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, slides and recordings are available on the event webpage.

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.

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.

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.

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 as well as the registration form 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 havw 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?
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• What are the quantities to extract form the finite-volume sector?
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• 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 can be found on the event 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.

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.

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 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.

There has been an accompanying Bethe Forum Program in the week following the conference.

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 9th Bethe Center Workshop "Computational Sciences and Reality" took place on October 2 - 6, 2017 in the 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 form are available here.

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.

The Bethe Forum on "SUSY breakdown confronting LHC and other data" took place from 29th May to 2nd June, 2017, in the Bethe Center for Theoretical Physics in Bonn.
The event was organized by Xerxes Tata (Hawaii), Manuel Drees (Bonn), Hans Peter Nilles (Bonn), and Stefan Pokorski (Warsaw).

For more information and the registration see the webpage.

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 here.

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

• 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 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.

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

More information is available here.

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.

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 were Oleg Lebedev (Helsinki), Lars Bergström (Stockholm), Manuel Drees (Bonn) and Alejandro Ibarra (TUM, Munich).

Further information can be found here.

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 were Rolf Kappl (Bonn), Herbert K. Dreiner (Bonn), Christophe Grojean (DESY, Hamburg) and Martin Winkler (Bonn).

Further information can be found here.

The lecture course started 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 were presented, and their phenomenology was highlighted. Our present knowledge about the signal that has been discovered at about 125 GeV was summarised, and possible interpretations were discussed. Prospects for the upcoming runs of the LHC and possible future colliders were 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 were 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 have hosted 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 were 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 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 had the following themes (preliminary):

• 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, registration 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

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.

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.

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.

The workshop took place from September 29th to October 3rd. There were pedagogical introductory lectures each day followed by research talks by the participants. The introductory talks were

• Andrea Brini: "Introduction to matrix models"
• Hans Jockers: "Topological Strings and Effective Interactions"
• Albrecht Klemm: "Introduction into Refined Topological String Theory"
• Johannes Walcher: "Introduction to Matrix Factorizations and D-branes"
• Alessandro Tomasiello: "Geometric aspects of supersymmetric field theories on curved manifolds"

The organizing committee consisted of Hans Jockers, Albrecht Klemm, Wolfgang Lerche, and Stefan Theisen.

String compactifications have mostly focussed on geometrical constructions. Prime examples that preserve a certain amount of target space supersymmetry are Calabi-Yau and orbifold compactifications. However, it has been realized very early on that string theory also admits constructions that do not admit any (easy) geometrical interpretation, for example asymmetric orbifolds, free-fermions and Gepner models.

Recently the field of non-geometrical string compactifications has revived. One motivation for this has been the search for constructions that provide a build-in mechanism for moduli stabilization. Another reason is that it has been realized that maximal (N=8) supergravities in four dimensions admit many gaugings, but only a small subset of those can be associated with compactifications of 10D supergravity. Some of the other gauge supergravities can be obtained by applying T-dualities to the geometrical compactifications. Hence, one expects that there must be some sort of lift of these 4D gauged supergravities to 10D string theory. They go under the name of non-geometrical flux backgrounds.

Since an underlying idea is that various configurations of fluxes are related by T-dualities, it would be useful to have a formulation of the low-energy theory of string theory that is T-duality covariant. Here, double field theory enters the scene: it is a construction in which the number of coordinates are doubled to make T-duality manifest.

Double field theory is one attempt to have a definite stringy description of non-geometry. Another approach is to use asymmetric orbifolds. Even though these orbifolds do not have a simple geometrical interpretation, they provide exactly solvable string solutions. The connection between them and the non-geometric fluxes has recently been investigated. In addition some first attempts have been made to do model building on such backgrounds. Furthermore, a natural description of asymmetric Z2xZ2 orbifolds are free-fermionic constructions. Also, quite recently, there has been a full classification of all symmetric orbifold geometries compatible with heterotic N=1 or more supersymmetry in four dimensions using the language of cristallography. It would therefore be very interesting to obtain a similar classification of asymmetric orbifolds. In addition the techniques to determine the nature of the non-geometrical fluxes might also be applicable to more involved non-geometrical string constructions like Gepner models.

In this workshop we wanted to bring together experts on the various aspects of non-geometry and exact string constructions to share their recent results and discuss how some of the open questions mentioned above can be addressed.

The homepage of the program is available here.

Discrete symmetries play an important role for model-building and phenomenology. Some examples are 1) discrete flavor symmetries used in order to explain the observed patterns of masses and mixings of quarks and leptons and 2) discrete symmetries that forbid unwanted operators (like those that induce rapid proton decay). As quantum-gravitational effects are believed to break discrete symmetries in a way that their phenomenological properties are lost, these symmetries need to be protected against such effects. In the traditional approach this is achieved when the discrete symmetry originates as a discrete remnant of a (spontaneously) broken (anomaly-free) gauge symmetry. For example, a Z_N symmetry can originate from a U(1) gauge symmetry, where the symmetry-breaking is induced by an object of charge N. Also a non-Abelian discrete symmetry can originate from a gauge symmetry, but typically the breaking is more involved: large representations of the non-Abelian gauge symmetry are needed to induce the breaking.

There is a second possibility to protect discrete symmetries against gravitational effects by relating their origin to the relevant energy scale: the scale where quantum effects of gravity become important, i.e. the planck scale. Hence, this approach needs a consistent theory of quantum gravity and string theory is a prime candidate. Within string theory discrete symmetries (Abelian and non-Abelian) can naturally originate from both, the traditional approach described above and, furthermore, from the compactification from ten to four dimensions. In the later case one can partially understand the origin of the discrete symmetry intuitionally from properties of the six-dimensional compactification space. But in addition to this intuition there can be vanishing couplings and relations between coupling strengths that only show up in the explicit computation of string amplitudes. Some of them can be interpreted as an enlargement of the intuitive symmetry, but some might not. Intersecting D-branes and heterotic orbifold compactifications provide consistent frameworks that allow to study the origin of discrete symmetries from string theory directly. Recently, discrete R-symmetries have been re-examined in this context. But a full study of couplings and their interpretation as discrete symmetries remains as an open problem.

The aim of this workshop was to bring together experts on discrete symmetry phenomenology with experts on their possible string theory origin.

The homepage of the program is available here.

In this Bethe-Forum on "Detector Physics" distinguished international experts in the field of detector development are invited to discuss the current advancements and trends in high-resolution detection of particles and radiation. The areas covered include micro-patterned semiconductor and gaseous detectors for tracking and imaging, scintillating crystals, calorimeters, as well as cryodetectors. The physics and consequences of radiation on the performance of the detectors will also be discussed. The invited guests will stay in the institute for some time and will be available for discussions.

The homepage of the program is available here.

Recent years have seen remarkable advances in our ability to compute on-shell scattering amplitudes in quantum field theories. These basic objects are crucial to our ability to provide the theoretical support needed for the experimental program at CERN's Large Hadron Collider. They are also objects worthy of study in their own right, and investigations into them have revealed new and unexpected aspects of gauge and gravity theories. The lectures will cover the basics of the developments of recent years: on-shell recursion relations, the unitarity method, and their application to QCD and maximally supersymmetric Yang--Mills theories. The lectures will also cover material related to applications of QCD to collider physics, such as infrared cancellations and subtraction methods. The lectures will sample some more advanced topics, such as unitarity at higher loops, Bern--Carrasco--Johansson duality, Grassmannians, and twistor strings. What lies ahead in the field of amplitudes is almost certainly as remarkable as what we have discovered already. These lectures are intended to prepare students to embark on their own research in this challenging and exciting area of high-energy physics.

The homepage of the program is available here.

The workshop will take place from September 30 to October 3 at the Physikzentrum Bad Honnef. The four days of the workshop shall be devoted to intense discussion between theory and experiment on 4 topics:

• Higgs: Understanding and Interpreting the new Boson
• SUSY+BSM: What's left for SUSY, how do we further improve the interpretation of the searches, and what other options should be explored?
• SM Precision: What needs to be calculated more precisely, and what needs to be measured more precisely, to best interpret the data?
• Flavour: How best to understand the flavour structure of the SM? How do we improve upon interpretation of `new physics' models in light of flavour and other precision measurements, negative search results, and the Higgs?

The organizing committee consists of Philip Bechtle, Klaus Desch, and Herbert Dreiner.

There will be two Bethe Forum Programs accompanying the Planck 2013 conference hosted at Bonn University. The programs will take place in the week before and after the conference. The Bethe Forum in the week before Plack 2013 from May 13th to May 17th carries the title "Planck and the Early Universe", and the Bethe Forum after Plack 2013 from May 27h to May 31st has the title "Supersymmetry: Tools meet Models". More information is available here.

The Bethe Forum lecture series by Prof. Baumann covers topics including

• Inflation
• Particle Physics
• Cosmic Microwave background

It is intended for graduate students and postdocs. The homepage of the program is available here.

The 4th Bethe Center workshop is part of a three weeks program on String Theory and Unification. The workshop takes place from October 1st to October 5th at the Physikzentrum Bad Honnef.
The homepage of the workshop can be found here.

The Bethe Forum on Unification and String Theory is a three week program focusing on

• Global Model Building with a bias towards the Heterotic String
• Local Model Building focusing on constructions in the context of type IIB/F-theory

The workshop takes place from September 24th to October 12th. In the second week, there will be the 4th Bethe Center workshop on Unification
and String Theory at the Physikzentrum Bad Honnef. The rest of the workshop will be held at the bctp.
The homepage of the program can be found here.here.

The Bethe-Forum "Lecture Series on Mathematical String Theory" from July 2nd to July 13th is a school on recent topics in Mathematical String Theory. It is intended as a preparation to the String-Math 2012 for graduate students and researchers alike. The aim is to introduce current research topics in the field to both mathematicians and theoretical physicists and to bring together the respective physics and mathematics communities.
The homepage of the program can be found here.

In the last years, the simple quark model picture of hadrons has been severely put into question by a cornucopia of experiments that show signals of so-called "exotic hadrons". At present, the nature of these states is not understood. The aim of this program is to sharpen the theoretical approaches to describe these states and pin down pertinent experimental signatures to differentiate between various options. Key issues of this program are:

• Charmonia and exotica (decays, transitions, ...)
• Theory of multiquark states
• Theory of hadronic molecules
• Hadron resonances in Lattice QCD

The homepage of the program can be found here.

The lecture series is intended for graduate and post-graduate students. The topics that are covered include

• From Large N Gauge Theories to Strings
• Basics of the AdS/CFT Correspondence
• Applications to Strongly Coupled Field Theories
• Lessons for Quantum Gravity, Black Holes and Cosmology

The homepage of the program can be found here.

The workshop’s intention is to bring together experts in two-dimensional conformal field theory and four-dimensional supersymmetric Yang-Mills theories to discuss the overlap of the two fields as suggested by AGT.

The homepage of the program can be found here.

The inaugural program of the Bethe forum was a three week program covering

• LHC and Collider Phenomenology
• Grand Unification and String Theory
• Dark matter

The homepage of the program can be found here.