On 8 August, the birth date of Nobel laureate Paul Dirac, the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy, announced that James D. Bjorken and Curtis G. Callan are this year’s recipients of the Dirac Medal, which honors contributions to theoretical physics and mathematics.
The two winners were cited for their “theoretical investigations in the 1960s and 1970s, which led to the use of deep inelastic scattering for shedding light on the nature of strong interactions.” Bjorken, professor emeritus on the high-energy physics faculty at SLAC, was the first to perceive the importance of deep inelastic scattering and the first to comprehend the scaling of cross sections, now called Bjorken scaling.
Callan, professor of physics at Princeton University, and Kurt Symanzik (now deceased) reinvented the perturbative renormalization group—in a form now known as the Callan–Symanzik equations—and recognized that these equations are measures of scale invariance anomalies. Callan...
