The study of unstable nuclei is important for the systematic understanding of the nucleon system. It is critical for understanding astronomical explosive phenomena and nucleosynthesis in the Universe. Dr. Nishibata has developed a new spin polarization method to study unstable nuclei.
Dr. Nishibata's spin-polarizing method is versatile; it is applicable to a wide variety of nuclear species. Using the method, Dr. Nishibata has discovered new levels of unstable nuclei and determined their spin and parity. Further studies of unstable nuclei are expected.

Planning Officer,
Research Planning Office, National Metrology Institute of Japan,
National Institute of Advanced Industrial Science and Technology

Positronium is a bound state of an electron and its antimatter counterpart, the positron, which further binds to another electron to form the positronium negative ion, which is one of the simplest three-body systems. Since this bound state is a three-body-system and does not contain perturbations due to strong interactions, it is possible to perform highly accurate theoretical calculations using quantum electrodynamics. It is possible to search for new quantum phenomena through comparisons with experiments.
Dr. Michishio pioneered positronium negative ion research as a particle-antiparticle bound state, and has been working on both basic and applied research. In his basic research, he first discovered an efficient method for generating positronium negative ions using a Na-coated tungsten surface. Next, a pulsed beam of positronium negative ions was produced by this generation method, and a cross-beam arrangement was developed to synchronize it temporally and spatially with a nanosecond pulsed infrared laser beam. Using this spectroscopic apparatus, he succeeded in observing photo-electron detachment and shape resonance for the first time. Furthermore, he found that the measured ground-state and shape resonance parameters and the electron affinity of positronium agree with the state-of-the-art three-body-system theoretical calculations. As applied research, he made it possible to generate a monochromatic positronium beam. He first created a pulsed beam of positronium negative ions, then accelerated it in an electric field, irradiated it with a laser beam, and desorbed it, thereby devising a method to obtain a monochromatic positronium beam. In an experiment, he succeeded in generating a single-energy positronium beam of up to 1.9 keV in an ultra-high vacuum. This result is expected to be applied not only to basic research but also to condensed matter physics.

Accenture Japan Ltd., Data Science Consultant, Research Center for Nuclear Physics,
Osaka University Cooporative Researcher

Dr. Hayato Motohashi has made important theoretical contributions to the field of extended gravity theory. He investigated the conditions under which extended scalar-tensor theories have solutions to the Einstein equations as exact solutions, where the scalar field has a non-trivial profile with a constant kinetic term.
Dr. Motohashi showed that such solutions, called stealth solutions, are generally strongly coupled and are inappropriate as models to explain reality without further modifications. Consequently, he has also shown that by introducing higher order derivative interactions, the issue of the strong coupling can be safely solved without introducing ghosts, which cause problematic quantum instabilities at low energy scales.
Dr. Motohashi has also had achievements covering a wide range of research, including studies of extended theories of gravity and in the analysis of inflationary universe models.