Obituaries

• Lev Lipatov 1940–2017 • John Smith 1938–2017 • Maria Krawczyk 1946–2017

Lev Lipatov 1940–2017

On 4 September our friend and colleague Lev Nikolaevich Lipatov of the Russian Academy of Sciences (RAS) passed away unexpectedly while attending a physics meeting in Dubna. Lev grew up in Leningrad (now St. Petersburg) and entered the physics faculty at the Leningrad State University in 1957. In 1963 he joined the group of Vladimir Gribov at the Ioffe Physical-Technical Institute of RAS, defending his dissertation in 1968. He remained in Gribov’s group when it moved to the Leningrad Nuclear Physics Institute in Gatchina in 1970 and obtained a permanent position. He became a professor of physics in 1990 and, since 1997, was the director of the theory division. In 1998 he also became a member of St. Petersburg State University, where he lectured, and in 2011 he was elected as a full member of the RAS.

Lev was a leading figure worldwide in the high-energy behaviour of quantum field theory. Supported by Gribov, he began to analyse the high-energy behaviour of QED processes and became involved in the investigation of the “double logarithms”. His main focus was first on the Regge limit (at the time, Regge theory had just started to become popular for analysing high-energy scattering processes), but the discovery of Bjorken scaling transferred his focus to the kinematic limit of deep inelastic scattering. It was after a seminar given by Gribov when Lev spotted a gap in the theoretical argument – leading to the famous “GL” paper, which later became a theoretical cornerstone of the DGLAP evolution equations. These are now an important pillar in the analysis of high-energy scattering processes at the LHC.

After the rise of non-abelian gauge theories in the early 1970s, it was again the Regge limit that attracted Lev’s interest: together with his collaborators in 1975 he derived an integral equation which, after applying it to QCD, became known as the “BFKL” equation. It took several years before this equation received international attention, but today the BFKL papers are among the publications with the highest numbers of citations in high-energy physics.

Lev’s scientific work extends much further, however. He found a new approach for investigating large orders in perturbation theory, generalized the concept of partonic evolution equations beyond the leading-twist approximation and spent several years computing the NLO corrections to the BFKL equation. He discovered that the BFKL Hamiltonian (after generalizing to many-gluon states) is equivalent to an integrable Heisenberg spin model, thus demonstrating that the concept of integrability plays an important role in high-energy physics, and developed a new formulation in terms of a gauge-invariant “effective action”. In gravity he discovered the reggeization of the graviton and within the conjectured AdS/CFT duality he pointed out the need for correcting the BDS formula using remainder functions, and worked on the duality of the BFKL pomeron with the graviton. Although Lev’s work was purely theoretical, he never neglected experimental data: his last papers studied the application of the QCD BFKL equation to HERA data, thus gaining a deeper understanding of his “favourite child”, the BFKL pomeron.

Lev was well known in the high-energy physics community and was invited to give talks at countless international meetings and conferences. He set up numerous collaborations, paid several visits to CERN and, since the early 1990s, made regular visits to DESY. Lev received many national and international prizes and awards, including the research award of the Alexander von Humboldt Foundation in 1993, the Pomeranchuk Prize in 2001, the Marie Curie Excellence Chair of the European Community, hosted by Hamburg University in 2006–2009, and the European Physical Society High Energy and Particle Physics Prize in 2015. As well as his research in Russia, he set up collaborations in Germany, France, England, Spain, Israel and Chile.

Those who had the privilege to know Lev up close experienced a very friendly person whose interest and understanding in physics was extraordinary. In any situation he was ready and more than happy to discuss physics, and was enthusiastic about new ideas. Behind this, Lev was a loving husband to his wife Elvira and a caring father of his daughters Irina and Katja, and their families. Last but not least, he was very attached to his home city of Leningrad and to his home country of Russia.

Together with his numerous collaborators and friends, we deeply regret that Lev is no longer with us.

• Jochen Bartels, on behalf of his collaborators and friends.

John Smith 1938–2017

John Smith, an eminent theoretical particle physicist at the C. N. Yang Institute for Theoretical Physics (ITP) at Stony Brook University in the US, passed away on 16 July aged 79. John, who was known by everyone as “Jack”, was born in Selkirk, Scotland, and earned a BSc, MSc and PhD at the University of Edinburgh. During his graduate study, he spent a year at the Joint Institute for Nuclear Research (JINR) in Dubna, receiving his doctorate in 1963. He held postdoctoral positions at Nordita as a NATO fellow and at the University of Adelaide as a Rothman fellow. In 1967 he joined the ITP as a research associate, becoming a key member of the faculty for more than three decades. Jack retired in 2007 but kept active in research as professor emeritus.

Jack made important contributions spanning a range of areas in particle physics, and a constant theme in his work was to perform calculations that could be compared with data. Among his early works were papers on weak interactions, calculating predictions of various electroweak gauge theories for neutral-current reactions and using these in conjunction with new data to constrain the theories. In a 1983 paper he co-authored, Jack demonstrated the power of the Jacobean peak in determining the mass and width of the W boson – a method still in use today at the LHC. Over the ensuing years, Jack’s often-legendary calculations in perturbative QCD contributed mightily toward establishing the contemporary picture of fundamental interactions. These included several papers in 1989 and the early 1990s with various co-authors, in which calculations of the production of heavy quark–antiquark pairs in pp and pp collisions were presented. These provided valuable and timely input for the analysis of Fermilab data by the CDF and D0 collaborations that led to the discovery of the top quark in 1995.

In 2003, together with his colleagues Willy van Neerven and Vajravelu Ravindran, Jack published a landmark calculation of higher-order QCD corrections to the cross-section for Higgs-boson production in hadronic collisions. This work was valuable in the analysis of LHC by the ATLAS and CMS collaborations that led to the discovery of the Higgs boson in 2012. It was quite fitting that Jack was invited to attend the 2013 ceremony at which his doctoral advisor, Peter Higgs, received the Nobel Prize (shared with François Englert).

Jack was renowned for his modest and gentle personality. He gave generously of his time to colleagues and students, and taught the full range of courses, from advanced quantum field theory to freshman physics. Students were very much aware of his expertise in research, his dedication to teaching and mentoring, and his kind nature. Jack served as the supervisor for many doctoral thesis students and as a mentor for a number of postdoctoral research associates at Stony Brook. His excellent pedagogical skills were evident in the textbook Field Theory and Particle Physics (1986), and one of the last projects he worked on was the completion of a new textbook on quantum field theory.

Jack Smith’s research accomplishments were recognised with a Humboldt Research Award and as a fellow of the American Physical Society. In the autumn of 1993 he held the visiting Kramers chair at Utrecht University, in 2005 he received the Stony Brook President’s Award for Excellence in Scholarship and Creative Activities, and in October 2016 we were honoured when he was able to participate in a symposium celebrating the anniversary of the establishment of the ITP, in whose development he played such an important role.

We miss Jack greatly. He will always be remembered by his former students, postdocs, colleagues and co-authors, and, indeed, by all the people who knew him across the world.

• Bernard de Wit, Rohini Godbole, Eric Laenen, Robert Shrock, George Sterman, and Jos Vermaseren.

Maria Krawczyk 1946–2017

Maria Krawczyk passed away suddenly on 24 May 2017. It was a shock not only for her family but also for many of the physicists and her friends in the faculty of physics at the University of Warsaw and abroad. She was a very well-known and respected scientist within the physics community for her passion and involvement in research, teaching and outreach.

Maria graduated from the University of Warsaw, and her scientific career was intertwined with the university, first as an assistant, then adjunct university professor and full professor. In 1975 she defended her PhD thesis under the supervision of Grzegorz Białkowski based on studies of the charge exchange reaction πp → π0n. During a postdoc at the Max Planck Institute in Munich in 1977/78 her scientific interest shifted towards the parton model and quantum chromodynamics (QCD). She worked on the hadronic properties of photons within QCD, where her speculations on direct photon pair production in hard collisions were then verified by experiments. Later she worked on the resummation of higher order QCD corrections.

In 1990 Maria became interested in electroweak interactions, in particular the Brout–Englert–Higgs mechanism of spontaneous electroweak symmetry breaking and the Higgs sector. The Higgs particle became her main research direction, including the two-Higgs-doublet models, searches for light Higgs particles in existing and planned accelerators, the CP properties of the scalar sector, the role of the Higgs in astrophysics and cosmology, and the structure of the vacuum. She was an enthusiast for studying photon collisions at a future linear collider, and took an active role in workshops devoted to the physics potential of future experiments. During a stay at CERN in 2002 she initiated discussions and studies of CP violation in non-standard Higgs models, becoming an organiser of the workshop on CP studies and non-standard Higgs physics – which culminated in the delivery of a CERN Yellow Report. With the advent of the LHC, she concentrated mainly on LHC physics.

During her career, Maria collaborated with many distinguished physicists around the world and coordinated a number of scientific grants financed by Polish and European agencies – right up to her last project, HARMONIA. She served in a number of advisory committees and was involved in several international workshops and conferences. Maria served on the TESLA collaboration board, represented Poland in outreach within the European linear collider steering group, and in 2004 was invited to join the programme committee of the Rencontres de Moriond series of conferences on QCD.

Maria enjoyed contact with students. She was concerned not only with their scientific development but also their living conditions, and helped in sending them to physics schools and conferences, finding grant opportunities and editing grant applications. She was very active in daily matters at the faculty and university, and engaged heavily in outreach activities, giving radio and TV interviews, lecturing at scientific festivals and organising LHC exhibitions.

Maria was a very kind and helpful person. Her advice, including in private matters, and friendliness will be greatly missed. She was also a beloved wife, a mother of two children and grandmother of four grandchildren.

• Colleagues and friends from the University of Warsaw.