# News

75 news in 2018

2018-12-20

## Hiroshi Suito to receive MIMS MIMURA AWARD

Hiroshi Suito (iTHEMS senior visiting scientist) will receive "2018 MIMS Mimura Award" for his contributions to the alliance of mathematical science and clinical medicine. The ceremony will be held on Dec.22 (Sat) 2018. Congratulations, Hiroshi !! Note also that the 2017 MIMS Mimura award was given to Atsushi Mochizuki (iTHEMS deputy director).

2018-12-18

## Mystery of coronae around supermassive black holes deepens

Researchers from RIKEN and JAXA have used observations from the ALMA radio observatory located in northern Chile and managed by an international consortium including the National Astronomical Observatory of Japan (NAOJ) to measure, for the first time, the strength of magnetic fields near two supermassive black holes at the centers of an important type of active galaxies. Surprisingly, the strengths of the magnetic fields do not appear sufficient to power the “coronae,” clouds of superheated plasma that are observed around the black holes at the centers of those galaxies.

2018-12-13

## Di-Omega in QCD on the front page of an in-house magazine

Di-Omega in QCD reported in the previous iTHEMS NewsLetter became a front page of the latest news letter of "Science and technology companies pension fund". It is amazing that the pension fund organization is interested in elementary particle physics!

2018-12-13

## Snapshot of a Discussion

iTHEMS members have discussions not only on natural science and mathematical science but also on social science and history. Here is a snapshot of a discussion on ancient history of China by Yongjia Huang and Hiro Nagataki at our common room 246-248 on Nov.30, 2018.

2018-12-13

## The RIKEN-NTU Workshop on Recent Developments of Chiral Matter and Topology

The RIKEN-NTU Workshop on Recent Developments of Chiral Matter and Topology was held at Centre for Theoretical Physics in National Taiwan Univ. (NTU). on Dec.6-9, 2018. There were about 80 participants both from particle/nuclear physics and condensed matter physics from Japan, Taiwan, China, and US. There were about 30 scientific talks with very stimulating discussions on chirality and topology from low-energies to high-energies. From RIKEN, A. Furusaki (CPR/CEMS), Y. Hidaka (RNC/iTHEMS), M. Hongo (iTHEMS), N. Nagaosa (CEMS), T. Ozawa (iTHEMS) and T. Hatsuda (iTHEMS) gave talks. The workshop was held in the new building "NTU Cosmology Hall" which was just completed at the north end of the NTU campus in Taipei.

2018-11-30

## Engaging the Public with Supernova and Supernova Remnant Research Using Virtual Reality

On April 21, 2018, residents of Wako came to RIKEN for the Open Day. Over one hundred people visited the exhibit of the Astrophysical Big Bang Laboratory (ABBL) and interacted with real scientific data using virtual reality (VR). With the help of the entire ABBL and several students from Rikkyo U, people as young as 2 and as old as 80 got to explore a supernova remnant in 3-D, as if it was in the room with them. (A supernova remnant results from the explosion of a star; ABBL does numerical simulations to understand the explosion mechanism.) In this report, Gilles Ferrand (ABBL/iTHEMS) and Don Warren (iTHEMS) explain what makes VR exciting to explore your data and communicate your research, and how to make your own VR booth at next year's Open Day — or any other event! We are happy to discuss this exhibit, and answer any questions you have, at a coffee meeting, wine meeting, or another occasion.

2018-11-27

## Self-introduction: Eren Mehmet Kiral

Hello, I am Eren Mehmet Kıral, I am currently a JSPS fellow at Sophia University working with Prof. Nakasuji on Bruhat cell decompositions of various matrix groups with a view towards finding number theoretic applications. I am also a visiting scientist here at ITHEMS. Starting March 2020 I will be an SPDR at RIKEN working at the Mathematical Science team of Advanced Intelligence Project (AIP) with Prof. Bannai. My research interest is in automorphic forms, and their associated L-functions, including the Riemann zeta function. Automorphic forms can be thought of generalizations of harmonics. Just like sin(nx), cos(nx) are the periodic harmonics on the real line, automorphic forms are the harmonics on more general homogeneous spaces. However unlike the real line, the group of transformations on the space forms a non-commutative Lie group, and hence the harmonic analysis (or equivalently the representation theory) on this group is more involved. It is fascinating that simply the setup of a discrete subgroup sitting inside a homogeneous space, spawns objects that are intrinsically related to number theory. I am looking forward to talking to physicists who work with Lie group representations on a regular basis.

2018-11-27

## iTHEMS-Kyushu WS - from particles and nuclei to cosmos -

On Nov.21-22, 2018, iTHEMS-Kyushu WS - from particles and nuclei to cosmos - was held at iTHEMS Kobe office (SUURI-COOL Kobe). About 20 researchers got together from iTHEMS and Kyushu Univ. to discuss various aspects of quantum many-body theory, quantum field theory and explosive astrophysical phenomena in a very relaxed atmosphere. We will continue to organize such intensive workshop between iTHEMS and Kyushu Univ. in various fields of mathematical sciences in the future.

2018-11-27

## iTHEMS Public Lectures at RIKEN Kobe Campus Open House

On Nov. 28, 2018, the annual open campus of RIKEN Kobe was held. From this year, iTHEMS, which has a Kobe office (SUURI-COOL Kobe), joins this event and organized public lectures "Hot topics in Mathematical Sciences". This year 's program was Tetsuo Hatsuda "The world that mathematical sciences open" Ade Irma Suriajaya "How can something infinite become finite?" Jeffrey Fawcett "What are genomes? - Toward decoding the language of life - " Masato Taki and Noriaki Ogawa "Artificial intelligence and its medical application" Shigenori Otsuka and Shunji Kotsuki "Frontiers in weather forecast research" The lectures were held in the auditorium at the 8th floor of the Kobe IIB building (iTHEMS office is in the 7th floor). Each speaker gave a 30-40 min. talk followed by lots of interesting questions from the audience. It was amazing to see that iTHEMS researchers are not only extraordinary in their own research but also super science communicators !

2018-11-21

## Self-introduction: Yongjia Huang

I am Yongjia Huang, an International Program Associate (IPA) student studying in iTHEMS. My research interest is to explore what are the new states of matter at exceedingly high density and temperature. In the universe, various compact objects can reach more extreme condition than laboratory, thus they would be ideal candidates. I am studying the GRMHD simulation of binary neutron stars and neutron star-black hole mergers, which would generate various observable outcomes like gravitational wave (GW) radiation, kilonova, outflow and so on. With the GW astronomy era in progress, we would have a good chance to get the information like chirp mass and tidal deformability of the objects. Combining the GW data with the simulation works, then we can determine the equation of state of neutron stars efficiently. I am glad to have colleagues from different fields, and I believe our communication would play an important role in research.

2018-11-12

## The Nobel Prize in Chemistry 2018

This year’s Nobel Prize in Chemistry was awarded to Frances H Arnold for “the directed evolution of enzymes”, and jointly to George P Smith and Gregory P Winter for “the phage display of peptides and antibodies”. A major goal in chemistry is to develop new proteins, such as enzymes or antibodies. A protein is typically a string of hundreds or thousands of amino acids linked together that fold up in three-dimensional structures. Because there are 20 kinds of amino acids, the possible number of proteins (i.e. combination of amino acids) one can design is astronomical, and most of them don’t work. Both studies succeeded in developing a method to develop proteins based on a similar principle. Instead of trying to logically design a particular protein based on existing knowledge, they adopted the principle of evolution. Basically, first, they create several new proteins by introducing random mutations to existing proteins. Next, they select the best performing proteins and then introduce a new round of random mutations to create several new proteins. After a few cycles, a new protein that is much more effective than the original one can be obtained. This principle is the same as in the evolutionary or genetic algorithms used in machine learning. Who knows, maybe there are other problems the principle of evolution can be applied to!?!?

2018-11-12

## Gamow-Teller transitions from high-spin isomers in $N=Z$ nuclei

Atomic nuclei are composed of protons and neutrons. We may imagine like a certain number of (quantum) balls putting in a (self-bound) container. On the one hand, the nuclear magic numbers show the single-particle features of nuclei; On the other hand, the giant resonances show the emergent collective features. For example, an intuitive image of giant dipole resonance is: All protons form a group while all neutrons form another group, and these two groups oscillate against to each other collectively. Gamow-Teller resonance is an important kind of giant resonances involving not only the spin but also the isospin degrees of freedom in nuclei. So far, most, if not all, of experimental and theoretical studies on this direction focus on the resonances from the nuclei being in their ground states, largely due to the experimental limitations. However, it is expected that, in the near future, our world-leading nuclear facility in RIKEN can generate high-quality radioactive beams with nuclei being in their high-spin isomeric states. Motived by this perspective, we predict that the Gamow-Teller transitions from the high-spin isomers could be much more collective than the corresponding transitions from their ground states, by taking nuclei 52Fe and 94Ag as examples. This would be one of the promising collaborations between theorists and experimentalists in RIKEN.

2018-11-08

## Susumu Inoue (iTHEMS Research Scientist) was highlighted in a recent article of RIKEN RESEARCH "Highly energetic neutrino traced back to a blazar"

"The spectrum measured by MAGIC strongly points to the neutrino being generated by a high-energy proton in the blazar’s jet interacting with low-energy photons,” says Susumu Inoue of RIKEN’s Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program, who is part of the MAGIC team.

2018-11-02

## Effective field theory of time-translational symmetry breaking in nonequilibrium open system

Although we know "all things are in a state of flux. (Patna rhei.)", it has been still an interesting question whether we have "universal" features in such time-evolution of all things. Considering the non-equilibrium open systems like the Brownian particles, we have tackled this problem from the point of view of time-translational symmetry. We regard the transient diffusive (or time-oscillating) behaviors as "symmetry-broken phases of matter", and develop a way to describe their spacetime evolution. Our formalism is based on the so-called effective field theory (EFT) originally developed in the context of particle physics and now used in almost every branches of physics. The advantage of the EFT is that it enables us to capture the possible universal properties in the large-scale (low-energy) behaviors of systems. As a result, we find the existence of the Nambu-Goldstone-like mode during transient time-evolution, which gives the universal diffusive behaviors of all things in a state of flux.

2018-11-02

## Self-introduction: Masahiro Nozaki

Hi everyone. My name is Masahiro Nozaki. I am a Special Postdoctoral Researchers at iTHEMS. I worked in YITP, Kyoto University as a JSPS fellow, and then in The Kadanoff Center for Theoretical Physics, The University of Chicago as a Kadanoff Center fellow. I have been studying theoretical physics such as holography and non-equilibrium physics in terms of quantum entanglement. Currently, I am interested in and studying quantum chaos, scrambling and so on. I am very happy if I can interact with researchers in iTHEMS, broaden my research fields, and have fruitful collaborations!!

2018-10-25

## Coffee Meeting on Oct.19

At the weekly coffee meeting on Oct.19(Fri.), Hiroki Kodama (AIMR/iTHEMS) gave a nice explanation on the properties of "flat functions" which often appear in mathematics and physics. He also told us an interesting story about the reference in the arXiv paper below.

2018-10-18

## Non-equilibrium Chiral Magnetic/Vortical Effects in Viscous Fluids

Chiral magnetic and vortical effects are novel effects in quantum fluids with chiral anomaly. We utilize the chiral kinetic theory in a relaxation-time approximation to investigate the nonlinear anomalous responses of chiral fluids with viscous effects. Unlike the cases in equilibrium, it is found that the chiral magnetic effect and chiral vortical effect are modified by the shear and bulk strengths. Particularly, the shear strength could result in charged Hall currents for chiral magnetic and chiral vortical effects, which propagate perpendicular to applied magnetic fields and vorticity. These quantum corrections stemming from side jumps and anomalies are dissipative and pertinent to interactions.

2018-10-16

## The First Telescope of a New Observatory for High-Energy Gamma-Ray Astronomy Makes its Debut

Several iTHEMS members are actively involved in a brand-new, cutting edge astronomical project, called the Cherenkov Telescope Array (CTA). CTA will be the foremost global observatory for very high-energy gamma-ray astronomy over the next decade and beyond and will be the first ground-based gamma-ray astronomy observatory open to the world-wide astronomical and particle physics communities. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. With its ability to cover an enormous range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. From iTHEMS, Susumu Inoue and Yoshiyuki Inoue in particular have been actively contributing to the science case studies of multi-messenger transient phenomena and supermassive black holes as members of the CTA Consortium. On Wednesday, 10 October 2018, more than 200 guests from around the world gathered on the northern array site of the CTA to celebrate the inauguration of the first prototype Large-Sized Telescope (LST). The telescope, named LST-1, is intended to become the first of four LSTs on the north site of the CTA Observatory, which is located on the existing site of the Instituto de Astrofisica de Canarias’ (IAC’s) Observatorio del Roque de los Muchachos located in the municipality of Villa de Garafia on the island of La Palma. The plan for the site also includes 15 Medium-Sized Telescopes (MSTs). The LSTs will expand the science reach to cosmological distances and fainter sources with soft energy spectra. Both the repositioning speed and the low energy threshold provided by the LSTs are critical for CTA studies of transient gamma-ray sources in our own Galaxy and for the study of active galactic nuclei and gamma-ray bursts at high redshift.

2018-10-11

## Coffee Meeting on Oct. 5

At the weekly coffee meeting on Oct.5 (Fri.), we enjoyed lots of good sweets from all over the world after a nice 15 min. talk by Chacha san (iTHEMS) on "A unique pair of triangles".

2018-10-11

## X-ray telescope reveals the Milky Way’s halo of hot gas is fed by supernovae

The Milky Way is a spiral galaxy up to 100,000 light years across, and our Sun is just one of hundreds of billions of stars within it. The galaxy has a halo, which is partly made up of gas accumulated from the vast expanses of intergalactic space but is also molded and supplemented by matter ejected from the galaxy’s stars. The balance between these two sources is not fully understood, and there is ongoing debate about the halo’s size and shape. RIKEN Researchers have mapped this halo gas using the Suzaku X-ray telescope and revealed how exploding stars have helped to shape this blazing shroud.

2018-10-09

## Online Model Parameter Estimation With Ensemble Data Assimilation in the Real Global Atmosphere

When and where will it rain, and how heavy? – this is a central question that meteorology tries to address. Numerical weather prediction (NWP) is a major approach using data assimilation with mathematical models to predict the weather. The NWP models discretize the earth atmosphere into 3-dimensional grids, and compute the evolution of the atmospheric states based on physical processes (e.g., fluid dynamics, radiation, and water phase changes). The NWP models cannot include subgrid-scale and complex processes explicitly, and these complex phenomena are represented by simplified equations so-called “parameterization”. Parameterization usually contains tunable model parameters, and manual tuning of these parameters is a tedious but important task. This study explores an objective and autonomous approach to optimizing these parameters using data assimilation. We chose a parameter of the subgrid-scale parameterization of raindrop initiation processes of a global NWP model. We successfully mitigated the overproduced precipitation of the NWP model by estimating the model parameter with satellite-observed precipitation data. Figure: Global precipitation forecasts (mm 6h-1) at 0000 UTC on 16 June 2014 by an NWP model. (left) control experiment with the default model setting, (middle) test experiment with the model parameter estimation, and (right) satellite observation, respectively. Overproduced precipitation over ocean in the control experiment is successfully mitigated by the model parameter estimation.

2018-10-04

## iTHEMS colloquium held on October 3rd

Prof. Hideaki Aoyama from Kyoto University was the lecturer of the latest iTHEMS colloquium held on October 3rd. Prof. Aoyama has just joined iTHEMS as a senior visiting researcher. Welcome to iTHEMS, Prof. Aoyama! The colloquium was entitled "Economic Networks: a Physicist's View. " In the opening of the talk, Prof. Aoyama shared his personal recollection of Richard Feynman, one of the greatest physicists of the last century, and quoted his words. He went on to explain the techniques developed to explore the correlations and hidden relations buried in the huge amount of complex data which concern the economic activities of the real world. He pointed out that a certain kind of similarities can be observed between physics and economics, for example, the time correlation of the aftershocks of earthquakes and the bankruptcies occurred after calamities. The colloquium attracted a wide range of audience including those from outside RIKEN.

2018-10-01

## Self-learning Monte Carlo method with Behler-Parrinello neural networks

Self Learning Monte-Carlo (SLMC) method is one of the recent promising applications of machine learning techniques to computational physics especially Marcov-Chain Monte-Carlo (MCMC) simulations in statistical physics systems. In SLMC, we prepare an effective Hamiltonian with tunable coupling constants and try to reproduce the value of the real Hamiltonian by adjusting the coupling constants. This procedure corresponds to the supervised machine learning. After the learning, we employ it for global updates in MCMC, and it drastically reduces the autocorrelation, i.e. similarity of configurations in the Marcov-Chain, thanks to the local structure of the effective Hamiltonian. In our paper, we present two novel techniques for SLMC in a quantum Monte-Carlo simulation. First technique is the use of neural networks. Based on the neural net architecture by Behler and Parrinello in the context of molecular dynamics machine learning, we develop how to construct general purposed effective Hamiltonian for SLMC. Second contribution is a new proposal for regularization in SLMC that we call batch-atom normalization. It is a generalization of the well-known technique in deep learning, and we observe it drastically improve the learning procedure for effective Hamiltonian represented by neural network.

2018-09-26

## Tightening the noose on neutron star radii

The study by Oliver Just (Nagataki's lab.) and his collaborators in Germany and Greece has added much needed clarity to limiting the neutron star radius, a parameter that provides vital clues about the microphysics of neutron stars and hence also about the microphysics of nuclei on Earth. “Before our study, the radius of a neutron star was only weakly constrained from below,” Just says.

2018-09-19

## The relative Mishchenko--Fomenko higher index and almost flat bundles

Existence of a positive scalar curvature (PSC) metric has been one of the central topics in differential topology of higher dimensional manifolds. Index theory provides a topological invariant whose vanishing is an effective necessary condition of the existence of a PSC metric. Recently, Chang-Weinberger-Yu introduce a new index theoretic invariant called the relative higher index detecting the non-existence of a PSC metric on spin manifolds with boundary. The aim of this paper is to understand this invariant from Riemannian gemetric point of view. Firstly, we introduce a new definition of the relative higher index and prove that it is equivalent to the existing definitions. Secondly, by using our new definition, we relate the relative higher index with a Riemannian geometry of vector bundles; the index pairing with almost flat vector bundles. This is a relative analogue of the theory of Gromov-Lawson for closed spin manifolds.

2018-09-11

## An unstable isotope Technetium-98 (98Tc) could be synthesized by neutrinos emitted from supernova explosions

A joint research group consisting of Masaomi Ono, a Research Scientist at RIKEN, and others has theoretically predicted that an unstable isotope Technetium-98 (98Tc) could be synthesized by neutrinos emitted from supernova explosions. Supernovae are important events in the evolution of stars and galaxies, but the details of how the explosions occur are still unknown. This research found a method to investigate the role of electron anti-neutrinos in supernovae. By measuring the amount of 98Ru (an isotope of Ruthenium) in meteorites, it should be possible to estimate how much of its progenitor 98Tc was present in the material at the time when the Solar System formed. The amount of 98Tc in turn is sensitive to the characteristics, such as temperature, of electron anti-neutrinos in the supernova process; as well as to how much time passed between the supernova and the formation of the Solar System. (This work appeared in Physical Review Letters on Sept. 4, 2018.) Caption: We can estimate the age of heavy elements in the primordial Solar System by measuring the traces left in meteorites by specific radioactive nuclei synthesized in certain types of supernovae. Credit: NAOJ (National Astronomical Observatory of Japan)

2018-09-10

## Book on "Origins of the Gravitational Wave"

Kotaro Kyutoku (Assistant Prof. in KEK and iTHEMS visiting researcher. Former iTHEMS SPDR) has published a book "Origins of the Gravitational Wave" in Japanese with Masaru Shibata (Max Planck Institute and Kyoto Univ.). It contains excellent explanations on general relativity and black holes, structure of neutron stars, supernova explosion, gamma-ray burst, gravitational wave, mergers of black holes and neutron stars, and current/future gravitational wave detectors on earth and space. Everybody who is interested in GW should have one in his/her bookshelf. English translation will be called for.

2018-09-10

## Self-introduction: Gen Kurosawa

My name is Gen Kurosawa. I study “Biological Timing”. We know timing of meal influences timing of sleep. Similarly, we know timing of taking medicine influences its efficacy. We know these facts, but we do not really know why. To answer these questions, my approach is to use two types of models. Mainly, I try to develop simpler models to understand the essence in Biological Timing. Simultaneously, I use realistic models (ex. 180 variable ODE model with genes and proteins) to make detailed predictions which can be tested experimentally in a very near future. At iTHEMS, I am happy that I can interact with colleagues from various disciplines.

2018-09-03

## The Black Coffee and Dr. Hawking

A short essay "Black coffee and Dr. Hawking" (in Japanese) by Yuki Yokokura (iTHEMS) was published in RIKEN News (vol.446, 2018). Similarity and difference between the black coffee and the black hole is explained in plain terms. Please enjoy!

2018-09-03

## The Di-Omega Picture

The image of Di-Omega (an exotic particle with 6 strange quarks) was selected as the front page picture of the August issue of RIKEN NEWS (vol.446, 2018). This is based on the work done by HAL QCD Collaboration composed of 6 institutions (RIKEN Nishina Center, RIKEN iTHEMS, YITP in Kyoto Univ., CCS in Univ. Tsukuba, RCNP in Osaka Univ. and Nihon Univ.).

2018-08-28

## Two Ck1δ transcripts regulated by m6A methylation code for two antagonistic kinases in the control of the circadian clock

Thanks to the accumulation of molecular knowledges about biological clock, we can predict a missing link “X” in the system by using a realistic simulator. Meal-time is known to influence our sleep-wake timing. But the mechanism has been unknown. This time, the group of Dr. Okamura at Kyoto University discovered a new enzyme (named, Ck1δ2) that possibly links between our metabolic system and biological clock. Based on the experimental results by Dr. Okamura, two iTHEMS members (Gibo and Kurosawa) predicted the specific biochemical process, activated by the new enzyme. The prediction was conducted by using a 190 variables model with all genes and proteins. Fortunately, the prediction was confirmed experimentally. The point for the prediction was the activation of the new enzyme “slowed” the biological clock in the experiment while the activation of most enzymes “accelerate” the clock in the simulator. Now, the mechanism is studied by using a simpler model. Then, a possible scenario is that amino-acids in our food influence our sleep-wake timing via the new enzyme.

2018-08-28

## iTHEMS Coffee Meeting is held on every Friday

iTHEMS Coffee Meeting is held on every Friday from 12:30- at our common room. From this fiscal year, we have changed the style of the short talk at the coffee meeting. The speaker will give a 15 min. talk only using blackboard without taking questions. The talk could be a scientific problem that the speaker is facing and wants to ask advise, an interdisciplinary scientific proposal that the speaker wants to form a collaboration, an elementary introduction to a particular topic or notion, etc. So far, this new attempt is working very well. For example, the speaker last week (Aug.24) was Gen Kurosawa who gave a talk “On the unsolved mystery of biological clock”. He posed unsolved questions on biological clock which induced lots of questions and discussions by the iTHEMS members after his talk. As usual, we have nice cookies and candies brought from all over the world by the iTHEMS members and coffee/tea/soft-drinks prepared by iTHEMS assistants. Thanks all for supporting the coffee meeting!

2018-08-25

## Origin of the Gravitational Waves

Author: Masaru Shibata and Koutarou Kyutoku Language: Japanese

2018-08-14

## International Congress of Mathematicians (ICM) held at Rio de Janeiro, Brasil on August 1 - 4

On the first day August 1, 2018 of the International Congress of Mathematicians (ICM) held at Rio de Janeiro, Brasil, the Fields Medals were awarded to the following four mathematicians. Caucher Birkar: For the proof of the boundedness of Fano varieties and for contributions to the minimal model program. Alessio Figalli: For contributions to the theory of optimal transport and its applications in partial differential equations, metric geometry and probability. Peter Scholze: For transforming arithmetic algebraic geometry over p-adic fields through his introduction of perfectoid spaces, with application to Galois representations, and for the development of new cohomology theories. Akshay Venkatesh: For his synthesis of analytic number theory, homogeneous dynamics, topology, and representation theory, which has resolved long-standing problems in areas such as the equidistribution of arithmetic objects. At the same time, the Rolf Nevanlinna Prize was awarded to Constantinos Daskalakis: For transforming our understanding of the computational complexity of fundamental problems in markets, auctions, equilibria, and other economic structures. His work provides both efficient algorithms and limits on what can be performed efficiently in these domains. You might know that the Fields Medal of Caucher Birkar was stolen just after the celemony and he was given the medal again on August 4. On August 4, the Carl Friedrich Gauss Prize was awarded to David L. Donoho: For his fundamental contributions to the mathematical, statistical and computational analysis of important problems in signal processing. On August 4, the Chern Medal Award was given to Masaki Kashiwara (the photo above) : For his outstanding and foundational contributions to algebraic analysis and representation theory sustained over a period of almost 50 years. On August 9, Leelavati Prize 2018 was awarded to Ali Nesin: For his outstanding contributions towards increasing public awareness of mathematics in Turkey, in particular for his tireless work in creating the "Mathematical Village" as an exceptional, peaceful place for education, research and the exploration of mathematics for anyone. The 2018 ICM Emmy Noether Lecturer is Sung-Yung Alice Chang for her leading contributions to harmonic analysis, geometric analysis, differential geometry and partial differential equations. The lecture was given on August 3 and the award was given after the lecture.

2018-08-14

## Self-introduction: Takumi Doi

My name is Takumi Doi. My main research subject is to unravel the mysteries of nuclear forces from the fundamental theory, quantum chromodynamics (QCD), and hereby to establish the bridge between different hierarchies in physics, from quarks to nuclei and cosmos. In my research, I employ the so-called lattice QCD method, which can perform the first-principles calculation of QCD by numerical computations. Nowadays, numerical computations serve a unique role not only to bridge the theory and phenomena but also to bridge different fields of science. iTHEMS is hosting good computational resources to pursue such interdisciplinary studies, and I wish to support your computational studies and seek new collaborations at iTHEMS.

2018-08-06

## Self-introduction: Don Warren

I grew up in America, but lived in Japan for a year before starting my Ph.D. course. I earned my doctorate at NC State University, studying cosmic ray acceleration and the morphology of supernova remnants. I currently study the afterglows of gamma-ray bursts, focusing on applying modern numerical results to the existing model for afterglow emission. My other interests include virtual reality as a tool for scientific visualization, and science communication to the public. I also recently embarked on a project in virology, with iTHEMS' Catherine Beauchemin.

2018-07-30

## Structural Bifurcation Analysis in Chemical Reaction Networks

In living cells, large numbers of chemical reactions form complicated networks (e.g. metabolic networks). It is considered that dynamics arising from such networks are the origin of biological functions. In this study, we developed a theoretical method to analyze bifurcation properties, i.e. properties of structural changes of steady-state solutions, from topology of reaction networks. Such a topological approach is advantageous because reaction kinetics is not well known in detail. Specifically, we showed that a reaction network can be decomposed into subnetworks based on a certain topological criteria, and showed that any bifurcation point is associated with a particular subnetwork ((3) in the figure). Further, we identified the parameters inducing bifurcations ((4) in the figure) and chemical concentrations exhibiting bifurcating behaviors ((5) in the figure). Our method is particularly useful to study large networks, since it allows us network decomposition. Biologically, bifurcation properties are related with plasticity of living systems, i.e. qualitative changes of physiological states induced by environmental conditions or gene-expressions. Our result suggests that biological plasticity arises from network topology.

2018-07-30

## Self-introduction: Jeffrey Fawcett

My name is Jeffrey Fawcett and I've been working at iTHEMS since March 2018. My main interest is Genome Evolution, and I work on or have worked on a broad range of topics related to genomics, evolution, genetics, bioinformatics, and systems biology. I am a Biologist and have always been working in an environment surrounded by Biologists. So joining iTHEMS and being surrounded by so many physicists, mathematicians, formulas, blackboards, and blackholes is quite a transition for me. Yet, it is very stimulating and challenging, and I am so far enjoying this unique opportunity where I get to work alongside people with totally different backgrounds and hear about so many different topics that I would never have the chance to in a normal research environment.

2018-07-26

## Diffuse x-ray emission from the northern arc of loop I observed with suzaku

The research team, including Yoshiyuki Inoue (Senior Research Scientist, iTHEMS), have published a press release.

2018-07-23

## iTHEMS-CEMS Joint Colloquium was held on July 19

iTHEMS-CEMS Joint Colloquium was held on July 19 at Okochi hall with a distinguished speaker, Prof. A. J. Leggett (Univ. Illinois at Urbana-Champaign). The hall was packed with full of audience (more than 150 participants) to listen the talk by the world's leading theorist in quantum physics. Prof. Leggett started his lecture with elementary considerations on classical radiation. Then he moves on to describe two photons emitted back-to-back in atomic transition and subsequent observation of the photon polarizations. In the "objective local theory" in which (i) local causality, (ii) induction and (iii) microscopic realism are assumed, one can prove an inequality for certain correlation measurement (Bell's theorem). Since quantum mechanics violates the inequality, the natural consequence is that (iii) is not satisfied in quantum mechanics. The key idea behind is the "entanglement" in which information is stored in non-local manner in quantum mechanics. Then, he talked about the notions of quantum teleportation, quantum cryptography and quantum computer where entanglement plays the essential role. The audience listened his lecture attentively and was fascinated by the interesting aspect of quantum mechanics and its applications.

2018-07-23

## Hilbert schemes of two points on K3 surfaces and certain rational cubic fourfolds

The goal of birational geometry is the classification of algebraic varieties up to birational equivalence. An algebraic variety is called rational if it is birationally equivalent to the projective space. In this paper, Genki Ouchi studied the rationality problem of (complex) cubic fourfolds, that is four dimensional complex hypersurface defined by a polynomial of degree 3. Conjecturelly, very general cubic fourfolds are irrational. However, no cubic fourfold has been proven to be irrational so far. On the other hand, there are five known examples of rational cubic fourfolds. They expect that the mysterious relation between rational cubic fourfolds and K3 surfaces is a key to solve the rationality problem. There are two inconsistent conjectures about it. So they should modify one of them at least. Together with previous works, he proved that known rational cubic fourfolds satisfy both conjectures. To modify the conjectures, we have to find a new rational cubic fourfold.

2018-07-20

## Spatial Distribution of the Milky Way Hot Gaseous Halo Constrained by Suzaku X-Ray Observations

The research team, including Yoshiyuki Inoue (Senior Research Scientist, iTHEMS), have published a press release.

2018-07-17

## High-energy neutrinos from a gamma-ray emitting supermassive black hole: the dawn of the electroweak sector of multi-messenger astronomy

Background: Since 2010, the IceCube Observatory, utilizing a cubic-km volume of ice in Antartica, has been detecting neutrinos with energies exceeding 100 TeV (~10^13 times the energy of a visible photon), which likely originate from astrophysical sources outside of the Milky Way Galaxy. However, their sources remained unknown, mainly due to the limited accuracy of their localizations in the sky. From 2016, IceCube initiated a new, automated alert program that rapidly identifies significant neutrino candidates and widely disseminates their sky positions, so that telescopes around the world can immediately search for potential counterparts at various wavelengths. Result: On September 22, 2017, a neutrino with energy ~300 TeV (dubbed IceCube-170922A) was detected with relatively good sky localization, and was rapidly followed up by numerous telescopes operating across the electromagnetic spectrum. The Fermi-LAT satellite and the MAGIC telescopes identified an object (named TXS 0506+056) shining brightly in gamma-rays (Fig. 1). The object is classified as a “blazar”, a type of supermassive black hole that is actively ejecting “jets" of plasma at relativistic velocities nearly toward us. This is the first time that a likely source of high-energy neutrinos has been identified with reasonable confidence [1]. These results were published in the July 13 issue of Science magazine, in a paper authored by more than 1100 scientits in 16 collaborations, including Susumu Inoue of iTHEMS as a member of the MAGIC Collaboration [2]. Implications: The production of such high-energy neutrinos requires the acceleration of hadrons (proton or nuclei) to extremely high energies. This implies special physical conditions in the jets from supermassive black holes, and offer valuable clues on the formation mechanism of the jets, which is not well understood. This may also be the first step in solving the long-standing mystery of the origin of ultra-high-energy cosmic rays, the highest energy particles known to exist in the Universe [3]. Finally, it may shed new light on the properties of neutrinos at energies far beyond the capability of terrestrial accelerator facilities. Prospects: Following on the heels of GW170817, the binary neutron star merger event discovered in August 2017 in gravitational waves and then identified in electromagnetic waves, this signals the dawn of the “electroweak" sector of multi-messenger astronomy involving neutrinos and photons. Vigorous efforts will continue in the next years, with bright prospects for elucidating the physics of supermassive black holes and their jets, the origin of high-energy neutrinos and cosmic rays, etc. Figure 1: Image of the sky at optical wavelengths of the region of interest. Overlayed are the positional uncertainties of the neutrino IceCube-170922A, and those of the blazar TXS 0506+056 at optical wavelengths and in gamma rays observed by Fermi and MAGIC.

2018-07-17

## Series of lectures at Komaba Campus, Univ. of Tokyo

Series of lectures "Frontiers of Mathematical Sciences: Universe, Matter, Life and Information" were at Komaba Campus, Univ. of Tokyo, on every Wed. April-July, 2018, for the 1st and 2nd year undergraduate students in Univ. Tokyo. Six researchers from RIKEN iTHEMS (Y. Inoue, Y. Yokokura, M. Tachikawa, J. Fawcett, T. Doi and M. Taki) gave 14 lectures altogether. The photo is the very last slide of M. Taki and himself (left) who gave the last lecture on July 11, as well as T. Tsuboi who organized this class. Undergraduate students seem to enjoy these lectures which cover the wide range of topics selected from the point of view of mathematical sciences. We plan to publish these lectures as a book in the near future.

2018-07-17

## Production of intense episodic Alfvén pulses: GRMHD simulation of black hole accretion disks

The episodic dynamics of the magnetic eruption of spinning black hole (BH) accretion discs and the associated intense shape-up of their jets are studied via three-dimensional general-relativistic magnetohydrodynamics (GRMHD). The embedded magnetic fields in the disc are amplified by a magnetorotational instability (MRI) so large as to cause an eruption of the magnetic field (reconnection) and large chunks of matter accrete episodically toward the roots of the jets upon such an event. We also find that the eruption events produce intensive Alfvén pulses, which propagate through the jets. After the eruption, the disc returns to the weakly magnetic state. Such disc activities cause short-time variabilities in mass accretion rate at the event horizon, as well as electromagnetic luminosity inside the jet. Since the dimensionless strength parameter a0 = eE/m_eωc of these Alfvén wave pulses is extremely high for a substantial fraction of Eddington accretion rate accretion flows on to supermassive black holes, the Alfvén shocks turn into ultrarelativistic (a0 >> 1) bow wake acceleration, manifesting as ultra-high-energy cosmic rays and electrons, which finally emit gamma-rays. Since our GRMHD model has universality in its spatial and temporal scales, it is applicable to a wide range of astrophysical objects, ranging from active galactic nuclei (AGNs, the primary target of this research) to micro-quasars. Properties such as the time variabilities of blazar gamma-ray flares and the spectrum observed by the Fermi Gamma-ray Observatory are explained well by linear acceleration of electrons by a bow wake. Figure caption: A snap shot of accreting gas onto a spinning black hole and Poynting flux dominated jet formation by 3-dimensional general relativistic magneto-hydrodynamic simulation. Log-scaled inverse of plasma beta (magnetic pressure / thermal pressure) (x-y plane), mass density (y-z plane), and magnetic pressure (x-z plane) are shown.

2018-07-09

## A first joint meeting between iCeMS (Kyoto Univ.) and iTHEMS on interdisciplinary biology was held on July 4

On July 4, a first joint meeting between iCeMS (Kyoto Univ.) and iTHEMS on interdisciplinary biology was held at the 2nd floor of the Maskawa building in Kyoto Univ. After the welcome address by Prof. Shigefumi Mori (Director of KUIAS, Kyoto Univ. and the science advisor of iTHEMS) followed by the introductions to iCeMS and iTHEMS, there were 8 talks on experimental and theoretical studies on biology from both institutes. It turned out that all 8 talks were extremely interesting and stimulating for more than 40 participants from Kyoto Univ. and RIKEN. There were many questions and discussions during the talks and at the coffee breaks. We were very much excited about the fruitful interactions between experimentalists and theorists, so that we expect to have the 2nd joint workshop in the near future. All the slides can be seen from the workshop web page.

2018-07-09

## Self-introduction: Yosuke Kubota

I am Yosuke KUBOTA, a mathematician who have joined the iTHEMS from 2017. I'm basically working in the area of mathematics called index theory or noncommutative geometry (NCG), which has developed highly abstract theory related with a wide variety of other mathematics such as operator algebra, topology, geometry, group theory and mathematical physics. For example, a mathematics of topological insulators is one of the branches of NCG. I aspire to apply the theory of NCG to practical problems in mathematics and other areas. Please feel free to talk to me anytime.

2018-07-02

## Joint innovation seminar between RIKEN iTHEMS and Denso IT lab. was held on June 28

On June 28, joint innovation seminar between RIKEN iTHEMS and Denso IT lab. was held. After the general introduction to the Denso IT lab. There were two talks from Denso IT lab. (Human-car interface; Machine leaning and computer vision) and two talks from RIKEN iTHEMS (Topology in classical systems; Hadrons in quantum chromodynamics). It turned out that the background of all 4 speakers are theoretical physics. The iTHEMS coffee room was filled with people from both labs. and lively discussions among participants continued until 8pm. This meeting would be a model case where "real" interactions between researchers in academia and industry are made possible.

2018-07-02

## Mathematics activities in iTHEMS were featured in RIKEN Pamphlet 2018

Mathematics activities in iTHEMS were featured in RIKEN Pamphlet 2018 (in Japanese). Take a look at the photo of our colleagues, Takashi Tsuboi, Yuka Kotorii and Yosuke Kubota (from the left), trying to make a breakthrough with modern mathematics in page 19 of RIKEN Pamphlet.

2018-07-02

## Self-introduction: Jason Chang

I am Jason Chang, a research scientist at iTHEMS. I received my bachelors and PhD in physics from the University of Illinois at Urbana-Champaign. During my PhD, my focus was on calculating the hadronic contributions to flavor physics using lattice quantum chromodynamics (LQCD). Afterwards, I joined the LQCD group at Lawrence Berkeley National Laboratory (LBNL) to understand the contributions of the strong interaction in nuclear matter. My interests have since then also extended to explore the possibility of applying quantum annealing to machine learning techniques, and as led to new collaborations with scientists from condensed matter and quantum information science. I am very happy to join iTHEMS, and as a member who is primarily located at LBNL, I look forward to hosting and working with anyone interested in visiting the Bay Area for both the collaboration opportunities with scientists here, as well as industry experts around this area.

75 news in 2018