# News

179 news in 2021

2021-07-15

Paper of the Week

## 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

Hot Topic

## 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

Seminar Report

## 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

Paper of the Week

## 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

Event Schedule

## 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

Seminar Report

## 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

Seminar Report

## 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

Seminar Report

## 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

Person of the Week

## 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

Paper of the Week

## 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

Event Schedule

## 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

Seminar Report

## 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

Seminar Report

## 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

Seminar Report

## 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

2021-06-28

Research News

## RIKEN RESEARCH: Physics modeling of viral spread between cells

Prof. Catherine Beauchemin (Deputy Program Director, iTHEMS) was featured in the summer issue of RIKEN RESEARCH 2021. Describe your role at RIKEN - I first joined RIKEN in 2016 as a senior visiting scientist at iTHES, the predecessor of the Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program. In 2020, I became one of four iTHEMS deputy program directors. I am in a field I call ‘virophysics’; the application of physics methods to virology. Primarily, I construct computer and mathematical models to explain the experimental observations made when viruses infect cell cultures. In biology, such knowledge is usually advanced through experimental trial and error, but physics modeling can help streamline this process. To read more, please see the related links.

2021-06-28

Seminar Report

## Math Seminar by Dr. Kazuki Kannaka on June 18, 2021

There was a math seminar by Kazuki Kannaka on June 18. He gave an introductory talk on his research fields, representation theory and briefly explained his study. He first explained some basic definitions in representation theory. He then explained the mathematical tiling problem with the Lie group. In the second part, he explained how the distribution of the compact pseudo-Riemannian manifolds differs for parameters. He also introduced his example, which has a continuous spectrum. Reported by Keita Mikami

2021-06-25

Research News

## RIKEN NEWS: What is the Significance of Basic Research?

Program Director Tetsuo Hatsuda is interviewed on the RIKEN website and summer issue of RIKEN NEWS 2021. How did the universe begin? Why does matter exist? What is the origin of life? Basic research, which pursues such fundamental questions, is difficult for the general public to understand because it does not necessarily lead to immediate practical applications. We asked Tetsuo Hatsuda, Program Director (PD) of the Theoretical and Mathematical Sciences Program (iTHEMS), what exactly basic research is. To read more, please see the related link (in Japanese).

2021-06-25

Seminar Report

## Information Theory SG Seminar by Prof. Yoshiyuki Kabashima on June 23, 2021

With great honor, we have invited Prof. Yoshiyuki Kabashima to our information theory seminar to give a stimulating talk about “introduction to the replica method” on 23rd June. Replica method is a physics-based technique developed for analyzing disordered many-body problems, which is now becoming popular more in information science using the structural similarity between problems from these two different fields. Prof. Yoshiyuki Kabashima is a master of the replica method. He applied this method to many problems in information theory, such as CDMA, compressed sensing, clustering of networks, error correcting codes, etc. The talk contains two parts. In the first part, as an example of the concept, he explained the mathematical similarity of three problems whose origins are unrelated with one another--random energy model (Physics), error correcting codes (information theory) and random k-SAT problem (theoretical computer science). A unified perspective is the common structure of the three examples is the conditional distribution, and the key to solve the problems is the assessment of the average free energy. The replica method provides a systematic way to performing the configurational average. Even the mathematical justification is still an open problem, there is no known example to which the replica method leads to wrong results by appropriately taking into account the replica symmetry breaking if necessary. In the second part, Prof. Yoshiyuki Kabashima demonstrated the calculation of replica method using an example of random energy model of spin glass. This simple model has an exact solution without using the replica method. One can see how replica method can provide the correct solution by taking care of the assumptions of replica symmetry and 1-step replica symmetric breaking (1RSB) in different temperature ranges. In the end, he gave an expert perspective of large deviation statistics of replica method and 1RSB solution. Many excellent questions and stimulating discussions have happened during the 2.5-hour seminar. We absorbed by the world of “replicas”. We thank to Prof. Yoshiyuki Kabashima for giving us this great opportunity and hope new ideas of applications of the replica method appear in iTHEMS. Report by Yingying Xu

2021-06-25

Seminar Report

## iTHEMS Biology Seminar by Dr. Jeffrey Fawcett on June 10, 2021

On 10 June 2021, our iTHEMS member Jeffrey Fawcett gave a talk about “the origin and dispersal of buckwheat” at the Biology Seminar. Jeffery works on or has worked on a broad range of topics related to genomics, evolution, genetics, bioinformatics, and systems biology. This time, he talked about his recent worldwide collaboration work using genomic data of wild samples from China (around Yunnan, Sichuan, and Tibet) and cultivated samples from various parts of the world to understand “when”, “where”, and “how” buckwheat originated and then spread across the world and came to Japan. He explained the significance of studying "domestication", which can contribute to research on evolution, molecular breeding and implications for human history. Buckwheat, which soba noodles is made from, is now such a familiar everyday life related plant in Japan. We are surprised how such a genomic approach about soba revealed the history of ancient world and Japan and gave us a hint about the origin of Japanese people. We are looking forward to further discovery of this interesting research topic. Report by Yingying Xu

2021-06-25

Seminar Report

## iTHEMS Biology Seminar by Prof. Fumito Mori on June 24, 2021

In iTHEMS biology seminar on June 24, Fumito Mori (Assistant Professor, Faculty of Design, Kyushu University) gave us a talk on synchronization and variability of the periodicity. In the seminar, he introduced minimal models of coupled oscillators to discuss synchronization. Interestingly, the variability of the periodicity, in general, depends on which variables (or genes) we consider and on which timepoints we (or cells) measure the periodicity. He demonstrated this subtlety in the so-called repressilator system. He then discussed how noise and interaction parameters can be inferred from given data of periodicity. In the talk, he showed us many general results, which were very impressive to us. Finally, I am grateful to Mori-san because I asked him to do the seminar just two weeks before it, but he kindly accepted. Thank you very much for the fantastic talk, Mori-san! Reported by Takashi Okada

2021-06-24

Event Schedule

## Events for the 5th week of June 2021

Tuesday, June 29, 13:00- iTHEMS Theoretical Physics Seminar Thursday, July 1, 10:00- iTHEMS Biology Seminar Friday, July 2, 12:30- Coffee Meeting Friday, July 2, 16:00- iTHEMS Math Seminar

2021-06-24

Paper of the Week

## Week 4, June 2021

Title: XRP Network and Proposal of Flow Index Author: Hideaki Aoyama arXiv: http://arxiv.org/abs/2106.10012v1 Title: Holographic moving mirrors Author: Ibrahim Akal, Yuya Kusuki, Noburo Shiba, Tadashi Takayanagi, Zixia Wei arXiv: http://arxiv.org/abs/2106.11179v1

2021-06-17

Paper of the Week

## Week 3, June 2021

Sorry for the pile of new papers due to system error. Title: Emergence of the $ρ$ resonance from the HAL QCD potential in lattice QCD Author: Yutaro Akahoshi, Sinya Aoki, Takumi Doi arXiv: http://arxiv.org/abs/2106.08175v1 Title: Spatial variations of magnetic field along active galactic nuclei jets on sub-pc to Mpc scales Author: Soichiro Ito, Yoshiyuki Inoue, Jun Kataoka arXiv: http://arxiv.org/abs/2106.01788v1 Title: Simulated quantum annealing as a simulator of non-equilibrium quantum dynamics Author: Yuki Bando, Hidetoshi Nishimori arXiv: http://arxiv.org/abs/2106.00928v1 Title: A simple numerical method for Hele-Shaw type problems by the method of fundamental solutions Author: Koya Sakakibara, Yusaku Shimoji, Shigetoshi Yazaki arXiv: http://arxiv.org/abs/2105.14811v1 Title: Neutron star asteroseismology and nuclear saturation parameter Author: Hajime Sotani arXiv: http://arxiv.org/abs/2105.13212v1 Title: Analytical WKB theory for high-harmonic generation and its application to massive Dirac electrons Author: Hidetoshi Taya, Masaru Hongo, Tatsuhiko N. Ikeda arXiv: http://arxiv.org/abs/2105.12446v1 Title: Cross-match between the latest Swift-BAT and Fermi-LAT catalogs Author: Naomi Tsuji, Hiroki Yoneda, Yoshiyuki Inoue, Tsuguo Aramaki, Georgia Karagiorgi, Reshmi Mukherjee, Hirokazu Odaka arXiv: http://arxiv.org/abs/2105.11791v1 Title: Complex Langevin study for polarons in an attractively interacting one-dimensional two-component Fermi gas Author: Takahiro M. Doi, Hiroyuki Tajima, Shoichiro Tsutsui arXiv: http://arxiv.org/abs/2105.11072v1 Title: A global numerical model of the prompt emission in short gamma-ray bursts Author: Hirotaka Ito, Oliver Just, Yuki Takei, Shigehiro Nagataki arXiv: http://arxiv.org/abs/2105.09323v1 Title: Gamma-ray and Neutrino Signals from Accretion Disk Coronae of Active Galactic Nuclei Author: Yoshiyuki Inoue, Dmitry Khangulyan, Akihiro Doi arXiv: http://arxiv.org/abs/2105.08948v1 Title: On the Hubble constant tension in the SNe Ia Pantheon sample Author: Maria Giovanna Dainotti, Biagio De Simone, Tiziano Schiavone, Giovanni Montani, Enrico Rinaldi, Gaetano Lambiase arXiv: http://arxiv.org/abs/2103.02117v4

2021-06-17

Event Schedule

## Events for the 4th week of June 2021

Monday, June 21, 13:00- iTHEMS Theoretical Physics Seminar Wednesday, June 23, 13:30- Information Theory SG Seminar Thursday, June 24, 16:30- DMWG Seminar Friday, June 25, 12:30- Coffee Meeting

2021-06-11

Person of the Week

## Self-introduction: Yantao Wu

My name is Yantao Wu. I joined iTHEMS in June 2021. My research field is in computational and theoretical statistical physics. I'm also interested in quantum computing. I obtained my PhD in physics from Princeton University in May 2021. During graduate school, I have worked on renormalization group of quantum and classical statistical systems in the context of Monte Carlo simulations. I'm also quite familiar with path-integral molecular dynamics. Currently, I'm interested in developing tensor network algorithms for quantum dynamics in one dimension and ground state calculations in two dimensions. In particular, I'm interested in the approximate canonical form of 2D tensor networks, and its associated entanglement structure. I'm also interested in issues related to quantum dynamics, such as entanglement evolution and eigenstate thermalization hypothesis at the edge of the energy spectrum. I'm based in UC Berkeley, and would be glad to host any iTHEMS visitors in the bay area. Based in UC Berkeley, I have recently got interested in the hardware of quantum computing as well. I hope that we can one day see the ENIAC of our generation. In my spare time, I like soccer, climbing, poetry, and Go (not very good though).

2021-06-10

Event Schedule

## Events for the 3rd week of June 2021

Friday, June 18, 12:30- Coffee Meeting Friday, June 18, 16:00- iTHEMS Math Seminar

2021-06-07

Seminar Report

## iTHEMS Biology Seminar by Dr. Yingying Xu on June 3, 2021

On June 3rd, Yingying Xu who recently joined iTHEMS gave a talk at the Biology Seminar. She spoke about her past research on applying ideas from statistical physics to genetics, especially on what is called "epistasis". Statistics plays a crucial role in the study of genetics, and one of the main challenges now is to understand the combined effect of multiple mutations, which is often referred to as epistasis. This clearly requires input from statistical physics, so I was very excited to hear the progress made with people from statistical physics - Yingying and her colleagues being involved. Her talk was also very helpful for everyone to get an idea of how advanced statistics/mathematics is being applied to genetics. It was also great to see the expertise of Yingying, and we will be looking forward to further interaction with her. Reported by Jeffrey Fawcett

2021-06-01

Hot Topic

## The work of a research group, including Dr. Maria Dainotti and Enrico Rinaldi, has been featured in several institutional press releases and websites

The work of a research group, including Dr. Maria Dainotti and Enrico Rinaldi, has been featured in several institutional press releases and websites. One of the most famous open problems of modern cosmology is the Hubble constant (H0) tension. This consists in the discrepancy (>4 sigma) between the values of H0 measured with the late universe local probes, namely the Supernovae Ia (SNe Ia), and the early universe observations, the Cosmic Microwave Background (CMB) radiation. With our investigation we found that a slow evolution with redshift is present in this constant thus allowing to alleviate this discrepancy. The study is published in ApJ. The investigation started when Dr. Maria Dainotti (now Assistant Professor at NAOJ) and Enrico Rinaldi (now Research Fellow at Michigan University) were Senior Research Scientist and Visiting Scientist both at iTHEMS, respectively. See related links for details.

2021-05-31

Seminar Report

## Quantum Matter SG seminar by Dr. Rui-Xing Zhang on May 26, 2021

On May 26th, Dr. Rui-Xing Zhang from the University of Maryland gave a talk about the classification of anomalous floquet higher-order topological insulators. He started with a pedagogical introduction to floquet topological insulators, which possess robust boundary states. Notably, there are two types of non-trivial floquet topology. 1. The floquet bands inherit the topology of the static bands. 2. The non-trivial physics of the anomalous floquet topological insulators stems from dynamical phase bands. Dr. Zhang extended the idea of the second type to higher-order topological insulators, which have robust corner states or edge ones. Dr. Zhang specifically discussed the anomalous floquet topology for chiral symmetric systems preserving C2 rotation symmetry. Using this example, he generalized the classification of the topological phases to various point groups. We thank Dr. Zhang for giving this wonderful talk. Reported by Ching-Kai Chiu

2021-05-28

Person of the Week

## Self-introduction: Ryo Namba

Pursuit of the fundamental law that governs the evolution of our universe, is the end goal of cosmology. Our universe is known to be expanding. It is not only expanding, but has been, and perhaps will be, expanding. The driving force of the current accelerated expansion, often called dark energy, is still beyond our understanding, despite that the fate of the universe entirely depends on the nature of dark energy. Furthermore, cosmological observations provide indications that an accelerated expansion also took place at the earliest stage of our universe, known as inflation, and that the seeds of all the structures we observe today were encoded during this period. Thus the physics in the inflationary era is of essential importance, fixing the initial conditions of our universe. The forthcoming advancement of multi-messenger (photons, neutrinos, and gravitational wave), multi-frequency observations opens up the possibility of probing such cosmological signals in novel manners. My research focus is encapsulated in the studies of interactions at cosmological scales, ranging from the highest-energy processes at the onset of the universe to the laws of gravity at the largest distances, by making use of the knowledge of quantum field theory, elementary particle physics and gravitational theory as technical tools. Interactions in cosmology are inevitably those in a gravitating system, and they reserve a large domain of unresolved mysteries that provide a fascinating ground to explore. Understanding the physics in both ends of these extremes is necessary to reveal the origin and fate of our universe. Many different branches of physics are involved in this research adventure, and extending the border of scientific disciplines is of essential importance. [Brief academic history] I received my Ph.D. from the University of Minnesota (USA), and continued my research activities as a postdoctoral researcher at Kavli IPMU (Japan), McGill University (Canada), and Tsung-Dao Lee Institute (China), before joining RIKEN iTHEMS in May 2021. I have worked on research projects on particle production in the early universe, thermalization process (reheating), modified gravity theories (scalar-vector-tensor theories, massive/bimetric gravity), etc.

2021-05-27

Press Release

## First Clarification of the Network Structure of Money Flow

A collaborative research group, including Prof. Hideaki Aoyama (Senior Visiting Scientist, iTHEMS), has successfully used the latest big data network science to understand the structure of money flows between corporate accounts at regional banks. See related link for details.

2021-05-27

Seminar Report

## iTHEMS Biology Seminar by Dr. Kouki Uchinomiya on May 27, 2021

On May 27 (JST), we had online talk by Dr. Kouki Uchinomiya at iTHEMS Biology Seminar. He was one of active members of RIKEN iTHES, and currently he is at Central Research Institute of Electric Power Industry in Tokyo. This time, Kouki talked about radiation and cancer risk. Radiation can cause DNA damage for which it can cause cancer in our body. In the field of radiation and cancer, there has been a mystery that cancer risk decreases as the dose rate of radiation (Gy/h) decreases while the total dose of radiation fixed. By incorporating the competition between the normal and the damaged cells by radiation into a simple mathematical model, he successfully explained the mysterious phenomena. His model revealed that the key parameters including a relative reproductive ability of the damaged cells determine the cancer risk. According to him, those parameters will be experimentally measured in the near future, and we understand that the model should contribute to the quantitative estimation of cancer risk by radiation. During and after the talk, there were stimulating discussions as for the philosophy behind his very simple model and a possible extension to the model with the effect of immune system. We enjoyed his concise talk very much. Thanks Kouki! Reported by Gen Kurosawa

2021-05-27

Event Schedule

## Events for the 1st week of June 2021

Thursday, June 3, 10:00- iTHEMS Biology Seminar Friday, June 4, 11:30- Coffee Meeting

2021-05-27

Seminar Report

## Math Seminar by Dr. Michiya Mori on May 24, 2021

On May 24, there was an iTHEMS math seminar by Dr. Michiya Mori. In the first part, he explained his research on Lowebner theorems. He first described the notion of abstract order. He then introduced an order on the space of the hermitian matrix. He explained Molnar's results that the order-preserving map must be affine on a particular good subset of matrices. Lastly, he explained his results with his collaborator that a map on matrix domain is an order isomorphism if and only if it has a good extension to the upper half-space. In the second part, the speaker introduced the projective Hilbert space, the space of all quantum states, and Fubini-Study metric, an "argument" on the projective Hilbert space. He then introduced the result by Wigner that any bijective maps preserving Fubini-Study metric are unitary or anti-unitary. The speaker introduced Uhlhorn's variant of this result: if the dimension of the space is larger than three, any bijection preserving argument π/2 is unitary or anti-unitary. The speaker also explained that Gehér extended Uhlhorn's works for other cases, but there was one open case. The speaker explained his result with Gehér that the variant of the result by Uhlhorn holds for this last case. Reported by Keita Mikami

2021-05-24

Seminar Report

## Journal Club of Information Theory SG by Dr. Kyosuke Adachi on May 19, 2021

On May 19, Dr. Kyosuke Adachi talked about “Amino acid sequence and protein phase separation” at the journal club of information theory study group. First, he introduced the history of protein states, from its structure observed with X-ray to intrinsically disordered region (IDR) and liquid-liquid phase separation. In this talk, the speaker focused on IDR and phase separations. Second, he explained some biological functions of phase separation, such as compartmentalization of specific molecules, facilitation of biochemical reaction, and stress response. And the talk moved a question of what kind of sequence feature determines phase properties. Mainly, the speaker discussed coarse-grained models, which are expected to determine phase properties. Finally, he mentioned the problem of how to classifying IDRs and the importance of the coarse-grained sequence. Thank you, Adachi-san, for the interesting talk! Reported by Yukimi Goto

2021-05-21

Person of the Week

I'm Akira Harada, a RIKEN SPDR since April 2021. I'm interested in astrophysics, especially supernovae. The core-collapse supernova (CCSN) is the explosive death of a massive star. Because of the extreme environment realized at the center of the CCSN, the explosion mechanism involves a vast field of physics, namely hydrodynamics, nuclear physics, neutrino physics, and gravitational physics. Besides, understanding such a complicated phenomenon requires numerical simulations. I'm trying to reveal the mechanism by exploiting all these pieces of knowledge. I'd like to get stimulated from interdisciplinary conversations with iTHEMS people.

2021-05-20

Event Schedule

## Events for the 5th week of May 2021

Monday, May 24, 16:00- Math Seminar Thursday, May 27, 10:00- iTHEMS Biology Seminar Friday, May 28, 11:30- Coffee Meeting

2021-05-20

Paper of the Week

## Week 4, May 2021

Title: Signs of the plastid: Enzymes involved in plastid-localized metabolic pathways in a eugregarine species Authors: Euki Yazaki, Ryosuke Miyata, Yasuhiko Chikami, Ryo Harada, Takashi Kawakubo, Goro Tanifuji, Takuro Nakayama, Kensuke Yahata, Tetsuo Hashimoto, Yuji Inagaki Journal Reference: Parasitology International Volume 83, 102364, August (2021) doi: https://dx.doi.org/10.1016/j.parint.2021.102364 Title: Interstellar Gas Heating by Primordial Black Holes Authors: Volodymyr Takhistov, Philip Lu, Graciela B. Gelmini, Kohei Hayashi, Yoshiyuki Inoue, Alexander Kusenko arXiv: http://arxiv.org/abs/2105.06099v1

2021-05-20

Seminar Report

## Math Seminar by Dr. Iyan Mulia on April 22, 2021

On April 22, the iTHEMS Math seminar was held (Sorry for the delay of the report!). This time, we invited Dr. Iyan Mulia from RIKEN Cluster for Pioneering Research, Prediction Science Laboratory. The title of the talk was “Alternative tsunami observing and forecasting systems”. The main topic of the talk was his work about how to catch and predict tsunami. First, he proposed new approaches to construct tsunami observing systems. There exist various observing systems already, but they share a big problem that they are very expensive. Since observing systems need to be updated regularly, it is very important to reduce the cost. Iyan’s proposal is to make use of existing commercial vessels and airplanes. Since they already exist and form a dense network all over the world, it will suffice to let them observe the sea level altitude and transfer the information. Iyan and his collaborators already demonstrated in experiments that the proposed observing system is accurate enough to detect large tsunamis. Next, he moved to another topic. Once we observe the occurrence of tsunami, next step is to predict its impact in the areas near the coast. While there are conventional mathematical models which provide very accurate prediction, it needs relatively long time for calculation. This is a non-ignorable defect because it means the delay of the warning to residents. If we use linear models instead of the accurate model, the calculation becomes much faster but the accuracy of the prediction gets low. Iyan’s proposal is plug in the Machine Learning techniques to bridge these two models. He trained neural networks to predict the results of the accurate model from the results of the linear model. This method actually gives a satisfactory result: the prediction is very accurate and fast. If this method is accepted widely, it will be possible to predict the effect of tsunami very accurately in very short time. Reported by Hiroyasu Miyazaki

2021-05-19

Book

## Is the World written in the Language of Mathematics? -- Exploring the Mysteries of the Universe, Life, and Information

Authors: Yuki Yokokura, Jeffrey Fawcett, Takumi Doi and Masato Taki Editor: Tetsuo Hatsuda and Takashi Tsuboi Language: Japanese Release date: May 28, 2021

2021-05-19

Hot Topic

## Event to celebrate the publication of "The Future of Useless Research was held on April 28, 2021

On April 28, 2021, an online event "Ai Nishida x Tetsuo Hatsuda x Sayaka Oki x Ryosuke Shibato: What We Need to Talk About Now for a Happy Relationship between Researchers and Citizens" was held at B&B, a bookstore in Shimokitazawa. The event was held to celebrate the publication of "The Future of Useless Research," which was released on April 14. For details, please see the related link.

2021-05-17

Person of the Week

## Self-introduction: Naritaka Oshita

I am a theoretical physicist who works on gravity, cosmology, and quantum field theory. Quantum fluctuations of mater/gravitational fields in an expanding universe or a black hole exhibit thermal radiation and superradiance. These phenomena are important to understand the thermal nature of the gravitational systems and how information of matter is encoded there. Also, the classical linear perturbations of a black hole are characterized by the quasinormal modes of the black hole. This is useful to test classical/quantum gravity theories by the observation of gravitational waves. Beyond the linear perturbation in gravitational systems, I am also working on non-perturbative phenomena of quantum fields such as vacuum decay in strong gravity. The standard model of particle physics predicts that the Higgs field is metastable, which means that our Universe might eventually undergo a catastrophic vacuum decay and be filled with negative vacuum energy. The vacuum decay process is therefore important to understand the history and fate of the Universe.

2021-05-14

Seminar Report

## iTHEMS Biology Seminar by Prof. Yuji Sakai on May 14, 2021

In iTHEMS Biology Seminar on May 14th, Prof. Yuji Sakai (Univ. of Tokyo) talked about the theoretical model of the autophagosome. First, he explained the autophagosome formation process, where the disk-like and cup-like shapes of the membrane are observed. Then, he talked about the previous theories, where the spontaneous curvature is not considered. Next, he explained his theoretical model, in which the spontaneous curvature is induced and stabilized by the “curvature generator”. By minimizing the free energy in his model, he quantitatively reproduced the autophagosome formation via the disk and the cup. Finally, he mentioned the candidate of the curvature generator. His attractive talk induced various discussions and questions from the audience. Thank you very much for nice talk, Yuji! Reported by Hiroshi Yokota

2021-05-14

Seminar Report

## Quantum Matter Seminar by Prof. Christopher Bourne on May 12, 2021

Quantum Matter Study Group invited Prof. Christopher Bourne to give a talk on aperiodic and amorphous topological phases on May 12th, 2021. In the beginning, he reviewed topological phases in lattice systems and introduced integer Chern numbers. To generalize the topological phases, we extend the lattice to Delone sets, including quasicrystal and amorphous solid. The main talk focused on the topological phases for those types of solid. He provided examples to show the amorphous patterns exhibit gapped phases. He showed that the invariants can be defined as noncommutative Chern number and computed the non-zero Chern number in the gapped phase. It is interesting to see that quasicrystal and amorphous solid share similar integer Chern numbers, and the idea can be further extended to different spatial dimensions with symmetries. We thank Prof. Bourne for giving a wonderful talk. Reported by Ching-Kai Chiu

2021-05-13

Event Schedule

## Events for the 4th week of May 2021

Wednesday, May 19, 13:00- Information Theory SG Seminar Friday, May 21, 12:30- Coffee Meeting

2021-05-13

Person of the Week

## Self-introduction: Eiji Inoue

I'm Eiji INOUE, a new member of iTHEMS as a special postdoctoral researcher in mathematics. My current interest is Kahler geometry of algebraic variety. Algebraic variety is (locally) the solution set of polynomials, say x^2 + y^2 -1 = 0. While its origins trace back to ancient Greek, it still fascinates many mathematicians: you can find many Fields medalists, including all Japanese medalists, are awarded for their monumental works on algebraic variety. Calabi-Yau variety is a special class of algebraic varieties attracting attention in string theory. A Calabi-Yau variety admits a Kahler-Einstein metric, which can be thought of as a canonical 'shape' of the variety. Though a general variety in other classes does not necessarily admit such canonical metrics, it is gradually believed by not a few specialists that any variety has a unique degeneration to another variety admitting a canonical metric in some sense. My recent study gives a mathematical formulation of this problem. This framework has a special aspect: it naturally possesses a new parameter λ which plays a role analogous to the inverse temperature. When λ is sufficiently low, canonical metrics, which you may see as 'equilibrium states' of the variety, are unique if it exists. On the other hand, when λ is sufficiently high, canonical metrics are not unique and the absolutely stable states may break the symmetry of the variety. It is reminiscent of phase transition. I am looking forward to discussing this phenomenon with researchers in other areas.

2021-05-12

Seminar Report

## DMWG Seinar by Dr. Nishimichi: Cosmology, the Fundamental for the DM on May 12, 2021

What we have known about dark matter (DM) is that it occupies ~25% of the energy density of our Universe. The precise determination of the cosmological parameter is crucially important for determining this abundance of DM. Another important point here is that one the value of those parameters are determined assuming a specific cosmological model, such as vanilla (i.e., the simplest) lambda CDM and so on. So we might have a different DM relic density if the assumption of the simplest Lambda-CDM breaks. Hence the examination of the cosmological parameters and the model behind them is important two-fold for DM physicists. The basic observable for the cosmological parameter is cosmic microwave background, the large-scale structure, and so on. Those data are huge at the raw level, and still so large at the scientific data level. In order to derive a handful of cosmological parameters from such data, one must calculate the so-called summary statistics. By matching the summary statistics in simulation data of specific cosmological models (vanilla lambda-CDM, for example) adopting MCMC techniques, we arrive at the cosmological parameter that we need. Note that there is always degeneracy between cosmological parameters derived from observational data. The matching between the observational and simulated summary statistics takes a lot of costs in the calculation. By adopting analytical formula, the calculation becomes much quicker while the precision decreases at some level. The emulator, which is developed in the Dark Quest Project, solves this computational problem. It enables us to speed up the calculation while keeping the precision. The degeneracy between the parameters also becomes accessible. The precise summary statistics such as halo mass function, halo-matter cross-correlation, and far more... is crucially important for DM study. Halo formation theory and weak lensing search are kinds of examples for applications. With this new fantastic open-source tool of Dark Quest Project, the future for DM search study emerges definitely. We are looking forward to seeing a lot of cutting-edge as well as steady works implemented with this item in the near future! Reported by Nagisa Hiroshima

2021-05-12

Person of the Week

## Self-introduction: Kazuki Kannaka

I’m Kazuki KANNAKA, a special postdoctoral researcher (mathematician) in iTHEMS. I am interested in the global properties of locally homogeneous manifolds, especially those with Lorentzian structures (e.g., anti-de Sitter manifolds) which are used as models of spacetimes. I am currently studying the spectral theory of the hyperbolic Laplacian (the Klein-Gordon operator), which is a differential operator defined “intrinsically” on such manifolds. In iTHEMS, I would like to find interactions with other various research areas.

2021-05-11

Person of the Week

## Self-introduction: Michiya Mori

I am Michiya Mori, a new member of iTHEMS as a Special Postdoctoral Researcher. I received my Ph.D. at The University of Tokyo in March 2021. I am working on the mathematical theory of operator algebras. I am interested in examining certain structure of a collection of linear operators acting on a Hilbert space. In particular, I have studied the metric structure and the (lattice) order structure of, e.g., a domain of bounded self-adjoint operators, the collection of self-adjoint projections, the unit sphere. My research is often base on the classical study by, for example, von Neumann, Wigner, Loewner and Kadison, rather than modern operator algebraists. I believe that my research is closely tied with various fields of theoretical sciences. I hope to develop my research in an interdisciplinary direction.

2021-05-11

Person of the Week

## Self-introduction: Mizuki Oikawa

I am Mizuki Oikawa, a Junior Research Associate (JRA) student who joined iTHEMS in April 2021. I am interested in the mathematics of two-dimensional conformal field theory, such as vertex operator algebras, conformal nets, and Segal conformal field theories. In particular, my interest includes moonshine phenomena, which connect finite groups and modular forms via conformal field theories. I look forward to interacting with iTHEMS members in different research areas.

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