The Faddeev Medal was inaugurated in 2016 by the Topical Group on Few-Body Systems & Multiparticle Dynamics (GFB) of the American Physical Society and the European Research Committee on Few-Body Problems in Physics (ERCFBP) to recognize distinguished achievement in Few-Body Physics. It is co-sponsored by the journal *Few-Body Systems*, published by Springer. The medal, named in honor of distinguished theoretical physicist Ludwig Faddeev (1934-2017), is awarded every three years to a scientist or scientists who advanced the field of Few-Body Physics significantly—either through ground-breaking research or due to crucial progress achieved over the course of a career. The Faddeev Prize is supported by contributions from Springer and the GFB.

Nominations for the 2024 Faddeev prize were evaluated by an international panel of experts, chaired by Prof. Kimiko Sekiguchi of Tohoku University. The committee selected Professor Henryk Witała as the recipient of the 2024 Faddeev medal for his life-time achievements in few-nucleon physics, especially for solving the continuum Faddeev equations with realistic nuclear forces and comprehensive studies of three-nucleon dynamics.

**Henryk Witała** *"For the life-time achievements in few-nucleon physics, especially for solving the continuum Faddeev equations with realistic nuclear forces and comprehensive studies of three-nucleon dynamics**”*

The GFB and the ERCFBP wholeheartedly congratulate Prof. Witała. The prize consists of $2500 US, a medal, and an invitation to the 23rd International Conference on Few-body Problems in Physics (FB23) which will be held in 2024 in Beijing, China. Prof. Witała will receive his medal and give a lecture during a special session at the meeting; its text will be published by the journal Few-Body Systems.

Ludwig Faddeev’s autobiography states, “The treatment of the quantum scattering theory for the system of three particles, based on the integral equations, now bearing my name, brought me my first success. The work was highly appreciated by the specialists in nuclear physics.”. Faddeev’s contribution to the quantum mechanical three-body problem is largely responsible for the birth of the international few-body community and it is fitting that Professor Witała, being first to solve the three-nucleon scattering problem with realistic two-nucleon forces, is recognized by this prize named after Ludwig Faddeev.

Professor Witała’s achievement provided a solid foundation for the theoretical interpretation of experimental data and for studies of various ingredients in the nuclear Hamiltonian, without introducing any uncontrolled approximations. The results obtained by Professor Witała significantly influenced a surge of interest in few-nucleon systems, and gave a new impetus to undertake efforts for ab-initio calculations with even larger numbers of nucleons.

In the three-nucleon sector availability of solutions of Faddeev equations with realistic forces opened many opportunities to further detailed investigations and strongly stimulated both theoretical and experimental works. The two most important directions of such activities are studies of polarization phenomena and the role of the three-nucleon force. In the early 1990s numerical solutions of the three-nucleon Faddeev equations for nucleon-deuteron scattering, both below and above the breakup threshold, with inclusion of three-body forces, became available. Again, the role of Henryk Witała in this progress was dominant while working both on conceptual and technical issues.

The possibility to study the impact of three- nucleon forces has had a great impact on the field of few-nucleon physics and has driven experimental activity which resulted in Henryk Witała’s collaboration with experimentalists from the leading research centers. This includes groups from Bloomington, Bochum, Bonn, Cologne, Cracow, Erlangen, Fukoka, Katowice, KVI, PSI, RIKEN Nishina Center, RCNP, Tokyo and TUNL. Henryk Witała performed, himself or with collaborators from the Cracow-Bochum group, numerous calculations that enabled experimentalists to perform measurements sensitive to specific features of the nuclear Hamiltonian. Such calculations are prerequisite both for planning as well as for analyzing experiments.

Henryk Witała participated in a number of benchmark calculations, which provided crucial tests of complicated numerical calculations. All of these efforts and the progress achieved by other theoretical groups, proved for the first time that nuclear physics could be understood as a theory of nucleons interacting with two- and three-body forces arising from meson exchanges. Many important results obtained before the mid-1990s for the three-nucleon system were published in the review paper (Phys. Rep. 274 (1996) 107, “The three nucleon continuum: Achievements, challenges and applications” by W. Glöckle, H. Witała, D. Hüber, H. Kamada and J. Golak). This paper is an essential reference for anyone interested in three- nucleon calculations and is one of the most cited papers on few-nucleon systems.

Despite open questions in the pure three-nucleon system, it became clear that the methods and computer codes developed by Henryk Witała and co-workers can be applied to various processes, where either the nucleon and the deuteron or three unbound nucleons interact in the initial or in the final state. Henryk Witała worked together with collaborators on final state interactions in electron and photon induced break-up of 3He and nucleon- deuteron radiative capture. The key idea there was to build the essential nuclear matrix elements from solutions of the Faddeev-like equation, which had the same kernel as the original one appearing in nucleon-deuteron scattering reactions. The set of codes for exclusive, semi- exclusive and fully inclusive reactions prepared for these processes was based on Witała’s expertise and was used to analyze experimental data from NIKHEF, MIT Bates, Jefferson Lab, TUNL, Mainz, Fukuoka and Lund for the first time with realistic two-nucleon and three-nucleon forces. These important works brought information for example on the nucleon electromagnetic form factors, the momentum distributions inside 3He and 3H nuclei, and the Gerasimov-Drell- Hearn (GDH) sum rule for 3He.

In the late 1990s a new generation of two- and three-nucleon forces was derived. These forces were obtained by E. Epelbaum, U.-G. Meißner, W. Glöckle and others in the framework of chiral effective field theory. These chiral potentials were incorporated for the first time by Henryk Witała in three-nucleon continuum Faddeev calculations. Results of these calculations revealed new aspects of the nuclear interactions and significantly contributed to establishing this novel theoretical framework as the modern theory of nuclear physics. Henryk Witałan actively continues work on the chiral approach to the nuclear forces. His investigations are not only dealing with applications of the chiral forces; his recent investigations revealed the necessity of improving the nonlocal regularization scheme of chiral forces. Henryk Witała has also made an important contribution to fixing the free parameters of the chiral three-nucleon force.

Being aware of the limitations of the standard nonrelativistic approach, Henryk Witała has succeeded in solving the relativistic three- nucleon problem with inclusion of three- nucleon forces taking all dynamical ingredients consistently into account. It was the first time that exact relativistic solution of the three-body scattering problem with spin degrees of freedom, avoiding any approximations, had been obtained. Together with collaborators, he proposed the new formalism, which preserving the structure of Faddeev equations allowed for the first time to obtain relativistic predictions for nucleon-deuteron elastic scattering and the deuteron breakup process. The formalism bases on an exactly Poincaré invariant formulation of the three-nucleon problem. The practical implementation of this formalism was a challenging task, but Henryk Witała managed to prepare the corresponding codes and he was able for the first time to perform exact relativistic calculations of observables in elastic nucleon-deuteron scattering and deuteron breakup reactions, including such elements as boosts of the deuteron wave function and Wigner spin rotations. In an important series of papers Henryk Witałan and collaborators showed that relativistic treatment of three-nucleon systems does not fully remove existing discrepancies in data description. This in turn points on the necessity to improvement of the three-nucleon force and their consistency with two-body interaction. These results gave new stimulus to study three-nucleon forces and subsequent works are nowadays continued by various theoretical groups.

As mentioned above, Henryk Witała contributed significantly to fixing the properties of the chiral three-nucleon force, which at next-to-next-to-leading order (N2LO) and next-to-next- to-next-to-leading order (N3LO) possesses just two free parameters. At next-to-next-to- next-to- next-to-leading order (N4LO) the long- and intermediate-range interactions, generated by pion-exchange diagrams, as derived by the Bochum-Bonn group, are supplemented by thirteen short-range operators so the problem of establishing all the free parameters becomes much more difficult. Henryk Witała responded to this problem by publishing two papers in 2021, in which he presented a new powerful calculational scheme which allows him to take efficiently into account any number of contact terms of a chiral three-nucleon force in the 3N continuum Faddeev calculations! This approach is especially suited to repeated calculations with varying strengths of contact terms and reproduces very well exact predictions for 3N continuum observables. In this way the nuclear physics community has been given a new practical tool which, for the first time, opens up the possibility to establish the chiral N4LO 3N Hamiltonian parameters by fine tuning based on available 3N scattering data. We also expect that Henryk Witała’s idea will be applied to electroweak processes to efficiently fix free parameters of the chiral electroweak currents appearing at higher orders of chiral expansion.

In the last period since 2021 the scientific activity of Henryk Witała has concentrated on applications of the new chiral interactions to different few- body processes within the LENPIC collaboration. The new, efficient emulator he developed accelerated substantially the Faddeev calculations and enabled him to determine strengths of short-range three-nucleon terms in a phase- shift analysis of low-energy nucleon-deuteron scattering data. Further collaboration with experimental groups provided among others results for the effective range parameter from an analysis of quasi-free scattering exclusive configurations in low energy neutron-deuteron breakup reaction. The latest investigations of Henryk Witała focused on a new method of inclusion of the proton-proton Coulomb force in three-nucleon proton-deuteron scattering calculations. As a result, an alternative scheme to the well-established approach based on the Alt-Grassberge-Sandhas equation has been developed. That approach, including also a three-nucleon interaction, is presently being extended to electroweak processes with three-nucleon systems consisting of two protons and a neutron.

His very wide research activity has led to Henryk Witała’s impressive number (almost 400) scientific publications. Among the five most cited papers dealing with "three-nucleon force", two are co-authored by Henryk Witała. His initial paper on the solution of the Faddeev equation is the third most cited paper published in Few-Body Systems. (These data are taken from the Web of Science Core Collection). His distinguished scientific record resulted in official recognition of his achievements. In particular, Henryk Witała served as a member of the Editorial Board of Few-Body Systems from 1999 till 2009. Further, in 2007, he was elected Fellow of the American Physical Society “for his ground-breaking work in solving the three-nucleon continuum system using the Faddeev scheme in a numerical accurate manner with realistic nucleon-nucleon and three-nucleon forces”. Henryk Witała received several times the Rector’s of the Jagiellonian University award for his scientific achievements and twice the Polish Ministry of Science and Higher Education award, recently in 2010. In 2001 he received also Wojciech Rubinowicz Scientific Prize of the Polish Physical Society. The Few-body Community, in recognition of his achievements in the field of few-body physics dedicated to him a special issue of Few-Body Systems in 2012.

**Biography**

Henryk Witała, born in 1952, started studying physics in 1971 at the Jagiellonian University, one of the two leading Polish universities. He graduated, magna cum laude, in 1976 and bound his professional activity with the Institute of Physics of the Jagiellonian University, attaining the subsequent stages of academic career: assistant positions, Ph.D. student, Assistant Professor, Associate Professor and Full Professor (in 1995). Among his scientific collaborations the most important one was that with Professor Walter Glöckle from the Ruhr University. In 1985 Henryk Witała received a Humboldt Research Fellowship for post- doctoral researchers. He chose Professor Walter Glöckle and the Ruhr University in Bochum as his academic host and research institution in Germany. Henryk Witała stayed in Bochum from January 1986 till September 1988. That was a turning point in his career and the moment he got captivated by few-nucleon physics. It was in Bochum that Henryk Witała laid the foundations for his future achievements.

Henryk Witała is still very active and many exciting contributions are still ahead of him.

**The Faddeev Medal Committee:**

Prof. Kimiko Sekiguchi, Tokyo Institute of Technology, Chair

Prof. Jose D’lncao, JILA, University of Colorado, Boulder

Prof. Evgeny Epelbaum, Ruhr-Universität Bochum

Prof. Lev Khaylovich, Bar-Ilan University

Prof. Angels Ramos, University of Barcelona

Russian news sources announced that the Russian Mathematical Physicist, Ludwig Faddeev, died on Sunday February 26, 2017 "after a long illness". Faddeev is known for multiple seminal contributions to theoretical physics (e.g., Faddeev-Popov ghosts, Faddeev-Senjanovic quantization, Faddeev-Jackiw quantization). His work has been recognized by many prizes in different countries over the past 40 years, as well as memberships of several prestigious bodies, such as the Russian Academy of Sciences, the U.S. National Academy of Sciences, the French Academy of Sciences, and the Royal Society. He was the President of the International Mathematical Union from 1986 to 1990.

In 1961, when he was only 27, he published what became known as "the Faddeev equations". As the first mathematically well-posed formulation of the quantum-mechanical three-body problem, these equations are foundational in few-body physics. They have been used in innumerable studies over the subsequent five decades that solved three-body problems in atomic, nuclear, and particle physics.

In 2016 GFB, in conjunction with the European Research Committee for Few-body Problems (ERCFBP), established the Faddeev medal, to "recognize distinguished achievement in few-body physics". Professor Faddeev was present when this was announced during the 23rd European Conference on Few-Body Problems in Physics, and GFB and ERCFBP were hoping that he would present the medal to its first recipient at the International Few-Body Conference in Caen in 2018.

The Faddeev medalist will be selected by an international panel of experts, which is chaired by Prof. Giuseppina Orlandini. Nominations are open until May 31, 2017; details of the nomination requirements can be found on the European Few-Body Physics website.