# ニュース

165 news in 2021

2021-09-17

## 植物の多種共存を説明する新たなメカニズムの発見 －開花前の自家受粉の進化が引き起こす進化的救助－

岡山大学学術研究院環境生命科学学域（工）の勝原光希助教（当時所属：神戸大学大学院人間発達環境学研究科）、東京都立大学大学院理学研究科の立木佑弥助教、理化学研究所数理創造プログラムの入谷亮介研究員（当時所属：University of California Berkeley, University of Exeter）、神戸大学大学院人間発達環境学研究科の丑丸敦史教授は、個体ベースモデルを用いたシミュレーションを行い、同じ種の送粉者を共有し競争関係にある植物2種において、個体数の少ない種でより高い自家受粉率が進化することで個体数が増加に転じる進化的救助が発生し、それによって2種の長期的な共存が促進されることを明らかにしました。 本結果は、複数の植物種が同所的に開花して共存できる理由にまったく新しい理論を加えると共に、植物で多様な繁殖戦略が進化してきた要因についても新たな視点を与えるものです。陸上生態系の根幹を支える植物の多様性の創出・維持メカニズムを理解することは、生物多様性の源泉の理解のみならず、生態系と調和した持続可能な社会形成を考える上でも不可欠であり、基礎・応用の両面において重要な知見であるといえます。 詳細は関連リンクから岡山大学のプレスリリースをご覧ください。

2021-09-16

## Week 3, September 2021

Title: Equation of state of neutron star matter and its warm extension with an interacting hadron resonance gas Author: Yuki Fujimoto, Kenji Fukushima, Yoshimasa Hidaka, Atsuki Hiraguchi, Kei Iida arXiv: http://arxiv.org/abs/2109.06799v1

2021-09-15

## NEW WG Seminar by Prof. Yuta Murakami on September 15, 2021

Yuta Murakami from Tokyo Institute of Technology told us about "High-harmonic generation in strongly correlated systems." High-harmonic generation (HHG) by strong AC electric fields is one of the hottest topics in cond-mat physics. After a brief overview of HHG in various materials such as gasses and semi-conductors and also recent experimental results in Mott insulators, Yuta explained his recent numerical studies on HHG in strongly correlated systems and clarified unique features of HHG arising from the strongly-correlated nature. About 30 people joined the seminar and we enjoyed fruitful discussions during and after the seminar. Reported by Hidetoshi Taya

2021-09-13

## NEW WG Seminar by Prof. Matteo Baggioli on September 10, 2021

Matteo Baggioli (Jiao-Tong U. Shanghai) gave a talk on "Towards a description of amorphous solids and viscoelastic materials using effective field theory and holographic methods." Amorphous and viscoelastic materials appear in many places, not only in scientific problems but also in our daily life. Despite its ubiquity, there are many intriguing phenomena that are not yet understood, in particular, in the non-linear regime. In the talk, Matteo explained his recent attempts to formulate non-linear responses in amorphous and viscoelastic materials based on holographic and effective-field-theory techniques. Matteo also discussed open problems and future directions that we can pursue in the future. There were about 30 participants from various fields of physics, and we had fruitful discussions from a broad point of view during and even after the talk. Reported by Hidetoshi Taya

2021-09-09

## Events for the 3rd week of September 2021

Monday, September 13, 13:30- iTHEMS Theoretical Physics Seminar Tuesday, September 14, 9:30- DMWG Seminar Wednesday, September 15, 13:30- NEW WG Seminar Friday, September 17, 12:30- Coffee Meeting

2021-09-09

## Week 2, September 2021

Title: Subregion Spectrum Form Factor via Pseudo Entropy Author: Kanato Goto, Masahiro Nozaki, Kotaro Tamaoka arXiv: http://arxiv.org/abs/2109.00372v1

2021-09-09

## iTHEMS Biology Seminar by Dr. Euki Yazaki on September 9, 2021

Molecular phylogenetic analysis is one of the most important analysis methods in biology. If used well, it can help us understand how organisms diversified and how genes evolved. The methods of molecular phylogenetic analysis are subject to debate, so we are familiar with the mathematical background. However, we are not so familiar with how the data sets for phylogenetic analysis are made up. In this Biology Seminar, the main alignment algorithms for making data sets were explained and discussed. Scoring is important in alignment algorithms, and there was a discussion on scoring for amino acid and nucleic acid mutations and scoring for gap penalties. The discussion on alignment distance was also heated. I hope the audience all enjoyed it. I would like to have another discussion on phylogenetic analysis and mathematical background next time. Thank you very much!

2021-09-09

## ABBL-iTHEMS Joint Seminar by Dr. Yosuke Mizuno on September 3, 2021

Prof. Yosuke Mizuno (Tsung-Dao Lee Institute, Shanghai JiaoTong University) gave an excellent talk on "The Polarised ring ofthe Supermassive Black Hole in M87: EHT observations andtheoretical modeling". He introduced that the Event HorizonTelescope (EHT) had mapped the central compact radio source of theelliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Recently EHT provided new images of the polarised emissionaround the central black hole in M87 on event-horizon scale. Thispolarised synchrotron emission probes the structure of magnetic fieldsand the plasma properties near the black hole. He and hiscollaborators found that the net azimuthal linear polarisationpattern may result from organised, poloidal magnetic fields in the emission region. In a quantitative comparison with a large simulated polarimetric image library, he found that magnetically arrested accretion disks are favoured to explain polarimetric EHT observations. In this talk, he also discussed about a new modelling study of M87jets in the collimation and acceleration region. Reported by Shigehiro Nagataki

2021-09-08

## Self-introduction: Matthias Berwein

My name is Matthias Berwein and I'm from Germany. I did my undergraduate studies in physics at TU Munich from 2006 to 2011, followed by a PhD 2012-2016 also at TU Munich in the group of Nora Brambilla. Then I came to Japan for my first postdoc at Tohoku University in Sendai under a JSPS fellowship with Yukinari Sumino. Since 2018 I've been at RIKEN, first in the SPDR program at Quantum Hadron Physics Lab, and from 2021 in iTHEMS. The focus of my research lies in theoretical studies of the strong interactions through the theory of quantum chromodynamics and with a special emphasis on heavy quarks. I have worked on several projects on the static quark potential, heavy quarkonium hybrids, and heavy quarks at finite temperature, using perturbative calculations and effective theory methods. Currently, I'm studying properties of the energy-momentum tensor in these environments. I look forward to many fruitful interactions with fellow researchers here at iTHEMS.

2021-09-03

## Quantum Matter SG seminar by Dr. Levente Rózsa on September 1, 2021

Dr. Levente Rózsa gave a talk about Yu-Shiba-Rusinov (YSR) states and other localized states appearing in superconductors for Quantum Matter Study Group on September 1st, 2021. There are three distinct types of localized in-gap states in superconductors —- Majorana bound states, YSR states, and Caroli-de Genne-Matricon states. Dr. Rózsa first introduced Majorana bound states emerging in topological superconductors. Next, he talked about the anisotropic spacial distribution of the YSR states on the La surface (0001). The YSR state is a localized in-gap state induced by magnetic impurity in a superconductor. He showed that this anisotropy stems from the anisotropic Fermi surface. Furthermore, he discussed the localized states appearing in vortex cores are Caroli-de Genne-Matricon states, instead of Majorana bound states. He went through the experimental details and compared them with his theoretical simulation. The talk was well-organized and clear. We thank Dr. Rózsa for sharing his interesting research works. Reported by Ching-Kai Chiu and Thore Posske

2021-09-03

## iTHEMS Biology Seminar by Dr. Yingying Xu on September 2, 2021

In today's Biology Seminar, Yingying Xu (iTHEMS) introduced one paper arguing the quantitative explanation for immune-escape of virus by means of quasispecies dynamics models with Gillespie algorithm. She firstly explained the background information about the immune systems. She then taught us how the authors simulated the dynamics and made a comparison with experimental data. We finally discussed potential future directions to further development of quantitative modeling of chronic or acute infectious virus, highlighting a potential issue in estimating the mutation rate of virus. We learned a lot from this journal club, thank you so much for the great talk, Yingying! Reported by Ryosuke Iritani

2021-09-02

## Week 1, September 2021

Title: Anomaly-induced edge currents in hydrodynamics with parity anomaly Author: Takuya Furusawa, Masaru Hongo arXiv: http://arxiv.org/abs/2108.12192v1 Title: Near-threshold Spectrum from Uniformized Mittag-Leffler Expansion -Pole Structure of $Z(3900)$- Author: Wren A. Yamada, Osamu Morimatsu, Toru Sato, Koichi Yazaki arXiv: http://arxiv.org/abs/2108.11605v1 Title: Subregion Spectrum Form Factor via Pseudo Entropy Author: Kanato Goto, Masahiro Nozaki, Kotaro Tamaoka arXiv: http://arxiv.org/abs/2109.00372v1

2021-09-02

## Events for the 2nd week of September 2021

Friday, September 10, 12:30- Coffee Meeting Friday, September 10, 13:30- NEW WG Seminar

2021-08-31

## スパコンで予言する魅惑の新粒子「チャームダイオメガ」 －クォーク6個状態の謎の解明に新たな1ページが加わる－

理化学研究所（理研）数理創造プログラムの杉浦拓也特別研究員、初田哲男プログラムディレクター、土井琢身専任研究員含む研究グループは、チャームクォーク6個からなる新粒子「チャームダイオメガ（ΩcccΩccc）」の存在を理論的に予言しました。 続きは、関連リンクをご覧ください。

2021-08-30

## iTHEMS Biology Seminar by Dr. Gen Kurosawa on August 26, 2021

During this covid-19 crisis, we check our body temperature (Tb) every day since Tb is essential variable of our body. In fact, some organisms like humans try to keep Tb constant, but some other organisms chose completely different strategies, including hibernation (冬眠). On August 26, I talked about hibernation at the iTHEMS Biology Seminar. Hibernation is a strategy for the organisms, including a primate to survive in a severe season with limited food and water availability. Although there have been a lot of studies about hibernation since the era of Aristotle, fundamental problems of hibernation remain unknown. Recently, we started to investigate mathematically body temperature profile of hibernating hamsters. During hibernation, the organisms drastically decrease their basal metabolisms, drop their body temperature (Tb) more than 10 degree, and become immobile. Mysteriously, Tb during hibernation does not remain constant at very low value, but greatly fluctuates with inconstant period of several days. At the seminar, I showed that a simple model can reproduce well and forecast Tb data during hibernation. Thankfully, there were a lot of questions and suggestions about the method of time-series analysis, hibernating species, and so on which are precious to me. This study is the collaboration with Prof. Yoshifumi Yamaguchi at Institute of Low Temperature Science, Hokkaido Univ and Shingo Gibo at iTHEMS. I’m really enjoying this research. I am happy if the audiences enjoyed the seminar and forgot about the heat. Thanks!

2021-08-27

## RIKEN-Vancouver Joint Workshop on Quantum Computing was held on August 24-25, 2021

RIKEN-Vancouver Joint Workshop on Quantum Computing was held online on August 24-25. The main aim of this workshop is that the quantum people in RIKEN (iTHEMS and RQC) and Vancouver (Quantum BC) get together online to discuss scientific activities and explore future collaborations. There were altogether 164 registrations (90 from Japan, 62 from Canada and 12 from other countries). 12 scientific talks were presented together with 3 introduction to iTHEMS, RQC and Quantum BC. From iTHEMS, Jason Chang, Etsuko Itou, and Takumi Doi gave talks respectively on the Schroedinger equation, the U(1) gauge theory and combinatorial optimization. After each session, there were one-hour breakout sessions, so that people can ask further questions to the speakers, which worked very well. The workshop was an excellent first step toward a close tie between RIKEN quantum activities and Vancouver quantum activities.

2021-08-26

## Week 5, August 2021

Title: Intraspecific Adaptation Load: A Mechanism for Species Coexistence Author: Masato Yamamichi, Daisuke Kyogoku, Ryosuke Iritani, Kazuya Kobayashi, Yuma Takahashi, Kaori Tsurui-Sato, Akira Yamawo, Shigeto Dobata, Kazuki Tsuji, Michio Kondoh Journal Reference: Trends in Ecology & Evolution 35(10), 897-907 (2020) doi: https://doi.org/10.1016/j.tree.2020.05.011 Title: Reproductive interference hampers species coexistence despite conspecific sperm precedence Author: Ryosuke Iritani, Suzuki Noriyuki Journal Reference: Ecology and Evolution 11(5),1957-1969 (2021) doi: https://doi.org/10.1002/ece3.7166 Title: Temporal changes in spatial variation: partitioning the extinction and colonisation components of beta diversity Author: Shinichi Tatsumi, Ryosuke Iritani, Marc W. Cadotte Journal Reference: Ecology Letters 24(5), 1063-1072 (2021) doi: https://doi.org/10.1111/ele.13720 Title: A solution to a sex ratio puzzle in Melittobia wasps Author: Jun Abe, Ryosuke Iritani, Koji Tsuchida, Yoshitaka Kamimura, Stuart A. West Journal Reference: PNAS 118 (20) e2024656118 (2021) doi: https://doi.org/10.1073/pnas.2024656118 Title: Cooperative interactions among females can lead to even more extraordinary sex ratios Author: Ryosuke Iritani, Stuart A. West, Jun Abe Journal Reference: Evolution Letters 5(4),370-384 (2021) doi: https://doi.org/10.1002/evl3.217 Title: Construction of energy density functional for arbitrary spin polarization using functional renormalization group Author: Takeru Yokota, Tomoya Naito arXiv: http://arxiv.org/abs/2108.10787v1 Title: Femtoscopic study of coupled-channel $NΞ$ and $ΛΛ$ interactions Author: Y. Kamiya, K. Sasaki, T. Fukui, T. Hyodo, K. Morita, K. Ogata, A. Ohnishi, T. Hatsuda arXiv: http://arxiv.org/abs/2108.09644v1 Title: Product of Random States and Spatial (Half-)Wormholes Author: Kanato Goto, Yuya Kusuki, Kotaro Tamaoka, Tomonori Ugajin arXiv: http://arxiv.org/abs/2108.08308v1 Title: Band width and the Rosenberg index Author: Yosuke Kubota arXiv: http://arxiv.org/abs/2108.08506v1

2021-08-25

## iTHEMS Biology Seminar by Dr. Naohiro Kawamoto on August 19, 2021

In iTHEMS Biology Seminar on August 19th, Dr. Naohiro Kawamoto (Osaka University) gave a talk on cyanobacterial circadian oscillations. It is known that three proteins (KaiA, KaiB and KaiC) are sufficient for generating self-sustained circadian oscillations in cyanobacterium. In this talk, Dr. Kawamoto experimentally showed that the lack of kaiA causes damped oscillation. Then, he analyzed the benefit of the damped circadian oscillation by using a simple mathematical model of the interaction between the damped and self-sustained oscillators. This analysis revealed that kaiA-less damped oscillator can resonate to another oscillatory process. Finally, he talked about evolution of related to evolution of circadian clock system for future work. After the talk, we enjoyed discussion about mathematical modeling of various types of coupled oscillators. Thank you very much, Naohiro! Reported by Shingo Gibo

2021-08-25

## Quantum Matter SG seminar by Prof. Daw-Wei Wang on August 23, 2021

On August 23rd, 2021, Quantum Matter Study Group invited Prof. Daw-Wei Wang to give a talk on the application of machine learning in condensed matter physics. First, he briefly introduced learning and emphasized using supervised machine learning in condensed matter physics. The practical condensed matter problem he focused on is the physics of many-body systems since the many-body problem is challenging to solve. By randomly choosing small portions of a many-body Hamiltonian, machine learning can almost accurately predict the energy of the many-body system. Prof. Wang used the 1D Fermi-Hubbard model and the 1D Ising model to show the consistency between the learning prediction and the known solutions. The limitation of this approach is that the system size has to be fixed. To resolve this problem, he used the transfer learning approach to extend the prediction to a larger system size by learning from small systems. In the end, he talked about identifying the topological phase transition points by improving the machine learning approach in the literature. The talk is very comprehensive and informative. We thank Prof. Wang for giving a wonderful talk. Reported by Ching-Kai Chiu

2021-08-23

## 日本経済新聞朝刊: 量子の威力、併用で生かす

入江 広隆 客員研究員（企業）のインタビュー記事が日本経済新聞のテクノロジストの時代に掲載されました。 従来のコンピューターと量子コンピューターの良いところを組み合わせた「ハイブリッド型」について答えています。 詳細は関連リンクをご覧下さい。

2021-08-19

## Events for the 4th week of August 2021

Monday, August 23, 16:00- Quantum Matter Seminar Tuesday, August 24-25, RIKEN-Vancouver Joint Workshop on Quantum Computing Friday, August 27, 12:30- Coffee Meeting

2021-08-19

## Week 4, August 2021

Title: Observing Supernova Neutrino Light Curves with Super-Kamiokande: II. Impact of the Nuclear Equation of State Author: Ken'ichiro Nakazato, Fumi Nakanishi, Masayuki Harada, Yusuke Koshio, Yudai Suwa, Kohsuke Sumiyoshi, Akira Harada, Masamitsu Mori, Roger A. Wendell arXiv: http://arxiv.org/abs/2108.03009v1 Title: The generalized Nielsen-Ninomiya Theorem for the 17 wallpaper: Classification of 2D nodal superconductors, Dirac semimetals, and non-Hermitian nodal systems Author: Congcong Le, Zhesen Yang, Fan Cui, A. P. Schnyder, Ching-Kai Chiu arXiv: http://arxiv.org/abs/2108.04534v1 Title: Matrix Model simulations using Quantum Computing, Deep Learning, and Lattice Monte Carlo Author: Enrico Rinaldi, Xizhi Han, Mohammad Hassan, Yuan Feng, Franco Nori, Michael McGuigan, Masanori Hanada arXiv: http://arxiv.org/abs/2108.02942v1 Title: Universality of Interior Metric of Typical Black Holes Author: Hikaru Kawai, Yuki Yokokura arXiv: http://arxiv.org/abs/2108.02242v2 Title: Stability of the protoneutron stars toward black hole formation Author: Hajime Sotani, Kohsuke Sumiyoshi arXiv: http://arxiv.org/abs/2108.02484v1

2021-08-18

## iTHEMS Math Seminar by Dr. Yalong Cao on August 6, 2021

The final Math Seminar of this semester was held on August 9th. This time, we invited our new colleague Dr. Yalong Cao as a speaker. First, he gave an overview of the celebrated Yang-MIlls theory in real dimensions 3 and 4. Next, it was explained that one can complexify the above Yang-Mills theory on Calabi-Yau 3 and 4-folds. The point is that in algebro-geometric setting, moduli spaces of Yang-Mills connections admit nice compactifications. Finally, he explained the connection between the above story and the enumerative geometry, specifically on counting (stable) coherent sheaves and complex ASD connections on Calabi-Yau 4-folds. He and his collaborators proposed a conjectural sheaf-theoretic interpretation of Klemm-Pandharipande’s BPS invariants of CY 4-folds defined using Gromov-Witten theory. Reported by Hiroyasu Miyazaki

2021-08-17

## iTHEMS Theoretical Physics Seminar by Dr. Shunichiro Kinoshita on August 16, 2021

Shunichiro Kinoshita (Chuo U.) gave a talk on "Application of AdS/CFT to non-equilibrium phenomena in external electric fields. "After a brief introduction to the AdS/CFT correspondence, Shunichiro analyzed a holographic QCD system under strong electric fields constructed with D3/D7 branes. Shunichiro considered two kinds of electric-field configurations.The first one was a field with a sudden switching on (quenched setup). Shunichiro discussed how the confinement-deconfinement phase transition occurs and showed the possibility of deconfinement driven by turbulence. The second configuration was rotating electric fields. Shunichiro discussed how the frequency of the electric field affects the phase transition and argued the possibility of a novel state, distinct from the vacuum, for infinitesimally small electric fields with finite frequency. Reported by Hidetoshi Taya

2021-08-13

## 理化学研究所と沖縄科学技術大学院大学との連携大学院に関する協定締結について

理化学研究所（理研）と沖縄科学技術大学院大学（OIST）は、相互の研究交流を促進し、学術および科学技術の振興に資することを目的として、連携大学院に関する協定を2021年8月1日に締結しました。今後、理研とOISTは連携大学院制度の下、OISTの大学院生を理研に受け入れて研究指導等を行うとともに、理研の研究者がOISTで講義を行うなど、人材育成での連携を深めていきます。なお、任命される同制度の連携教授には、長瀧重博（iTHEMS副プログラムディレクター）が含まれます。

2021-08-10

## Information Theory SG Seminar by Prof. Masayuki Ohzeki on August 4, 2021

On August 4, Prof. Masayuki Ohzeki (Tohoku University/Tokyo Institute of Technology/Sigma-i Co., Ltd.) gave us a talk on the quantum annealing. In the first part, after a general introduction, he demonstrated how to use the D-Wave machine from our personal computers. It is remarkable that we can easily manipulate a number of quantum spins ourselves to solve an optimization problem. In the second part, he reviewed working principles for quantum annealing: he started from the original proposal in 1998 and explained more recent methods such as the reverse annealing. He also explained carefully the usefulness and the limits of the quantum annealing. After discussing the theoretical perspective and how the machine is implemented using the superconducting qubits, he presented the application of the quantum annealer to the real world. He showed his collaborations with many companies and how the quantum annealing can be used to solve real-life problems, such as the optimization of the evacuation routes or listing the hotel recommendation on the web. A lot of interactive discussions were made during and after the talk. We really thank Prof. Ohzeki for his great talk. Reported by Ryusuke Hamazaki

2021-08-06

## iTHEMS Biology Seminar by Dr. Ai Niitsu on August 5, 2021

In iTHEMS biology seminar on August 5th, Dr. Ai Niitsu (RIKEN Theoretical Molecular Science Lab.) gave a talk about the membrane peptide design and computational modeling. First, she mentioned the recent machine learning approach for the prediction of the protein structures. Then, she pointed out that the prediction of the membrane related structure and stoichiometry of protein complexes is still challenging. Next, she explained the computational design of the coiled-coil peptides in membrane. The amino acid sequence of the peptide is determined so that the interchain interaction is satisfied. As a result, she obtained some stable transmembrane assemblies of the peptide. Along with the modelling of the peptide assemblies and their conductance estimate, she experimentally measured the conductance of the peptide channel in membrane by imposing various voltages. The high voltage induces the multi-conductance state, which differs from the low voltage case where a stable single channel was observed. Based on further computational modelling and experiments, that multi-conductance state was suggested to come from the change in the peptide structures and stoichiometry of a single pore. Her computational method and experimental results attract the audience interests and induce various discussions. Thank you very much for great talk, Ai! Reported by Hiroshi Yokota

2021-08-05

## Week 2, August 2021

Title: LMC N132D: A mature supernova remnant with a power-law gamma-ray spectrum extending beyond 8 TeV Author: H. E. S. S. Collaboration arXiv: http://arxiv.org/abs/2108.02015v1 Title: Relativistic spin hydrodynamics with torsion and linear response theory for spin relaxation Author: Masaru Hongo, Xu-Guang Huang, Matthias Kaminski, Mikhail Stephanov, Ho-Ung Yee arXiv: http://arxiv.org/abs/2107.14231v1 Title: Convergence of a finite difference scheme for the Kuramoto--Sivashinsky equation defined on an expanding circle Author: Shunsuke Kobayashi, Shigetoshi Yazaki arXiv: http://arxiv.org/abs/2108.00593v1 Title: Locally equivalent quasifree states and index theory Author: Chris Bourne arXiv: http://arxiv.org/abs/2108.01230v1 Title: Toward ab initio determination of charge symmetry breaking strength of Skyrme functionals Author: Tomoya Naito, Gianluca Colò, Haozhao Liang, Xavier Roca-Maza, Hiroyuki Sagawa arXiv: http://arxiv.org/abs/2107.14436v1

2021-08-05

## Self-introduction: Congcong Le

My name is Congcong Le from China, and I join iTHEMS on August 1st 2021 as a Postdoctoral Researcher. After graduation, I came to the Institute of Physics, Chinese Academy of Sciences to study theoretical physics, and obtained my PhD in July 2017. My research focuses on the theoretical study in condensed matter systems, including unconventional superconductivity, strongly correlated system, and novel topological system (topological insulators, Dirac semimetal, Weyl semimetal), and I start to be interested in twisted bilayers and topological phases in the non-Hermitian systems. I have enjoyed using mathematics to explore condensed matter physics and working with theorists and experimenters. In my spare time, I like Chinese chess, badminton, table tennis and climbing.

2021-08-02

## Information Theory SG Seminar by Dr. Qibin Zhao on July 28, 2021

In the Information Theory SG seminar on July 28th, Dr. Qibin Zhao gave us an exciting talk about the basics and applications of tensor networks (TNs) in machine learning. His talk was divided into three parts, (i) tensor methods for data representation, (ii) TNs in deep learning modeling, and (iii) frontiers and future trends. In the first part, he started with a graphical introduction of tensors and dimension reduction methods. He then presented the important question of how the imperfect data represented by tensors can be completed using the low-rank approximation, and introduced several possible approaches with impressive examples. Here he explained the TNs and decomposition methods in detail using diagrammatic notations, which can concisely express the tensor operations such as the contraction. In the second part, he talked about the useful application of TNs to model compression in machine learning. He illustrated the ways to represent the neural network model by tensors and to learn the weights through the contraction. Interestingly, the density matrix renormalization group (DMRG), which was originally proposed in the quantum physics field, may be used as a learning algorithm. In the last part, he showed an overview of recent topics on TNs and machine learning such as TNs for probabilistic modeling and supervised learning with projected entangled pair states (PEPS). Intriguingly, the topological structure of TNs can be optimized for a given image, and the learned topology significantly depends on the input data and is more complex than conventional simple structures such as lines, trees, or cycles. The clearly structured talk took us from the basics to the cutting-edge subjects, and there were many questions and discussions during the talk. We are deeply grateful to Dr. Qibin Zhao for his excellent talk on the fast-growing interdisciplinary field. Reported by Kyosuke Adachi

2021-07-30

## iTHEMS Biology Seminar by Prof. Mayumi Seto on July 29, 2021

On July 29th, Mayumi Seto (Nara Women's University) gave a talk on the application of thermodynamics to microbial modeling. She first introduced some important concepts of adenosine tri-phosphate (ATP), its synthesis in biology, and chmotrophic interactions between microorganisms. She then moved on to mathematical models explicitly incorporating energy flows in the microbial interactions. She finally gave implications from her work for future and ongoing studies, and after the talk we casually discussed her exciting projects. For me, she was the person whom I met on the very first visitation at Kyushu University in 2009 when I was, as an undergrad student at another university, yet unsure to start my Ph.D. at Kyushu University or not, and I'm sure her kind and encouraging guidance was one of the decisive factors for me being here as a researcher. Thanks again for the fantastic talk, Mayumi! Reported by Ryosuke Iritani

2021-07-29

## Events for the 1st week of August 2021

Wednesday, August 4, 13:30- Information Theory SG Seminar Friday, August 6, 12:30- Coffee Meeting Friday, August 6, 16:00- iTHEMS Math Seminar

2021-07-29

## Week 5, July 2021

Title: A Fundamental Plane in X-ray Binary Activity of External Galaxies Author: Yoshiyuki Inoue, Kiyoto Yabe, Yoshihiro Ueda arXiv: http://arxiv.org/abs/2107.07775v1 Title: Three-body crossover from a Cooper triple to bound trimer state in three-component Fermi gases near a triatomic resonance Author: Hiroyuki Tajima, Shoichiro Tsutsui, Takahiro M. Doi, Kei Iida arXiv: http://arxiv.org/abs/2107.13232v1 Title: A mathematical model of network elastoplasticity Author: Hiroki Kodama, Ken'ichi Yoshida arXiv: http://arxiv.org/abs/2107.04310v1 Title: On regular $^*$-algebras of bounded linear operators: A new approach towards a theory of noncommutative Boolean algebras Author: Michiya Mori arXiv: http://arxiv.org/abs/2107.05806v1

2021-07-29

## RIKEN RESEARCH: Smoking-gun evidence for neutrinos’ role in supernova explosions

Supernova explosions are sustained by neutrinos from neutron stars, a new observation suggests. Shigehiro Nagataki (Deputy Program Director, iTHEMS) were interviewed in the article.

2021-07-27

## 広報誌 RIKEN 2021にiTHEMSの研究活動や研究員が掲載されました

広報誌 RIKEN 2021の複数の記事にiTHEMSの研究と研究員が掲載されました。 p.8-9: 蒸発するブラックホールの内部を理論的に記述し、その正体に迫る（横倉 祐貴） p.10-11: 扉イメージ（ドン・ウォレン） p.20-21: 数理モデルで生物学の謎に挑む（iTHEMS生物学セミナースタディーグループ）

2021-07-20

## Self-introduction: Yalong Cao

I am a mathematician doing research on algebraic geometry, differential geometry and mathematical physics. I am particularly interested in understanding Yang-Mills theory on Calabi-Yau 4-folds and how it is interacted with enumerative geometry. I am eager to understand how such theory could lead to unexpected relations with other areas. It is my great pleasure to join RIKEN iTHEMS and I am looking forward to having exciting discussions with you.

2021-07-15

## Week 3, July 2021

Title: A mathematical model of network elastoplasticity Author: Hiroki Kodama, Ken'ichi Yoshida arXiv: http://arxiv.org/abs/2107.04310v1 Title: On regular $^*$-algebras of bounded linear operators: A new approach towards a theory of noncommutative Boolean algebras Author: Michiya Mori arXiv: http://arxiv.org/abs/2107.05806v1

2021-07-15

## iTHEMS Science Outreach Workshop 2021 was held on July 11-12, 2021

On July 11 and 12, we had Journalist in Residence Workshop 2021 on Zoom. This year as last year, Tambara Institute of Mathematical Sciences of the University of Tokyo is closed because of COVID-19 and we again organized it on Zoom. The participants included more than 20 journalists, more than 20 participants from RIKEN and 10 from universities. 9 iTHEMS members mainly explained their working field and recent important achievements to the nonspecialists. There were 24 talks in total in a variety of fields. The discussion among the participants continued with joy in the evening of July 11 in ZOOM. We hope to organize it next year, in principle face to face and including remote participants by online.

2021-07-12

## iTHEMS Colloquium by Prof. Shingo Iwami on July 8, 2021

In his presentation for the iTHEMS Colloquium, Prof. Shingo Iwami discussed the foundational approach of his research: using a mathematical model-based approach to link experimental data from ever-improving experimental measurement technology in order to tackle problems in Biology, particularly in hematology, infectious diseases, cancer, etc. He illustrated his research approach through several examples that ranged from HIV, Hepatitis C virus, and the new SARS corona virus (SARS-CoV-2). He highlighted some of the key challenges that are faced when trying to extract specific information from limited data, and how properly calibrated models can be used to simulate experiments that cannot be performed. He also talked about his plans for the future, and introduced the research team he newly formed at Nagoya University, the interdisciplinary Biology Laboratory or iBLab. Reported by Catherine Beauchemin

2021-07-08

## Week 2, July 2021

Title: The maximal negative ion of molecules in Schrödinger, Hartree-Fock, and Müller theories Author: Yukimi Goto arXiv: http://arxiv.org/abs/2107.01826v2 Title: Positivity vs. Lorentz-violation: an explicit example Author: Katsuki Aoki, Shinji Mukohyama, Ryo Namba arXiv: http://arxiv.org/abs/2107.01755v1 Title: Effects of finite-light-speed correction for the Coulomb interaction on nuclear binding energies and radii in spherical nuclei Author: Tomoya Naito arXiv: http://arxiv.org/abs/2106.14270v1 Title: Goldstone Boson Scattering with a Light Composite Scalar Author: T. Appelquist, R. C. Brower, K. K. Cushman, G. T. Fleming, A. Gasbarro, A. Hasenfratz, J. Ingoldby, X. Y. Jin, J. Kiskis, E. T. Neil, J. C. Osborn, C. Rebbi, E. Rinaldi, D. Schaich, P. Vranas, E. Weinberg, O. Witzel arXiv: http://arxiv.org/abs/2106.13534v1 Title: Quantum hydrodynamics from local thermal pure states Author: Shoichiro Tsutsui, Masaru Hongo, Shintaro Sato, Takahiro Sagawa arXiv: http://arxiv.org/abs/2106.12777v2 Title: Modulus sheaves with transfers Author: Shane Kelly, Hiroyasu Miyazaki arXiv: http://arxiv.org/abs/2106.12837v1 Title: Unitary $p$-wave Fermi gas in one dimension Author: Hiroyuki Tajima, Shoichiro Tsutsui, Takahiro M. Doi, Kei Iida arXiv: http://arxiv.org/abs/2106.12909v1

2021-07-08

## Events for the 3rd week of July 2021

Sunday, July 11, 10:00- iTHEMS Science Outreach Workshop 2021 Friday, July 16, 12:30- Coffee Meeting

2021-07-07

## iTHEMS Theoretical Physics Seminar by Dr. Myungo Shim on July 5, 2021

On July 5, Myungo Shim from Kyung Hee University, Korea, gave the iTHEMS-physics seminar on a correspondence between three-dimensional gauge theories. He proposed a novel procedure of assigning a pair of non-unitary topological quantum field theories (TQFTs), TFT$_\pm [T_0]$, to a (2+1)D interacting $N=4$ superconformal field theory (SCFT) $T_0$ of rank $0$, i.e. having no Coulomb and Higgs branches. The topological theories arise from particular degenerate limits of the SCFT. Modular data of the non-unitary TQFTs are extracted from the supersymmetric partition functions in the degenerate limits. As a non-trivial dictionary, he proposed that $F = {\rm max}\{ - \log |S^{(+)}_{0\alpha}| \} = {\rm max}\{- \log |S^{(-)}_{0\alpha}|\}$, where $F$ is the round three-sphere free energy of $T_0$ and $S^{(\pm)}_{0\alpha}$ is the first column in the modular S-matrix of TFT$_\pm$. From the dictionary, he derived the lower bound on $F$, $F \geq -\log \left(\sqrt{\frac{5-\sqrt{5}}{10}} \right) \simeq 0.642965$, which holds for any rank $0$ SCFT. The bound is saturated by the minimal $N=4$ SCFT proposed by Gang-Yamazaki, whose associated topological theories are both the Lee-Yang TQFT. Before going to the technical part, he also provided some background materials including some peculiar features in 3d gauge theories, some supersymmetries, anyons, and some modular data of MTC in the talk. Reported by Toshihiro Ota

2021-07-06

## iTHEMS Math Seminar by Mr. Mizuki Oikawa on July 2, 2021

On July 2 Mizuki Oikawa gave a talk at the iTHEMS math seminar. He talked about the interaction among modular functions, conformal field theories and moonshine phenomena. Below is a recap of his talk. The j-invariant is an example of modular form. Its coefficients in the q-expansion is closely related to a certain sporadic simple group (the monster group), and the relation can be understood via the theory of vertex operator algebras (VOA), which is a mathematical model of conformal field theory (CFT). This gives an example of moonshine phenomena. On the other hand, there is another mathematical framework for CFT, called the conformal net, which depends on the theory of von Neumann algebras. Carpi-Kawahigashi-Longo-Weiner gave a correspondence between a certain class of VOAs (which includes the monstrous moonshine VOA) and that of conformal nets. Recently, Tener gave a geometric realization of some VOAs and the corresponding conformal nets via Segal CFT. The talk was highly stimulating, and the audience asked many questions that arise from both mathematical and physical sides. Reported by Michiya Mori

2021-07-06

## iTHEMS Biology Seminar by Prof. Takahiro Sakaue on July 1, 2021

On July 1st, Prof. Takahiro Sakaue (Aoyama Gakuin University) gave us a talk about chromatin dynamics in C. elegans embryos. He first introduced important factors for gene expression such as phase separation, topological constraints, and chromatin dynamics. After explaining how to see the chromatin dynamics under the microscope, he showed us interesting experimental results about the dependence of MSD on the nucleus radius. By considering polymer models, he showed that two kinds of typical length/time scales appear and discussed how the type of anomalous diffusion of chromatin is determined depending on the time/length scale. Moreover, he theoretically explained the observed nucleus-size dependence of MSD. We are grateful to Sakaue-san for the exciting talk! Reported by Kyosuke Adachi

2021-07-02

## Self-introduction: Etsuko Itou

I'm Etsuko Itou, a Postdoctoral Researcher (Concurrent) since July 2021. I'm interested in quantum field theories, in particular, quantum chromodynamics (QCD) in extreme regimes. Although QCD in the superfluid phase, which occurs in low-temperature and high-density regimes, is still an unsolved area due to the infamous sign problem, a theoretical understanding is urgently needed in relation to neutron star physics. I am working on various numerical approaches to understanding quantum field theories with the sign problem. For example, I utilize the conventional classical supercomputers to study qualitative properties of modified QCD without the sign problem, and I develop quantum computation algorithms based on a new formula where the sign problem does not emerge.

2021-07-01

## Week 5, June 2021

Title: Effects of finite-light-speed correction for the Coulomb interaction on nuclear binding energies and radii in spherical nuclei Author: Tomoya Naito arXiv: http://arxiv.org/abs/2106.14270v1 Title: Goldstone Boson Scattering with a Light Composite Scalar Author: T. Appelquist, R. C. Brower, K. K. Cushman, G. T. Fleming, A. Gasbarro, A. Hasenfratz, J. Ingoldby, X. Y. Jin, J. Kiskis, E. T. Neil, J. C. Osborn, C. Rebbi, E. Rinaldi, D. Schaich, P. Vranas, E. Weinberg, O. Witzel arXiv: http://arxiv.org/abs/2106.13534v1 Title: Quantum hydrodynamics from local thermal pure states Author: Shoichiro Tsutsui, Masaru Hongo, Shintaro Sato, Takahiro Sagawa arXiv: http://arxiv.org/abs/2106.12777v1 Title: Modulus sheaves with transfers Author: Shane Kelly, Hiroyasu Miyazaki arXiv: http://arxiv.org/abs/2106.12837v1 Title: Unitary $p$-wave Fermi gas in one dimension Author: Hiroyuki Tajima, Shoichiro Tsutsui, Takahiro M. Doi, Kei Iida arXiv: http://arxiv.org/abs/2106.12909v1

2021-07-01

## Events for the 2nd week of July 2021

Monday, July 5, 13:00- iTHEMS Theoretical Physics Seminar Monday, July 5, 15:00- MACS Colloquium Thursday, July 8, 10:30- iTHEMS Colloquium Friday, July 9, 12:30- Coffee Meeting

2021-07-01

## iTHEMS Theoretical Physics Seminar by Dr. Yuki Fujimoto on June 29, 2021

On June 29th, Yuki Fujimoto (The University of Tokyo) gave the iTHEMS-physics seminar on the equation of state (EoS) in the dense baryonic matter. The EoS of dense baryonic/quark matter is the crucial ingredient for understanding neutron stars. He nicely reviewed the current state of the high-density matter EoS based on the QCD perspectives. His recent work on the EoS calculated within the pQCD framework with the resummation [Fujimoto & Fukushima, 2011.10891] gives the Hard Dense Loop resummation formula which turns out to reduce the uncertainty compared with the conventional pQCD estimate without resummation. His approach extends the applicability of the QCD-based EoS down to densities realized inside neutron stars and infers a smooth matching with the baryonic EoS. The audience asked a lot of questions and had fruitful discussions. Reported by Etsuko Itou

2021-06-29

## iTHEMS Theoretical Physics Seminar by Dr. Kanato Goto on June 21, 2021

On June 21st, Kanato Goto (RIKEN iTHEMS) gave the iTHEMS-physics seminar on the black hole information paradox. Recently, there is a proposal for the formula for a quantum black hole entropy, called the island formula, which is expected to reconcile the conflict between the thermal and quantum natures of the black hole. One may regard the island formula as a generalization of the so-called Ryu-Takayanagi formula for the entanglement entropy, but its derivation is yet to be clarified. In the talk, after reviewing the current status of the black hole information paradox, Kanato explained their work on a derivation of the island formula based on the replica method for the gravitational path integral. The audience asked a lot of questions and we really enjoyed the talk. Reported by Masaru Hongo

2021-06-28

## DMWG Seinar by Dr. Shirai on June 24, 2021

We are now living in the era of precision cosmology. The relic abundance of dark matter (DM) is now observationally well-determined, and its error is smaller than O(1)%. This means that the same or much higher precision is required when we make theoretical predictions. Weakly Interacting Massive Particle (WIMP) has long been the leading candidate for DM because of its beautiful mechanism to predict the observed relic abundance. WIMP is in the same thermal bath as the Standard Model particles in the beginning. At a certain point when the temperature of the Universe is smaller than the DM mass, it decouples to fix its number density. The yield of the DM is determined by its annihilation cross-section to the Standard Model sector. It seems that there is no ambiguity in the calculation of this process at first: the cross-section is purely theoretical and all the remainings are described in the Standard Model physics. However, the source of the uncertainty does remain in the Standard Model sector. The dilution of the number density of DM particle depends on the expansion rate of the Universe, which is determined by the Standard Model particles. The effective degree of freedom (d.o.f) of the relativistic species controls this factor. We have to deal with the non-equilibrium dynamics to precisely describe the time-evolution of the d.o.f, in which we need numerical approaches. In this talk, he introduced his work to update these calculations. By implementing the latest findings in the non-equilibrium dynamics in i) the neutrino decoupling, ii) the QCD phase transition, iii) the electroweak phase transition, and iv) the perturbative calculations, they found that the final d.o.f is smaller than the previous estimate in more than 1%. This is larger than the level of precision in observations. It is also important that the uncertainty is quantified by them. Another good news is that he makes the calculated d.o.f with its error publically available. With these updates, we now correctly know the points to probe DM! Reported by Nagisa Hiroshima

165 news in 2021