World Premier International Research Center Initiative (WPI) Executive Summary (For Extension application screening) Host Institution The University of Tokyo Host Institution Head Junichi Hamada Kavli Institute for the Physics and Mathematics of Research Center Center Director Hitoshi Murayama the Universe A. Progress Report of the WPI Center I. Summary The Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) was proposed to study five interrelated, basic, yet ambitious questions about the Universe: • How did the Universe start? • What is the Universe made of? • What is the fate of the Universe? • What are its fundamental laws? • Why do we exist? While these questions have been asked by humankind for millennia, advances in the last decade or two now make it possible to address them by scientific methods. The Kavli IPMU was founded from scratch with the WPI funding on October 1, 2007, as a unique interdisciplinary institute in the world that combines mathematics, theoretical and experimental physics, and astronomy. Since then, it has grown to an international research center of about 150 members. It has produced high impact signature papers with a clear “made in the Kavli IPMU” brand, with citation counts and the number of highly cited papers comparable to or better than world-leading institutes. We receive 800 visitors on average every year, half of them from abroad; about 700 job applications every year with more than 90% from overseas; and more than half of about 90 Ph.D. scientists on site are international. More than a third of the postdocs who have left the institute are already in faculty positions. We created an environment for strong mutual inspira- tion between mathematics and physics, and unexpected synergies between astronomy and math- ematics as well as connections with condensed matter physics have emerged. We proposed to carry out experimental and observational programs from accelerators, underground laboratories, and telescopes, and have launched major experimental initiatives such as HSC, XMASS, and Kam- LAND-Zen successfully. The interdisciplinary environment allowed us to spawn new initiatives such as SuMIRe and LiteBIRD, garnering strong international attention. Our outreach program has been highly successful and mobilized more than 22,000 people, with strong media attention providing close to a thousand instances of international coverage. We spearheaded many unprecedented achievements in system reform at the University of Tokyo, such as split appointments, merit-based salary scales, and endowment donation from a foreign foundation. II. Items 1. Overall Image of Your Center Overall, the Institute came out exactly as proposed. Our unique building allows mathematicians, physicists, and astronomers to be located under the same roof, sharing seminars and the daily teatime. Interdisciplinary discussions have become commonplace. The Institute is highly interna- tional. Thanks to several high profile papers and international visibility, our members are invited to major conferences as keynote or summary speakers, including Strings, Lepton Photon, Neutrino Conferences, International Congress of Mathematicians, and Nobel Symposium. Many of our faculty members have been invited to write major review articles. We fostered mutual inspiration of mathematicians and physicists despite big differences in pur- pose, culture, and language. We actively recruited key “interpreters” to overcome the barrier be- tween mathematicians and physicists, and they played critical roles to make the interdisciplinary research a reality. This is crucial for addressing “what are the fundamental laws?” Unexpected synergies emerged. We did not imagine that astronomers and mathematicians would interact, or phenomenologists and mathematicians would write joint papers, yet both hap- pened. Our research building specifically designed to mix up people from different disciplines and The University of Tokyo -1 Kavli IPMU the mandatory daily teatime for informal interactions have proved extremely successful. The big projects proposed in the original proposal are well underway. XMASS was built and has produced the world’s best limits on some dark matter candidates, addressing “What is the Universe made of?” The KamLAND-Zen effort has produced the world’s best limit on possible transmutation between matter and anti-matter, addressing “Why do we exist?” The new 3-ton digital camera HSC with 870 million pixels was designed, built, and commissioned. An unprecedented 300-night survey is now approved and started, addressing “What is the fate of the Universe?” 2. Research Activities Our research activities span a very wide spectrum from pure mathematics and theoretical phys- ics to experimental physics and astronomy as summarized in the Progress Report. Here we do not try to cover more than 1500 papers exhaustively, but rather focus on a very few select results. What is the Universe made of? It has been known since 2003 that more than 80% of the matter in the Universe is mysterious dark matter not made of atoms. It is responsible for building up the stars and galaxies we see in the Universe today, yet its nature is completely unknown. Without it, we would not be here today. We have created maps of dark matter in the Universe, even though we cannot see it directly in telescopes. According to Einstein’s theory of relativity, gravity from dark matter acts on light, dis- torting the images of background galaxies (gravitational lensing). By studying the distortion of images, we can reconstruct 2D maps of dark matter, and “see the invisible.” Our Professor Takada and collaborators carefully examined 30 clusters of galaxies with the Subaru telescope, and proved that the dark matter maps are consistent with what was expected based on our numerical simula- tions. In addition, we could demonstrate for the first time that they are not round but rather shaped like rugby balls. This work currently has 112 citations. We will extend this technique to build 3D maps of dark matter with SuMIRe (see B.1), and Takada is the co-chair of its science team. It is believed that dark matter is composed of yet-to-be-discovered tiny particles. PI Suzuki leads the XMASS experiment trying to detect dark matter particles directly with a highly sensitive device in the Kamioka underground laboratory. It has demonstrated a versatile capability in looking for many different reactions, producing the world’s best limit on certain candidates of dark matter. What are its fundamental laws? This is the area where ideas from theoretical physics and new development in mathematics intersect. The best physical theory that attempts to unify all matter and forces is string theory, which says that our Universe is actually nine dimensional rather than three; six extra spatial di- mensions are made small on special types of spaces called Calabi-Yau manifolds. Because each possible Calabi-Yau manifold represents a solution to string theory, hence to a possible Universe of its own, we need to understand how many of them there are, to explain why the Universe is the way it is. We distinguish them from one another using quantities called topological invariants. Using inspiration from physics, our young Associate Professor Toda could prove a conjecture by Fields Medalist Okounkov on equivalence of various topological invariants of Calabi-Yau manifolds. Yamazaki, then a graduate student in physics and now our Assistant Professor, pointed out to him that a paper in physics might be relevant to this research in mathematics. Thanks to Professor Hori, who came from a position both in the physics and mathematics departments at Toronto, and acts as a key “interpreter” between physics and mathematics at our Institute, Toda could use the inspi- ration from the physics paper and prove this conjecture. As a result, he was invited to give a talk in the summer of 2014 at the International Congress of Mathematicians, which is held only once every four years, and also received two Prizes from the Mathematical Society of Japan. Some of the manifolds with completely different shapes mysteriously lead to the same Universe. Professor Hori discovered a new type of this phenomenon called duality. Using the combination of these results in mathematics in physics, we hope to generate a list of all possible Universes. Why do we exist? To understand why we exist, we need to understand how stars are born. Yoshida, who became the youngest Professor in the Faculty of Science, managed to simulate how the very first stars in the Universe formed from first principles without assumptions. This was published in Science, with 106 citations; he received a prize from International Union of Physics and Applied Physics. In what types of galaxies do stars form best? By combining observations that study not only stars but also dark matter, our Assistant Professors Leauthaud and Bundy discovered that there is a “just right” size of galaxy to form stars most efficiently. This paper received 94 citations and was tied for 9th most cited paper in astrophysics in 2012. For life to emerge, we need chemical elements beyond helium. They are formed inside stars and spread by explosions called supernovae. How? Associate Professor Maeda and PI Nomoto observed a number of supernovae a year later and could see “inside” after the ejected materials became transparent. They discovered for the first time that most of the supernova explosions were not spherical and the gas is spreading out in a bipolar jet-like form. It received 85 citations. The University of Tokyo -2 Kavli IPMU Another essential ingredient to answering this question is to understand why anti-matter disap- peared, leaving matter behind. Our members proposed a theory that neutrinos are responsible for this miraculous feat because they are the only elementary matter particles without an electric charge. Our Assistant Professor Kozlov pushed the KamLAND group to look for a possible conver- sion between matter and anti-matter through neutrinos, and the resultant KamLAND-Zen effort has produced the best limit in the world.