Léon Rosenfeld

Léon Rosenfeld (French: [ʁɔzɛnfɛld]; 14 August 1904 in Charleroi – 23 March 1974) was a Belgian physicist and a communist activist.

Rosenfeld was born into a secular Jewish family. He was a polyglot who knew eight or nine languages and was fluent in at least five of them.

Rosenfeld obtained a PhD at the University of Liège in 1926, and he was a close collaborator of the physicist Niels Bohr from 1930 until Bohr's death in 1962. Rosenfeld published in 1930 the first systematic Hamiltonian approach to Lagrangian models that possess a local gauge symmetry, which predates by two decades the work by Paul Dirac and Peter Bergmann. Rosenfeld contributed to a wide range of physics fields, from statistical physics and quantum field theory to astrophysics. Along with Frederik Belinfante, he derived the Belinfante–Rosenfeld stress–energy tensor. He also founded the journal Nuclear Physics and coined the term lepton.

In 1933, Rosenfeld married Yvonne Cambresier, who was one of the first women to obtain a Physics PhD from a European university. They had a daughter, Andrée Rosenfeld (1934–2008) and a son, Jean Rosenfeld.