# History of the Institute

### Background

In 1919, the Physikalisches Staatsinstitut (founded in 1885) was integrated into the newly founded Universität Hamburg. In 1921, Wilhelm Lenz was appointed to the first professorship for theoretical physics. One of his first assistants was Wolfgang Pauli. It was here that Pauli discovered his exclusion principle for which he was later awarded the Nobel Prize in Physics. Another Nobel laureate of theoretical physics was Hans Daniel Jensen, a student of Wilhelm Lenz.

After World War II, Pascual Jordan came to Hamburg and established a group here that worked on general relativity. One prominent member of this group was Jürgen Ehlers, who later founded the Max Planck Institute for Gravitational Physics, the Albert Einstein Institute in Golm.

### Foundation of the II. Institute for Theoretical Physics

In 1956, Willibald Jentschke was appointed to a professorship in experimental physics. As part of this appointment, the Deutsches Elektronensynchroton (DESY) was founded. In theoretical physics, Harry Lehmann was appointed to succeed Wilhelm Lenz. At that time, Harry Lehmann was already a leading figure in quantum field theory. In particular, the fundamental connection between time-ordered functions and the S-matrix had been understood by the LSZ relation (named after Harry Lehmann, Kurt Symanzik and Wolfhart Zimmermann). To promote cooperation with experimental particle physics, the theory institute was divided, and Harry Lehmann and his staff moved to the DESY site. The DESY Theory group was founded in parallel to the II. Institute for Theoretical Physics, whereby the two cooperated closely in the time that followed. Its first head was Hans Joos.

### Development of the Institute until the late 1990s

Under the leadership of Harry Lehmann, the Institute developed into a leading center for quantum field theory and its application to elementary particle physics.

A new emphasis was placed in 1966 with the appointment of Rudolf Haag, establishing Mathematical Physics and Algebraic Quantum Field Theory as focal points of the Institute. It was during this time that Sergio Doplicher, Rudolf Haag, and John Roberts completed their work on the superselection structure of quantum field theory. Klaus Pohlmeyer and Gert Roepstorff also worked on the mathematical analysis of quantum field theory until they were offered appointments in Heidelberg and Aachen, respectively. Important was also the close contact to Kurt Symanzik, who joined the DESY Theory Group in 1968 and gave essential impulses with his work on the renormalization group (Callan-Symanzik equation).

With the appointment of Gerhard Mack (1975), conformal field theory and lattice gauge theory were added as new foci, which were later extended to a general theory of complex systems. Algebraic quantum field theory was strengthened by the appointment of Detlev Buchholz (1979), who left the institute in 1996 to take up an appointment in Göttingen.

Harry Lehman (emeritus 1985), was succeeded by Hermann Nicolai. Appointed in 1987, Nicolai established supersymmetry as a research focus. Rudolf Haag, who became emeritus in 1987, was in 1990 succeeded by Klaus Fredenhagen, whose work investigated the renormalization of quantum field theories on curved spacetimes. Hermann Nicolai, who had previously declined an appointment in Karlsruhe, left the institute in 1995 to become director of the Albert Einstein Institute in Golm.

In addition to the more formal aspects of quantum field theory, particle phenomenology was established as a central resesarch field at the institute. This involves the development of methods of quantum field theoretical perturbation theory and their application to the analysis of experimental data, here in particular those from the ring accelerator DESY, later from DORIS, PETRA and finally from HERA. Following initial work by Peter Stichel (from 1959), the appointment of Gustav Kramer in 1961 thereby laid the foundation for the establishment of a larger research group in this area, which was later expanded by further professors (Kurt Meetz in 1965, Bruno Renner in 1970, Frank Steiner in 1974, Jochen Bartels in 1978). Stichel, Meetz, and Steiner later accepted appointments in Bielefeld, Bonn, and Ulm, respectively. Renner died in an accident. Kramer and Bartels were also offered appointments elsewhere — in Wuppertal and Leipzig, respectively — but chose to decline.

Important contributions to the description of photoproduction processes were made early on, whereby Regge theory played a central role. After quantum chromodynamics was formulated as a field theory of the strong interaction in the early 1970s, the focus shifted to the perturbation-theoretical evaluation of non-Abelian gauge theories, especially QCD. The 3-jet calculations in electron-positron annihilation, which contributed significantly to the experimental detection of the gluon at the PETRA ring, should be mentioned here in particular. During operation of the HERA ring, the phenomenology group was mainly involved in the analysis of structure and fragmentation functions. The analysis of the jet production remained of great interest, both for photoproduction and electroproduction. A further theoretical focus of HERA physics was the investigation of small-x physics, the behavior of structure functions at small Bjorken-x values.

### More Recent Developments: String Theory and Astroparticle Physics

With the appointment of Jan Louis in 2000 as Hermann Nicolai’s successor, the institute’s research areas were complemented with string theory. Following the retirement of Gerhard Mack, theoretical astroparticle physics was also added as a new research area with the appointment of Günter Sigl in 2007. This group collaborates closely with observational astroparticle physics. The research into phenomenology was continued with the appointment of Bernd Kniehl in 1999 as Gustav Kramer’s successor and of Sven-Olaf Moch in 2012 as Jochen Bartels’ successor. Special emphasis lies in precision calculations in electroweak theory and QCD. Two new DESY funded professorships were established for which Gudrid Moortgat-Pick (2009) and Geraldine Servant (2014) were appointed. Gudrid Moortgat-Pick looks at the physics of a future electron-positron linear accelerator. Geraldine Servant considers the applications of elementary particle physics in cosmology. In 2014, Gleb Arutyunov succeeded Fredenhagen as the chair for quantum field theory and mathematical physics. He primarily concerns himself with integrable structures in quantum field theory.

### Participation in University and DESY Management

After the faculty structure was abolished in 1970 and replaced with departments, Gustav Kramer, Harry Lehmann, and Gerhard Mack acted as department spokespersons. After the faculties were reintroduced in 2006, Jochen Bartels served as head of the department, as well as after him Jan Louis and Günter Sigl. From 2016 to 2023, Jan Louis served as a vice president of Universität Hamburg. Harry Lehmann and Gustav Kramer both served in DESY management committees for many years.

### Research Training Groups, Collaborative Research Centers, and Cooperations

The institute established two DFG Research Training Groups: “Theoretical Elementary Particle Physics” (1990–1999; spokespersons: Hermann Nicolai, Klaus Fredenhagen) and “Future Developments in Particle Physics” (2000–2009; spokesperson: Jochen Bartels). It has also been instrumental in the Collaborative Research Center “Particles, Strings and the Early Universe” (2006–2018; spokespersons: Jan Louis, Johannes Haller) and currently is in the Cluster of Excellence “Quantum Universe” (since 2019; spokespersons: Erika Garutti, Jan Louis, Peter Schleper, Geraldine Servant, Timo Weigand).

The institute has been involved in the Center for Mathematical Physics since 2003 (together with the Department of Mathematics and the DESY Theory group) and in the Wolfgang Pauli Centre for Theoretical Physics since 2013 (together with the I. Institute for Theoretical Physics and the DESY Theory group).

### Awards

Current and former members of the institute have been conferred numerous prizes. These include the Max Planck Medal of the German Physical Society, which has been awarded to Harry Lehmann, Rudolf Haag, Martin Lüscher (doctorate at the institute in 1976), and Detlev Buchholz. Harry Lehmann received the Dannie Heineman Prize for Mathematical Physics, and Rudolf Haag won the Henri Poincaré Prize of the International Association of Mathematical Physics (IAMP). Gerhard Mack and Hermann Nicolai were conferred the Klung Wilhelmy Science Award, and Klaus Pohlmeyer, Detlev Buchholz, Klaus Fredenhagen, Hans Werner Wiesbrock (research associate at the institute 1987–89), and Volker Schomerus (assistant at the institute 1995–2000) have all been honored with the physics prize of the Göttingen Academy of Sciences and Humanities. Gustav Kramer was a visiting scientist at Argonne National Laboratory in 1968–69 and a distinguished visiting professor at Ohio State University in 1983–84. Klaus Fredenhagen acted as Leibniz professor at the University of Leipzig in 1997. Jochen Bartels was granted an honorary professorship by the Faculty of Physics at St. Petersburg State University (Russia) in 2011 and accorded the Abate-Molina (Humboldt) Prize for excellence in science from the Chilean National Commission for Scientific and Technological Research (CONICYT) in 2012.

### Institute Professors

- Harry Lehmann 1956–1986 (emeritated)
- Peter Stichel 1959–1970 (appointment in Bielefeld)
- Gustav Kramer 1961–1998 (emeritated)
- Kurt Meetz 1965–1967 (appointment in Bonn)
- Rudolf Haag 1967–1987 (emeritated)
- Bruno Renner 1970–1973 (deceased)
- Gert Roepstorff 1972–1974 (appointment in Aachen)
- Klaus Pohlmeyer 1972–1975 (appointment in Heidelberg)
- Frank Steiner 1974–1995 (appointment in Ulm)
- Gerhard Mack 1975–2005 (emeritated)
- Jochen Bartels 1978–2011 (emeritated)
- Detlev Buchholz 1979–1997 (appointment in Göttingen)
- Hermann Nicolai 1987–1995 (appointment at the Max Planck Institute for Gravitational Physics, the Albert Einstein Institute in Golm)
- Klaus Fredenhagen 1990–2013 (emeritated)
- Bernd Kniehl (since 1999)
- Jan Louis (since 2000)
- Günter Sigl (since 2007)
- Gudrid Moortgat-Pick (since 2009)
- Sven-Olaf Moch (since 2012)
- Gleb Arutyunov (since 2014)
- Geraldine Servant (since 2014)
- Timo Weigand (since 2020)

(Sources: Prof. Dr. Jochen Bartels, Prof. Dr. Klaus Fredenhagen, Prof. Dr. Gustav Kramer)