Lev Lipatov
Lev Lipatov (1940-2017)

     Lev Nikolaevich Lipatov, an outstanding theoretical physicist, fellow of the Russian Academy of Sciences and Director of the Theory Division of the Petersburg Nuclear Physics Institute passed away September 4th, 2017, at the age of 77. Lev Lipatov is a world renowned scientist, one of a small group of the most brilliant minds of the modern theoretical physics. He created a scientific school that brought together theorists from Russia, Germany, United States, Spain, Israel, Slovakia and other countries.
     It is hard to overestimate Lipatov's contribution to the creation and development of Quantum Chromodynamics. For many years he was (and remained up to the very last moment) the world leader in the field perturbative QCD theory. The method of summation of the leading logarithms suggested and developed in the groundbreaking works by V. N. Gribov and L. N. Lipatov became the backbone of the modern theory of hard QCD processes. A self consistent QCD parton model that followed from the summation of the leading logarithms predicted logarithmic evolution of the structure functions with the transferred momentum. The respective evolution equations are now known as the DGLAP equations (after Dokshitzer, Gribov, Lipatov, Altarelli, and Parisi).
     All his life L. N. Lipatov was deeply involved in the research on the high energy scattering in QCD. He (in collaboration with others) obtained the famous BFKL (Balitsky, Fadin, Kuraev, Lipatov) equation. This equation allows to find the structure of the scattering amplitude singularities in the complex angular momentum plane, and therefore, determines the high energy asymptotic behavior of the scattering amplitudes. The BFKL theory is nowadays the basic tool for description of scattering at high energy accelerators. It is not an exaggeration to say that all our understanding of high energy scattering is based on the works of L. N. Lipatov and his school.
     Lev Nikolaevich Lipatov excelled in research of the perturbative Quantum Field Theory. He had an amazing ability to find elegant and mathematically rigorous solutions of prohibitively difficult problems. He had suggested and developed an effective method for analysis of the asymptotic behavior of the perturbation theory series in Quantum Field Theory. His works on this subject acquired now the status of the theoretical physics classics. They now form the basis of our knowledge about the behavior of the perturbation theory series and their singularities in the complex coupling constant plane.
     In recent years L. N. Lipatov's attention was drawn to the N=4 supersymmetric Yang-Mills theory. He used the BFKL approach to show that this remarkable theory is completely integrable and (probably) is even exactly solvable. He also worked a lot on the reggeon theory in quantum chromodynamics and gravity. This project, unfortunately. remained unfinished...
     L. N. Lipatov is well known and highly respected by his peers around the world. His publications collected more than 26000 citations what emphasizes wide recognition and high appreciation of his results. Scientific achievements of L. N. Lipatov were acknowledged by numerous prizes and awards. Among his other awards are the 2001 I.Ya. Pomeranchuk prize and the 2015 European Physical Society High Energy and Particle Physics Prize.
     Besides the research activity L. N. Lipatov was teaching at the Saint Petersburg State University, participated in organizing a number of national and international physics schools and conferences, in particular the annual PNPI wither schools. He was a co-chairman of the well known international conference series on Quantum Chromodynamics and Hadron Structure (HSQCD).
     Memory of Lev Nikoleavich will forever live in our hearts.

     The funeral will be held on Friday, September 8, in Petersburg Nuclear Physics Institute.

Theory Division faculty and staff.