# Prizes & Awards

### Evgeny Epelbaum wins Faddeev Medal

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 Ludvig 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.

An international panel of experts, chaired by Prof. Doerte Blume (U. of Oklahoma, USA), has selected the recipient of the 2021 medal:

Evgeny Epelbaum (Ruhr Universität Bochum, Germany) “For his groundbreaking work on developing high-precision chiral two- and three-nucleon forces that transformed few- and many-body nuclear physics.”

The prize consists of US$2500, a medal, and an invitation to the 23rd International Conference on Few-body Problems in Physics (FB23) which will be held (COVID permitting) in Summer 2022 in Beijing, China. Prof. Epelbaum 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. GFB and the ERCFBP wholeheartedly congratulate Prof. Epelbaum. We also want to express our gratitude to Springer and FB23 for the financial support that made this award possible. The next Faddeev medal will be awarded at the 24th International Few-body Conference. It is anticipated that nominations will open in Summer 2023. Context For almost ninety years, physicists have sought to understand the force that holds the atomic nucleus together. In 1935, Hideki Yukawa proposed that the exchange of sub-atomic particles called pions generated this force. But development of a rigorous, computable theory of the nuclear force was bedeviled by the absence of any obvious way to organize the slew of different pion-exchange mechanisms by which neutrons and protons (nucleons) interact. And in fact, the modern microscopic theory of strong interactions between the quarks and gluons of which nucleons are comprised, Quantum Chromodynamics (QCD), generates a myriad of other contributions to inter-nucleon forces at the femtometer-or-so distances relevant in nuclei. Describing the QCD forces between nucleons in terms of the fundamental quarks and gluons is thus very complicated. In 1990, Steven Weinberg posited that these forces could be more simply (“more effectively”) calculated using “Chiral Perturbation Theory” (ChiPT). This is an “Effective Field Theory'' that rigorously and systematically describes the forces between pions and non-relativistic nucleons in a way that respects the symmetries of QCD: ChiPT is QCD for low-energy particles. At its heart is a perturbative expansion that organizes these forces so that more complicated mechanisms have a smaller impact on quantities measured in the laboratory–provided the energy of the particles involved is not too large. Weinberg’s proposal opened the door for thirty years of intensive development and application of ChiPT to nuclear physics. Evgeny Epelbaum walked through that door during his Ph.D. research and has been at the forefront of the field ever since. Building on pioneering work by van Kolck and collaborators, Prof. Epelbaum led the development of high-precision nucleon-nucleon forces based on Weinberg’s idea. He and his collaborators have calculated the force between nucleons at second, third, fourth, and fifth order in the ChiPT expansion. The resulting nuclear forces are systematically organized and provide an increasingly accurate description of nuclei as they are worked out to higher order in the expansion. Crucially, the ChiPT expansion for nuclear forces also predicts the existence of forces between triplets of nucleons. These “three-nucleon forces” are a small but important correction to the traditional picture of nuclei that are bound only by pairwise interactions. One place three-nucleon forces are manifest is in experiments in which a beam of neutrons is scattered from the simplest nucleus, deuterium, which consists of a neutron and a proton. Epelbaum and collaborators made the first detailed comparison of ChiPT three-nucleon forces against neutron-deuteron scattering data, and thereby established that ChiPT’s systematic organization of the nuclear force is a viable description of both nuclear structure and the scattering reactions that probe it. Prof. Epelbaum’s nucleon-nucleon and three-nucleon forces, in concert with new methods for solving the quantum-mechanical A-body problem that is a nucleus, have brought new rigor to the study of nuclei. In few-nucleon systems, nuclear structure and many scattering reactions (neutron-deuteron scattering, processes involving four nucleons, electron and photon scattering from nuclei, etc.) can be calculated very accurately. This facilitates detailed assessment of how well our understanding of the nuclear force compares to reality–in the best few-body physics tradition. Epelbaum et al.’s ChiPT nuclear forces provide an excellent description of a tremendous amount of reaction data, and reproduce properties of nuclei containing up to about eight nucleons. A number of open questions remain, but the paradigm suggested by Weinberg, and implemented by Epelbaum and collaborators, has brought a clarity to the study of the nuclear force that has transformed research on few- and many-nucleon systems. Biography Epelbaum started studying Physics at the Sankt-Peterburgskiy Politekhnicheskiy Universitet Petra Velikogo in St. Petersburg (Russia), before changing to the Ruhr-Universität Bochum (Germany) for his Diplom (1997). There, he also received his doctorate in 2000, with a dissertation on "The nucleon-nucleon interaction in a chiral effective field theory" which was co-supervised by Profs. Walter Glöckle (RU Bochum) and Ulf-G. Meißner (Forschungszentrum Jülich and Rheinische Friedrich-Wilhelms-Universität Bonn, both Germany). After a Postdoc in Bochum and Université Paris-Sud, he was the inaugural Nathan Isgur Distinguished Postdoctoral Fellow at the Thomas Jefferson National Accelerator Facility (Newport News VA, USA; 2003-2006). Upon his return, he led the Helmholtz Young Investigator Group "Few-nucleon systems in chiral effective field theory" in Jülich and Bonn (temporary professor, 2006-2011). Since 2010, he is Full Professor for Theoretical Physics at Ruhr-Universität Bochum. The Faddeev Medal Committee: Prof. Doerte Blume (U. of Oklahoma, USA, chair) Prof. Arnoldas Deltuva (Vilnius U., Lithuania) Prof. Rudi Grimm (U. of Innsbruck, Austria; previous medal recipient) Prof. Gastao Krein (Universidade Estadual Paulista Sao Paulo, Brazil) Kimiko Sekiguchi (Tohoku U., Sendai, Japan) ### Vitaly Efimov and Rudolf Grimm Win Inaugural Faddeev Medal The Faddeev medal was inaugurated in 2016 by the Topical Group on Few-Body Systems & Multi-particle Dynamics (GFB) of the American Physical Society and the European Research Committee on Few-Body Problems in Physics (ERCFBP) to recognize distinguished colleague Ludwig Faddeev. The medal 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. An international panel of experts, chaired by G. Orlandini (Trento), has selected the winners of the 2018 award. They are: Vitaly Efimov: "For the theoretical discovery of a series of weakly-bound three-body quantum states known as Efimov states." Rudolf Grimm: "In recognition of his ground-breaking experiments confirming the Efimov effect." The prize consists of US$1250 for each of the winners, a medal, and an invitation to the 22nd International Conference on Few-Body Problems in Physics in Caen, France, next July, to participate in a special session there, devoted to the presentation of the medals.

In the early 1970s Vitaly Efimov was studying the binding of the three-nucleon system and realized that the two-nucleon system has a near-threshold bound state. Efimov showed that, if a two-body interaction generates a bound state at threshold then the corresponding three- body system has an infinite number of three-body bound states, all of which are copies of one another, related via magnification by a specific factor which he calculated. Efimov also computed the impact that finite two-body binding energy would have on his prediction. This remarkable result was followed by an intensive search for systems that manifested this behavior, but no nuclear systems could be firmly established as candidates for the “Efimov effect”.

This is one of the most counterintuitive quantum phenomena present in a system of just a few particles, but it is also a very general result. The universality of the phenomenon predicted by Efimov led to a search for its signatures in various branches of physics, and the hope that it could provide a more profound insight into strongly-correlated systems.

For approximately three decades, the Efimov effect remained largely a purely theoretical curiosity; nature seemed to not co-operate by producing the conditions necessary for its occurrence. This changed in 2006 when a team led by Rudolf Grimm, from the University of Innsbruck, Austria, used the unique properties of ultracold quantum gases to control interatomic interactions in a gas of Cesium atoms. They produced the first Efimov resonance in a sample of Cesium atoms at temperatures of 10’s of nano-Kelvin. This observation brought to life the Efimov effect, and initiated a new, highly active, research field dedicated to probing its intimate properties. Today, the Efimov effect has been verified by several other groups triggering an evergrowing number of opportunities to explore new physics associated with it in different fields, including atomic, nuclear, hadronic, chemical, and condensed matter physics.

GFB and the ERCFBP are delighted to have two such distinguished recipients of the inaugural Faddeev medal. We also want to express our gratitude to Springer and to FB22, for financial support that made this award possible.

The next Faddeev medal will be awarded at the 23rd International Few-body Conference in 2021. It is anticipated that nominations will open in Summer 2019.

### Ludwig Faddeev Dies After a Long Illness

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.