M. R. Hadizadeh⋅ M. Radin ⋅ M. Moeini Arani ⋅ H. R. Moshfegh ⋅ N. Kalantar-Nayestanaki
M. R. Hadizadeh Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA M. Radin Department of Physics, K. N. Toosi University of Technology, P.O.Box 16315-1618, Tehran,Iran M. Moeini Arani⋅ H. R. Moshfegh Department of Physics, University of Tehran, P.O.Box 14395-547, Tehran, Iran N. Kalantar-Nayestanaki ESRIG, Faculty of Science & Engineering, Univ. of Groningen, Groningen, The Netherlands
On May 5, 2021, the Iranian physics society and the international few-body
physics community lost one of their respected members, Shahriar Bayegan. Bayegan
was born in Tehran on Oct. 19, 1951, and passed away at the age of 69 in Tehran
after a short battle with Covid-19. He received his undergraduate degree at Pars
College (Iran) in 1974, and immediately started his graduate education at Queen
Mary University of London, and earned a Master’s degree in 1977. He then
pursued a Ph.D. in theoretical nuclear physics at the University of Edinburgh
(Scotland) and met his wife and the love of his life, Zohreh Abdi Daneshpour.
Bayegan received a Ph.D. in 1983 after completing a doctoral dissertation
titled “A study of pre-equilibrium phenomena in photo-nuclear reactions”
under the supervision of Prof. Alan C. Shotter. Bayegan and Daneshpour
moved to Tehran in 1983, right in the middle of the Iran-Iraq war, where
shortly after their move, their son, Siavash, was born in 1984. Bayegan
joined the University of Tehran (UT) in 1983 as an assistant professor
of physics and spent his entire professional life in higher education as a
faculty member at the Department of Physics of UT for about four decades.
The UT has been identified with the training and education of the first
generation of Iranian physicists since 1935, when a Bachelor of Science in
Physics program was established there. This program was later extended
to a Master’s program at the beginning of 1970. When Bayegan joined
the UT in 1983, he was appointed as the graduate program director for
seven years to maintain and develop the Master’s program in physics. The
program’s key goal was to train graduate students for academia and industry in
different sectors of physics, from atomic, molecular, and optical physics to
nuclear and particle physics. Many graduate students find this Master’s
program a bridge between undergraduate studies and the Ph.D. program
later established at the UT. In 1988, Bayegan was invited to establish the
Department of Natural Sciences at the Shahid Sattari University of Aeronautical
Engineering and served as the first department head for five years. Subsequently,
Bayegan established his research group at the UT and focused more on
research-based training. In 1998, Bayegan and his colleagues, Majid Modarres,
Ali Pazirandeh, and Hamidreza Moshfegh developed a Ph.D. program in
theoretical nuclear physics focusing on the quantum mechanics of few- and
many-body systems. A few years later, Masoud Mahjour-Shafiei, joined
the nuclear physics faculty and was actively involved in mentoring the
graduate students and expanding on the activities in the area of experimental
nuclear physics. During his tenure as the department chair from 2003 to
2005, Bayegan made an extraordinary effort to expand and reorganize the
department that became the school of physics in 2005. He became and
served as the founding head of the school for three years to 2008. From then
on, he was the head of the theoretical nuclear physics group (2009-2021).
Throughout his service at the UT faculty, Bayegan taught a wide range
of undergraduate and graduate physics courses. He also developed many
courses in mathematical physics, differential equations, thermodynamics,
introductory and advanced nuclear physics, classical and quantum mechanics,
nuclear structure, and quantum chromodynamics. Bayegan served on the
Journal of Theoretical and Applied Physics editorial board for about one
decade and reviewed many journal articles, conference papers, and research
proposals. During his impressive career, Bayegan successfully supervised 43
Master’s theses and 11 Ph.D. dissertations and published 33 peer-reviewed
journal articles with 19 coauthors in the most prestigious physics journals.
At the beginning of the 21st century, Bayegan’s research activities were mainly
divided into two lines of research going on in parallel to the end of his carrier. The
first one was concentrated on applying a three-dimensional (3D) approach for the
few-body bound and scattering states, without using a partial wave decomposition.
In the second one, Bayegan was interested in applying the effective field
theory (EFT) approach for investigating the low-energy few-body reactions.
The 3D approach was first introduced and implemented in the calculations of
two- and three-body bound and scattering states by Walter Glˆckle, Charlotte
Elster, and collaborators starting in 1997. Then, Bayegan conducted the first
extension of the 3D scheme to a four-body bound state, with and without
three-body forces in 2007 (with Hadizadeh). Furthermore, Bayegan included the
spin and isospin degrees of freedom in 3D formalism for the first time in
triton calculations with nucleon-nucleon and three-nucleon forces (with
Hadizadeh, Radin, and Tomio). The developed Yakubovsky formalism and
computer codes were later employed by Hadizadeh and Brazil few-body
group to explore the universality and Efimov physics in weakly four-body
bound states. In parallel to Bayegan’s attempts for a 3D representation of
nucleon-nucleon chiral potentials (with Shalchi and Hadizadeh), he derived and
solved the Yakubovsky equations with realistic two- and three-nucleon
interactions (with Hadizadeh, Walter Glˆckle, and Lauro Tomio). Bayegan
further implemented the 3D scheme in three-nucleon scattering and triton
photodisintegration (with Radin and Shalchi), and also in the calculation of
low-momentum effective interactions Vlow-k using spin-independent and
modern nucleon-nucleon potentials that were later used in two-, three-, and
four-body bound state calculations (with Radin, Shalchi, and Hadizadeh).
Bayegan’s EFT research was initially focused on the electromagnetic
radiative capture of the 3N systems by applying the pionless EFT formalism
to the neutron capture by deuteron at thermal and low energies (with
Sadeghi and H. W. Griflhammer). The reaction was later comprehensively
studied in 2014 and then extended to pd radiative capture by considering the
Coulomb effects (with Moeini Arani, Nematollahi, and Mahboubi). Since
2009, Bayegan started developing the EFT approach to determine the
parity-violation low-energy coupling constants by calculating the photon
circular polarization and asymmetry in n + d →3H + γ reaction, which was
later advanced to pd scattering and p + d →3He + γ reaction (with Moeini
Arani, Nematollahi, and Mahboubi). Bayegan expanded the EFT approach
to halo nuclei by studying two-neutron radiative capture by alpha, and
calculating the 6He charge form factor (with Moeini Arani, Radin, and Jesri).
In his last EFT projects, Bayegan calculated the proton-proton fusion
S-factor with a new power counting (PC) pursued as a testing ground (with
Moeini Arani and Behzadmoghaddam) and proposed a new regularization
scheme in the lattice EFT calculations of two-nucleon systems (with Ahmadi,
Hadizadeh, and Radin). Bayegan had several in-progress projects that are not
yet published, including the investigation of the new PC in pionfull EFT
up to NLO for pp fusion, the evaluation of the E1 strength function for
two-proton radiative capture by 15O, and also the study of four-body force
effect on the universality and scaling limit of weakly bound tetramers.
With deep knowledge and experience in few-body physics, Bayegan
crucially led the Tehran few-body group for over two decades and trained
numerous young researchers in this physics area, some of whom now have leading
positions in academia and are active in preparing the next generation of
theoretical few-body physicists. In addition to the few-body community in
particular and the physics community as a whole, Bayegan left behind
his beloved family, including his wife and their son. In the hearts of his
colleagues and students, he will be forever remembered as an inspirational
and cherished colleague and friend, and we will never forget his honesty,
charismatic personality, discipline, passion, and dedication to duty. We will miss
Bayegan immensely, his positive attitude, his bright smile, and his kind
heart.
