Professor Iosif Khriplovich

The Silver Dirac Medal for the Advancement of Theoretical Physics is awarded to commemorate the visit to the University in 1975 of Professor P.A.M. Dirac, one of the greatest theoretical physicists of the twentieth century. Two medals were awarded in 2004.

The first medal was awarded to Professor Edward Shuryak, the Director of the Institute for Nuclear Theory at the State University of New York at Stonybrook. He proposed the so-called ‘instanton liquid’ model of the QCD vacuum, considering the “vacuum” (ground state) as an ensemble of interacting non-linear fluctuations called instantons. This picture has recently been shown to predict the spectrum of elementary particles very well. Another theme of his research has been the behaviour of matter at extreme temperatures and pressures, when ‘elementary’ particles melt to form a completely new phase of matter, called the ‘Quark-Gluon Plasma’ (QGP), He showed that under such conditions the ‘colour’ charges of the quarks are screened rather than confined.

Professor Shuryak gave a public Dirac lecture on the topic ‘Quark-Gluon Plasma: Part of the Big Bang Recreated in the Laboratory’. To observe and study the Quark-Gluon Plasma (QGP), a dedicated collider complex RHIC has been built, at Brookhaven National Laboratory. Two gold nuclei, accelerated to 200 GeV per nucleon each, are smashed together, producing a small fireball of QGP. It was found that it explodes hydrodynamically, in what was called a Little Bang, with many amusing parallels to the Big Bang.

The second medal was awarded to Professor Iosif B. Khriplovich, Chief Scientist at the Budker Insititute of Nuclear Physics at Novosibirsk in Russia, and Chair of Theoretical Physics at Novosibirsk University. Professor Khriplovich is a Member of the Russian Academy of Science. His most striking discovery is that in so-called non-Abelian gauge theories the interaction is reduced at small distances (‘asymptotic freedom’). The Standard Model of elementary particles was constructed on the basis of these theories. Khriplovich published his calculation in 1969 for the SU(2) theory describing the weak interaction part of the Standard Model. Four years later a similar result was obtained for the strong interaction part of the Standard Model (Quantum Chromodynamics) by Politzer, Gross and Wilczek. The discovery of asymptotic freedom made a revolution in high energy physics, and last year Politzer, Gross and Wilczek were awarded the Nobel Prize for this work. Khriplovich has also made an important contribution to the discovery of violations of the fundamental symmetry – parity – in atoms, and the discovery of an electromagnetic moment violating fundamental symmetries – the nuclear anapole moment. He gave a public Dirac Lecture on ‘Black Holes, Classical and Quantum’, demonstrating that black holes should possess entropy and temperature. Thus, black holes should radiate.

Chris Hamer