Dirac Medallists 1991

Stanley Mandelstam, University of California, Berkeley, USA

in recognition of his contributions to the development of theoretical physics. His representation of the analytic properties of scattering amplitudes in the form of double dispersion relations (Mandelstam representation) is basic to the modern understanding of relativistic particle scattering and his seminal work on the quantization of string theories, exploiting their conformal properties, led to a more profound understanding of this subject. Mandelstam was among the first to apply path integral quantization methods to string theory. This work was generalized and extended by many others in the following years and now forms an integral part of the modern formulations.

Jeffrey Goldstone, Massachusetts Institute of Technology, Cambridge, USA

for his fundamental clarification of the phenomenon of spontaneous symmetry violation in relativistic quantum field theory. This phenomenon has come to occupy a central role in our understanding of elementary particles, and Goldstone's work is now among the foundations of the standard model of fundamental interactions. The ensuing massless bosons, known as Goldstone bosons, have found crucial applications also in many spontaneous symmetry breaking processes in condensed matter physics.