions, discussions and presentations in future.

Read more about the jDPG meeting here.

From 7th to 9th October, 2015, the collaborators of the SFB/TR 16 "Subnuclear Structure of Matter" held their annual meeting in the BCTP. The collaborators from the University of Bonn, Ruhr University Bochum, and Justus Liebig University Giessen exchanged results and discussed further development of the project.

More information about the SFB/TR 16 can be found here.

We were happy to organize this year’s Bethe Center Workshop from September 29th to October 2nd, 2015, in the Physikzentrum Bad Honnef, Germany. The topic was Challenges in Strong Interaction Physics with foci on nuclear and hadron physics. The four workshop days will had the following themes:

• Non-perturbative Hadron-Hadron Interactions: few-particle systems
• Strongly interacting many-body systems
• Hadronic transitions form factors and (g-2)
• Hunting for physics beyond the SM

There were three topical sessions each day. Further information and updates on the program can be found here.

Local Organising Committee
Christoph Hanhart, Ulf-G. Meißner, Bastian Kubis, Evgeny Epelbaum, Hans-Werner Hammer, Carsten Urbach

July's Bethe Colloquium took place on July 2nd (3:15 pm) in Hörsaal I:

• Peter Koepke (Mathematical Institute, University of Bonn)
• Turing Machines: Exploring the Limits of Computability
• Hörsaal I, Physikalisches Institut

Abstract: To demonstrate the computability of a function it suffices to exhibit a concrete computational procedure like some algorithm for decimal arithmetic or a computer program. Proofs of incomputability, however, require a general notion of computability and an argument that each of those computable functions disagrees with the given function.
In 1936, Alan Turing proposed a mathematical model of computation by abstract machines, and he used it to give a negative answer to the Entscheidungsproblem of David Hilbert: there is no general procedure which decides the truth or falsity of every mathematical statement within some finite time. Turing machines soon became universally recognized as the correct model of intuitive computability: they are mathematically simple, correspond to idealized digital computers, and they are equivalent to notions of computability based on other paradigms.
In my talk I shall survey the origins of computability theory and illuminate some aspects of Turing's biography and his general views on computability and (artificial) intelligence. I shall also mention research intended to overcome the limitations of Turing computability by allowing infinitary computations. There are investigations and speculations whether such computations can be physically "realized" by letting a classical Turing machine work in an orbit around a black hole.

(Photo: Creative Commons License Attribution-Share Alike 2.0 Germany)

The Bethe Forum on String Cosmology was a one week program which brought together experts in cosmology and string theory. Among other topics, the advances and challenges in embedding inflation in string theory were discussed. The workshop took place from June 15th to June 19th. More information about the program and the registration can be found here.

June's Bethe Colloquium took place on June 18th (3:15 pm) in Hörsaal I:

• Henry S.-H. Tye (Cornell University)
• Sphaleron and Baryon Number Violating Processes
• Hörsaal I, Physikalisches Institut

Abstract: It is known that baryon number violating processes are allowed in elecrotroweak theory, but they are believed to be exponentially suppressed. I like to argue otherwise. The reasoning is based on the periodicity property of the sphaleron potential in the electroweak theory, where we write down the one-dimensional time-independent Schr\"{o}dinger equation with the Chern-Simons number as the coordinate. The baryon-lepton number violating processes may even take place at LHC soon.

May's Bethe Colloquium took place on May 7th (3:15 pm) in Hörsaal I:

• Urs Achim Wiedemann (CERN-PH/TH)
• Heavy-ion collisions at the LHC
• Hörsaal I, Physikalisches Institut

Abstract: The “standard model” of ultra-relativistic heavy ion collisions is based on the picture that viscous relativistic fluid dynamics can account for the time evolution of dense QCD matter produced in the nuclear overlap area, and that this transient QCD fluid attenuates the production of high momentum-transfer processes. My talk will review the experimental evidence supporting this picture, as well as the questions for a theory of heavy ion collisions arising from it. One recurrent theme will be that the little bangs produced in heavy ion collisions and the Big Bang are the smallest and largest physical systems respectively, for which fluctuation analysis can inform us about material properties. I shall discuss recent efforts that raise this observation beyond the level of a mere analogy by exploiting techniques of modern cosmology in heavy ion physics and vice versa.

April's Bethe Colloquium took place on April 16th (3:15 pm) in Hörsaal I:

• Andreas Ringwald (DESY)
• The Hunt for Axions and other WISPs
• Hörsaal I, Physikalisches Institut

Abstract: Many theoretically well-motivated extensions of the standard model of particle physics predict the existence of very weakly interacting slim (in the sense of ultralight) particles (WISPs), such as the axion. WISPs may constitute the mysterious dark matter in the universe and solve some puzzles in stellar and high-energy astrophysics. There are new, relatively small experiments around the globe, which started to hunt for these elusive particles and complement the search for physics beyond the standard model at the Large Hadron Collider.

Lattice field theories have become important tools to study non-perturbative phenomena in Quantum Chromodynamics and nuclear physics. In both fields, the lattice regularisation allows investigation of phenomenologically important observables from first principles. In order to further reduce systematic uncertatinties and to tackle more observables, advanced methods need to be deviced and applied. The aim of the program was to bring together world leading experts for methods in lattice field theory and trigger discussions and future developments in this research area.

Topics included:

• Finite volume methods on the lattice
• Scattering observables
• Exotic bound states and resonances
• All mode averaging and distillation
• Analysis methods for time series of large correlator matrices
• Algorithms for nuclear correlation functions
• Nuclear lattice simulations

For more informations and registration see the webpage.

From March 16th to March 19th, 2015, the yearly workshop "Beyond the Standard Model" took place at the Physikzentrum Bad Honnef. The workshop focused on recent developments in the theory of fundamental particles, the physics of the early universe, and mathematical physics. The deadline for registration was February 6th, 2015.
The topics and speakers of the pedagogical lectures were:

• Daniel Baumann (Cambridge University): Recent Developments in (String) Cosmology
• Stefano Cremonesi (King's College London): New exact Results in Supersymmetric Field Theories
• Henning Samtleben (ENS Lyon): Introduction to Exceptional Field Theory
• Eran Palti (Heidelberg University): Prospects in String Phenomenology

For more information and registration see the webpage.

Topics included

• Basics of the Strong CP Problem and Axion Solution
• Axion Models and Low Energy Couplings
• Axion-like-Particles and Other Light States
• Axions in Cosmology
• Axions in String Theory

The homepage of the program can be found here.

Dessins d'enfants and their realization as Belyi maps of compact Riemann surfaces were originally discovered by Felix Klein. Their importance and relevance was finally understood by Alexander Grothendieck who rediscovered and named them in his "Esquisse d'un programme" in 1984. The most important aspect of dessins is the operation of the absolute Galois group on them. Accordingly, dessins d'enfants provide fascinating insights and fundamental links between different fields of mathematics like inverse Galois theory, Teichmüller spaces, hypermaps, algebraic number theory and mathematical physics. The related problem of the construction of Riemann surfaces with given automorphism group turns out to be rather challenging.

Recently there have been several attempts to attack this difficult problem with some success. However we are still far from understanding what Grothendieck called the tower of Teichmüller groupoids. The goal of the workshop is to bring together experts from different fields of mathematics to share their insights and enlighten the connections between the algebraic, geometric and number theoretic aspects of the problem.

The homepage of the program can be found here.

Janurary's Bethe Colloquium will take place on January 15th (3:15 pm) in Hörsaal I:

• Arthur Hebecker (Heidelberg University)
• String Theory Landscape and Cosmological Inflation
• Hörsaal I, Physikalisches Institut

Abstract: The talk will start by motivating string theory as a theory of quantum gravity. Then the resulting 10-dimensional effective field theory and its compactification to 4 space-time dimensions will be discussed. It turns out that this leads to a very large number of possibilities - the "string theory landscape". This landscape is populated through eternal inflation, creating the so-called multiverse. To describe our observed cosmology, eternal inflation has to be supplemented by slow-roll inflation which leaves its imprint on the cosmological microwave background, measured e.g. by the Planck satellite. Recent progress in the string-theoretical understanding of this inflationary period of our universe will be briefly discussed at the end.