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The Kavli Institute for the Physics and Mathematics of the Universe
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The Kavli Institute for the Physics
and Mathematics of the Universe


Fig. 1: The Kavli IPMU, Kashiwa Campus, The University of Tokyo. (Credit: Kavli IPMU)


Founded in 2007, the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) started as an idea for a globally visible and dynamic research institute. Today, the institute has gone on to make groundbreaking discoveries and further human knowledge about the origin of our Universe.

In the late 2000s, it was clear that fierce international competition was growing among academic organizations to recruit the world's best minds. Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) recognized there was a need to build research centers of high excellence to attract outstanding researchers and to maintain and further Japan's level of scientific research. Consequently in 2007, MEXT established the World Premier International Research Center Initiative (WPI Program). Afterwards, the Japan Society for the Promotion of Science, under MEXT, selected five WPI center projects for funding. Each institute has the same mission: to create centers capable of outstanding research and globally visible enough to attract leading researchers from around the world.

The IPMU, as it was called at the time, was selected as one of the first five institutes, promising to become a center for the most fundamental questions about the Universe by integrating mathematics, theoretical and experimental particle physics, and astronomy.

In the beginning, the IPMU started off with no resident researchers and no building.

Under the leadership of its Director, Hitoshi Murayama, also University of California Berkeley Professor of Physics, eight years later today, the institute is home to about 85 core researchers, 40 administrative staff, and 250 affiliated members, students, and visitors. More than half of its researchers come from overseas, and in 2012 the IPMU was renamed Kavli IPMU after the University of Tokyo decided to accept an endowment from the Kavli Foundation.

The institute is located at the University of Tokyo's Kashiwa campus, north of Tokyo City, a campus the university had opened in 2000 as a model for pursuing internationalization. In addition, it has a branch office in Kamioka, central Japan, and a satellite office at the University of California, Berkeley.


In 1998, scientists discovered that the Universe was expanding at an accelerated rate, changing the world's understanding of the Universe. Prior to 1998, the Universe was believed to be entirely made up of atoms. In fact, atoms only make up 5% of the Universe; the remaining 95% of the Universe is made up of dark matter (27%) and dark energy (68%).

Fig. 2: Tea time at Kavli IPMU allows researchers to have discussions every day. (Credit: Kavli IPMU)

Uncovering the nature of this deep mystery requires a new paradigm of the Universe. For research, combining physics and mathematics was an obvious choice.

Theoretical physicists can develop new or improved descriptions of the first moments of the Universe, which act as a guide for experimental physicists working with next-generation equipment, such as underground detectors and land telescopes.

But the development of a theoretical framework capable of explaining the mystery of the Universe requires the existence of a new, pure mathematics. Historically, new mathematics has helped explain physics whenever a paradigm shift was inevitable. The aim of Kavli IPMU is to create an environment that places scientists from different disciplines under one roof and encourages them to discuss research, leading to new collaborations and new solutions.


Underneath the Japanese Alps might seem like a strange place to study neutrinos, but this is where Kavli IPMU is involved with three projects: XMASS, Super-Kamiokande, and KamLAND.

Fig. 3: XMASS detector aiming to detect dark matter directly. (Credit: Kamioka Observatory, ICRR, The University of Tokyo)

The XMASS (xenon detector for weakly interacting massive particles) project, an inter-university cooperative research program, is aimed at directly detecting dark matter particles that are thought to populate our Milky Way galaxy. Some theorists predict that dark matter is made up of WIMPs (weakly interacting massive particles) since observations to date have never detected dark matter interactions with normal matter, which would only be plausible if dark matter interacts weakly. By using a detector filled with 800 kg of liquid xenon, which acts as target material for dark matter particle interaction, XMASS detects scintillation signals generated by recoiling charges in its inner volume. Currently, the project is in the middle of the first extensive search of whether dark matter follows an annual modulation.

Fig. 4: Inside the Super-Kamiokande detector tank. (Credit: Kamioka Observatory, ICRR, The University of Tokyo)

Other projects underground focus on the study of neutrinos. The Super-Kamiokande is a Cherenkov detector made up of a 50,000 ton stainless-steel tank of water, measuring almost 40 m across and more than 40 m tall, with its inside walls lined with approximately 13,000 photo-multiplier tubes. Today, the detector is operated by an international collaboration of more than 100 researchers from 30 institutes in Japan, the United States, South Korea, China, Poland, Spain and Canada.

Kavli IPMU researchers are working on the SK-GD Project, an initiative to enrich the ultra-pure water inside the Super-Kamiokande tank with a gadolinium compound. When an anti-electron-neutrino travels through the Super-Kamiokande and interacts with proton, it will release an electron and a neutron. Taking advantage of the gadolinium nuclei's ability to capture neutrons and emit a cascade of observable gamma rays, the new water-gadolinium solution would produce two flash of lights, one for the charged lepton and another for the neutron. In contrast, other kind of neutrinos and other particles originating from cosmic particles will only produce one flash of light. So, gadolinium would significantly reduce background noise, and raise the sensitivity of the detector, making it possible to detect a constant stream of the anti-electron-neutrinos from past supernovae for the first time.

The KamLAND neutrino detector is located in the same underground mine as the Super-Kamiokande detector, but instead of pure water, it is filled with 1000 tons of liquid scintillator. The liquid scintillator gives the collaborating team of researchers, including those from Kavli IPMU, the ability to make KamLAND sensitive enough to detect very low energy solar neutrinos produced by beryllium-7 reactions in the Sun.

In addition, the KamLAND-Zen collaboration is searching for the possibility of neutrinoless double beta decay. In normal double beta decay, two neutrons inside an atomic nucleus transform into two protons, and eject two neutrinos and two electrons. But if the neutrino and its anti-neutrino were exactly identical, only two electrons would be ejected, hence the addition of 'neutrinoless' to the name. A positive observation would show that neutrinos and anti-neutrinos can transform into each other and can in principle have changed the balance between matter and anti-matter of the Universe so that matter could survive to date.


Looking up at the night sky is an important experimental approach to exploring the Universe and uncovering its identity. By using both land-based and space-based observational tools, researchers have been able to gain insight into the composition of the Universe above us. Studying a particular astronomical object, such as supernovae or galaxy clusters, can provide researchers with vital information relevant for understanding and interpreting wide-scale survey results.

Fig. 5: How one galaxy's image appears distorted due to another galaxy. (Credit: Kavli IPMU)

Astrophysicists at Kavli IPMU use large-scale galaxy surveys to study gravitational lensing in order to detect and measure dark matter. While dark matter itself does not emit light, its effect on bending the light rays of galaxies, which emit a great deal of light, makes it possible to measure the dark matter distribution around galaxies, and the masses of dark matter halos. Wide-scale surveys, such as the Sloan Digital Sky Survey III obtained from the Canada-France-Hawaii Telescope Legacy Survey, is one data source researchers are currently analyzing.

The Kavli IPMU has also been involved with the SuMIRe project, an international collaboration using the Subaru telescope in Maunakea, Hawaii, since 2007. This project combined an originally planned imaging survey with a newly proposed spectroscopic survey.

Fig. 6: The Hyper Suprime-Cam (HSC) instrument is a large digital camera built by the National Astronomical Observatory of Japan in collaboration with international academic and industrial partners including the Kavli IPMU. (Credit: NAOJ)

The 870 million-pixel Hyper Suprime-Cam instrument installed on the telescope in 2012 has been recognized as the world's largest digital camera. It was built by the National Astronomical Observatory of Japan, in collaboration with universities and research institutes throughout the world, including the Kavli IPMU. The SuMIRe project began running a large imaging survey since March 2014 as part of the Subaru Strategic Program. Once completed, it will provide researchers with high quality images of 1400 square degrees of the sky. Its results have already been breaking boundaries, making headlines in 2015 for capturing nine large dark matter concentrations, each the mass of a galaxy cluster.

Fig. 7: The Andromeda Galaxy (M31) processed with the data analysis software developed for the Subaru Telescope's Hyper Suprime-Cam. (Credit: HSC Collaboration / Kavli IPMU)

The Prime Focus Spectrograph (PFS) is another Kavli IPMU initiative. The instrument is currently being built, assembled, and tested in the US, France, Brazil and Taiwan, and is expected to be shipped to the Subaru telescope by 2018. Once set up, PFS will make it possible to obtain spectra of up to 2400 celestial objects at a time, creating a "census" of the Universe much more quickly than before. This is crucial for any measurements needing a large amount of data.

Fig. 8: Researchers at work at the Kavli IPMU. (Credit: Kavli IPMU)

However, observations of the sky are only part of the research. The data needs to be interpreted in the context of a theoretical framework in order to understand the evolution and structure of the Universe.


At Kavli IPMU, mathematicians work closely with physicists. This is particularly true for physicists studying string theory, which is a consistent description of matter and gravity at the quantum level. In 2015, an international collaboration of these researchers made a significant step toward unifying general relativity and quantum mechanics, focusing on the holographic principle.

The institute also gives mathematicians the space to focus on their own research, which branches out from geometry and algebra.


The final method to studying the origin of the Universe is to recreate the Big Bang in a laboratory using particle accelerators. The Belle II experiment at Super KEKB is one of the projects that Kavli IPMU is helping by building parts of the silicon vertex detector that are to be put inside the accelerator. The aim is to study the flavor sector of the Standard Model by carrying out measurements of B meson decays. Once running, it is hoped the accelerator will discover new particles and interactions beyond the Standard Model.

Another project, the T2K experiment, or Tokai-to -Kamioka, is a unique mixture of accelerator-based and underground-based experiments, and uses a beam of muon neutrinos to study neutrino oscillations. The beams are produced at J-PARC on the east coast of Japan and are detected at Super-Kamiokande in central Japan. To date, T2K has successfully observed muon neutrino to electron neutrino oscillations.


Fig. 9: Kavli IPMU Director Hitoshi Murayama. (Credit: Kavli IPMU)

Almost a decade after its establishment, Kavli IPMU has managed to draw talent from around the world, and drive world-class research. Professor Murayama, the institute's director, has said that the institute has always set out to be a place for all curious minds. "The institute I founded in Japan is open to anybody, irrespective of their origins. I named it the Institute for the Physics and Mathematics of the Universe. Laws of physics, and the mathematics that describe these laws, are not only applicable to the entire planet Earth, but also throughout the whole Universe."


Motoko Kakubayashi is a press officer at the Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo. She received her MSc in Physics from Massey University, New Zealand, in 2008, before going back to graduate school to complete a graduate diploma in journalism, Massey University, in 2009. She has worked as the international officer at the Science Media Centre of Japan, and as an investigator at the Japan Science and Technology Agency. Her main interests are in science communication and science journalism. She is also a reporter for Radio New Zealand, and a freelance science communicator.

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