セミナーレポート
325 ニュース

20220215
セミナーレポートiTHEMS Biology Seminar by Dr. Gilberto Nakamura on February 10, 2022
Stochastic processes describe systems in which one or more variables fluctuate randomly. In the first part of the talk, I reviewed basic concepts in stochastic processes and how to express them in terms of localized spin operators and the probability vector (PV). This framework is convenient to compute statistics away from meanfield approximations because it can borrow methods traditionally used in manybody problems in Physics. The second part of the talk addressed the equation for the squared norm of the PV and its correspondence with the Rényi entropy. The general idea and challenges of employing estimates of the Rényi entropy were discussed shortly after. As a practical biological application, I explained the dynamical equations for averages and fluctuations in a simple stochastic epidemic model, highlighting the effects of noise and correlations in heterogeneous finite systems.

20220214
セミナーレポートiTHEMS Biology Seminar by Dr. Takashi Okada on December 23, 2021
The Hidden Markov Models (HMM) have been used in a variety of fields for different purposes. I reviewed HMM and basic algorithms such as the forward algorithm. Then, I explained how this statistical framework can be applied to biological problems.

20220202
セミナーレポートDMWG Seminar by Dr. Kenji Kadota on January 31, 2022
Weakly Interacting Massive Particles (WIMPs) have long been a leading candidate of dark matter(DM). However, no signatures are found in any kinds of experiments. Investigation of the alternatives is now rapidly growing. Primordial black holes (PBHs), which are formed in the early Universe and source the gravitational potential for baryonic components to evolve, are being widely discussed and searched now. Recent progress of the gravitational, as well as electromagnetic, observations of the Universe already excludes a large portion of the parameter space of PBH as DM. So if it contributes to DM, it is natural to also consider contributions from other components such as WIMPs. In such a situation, PBHs are dressed with WIMP halos. Then WIMP annihilation proceeds in the vicinity of the central PBH and a cored structure is expected depending on the annihilation rate. This dependence of the core structure on the annihilation rate leads to a tricky behavior in the constraints for PBHWIMP mixed scenarios. Also, when PBHs are abundantly formed, we cannot neglect their clustering effects on the constraints obtained in the observable Universe because the dressed PBH with WIMP indicates the clustering of WIMP halos in host galaxies. In this case, the boost factor, which appears naturally in the scenario of pure WIMP DM models, needs to be evaluated in such a way that regarding the clustering of PBHs. Those interesting phenomena are only a part of examples that we can expect in the PBHWIMP mixed scenario for DM. Varieties of possibilities are waiting for our investigations. Discussions are blooming now! Reported by Nagisa Hiroshima

20220128
セミナーレポートQuantum Matter SG seminar by Prof. Rafael I. Nepomechie on January 26, 2022
The Quantum Matter Study Group invited Prof. Rafael Nepomechie from the University of Miami to talk about the Bethe ansatz and realizing Bethe states in quantum computers. In the beginning, he used the Heisenberg chain to introduce the coordinate Bethe ansatz. In condensed matter physics, it is extremely difficult to solve manybody Hamiltonians. For this specific Heisenberg model, Bethe came up with a judicious method for finding the exact manybody wave function. The manybody problem is transformed to solving the Bethe equations. Unfortunately, it is also hard to solve these equations completely. Prof. Nepomechie presented an alternative approach to find the exact wave function and hence the solution to the Bethe equations through quantum computation. He found that, by using specific quantum operations, the exact wave function of the Heisenberg model can be presented in the quantum computer with a probability decaying as the factorial of the number magnons that make up the wave function. It is interesting to learn about this connection between the Bethe ansatz and quantum computing. Discussions were made how to increase the probability of the discussed scheme and how to extend it to find the complete set of Bethe roots for larger systems. Reported by Thore Posske (University of Hamburg, Germany) and ChingKai Chiu

20220128
セミナーレポートiTHEMS Biology Seminar by Prof. Kenta Ishimoto on January 27, 2022
We successfully had a great time thanks to Dr. Kenta Ishimoto's fantastic talk, in which he talked about the basic background of fluid dynamics, followed by two topics of his own research. Thank you again for the fantastic talk! Reported by Ryosuke Iritani

20220125
セミナーレポートNEW WG Seminar by Mr. Tomohiro Tanogami on January 20, 2022
Tomohiro Tanogami from Kyoto University gave a talk titled "A simple XY model for cascade transfer." Cascade transfer is a ubiquitous phenomenon that appears in various physical systems. During a cascade transfer an inviscid conserved quantity such as energy is transferred conservatively from large/small to small/large scales, which results in a universal scaling law in the spectrum (e.g., Kolmogorov energy spectrum). In the talk, Tomohiro proposed a simple XY model which shows inverse energy cascade with a nonKolmogorov energy spectrum and pointed out that the model may characterize a novel "universality class" of cascade transfer. Tomohiro also explained possible relations between his model and, e.g., spin and atmospheric turbulences. About 20 physicists have joined the seminar and enjoyed discussions from various viewpoints. Reported by Hidetoshi Taya

20220120
セミナーレポートiTHEMS Biology Seminar by Dr. Hiroyasu Miyazaki on January 20, 2022
In the iTHEMS Biology Seminar on 20th January, Dr. Hiroyasu Miyazaki (RIKEN iTHEMS) gave a talk on the topological aspect of chemical reaction network. His talk is composed of two parts: motivation and result part and method part. In the first part, he mentioned the reduction of the chemical reaction network in E. Coli and its result which shows the same steady state as that before the reduction. In the second part, he explained how the network should be reduced. The topological information of the network can be described by using the matrix and the vector. He explained that the quotient network is defined to have a sequence of linear maps called “exact sequence”, which describes the relation among the original network, the subnetwork and the quotient network. We enjoyed his beautiful talk. From the audiences, the lively discussion arose during and after the talk. Thank you very much, Hiroyasu! Reported by Hiroshi Yokota

20220118
セミナーレポートDMWG Seminar by Dr. Kanji Mori on January 17, 2022
In this era of multimessenger astronomy, axionlike particle (ALP) searches using astrophysical transients are now excitingly discussed. ALPs are an extended class of particles from QCD axion, which could solve the strong CP problem of the Standard Model, and dark matter (DM) candidates of various connections to the physics beyond the Standard Model. ALPs could interact with our sector through their coupling to the photon, electron, and/or nucleons. The coupling of ALP to the photon is previously investigated using observations of SN 1987A, the most famous supernova explosion. MeV gammaray signals are expected when considering the conversion of ALP outside the stellar envelope, hence no observations of the associated gammaray emission to the supernova lead to the constraint on the coupling strength, for example. Also, the existence of such coupling should modify the dynamics of supernovae. When a star explodes, the difference between the masses of the progenitor star and the resulting compact object sources the radiation, neutrino emission, and kinetic energy of the ejecta material. ALP could be an additional channel for the energy release while its absorption heats the supernova. The balance between heating and cooling controls the supernova dynamics and shock restoration, which directly relates to the electromagnetic observables. Dr. Mori has shown that the heating rate is very sensitive to the coupling strength and enhancement of the electromagnetic emission is expected in the presupernova stage. The signatures could also be visible in the neutrino sector after the explosion. The results are fantastic, and there are a lot of things to do. For example, the inclusion of the ALPnucleon coupling effects is an interesting direction to pursue. Updates in the understanding of stellar models are important as well. We should see the signature of ALP in the near future in this field! Reported by Nagisa Hiroshima

20220117
セミナーレポートiTHEMS Biology Seminar by Dr. Wataru Nishima on January 13, 2022
Dr. Wataru Nishima (New Mexico Consortium, USA) gave a very interesting presentation about his published paper on the spike protein of the SARSCoV2, the virus which causes COVID19 [1]. He described the conformational change which the SARSCoV2 spike protein undergoes when it fuses with the host cell to initiate infection. His work offers and interesting alternative view of the process wherein parts of the spike protein ends up inside the host cell. This differs from the usual view where the spike protein would be left on the outside of the cell after virus fusion with the host. This alternative hypothesis could have important implication for better understanding disease severity, e.g. based on the possible toxic effect of spike protein components shed as part of the fusion process. Dr. Nishima's expertise is primarily in Molecular Dynamics and Bioinformatics and he is very interested to establish new collaborations with iTHEMS members. Reported by Catherine Beauchemin

20220112
セミナーレポートiTHEMS Biology Seminar by Prof. Tetsuya Yamamoto on January 6, 2022
On January 6th, Prof. Tetsuya Yamamoto gave us a comprehensive talk about the physical aspects of nuclear bodies. He first introduced the liquidliquid phase separation and other selfassembly mechanisms in softmatter physics, such as micelle formation, with motivations from the experimental side. In the main part, he told us about three recent topics regarding how RNAs' dynamics and sequence properties lead to different types of assembly of nuclear bodies. The mathematical formulation, schematic figures, and comparisons with experiments were clear to understand. We are very grateful to Prof. Yamamoto for the exciting seminar. Reported by Kyosuke Adachi

20211228
セミナーレポートiTHEMS Math Seminar by Prof. Yosuke Morita on December 3, 2021
On December 3, Yosuke Morita from Kyoto university gave a talk titled “The Conley index of topological dynamical systems” at the iTHEMS math seminar. He reviewed the fundamental concepts of study of topological dynamical systems and introduced the notion of index neighborhood which is used to define his refined Conley index. His talk contained many instructive examples which enable us to understand his talk easily. Finally, his refined Conley index is defined as a functor into a category of (equivariant) condensed sets. This gives new conceptual understanding of Conley index in terms of condensed set introduced by Clausen and Scholze recently. His talk was very interesting and stimulated many questions and discussions. I believe it was a very worthwhile time for many participants. Reported by Masaki Taniguchi

20211228
セミナーレポートDMWG Seminar by Prof. Hidetoshi Otono on December 15, 2021
Among kinds of approaches for dark matter (DM), collider experiments are advantageous in their high precision. The FASER (ForwArd Search ExpeRiment at the LHC) is equipment to probe longlived particles created at the interaction point of the LHC at the distance of about 400m. Particles pass through the absorber between the FASER detector and the interaction point and have enough lifetime to reach the FASER detector should leave signatures there. Dark photon and axionlike particles are good candidates for such species, as well as DM. The equipment is set at the front of the LHC beam direction. The position is really good at reducing the background particles and making use of already existing but not used space. Multiple layers of scintillators, emulsion for neutrino detection, silicon trackers, the decay volume for new particles with dipole magnets, and calorimeter at the endpoint consists of the facility. In combination with the works of these pieces, new longlived particle signatures as raredecay signatures of neutral pion decay can be searched. It is already working well with LHC Run 3 and neutrino properties are now being probed. Furthermore, a new piece of the facility is decided to be installed to enhance the accessibility to axionlike particle signature in the channel of 2 photon decay. The installation does not disturb the current measurement and will be completed by the end of 2023. The FASER experiments should become a key facility to probe new particles at m~O(1) GeV scale. In addition, our understanding of the Standard Model sector is also significantly improved with its measurements. The collaboration is now intensively working. The idea for physics with FASER is highly welcomed. Stay tuned and work hard! Reported by Nagisa Hiroshima

20211222
セミナーレポートNEW WG Seminar by Dr. Tomoki Ozawa on December 20, 2021
Tomoki Ozawa (Tohoku/AIMR) gave a talk on "Quantum metric of topological and nontopological insulators in AMO and other systems." Quantum metric, or more generally quantum geometry, is attracting great interest recently in condensedmatter physics. Tomoki gave a pedagogical introduction to the concept of quantum metric as well as recent experimental progresses including the first detection of the quantum metric using a diamond NV center. Tomoki then explained his recent results on this topic, in particular, on relations among quantum metric, topology, and the Kähler geometry. More than 30 people have joined the seminar and enjoyed fruitful discussions. Reported by Hidetoshi Taya

20211222
セミナーレポートNEW WG Seminar by Dr. Yusuke Yamada on December 15, 2021
Yusuke Yamada (RESCEU/Tokyo) gave a talk on "Cosmological particle production as Stokes phenomena." Particle production from the vacuum takes place in the presence of timedependent backgrounds, and is of interest in various fields of physics. Yusuke reconsidered the particle production from a viewpoint of the Stokes phenomenon, a mathematical concept in theory of differential equations, and discussed its application to the early Universe. Yusuke pointed out that the Stokesphenomenon viewpoint gives a systematic and powerful framework to investigate the realtime dynamics of the particle production. About 20 people have joined the seminar, and enjoyed active discussions during and even after the seminar. Reported by Hidetoshi Taya

20211217
セミナーレポートiTHEMS Biology Seminar by Prof. Hidetoshi Shimodaira on December 16, 2021
On December 16, Dr. Motomu Matsui (University of Tokyo) gave a lecture titled "Revisiting Standard Methods for Phylogenetic Tree Inference" at the iTHEMS Biology Seminar. He described the Graph Partitioning (GS) method, a new molecular phylogenetic analysis method based on graph theory and clustering, and explained its usefulness when used with real data. The GS method can reveal protein family relationships that cannot be clarified by conventional molecular phylogenetic analysis using maximum likelihood or distance methods. It was a very meaningful seminar for many participants. Thank you very much! Reported by Yuki Yazaki

20211217
セミナーレポートABBL/iTHEMS Astro Seminar by Prof. Jin Matsumoto on December 10, 2021
Prof. Jin Matsumoto (Assistant Professor, Keio Institute of Pure and Applied Sciences (KiPAS), Graduate School of Science and Technology, Keio University) gave a nice presentation on "Magnetic field dependence of neutrinodriven corecollapse supernova models". In the presentation, Prof. Matsumoto introduced his neutrinoradiationhydrodynamics supernova code (3DnSNe, Takiwaki et al. 2016) to include magnetohydrodynamics (MHD). Using this code, he performed threedimensional MHD simulations for the evolution of nonrotating stellar cores focusing on the difference in the magnetic field of the progenitors. He found that the neutrinodriven explosion occurs in both the weak and strong magnetic field models. It was concluded that the neutrino heating is the main driver for the explosion in his models, whereas the strong magnetic field slightly supports the explosion. Reported by Shigehiro Nagataki

20211210
セミナーレポートiTHEMS Math Seminar by Dr. Ryosuke Iritani on December 8, 2021
On December 8, Dr. Ryosuke Iritani (iTHEMS) gave a talk in Math Seminar. He talked about expectation value of certain random variables. He and his collaborators obtained a result on its explicit formula together with an algorithm of its fast calculation. This was the last Math Seminar talk of the year 2021. After the seminar there was an online Christmas party. Reported by Michiya Mori

20211210
セミナーレポートiTHEMS Biology Seminar by Prof. Hidetoshi Shimodaira on December 9, 2021
In this week’s biology seminar, the invited speaker Prof. Hidetoshi Shimodaira introduced his recent work about selective inference. Selective inference is an important statistical problem described also by another word “the filedrawer effect”. For example, Journals are much more likely to publish studies with low P values, and the readers never hear about the great number of studies that showed no effect and were filed way. This makes it difficult to assess the strength of a reported P value. The challenge of correcting for the effects of selection is a complex one. Prof. Hidetoshi Shimodaira explained a method to improve the previously proposed approximately unbiased test by adjusting the selection bias. This method is applied to predict trees and edges in phylogeny. In the seminar, he started by an interesting introduction of Darwin's theory of evolution and the tree of life. Based on this theory, modern phylogenetic inference is developed by analyzing DNA sequences of species as system relationships like trees. He also showed us, different statistical tests can give different P values of trees and edges in the trees. Therefore, we should be careful doing the tests and aware of the bias types in the problem. We thank Prof. Hidetoshi Shimodaira for his great talk and precious time with us! Reported by Yingying Xu

20211207
セミナーレポートiTHEMS Biology Seminar by Dr. Yuka Suzuki on November 18, 2021
On November 18, Yuka Suzuki from Okinawa Institute of Science and Technology (OIST) gave a talk titled "Spatial structure in ecology: the effects of dispersal network structure on biodiversity pattern and stability in metacommunities" at the iTHEMS Biology Seminar. She introduced the basic concepts of spatial structure in ecology and explained how computational tools and network theoretical concepts are used to investigate spatial structures in ecology using her own study. Her talk was easy to understand and also very interesting and stimulated many questions and discussions. I believe it was a very worthwhile time for many participants. Thanks Yuka! Reported by Jeffrey Fawcett

20211207
セミナーレポートiTHEMS Math Seminar by Prof. Koichi Taira on November 26, 2021
In November 26, there was a seminar by professor Kouichi Taira. He explained the relations between selfadjointness and the completeness of the classical dynamics. He especially explained a conjecture that selfadjointness and completeness of classical dynamics are equivalent. He then gave some examples on this conjectures. Reported by Keita Mikami

20211207
セミナーレポートiTHEMS Math Seminar by Dr. Shinichiro Seki on November 19, 2021
On November 19, we invited Professor Shinichiro Seki from Aoyama Gakuin University to give a talk in the Math Seminar. He explained about the graph removal lemma, which is one of the key ingredients of the proof of his recent joint work with Kai, Mimura, Munemasa and Yoshino on a generalization of the celebrated GreenTao theorem. In the first half of the talk, he gave a survey of Szemerédi's regularity lemma and the graph removal lemma, and explained how to extend the removal lemma to the case of (weighted) hypergraphs. In the second half of the talk, he presented Fox's result on a quantitative version of the graph removal, and discussed the prospects for future research. After the seminar, we had an online drinking party, and enjoyed a lot of discussion with the speaker. Reported by Hiroyasu Miyazaki

20211207
セミナーレポートNEW WG Seminar by Prof. Ryosuke Oketani on November 25, 2021
Ryosuke Oketani from Kyushu University gave a talk on "Imaging Theory of Optical Microscopy: Basic to Super Resolution." Optical microscopy is a powerful tool to observe microscopic objects such as living microorganisms. Recently, several superresolution techniques have been developed, which enabled us to overcome the limit in spatial resolution caused by the wave nature of light. Ryosuke explained the basics and recent theoretical developments of optical microscopy and the superresolution techniques. We also had fruitful discussions on the theory of optical microscopy from an interdiciplinary point of view. Reported by Hidetoshi Taya

20211201
セミナーレポートABBL/iTHEMS Astro Seminar by Dr. Hirotaka Yoshino on November 12, 2021
Dr. Yoshino gave us a talk on his recent work on axions around rotating black holes. He showed results of his numerical simulations of socalled “superradiant instability” in which an axion field around a rotating black hole extracts the energy of the black hole. These results suggest that every astrophysical black hole is expected to wear a cloud of the axion. Reported by Akira Mizuta (ABBL, RIKEN)

20211130
セミナーレポートQuantum Matter SG seminar by Prof. Harshman Nathan on November 17, 2021
From American University, Prof. Nathan Harshman gave a seminar talk about topological exchange statistics in one spatial dimension on Nov. 17th, 2021. To introduce exchange statistics as done in the literature, he started with statistics for bosons and fermions and extended fractional and nonabelian exchange statistics. Then, the speaker raised questions about particle exchange in 1D and the collisions of the particles. Can a collision and an exchange at all be distinguished in one dimension? Is it reasonable to include points of coincidence in the configuration space? The way to resolve these problems is to introduce orbifolds. After pedagogically explaining the concepts of the orbifolds, he began to use the orbifold topological approach to study exchange statistics for any dimension. This approach offers great chances for novel abelian and nonabelian anyons in effectively 1D cold atom and condensed matter systems. Reported by Thore Posske (University of Hamburg, Germany) and ChingKai Chiu

20211130
セミナーレポートiTHEMS Biology Seminar by Prof. Catherine Beauchemin on October 14, 2021
Defective interfering virus particles (DIPs) are viruses that are defective in a very specific way that allows them to outcompete standard, nondefective virus. It is difficult to count DIPs because they can look too similar to standard virus. So instead, people are counting them based on their effect on suppressing the standard virus population. In this talk, C. Beauchemin explained the basic biology of virus replication, what are DIPs, and how they compete with standard virus. She presented her group's mathematical model (ordinary differential equation) that describes coinfection competition with DIPs and standard virus. She also showed applications of the mathematical model to show how experiments to count DIPs can give incorrect results, and proposed some solutions.

20211130
セミナーレポートInformation Theory SG Seminar by Dr. Enrico Rinaldi on November 29, 2021
In the first part, he introduced the concept of simulationbased inference (SBI), which is inference methods driven by machine learning, and show some examples. In the later part, he showed some preliminary results of SBI on a biological neural circuit. We had a great discussion during Enrico’s talk. Thanks again for the fantastic talk, Enrico! We look forward to working with you. Reported by Akinori Tanaka

20211124
セミナーレポートiTHEMS Math Seminar by Prof. Song Sun on October 22, 2021
In this seminar, Professor Song Sun started with explaining the most basic concepts like, Riemannian metric, curvature in differential geometry. He then introduced one of the most important equations differential geometry, the socalled Einstein equation. After defining the holonomy group of a Riemannian manifold, he explained Berger's classification of holonomy groups of Riemannian manifolds which are not locally symmetric. He then pointed out the importance of studying Riemannian manifolds with special/exceptional holonomy groups, e.g. CalabiYau manifolds, hyperkahler manifolds, G2 and Spin(7) manifolds. He concentrated on hyperkahler 4manifolds and explained their geometry and topology in more details. In the end, he introduced his recent research result on studying GromovHausdorff limit of hyperkahler 4manifolds. Reported by Yalong Cao

20211124
セミナーレポートiTHEMS Math Seminar by Prof. Siqi He on October 15, 2021
In this seminar, Professor Siqi He started with mean curvatures and minimal submanifolds in differential geometry. Then he introduced the notion of calibrated geometry of HarveyLawson. As important examples of calibrated submanifolds, special Lagrangian submanifolds in CalabiYau manifolds are introduced. Then he explained a branch cover problem raised by Simon Donaldson and sketched a proof of it. Reported by Yalong Cao

20211124
セミナーレポートiTHEMS Math Seminar by Prof. Chen Jiang on October 8, 2021
In this seminar, Professor Chen Jiang started with several basic notions like geometric genus and canonical volume in birtaional geometry and introduced the question of geography problem. On algebraic surfaces, the boundary of geography problem is given by MiyaokaYau inequality and Noether inequality. Then he explained generalizations of the story on 3folds, including his joint work with M. Chen and J.K.Chen. Finally he gave an outline for the proof of his main theorem. Reported by Yalong Cao

20211124
セミナーレポートiTHEMS Math Seminar by Prof. Yukinobu Toda on October 1, 2021
In this seminar, Professor Yukinobu Toda started with the example of counting rational curves on hypersurfaces in complex projective spaces to illustrate ideas in enumerative geometry. Then he introduced several advanced topics including DonaldsonThomas theory and mirror symmetry. Finally he explained his recent work on wallcrossing formulae for categorified DT invariants on resolved conifold. Reported by Yalong Cao

20211118
セミナーレポートNEW WG Seminar by Prof. Naoto Nagaosa on November 15, 2021
Naoto Nagaosa (Tokyo/RIKEN) gave a talk on "Geometry in optical responses of quantum materials." Geometry and topology provide new insight into optical responses of solids and are of interdisciplinary interest in physics. After an excellent review on this topic made over the past decade, Naoto mainly discussed (i) shift current in noncentrosymmetric quantum materials driven by Berry phases, and (ii) Riemannian geometry in nonlinear optical responses. About 50 physicists from various fields have joined the seminar and enjoyed fruitful discussions during and after the seminar. Reported by Hidetoshi Taya

20211117
セミナーレポートiTHEMS Biology Seminar by Dr. Takaharu Mori on November 4, 2021
On Nov 4th 2021, Dr. Takaharu Mori from Molecular Science Lab (Sugita Lab), RIKEN gave an online talk, entitled, "Protein structure modeling from cryoelectron microscopy data". He talked about the theoretical method to determine threedimensional structures of biomolecules at nearatomic resolution, using a molecular dynamics (MD) simulation and also microscopy data. In addition, he showed their combined approach of coarsegrained model and allatom model. According to him, Bayesian inference and machine learning are useful for the determination of biomolecule's 3D structure which can be the seeds of future collaborations between us. During the seminar, there were many discussions with iTHEMS members especially about the theoretical method to use recent microscopy data. We enjoyed his talk very much. Thanks, Morisan! Reported by Gen Kurosawa

20211117
セミナーレポートiTHEMS Biology Seminar by Dr. Jae Kyoung Kim on November 11, 2021
On Nov 11th 2021, Prof. Jae Kyoung Kim from KAIST, South Korea gave an online talk at iTHEMS. The title of the talk is “Toward mathematical medicine: development of a new drug and digital medicine for sleep disorders”. In the seminar, Dr. Kim talked about mathematical model (e.g. IBM) of our daily rhythms when environment within cells is crowded by lipids, and its implication for obesity. In addition, he showed their successful collaboration with Pfizer and Samsung medical center. The talk thrilled us very much. There were many intensive discussions with iTHEMS members and also experimental biologists from outside. Thanks, Jae! Reported by Gen Kurosawa

20211115
セミナーレポートiTHEMS Math Seminar by Prof. Todor Milanov on November 12, 2021
Professor Todor Milanov gave a talk on his recent research on Ktheoretic GW theory. He first recalled the definition of GromovWitten invariants and its Ktheoretic generalization. Then he mentioned how to use genus 0 GW invariants to define quantum product on the usual cohomology group of a symplectic manifold. Such formulation has deep connection to integrable systems. He then introduced his research results, including a proof of the fact that small Jfunction in quantum cohomology of a Fano manifold can be obtained as a limit q >1 of the small Jfunction in quantum Ktheory. Reported by Yalong Cao

20211115
セミナーレポートiTHEMS Math Seminar by Prof. Naichung Conan Leung on November 5, 2021
Professor Conan Leung gave an introductory talk to mirror symmetry. He first started with the discussion on the sum of inner angles of a triangle to illustrate the difference between our familiar Euclidean spaces and spaces with nontrivial curvature. He then introduced the notion of complex numbers and how it is related to solving polynomial equations in algebra. Recalling that gravity theory and quantum theory having very different nature of behaviour, he introduced super string theory as a potential unification of these two theories and its great impact to the study of modern mathematics, e.g. enumerative geometry, geometry of special holonomy. Finally he introduced mirror symmetry and how to understand it from the perspective of Fourier transform following a proposal of Strominger, Yau and Zaslow. Reported by Yalong Cao

20211111
セミナーレポートInformation Theory SG Seminar by Dr. Michiya Mori on November 4, 2021
On November 4, Dr. Michiya Mori gave a talk entitled “Boolean algebras and operator algebras” at the Information Theory SG Seminar. He explained some of the basic concepts of Boolean algebra. Then he talked about some interesting issues and his contributions in the field. It was a very informative and stimulating talk. Reported by Yukimi Goto

20211111
セミナーレポートAstroAI WG/Information Theory SG Joint Seminar by Dr. Takehiko Saito on November 8, 2021
The seminar was held online plus 4 people onsite. Dr.Saito gave a talk about “hunting hypernuclei by machine learning in nuclear emulsions”. Recent experimental studies with heavy ion beams have revealed that the nature of the hypertriton is unclear, especially on its biding energy and lifetime. The group led by Dr. Saito conducted measurements of them using nuclear emulsion, which requires a huge human load on visual image analyses. Therefore, they have developed machine learning models to detect events associated with production and decay of hypertriton in nuclear emulsions data, and successfully have discovered hypertriton events. Reported by Naomi Tsuji

20211110
セミナーレポートiTHEMS Theoretical Physics Seminar by Prof. Katsuki Aoki on November 2, 2021
On November 2, 2021, at a seminar as part of the iTHEMSphys seminar series, Dr. Katsuki Aoki (YITP, Kyoto University) delivered a talk on the topic of consistency conditions on the Standard Model of particle physics imposed from the requirements of a more fundamental ultraviolet (UV) theory. Underlying assumptions on UV completion can impose constraints on its lowenergy effective field theories (EFTs). The swampland program aims to clarify consistent and inconsistent EFTs with quantum gravity and aims to understand quantum gravity from lowenergy physics and vice versa. One of the most wellestablished constraints is called positivity bounds, provided that general assumptions such as Poincare invariance and unitarity are satisfied at all scales. Dr. Aoki first explained how these consistency conditions arise especially in the presence of gravity. He then showed that the positivity bound is violated if the Standard Model coupled to General Relativity is extrapolated up to 10^16 GeV, requiring new physics there or below. The precise value of the cutoff is determined by hadronic physic while it is insensitive from nongravitational physics beyond the Standard Model. This is a signal from established physics for the necessity of quantum gravity below 10^16 GeV. Reported by Ryo Namba

20211102
セミナーレポートReport of iTHEMS colloquium  HighEnergy Neutrino Astrophysics in the Multimessenger Era
Our Universe is filled with mysterious highenergy emissions: Cosmicrays (CR), neutrinos, and gammaray photons. They could be generated at the same source populations although we have not yet confirmed. Among these messenger particles, the neutrino is a special one to probe their origins. Cosmic rays are deflected by the magnetic field, while highenergy photons are attenuated during its propagation. Only the neutrino could preserve the information about the production sites. Also, the neutrino should be a messenger to physics beyond the Standard Model. The fact that the neutrinos have finite masses itself requires the extension of the Standard Model. Its origin could be related to dark matter, new kinds of interactions, and so on. Ongoing and planned experiments should enable us to access these problems by combining spectrum, timing, and flavor information. In this colloquium, Prof. Kohta Murase reviewed the above contents focusing on the latest results from neutrino observations and the development of the source modeling in the multimessenger approach. About 100 people have enjoyed his talk. Lots of questions and some deep discussions related to the topic continued after the main part of the talk. We would like to thank him again and express our great appreciation for your attendance. Reported by Nagisa Hiroshima

20211029
セミナーレポートiTHEMS Biology Seminar by Prof. Ikkyu Aihara on October 28, 2021
In the Biology Seminar on 28th October, Ikkyu Aihara (University of Tsukuba) gave a talk on frog chorus and its synchronization phenomena using experimental, fieldwork, and mathematical models. An earthquake that had occurred just before the seminar made me a bit nervous about whether we can hold the seminar, but the talk thankfully went very well. As I'm a big fan of Kuramotomodel as well as Ikkyu's work, I really enjoyed the talk on the whole. I saw one of the most interesting experiments of his ongoing work, and so I'm really looking forward to seeing the work being published. I also enjoyed a private conversation between Ikkyu and Kazuyuki Aihara before and during the talk! Thank you again for the great talk, Ikkyusan! Reported by Ryosuke Iritani

20211027
セミナーレポートQuantum Matter SG seminar by Dr. Robert Peters on October 20, 2021
The Quantum Matter Study Group invited Dr. Robert Peters from Kyoto University to talk about nonlinear responses in strongly correlated systems. In the beginning, the speaker introduced nonlinear responses by reviewing several related experimental data, including a nonlinear photoinduced current. Then, going beyond linear response theory, he explained the approach to compute nonlinear responses in strongly correlated systems. Here, the essential step of his work was to neglect vertex corrections, which enables the analysis of higherorder correlation functions within established frameworks of, e.g., dynamical mean field theory. Equipped with this tool, he showed nonreciprocal conductivity in a ferromagnetic noncentrosymmetric heavy Fermion compound and giant nonlinear Hall effect in a WeylKondoSemimetal. Reported by Thore Posske (University of Hamburg, Germany) and ChingKai Chiu

20211027
セミナーレポートDMWG Seminar by Prof. Takashi Toma on October 20, 2021
Among the varieties of dark matter (DM) candidates, the socalled WIMP (an abbreviation of the weakly interacting massive particle) is famous for its beautiful mechanism to achieve the current DM density. In the early Universe, WIMP was in the thermal bath of the Standard Model (SM) particles. In this stage, (i) DM+DM>SM+SM, (ii)SM+SM>DM+DM interaction as well as (iii)DM+SM> DM+SM interaction occur frequently enough. The strategy searching for each process corresponds to indirect, collider, and direct detection experiments. The crosssection (i.e., the interaction rate) of the above processes correlates with each other. The dropping off of the interaction rate of the process (i) below to the Hubble expansion rate of the Universe fixes the number density of DM particles. We need only two parameters in this WIMP freezeout scenario: mass and the interaction crosssection. Nowadays the constraints from direct detection experiments are so severe that WIMP in the low mass range of m
DM+SM, which is a process referred to as coannihilation, the crosssection of the process (iii) could be suppressed in a velocitydependent way. A concrete example introduced in this talk is the one considering the SM particle in the process (i)' as the neutrino. From the momentum conservation, DM accumulated in the Sun annihilates to produce boosted DM and neutrino, hence we expect a doublepeak spectrum in largevolume neutrino experiments for this case. The solution to the corecusp problems of usual WIMP and the origin of the neutrino mass, which is another important problem in the Standard Model, are also within the focus of this story. The world of DM is not closed on its own. It should be a key to understanding nature and obtaining a picture of our Universe! Reported by Nagisa Hiroshima 
20211027
セミナーレポートNEW WG Seminar by Mr. Akihiro Yamada on October 20, 2021
Akihiro Yamada (Keio U.) gaive a talk on "Floquet vacuum engineering: laserdriven chiral soliton lattice in the QCD vacuum" based on his recently published paper [1]. After briefly introducing the Floquet theory and the chiral perturbation theory, Akihiro showed emergence of chiral soliton lattice structure in the QCD vacuum under a very strong laser field with large frequency. About 20 people have joined the seminar, and we had fruitful discussions during and after the seminar. Reported by Hidetoshi Taya

20211027
セミナーレポートiTHEMS Biology Seminar by Dr. Hiroshi Yokota on October 21, 2021
In the iTHEMS Biology seminar on October 21, I talked about the driving force and the mechanism of the chromosome formation. The chromosome is constructed by chromatin fiber condensed into the rodlike shape. The rodlike shape comes from the consecutive chromatin loops. The driving force of the chromosome formation is one of the controversial issues. Two hypotheses on the driving force are considered: energy gain from ATP hydrolysis and thermal fluctuation energy. In this talk, I discussed the driving force derived from the free energy of the chromatin loop. Moreover, the mechanism associated with each driving force was also discussed by using the dynamical model based on the free energy. The result implies that these mechanisms dynamically switch. This study is collaborated with Masashi Tachikawa in Kyoto University who is also visiting scientist in iTHEMS. As there were various questions and discussions from the audiences, I was so happy. Thank you very much!

20211019
セミナーレポートQuantum Matter SG seminar by Mr. Seishiro Ono on October 12, 2021
Quantum Matter Study Group invited Seishiro Ono from the University of Tokyo to give a talk about symmetry indicators for topological (nodal) superconductors. First, he gave a review of symmetry indicators for topological insulators. In condensed matter physics, using topological invariants to search for topological materials is difficult; alternatively, symmetry indicators serve a simpler calculation to identify topological states of matter since this method considers the properties located at symmetry invariant momenta. After the introduction, the speaker extended the indicator approach to topological (nodal) superconductors. Although the different types of superconducting pairings lead to complications in the symmetrybased classification, the speaker showed that their work classifies all the (magnetic) space groups with possible superconducting pairings. Furthermore, he demonstrated their own database server listing all the classification of the topological superconductors by using the approach of symmetry indicators. The work serves as an important guide for hunting topological superconductors. Reported by ChingKai Chiu

20211018
セミナーレポートABBL/iTHEMS Astro Seminar by Dr. Nobuya Nishimura on October 15, 2021
At the seminar, there were lots of questions and answers for rprocess nucleosynthesis and kilonova events. The speaker presented lots of his excellent works on them, and the audience enjoyed his presentation with curiosity. Reported by Shigehiro Nagataki

20211012
セミナーレポートQuantum Matter SG seminar by Prof. BohmJung Yang on October 7, 2021
The Quantum Matter study group had the honor to invite Prof. BohmJung Yang to give a talk on October 7th. He talked about wave function geometry and anomalous Landau levels of flat bands. He started with a heuristic introduction by explaining the geometry matters in a flat band, including the notion of the (HilbertSchmidt) quantum distance and the quantum metric. Particularly, he used a Kagome lattice as an example of the singular touching point of the flat band and quadratic band locked by the geometry. Furthermore, in the presence of a magnetic field, the singular flat band evolves into very dense anomalous Landau levels. Remarkably, the relation between the Landau level spreading and the maximum of the quantum distance can be described by a universal formula, independent of material parameters. In consequence, deducing the Landau level spreading in (spectroscopic) experiments would allow for the measurement of the quantum distance, thus probing the quantum geometry of the wave functions. The study was extended to the (spinorbitcoupled) Lieb lattice with one flat band sandwiched by two dispersive bands. In this case, the Landau level spreading of the isolated flat band is determined by the fidelity tensor. This talk showed us the interesting and subtle interplay between the band flatness and the Landau levels. Reported by ChingKai Chiu and ChenHsuan Hsu (CEMS, RIKEN)

20211011
セミナーレポートiTHEMS Theoretical Physics Seminar by Prof. Keisuke Izumi on September 13, 2021
At the seminar organized by the iTHEMSphysics study group, Prof. Keisuke Izumi discussed the Smatrix unitarity toward UV completion. Einstein gravity is not renormalizable and does not hold perturbative unitarity at high energy. This is the main reason why the construction of quantum gravity is difficult. A conjecture was proposed by Llewellyn Smith, "renormalizablility and treeunitarity at high energy give the same conditions". This conjecture would be important because it shows that, if a theory is constructed such that unitarity is satisfied, renormalizablility holds automatically, and vice versa. Unfortunately, a counterexample was pointed out. If a theory involves higher derivatives, there exists a theory which is renormalizable but does not satisfy treeunitarity. A candidate of quantum gravity, the quadratic gravity (R_{\mu\nu}^2 gravity), is one of the examples. Therefore, Llewellyn Smith's conjecture would not be useful for the discussion of quantum gravity. Then, Prof. Izumi and his collaborators introduced a new conjecture, "renormalizablility and Smatrix unitarity (or often called pseudounitarity) at high energy give the same conditions". In his talk, Prof. Izumi explained Llewellyn Smith's conjecture and his contribution to it. Then, he introduced his new conjecture. Finally, he showed that his conjecture works well even in theories with higher derivatives. Reported by Ryo Namba

20210929
セミナーレポートReport of iTHEMS colloquium  Finding Gravitational Waves from the Early Universe
Prof. Eiichiro Komatsu, a director at the Max Planck Institute for Astrophysics (Germany), shared his enthusiasm for observational aspects of cosmology and in particular the primordial gravitational waves (GWs) generated during the earliest stage of our Universe, called cosmic inflation. Such GWs distort the space while propagating and leave footprints as the polarizations of the cosmic microwave background (CMB) and as a more direct signal at the GW interferometers. As a worldleading expert on all areas of cosmology, Prof. Komatsu explained the fundamental aspects of CMB and GW observations and their implications in understanding the physics of the primordial Universe (from his remark, "We all came from quantum fluctuations"). He made his talk visually accessible to nonexperts while providing fresh interpretations of the data in cosmological observations. He also clarified the importance and excitement of the upcoming LiteBIRD project, the first CMB mission led by Japan, which expects its launch toward the end of 2020's. After the official part of his talk, he remained to be available for both scientific and nonscientific discussions with the audience in an informal setting and exchanged more technically involved thoughts as well as his everydaylife experiences. Reported by Ryo Namba

20210917
セミナーレポートNEW WG Seminar by Prof. Yuta Murakami on September 15, 2021
Yuta Murakami from Tokyo Institute of Technology told us about "Highharmonic generation in strongly correlated systems." Highharmonic generation (HHG) by strong AC electric fields is one of the hottest topics in condmat physics. After a brief overview of HHG in various materials such as gasses and semiconductors 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 stronglycorrelated nature. About 30 people joined the seminar and we enjoyed fruitful discussions during and after the seminar. Reported by Hidetoshi Taya
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