Graham Ross, a distinguished Scottish theorist who worked mainly on fundamental particle physics and its importance for the evolution of the universe, passed away suddenly on 31 October 2021.
Born in Aberdeen in 1944, Graham studied physics at the University of Aberdeen, where he met his future wife Ruth. In 1966 he moved to Durham University where he worked with Alan Martin on traditional aspects of the strong interactions for his PhD. His first postdoctoral position began in 1969 at Rutherford Appleton Laboratory (RAL). It was around the time that interest in gauge theories began to flourish, for which he and Alex Love were among the first to investigate the phenomenology. He continued working on this theme after he moved to CERN in 1974 for a two-year fellowship. Among the papers he wrote there was one in 1976 with John Ellis and Mary Gaillard suggesting how to discover the gluon in three-jet events due to “gluestrahlung” in electron–positron annihilation. This proposal formed the basis of the experimental discovery of the gluon a few years later at DESY.
After CERN, Graham worked for two years at Caltech, where he participated in a proof of the factorisation theorem that underlies the application of perturbative QCD to hard-scattering processes at the LHC. He then returned to the UK, to a consultancy at RAL held jointly with a post at the University of Oxford, where he was appointed lecturer in 1984. Here he applied his expertise on QCD in collaborations with Frank Close, Dick Roberts and also Bob Jaffe, showing how the evolution of valence quark distributions in heavy nuclei are in effect rescaled relative to what is observed in hydrogen and deuterium. This work hinted at an enhanced freedom of partons in dense nuclei.
In 1992 Graham became a professor at Oxford, where he remained for the rest of his career as a pillar of the theoretical particle-physics group, working on several deep questions and mentoring younger theorists. Among the many fundamental problems he worked on was the hierarchical ratio between the electroweak scale and the Planck or grand-unification scale, suggesting together with Luis Ibañez that it might arise from radiative corrections in a supersymmetric theory. The pair also pioneered the calculation of the electroweak mixing angle in a supersymmetric grand unified theory, obtaining a result in excellent agreement with subsequent measurements at LEP. Graham wrote extensively on the hierarchy of masses of different matter particles, and the mixing pattern of their weak interactions, with Pierre Ramond in particular, and pioneered phenomenological string models of particles and their interactions. In recent years, Graham worked on models of inflation with Chris Hill, his Oxford colleagues and others.
Among his formal recognitions were his election as fellow of the Royal Society in 1991 and his award of the UK Institute of Physics Dirac Medal in 2012. The citation is an apt summary of Graham’s talents: “for theoretical work developing both the Standard Model of fundamental particles and forces, and theories beyond the Standard Model, that have led to new insights into the origins and nature of the universe”.
Graham had a remarkable ability to think outside the box, and to analyse new ideas critically and systematically. His work was characterised by a combination of deep thought, originality and careful analysis. He was never interested in theoretical speculation or mathematical developments for their own sakes, but as means towards the ultimate end of understanding nature.
Many theoretical physicists are competitive and pursue their ambitions aggressively. But this was not Graham’s way. Pursuing his ambitions with persistence and good humour, he was greatly admired as a talented physicist but also universally liked and admired, particularly by the many younger physicists whom he mentored at Oxford. He was a great teacher and an inspiration, not just to his formal students but also his daughters, Gilly and Emma, and latterly his grandchildren, James, Charlie and Wilfie.