Gunnar Källén

Anders Olof Gunnar Källén (13 February 1926 – 13 October 1968) was a Swedish theoretical physicist and a professor at Lund University, known for his work on correlation functions in quantum field theory. He died at the age of 42 as a result of a plane crash.

Biography
Anders Olof Gunnar Källén, son of Yngve Källén, was born in 1926 in Kristianstad, Sweden. His father teacher of physics and mathematics, Gunnar and Yngve published a paper togethers. Gunnar's brother was embryologist Bengt Källén.

Källén earned his doctorate at Lund in 1950 working with Torsten Gustafson, who was in close correspondence with Wolfgang Pauli. He worked from 1952 to 1957 at CERN's theoretical division in Copenhagen, which then became the Niels Bohr Institute. He also worked at Nordita 1957–1958 and then began a professorship at Lund University.

Källén's research focused on quantum field theory and elementary particle physics. His developments included the so-called Källén–Lehmann spectral representation of correlation functions in quantum field theory, and he made contributions to quantum electrodynamics, especially in renormalizing. He also worked with the axiomatic formulation of quantum field theory, which led to contributions to the theory of functions of several complex variables. He collaborated on the Pauli–Källén equation. The Källén function is named after him.

The Kallen–Yang–Feldman formalism and the Källén-Sabry potentials are also named after him.

Plane crash
Källén worked for several years at the Bohr Institute. Källén was a pilot an possessed a Piper PA-28 Cherokee Arrow. He was flying from Malmö to CERN when his plane crashed during an emergency landing in Hanover, Germany in 1968. His two passengers, one of them his wife, survived the crash.

Many years after his death, Cecilia Jarlskog edited the book Portrait of Gunnar Källén: A Physics Shooting Star and Poet of Early Quantum Field Theory (Springer, 2013) with 9 invited contributors, all of whom had a personal acquaintance with Källen. The book consists mainly of testimonies by Källén's colleagues. Steven Weinberg, whose first published physics paper was motivated by Källén, wrote one of the book's chapters. The chapter deals with Källén's research and is the written version of a 2009 lecture by Weinberg.