セミナーレポート
337 ニュース

20230918
セミナーレポートQuantum Matter Seminar by Ashley Cook on September 14, 2023
In a recent online seminar for RIKEN iTHEMS' QMSG series, Dr. Ashley Cook of the Max Planck Institute for Complex Systems delved into her interesting research on topological skyrmion phases in electronic systems. The talk was centered on noninteracting electronic topological phases that feature a skyrmion in their momentumspace spin polarization. After a succinct introduction that framed the talk within the broader context of topological classification in condensed matter physics, Dr. Cook pivoted to explore quantum skyrmion structures in momentum space. She specifically discussed these structures in the context of expected spin polarization in the ground state of centrosymmetric superconductors. Intriguingly, she demonstrated that the topological protection of the skyrmion number extends to the electronic structure through a generalized bulkboundary correspondence, after accounting for nonspin degrees of freedom. This results in the formation of unique edge states that bridge one types of the energy bands (conduction bands and valence bands). Moreover, Dr. Cook emphasized that the adiabatic pumping of these edge states signifies the flow of quantum skyrmions. She suggested that this insight necessitates a reevaluation of the theoretical framework for the quantum Hall effects, which was initially conceived around point charges nearly half a century ago. Her work, therefore, not only suggests a pathway to discover new forms of topological boundary states but also calls for a more nuanced classification of topological states in electronic matter, beyond the limitations of the "tenfold way." The talk sparked a lively discussion, underscoring its significance and the excitement it generated among the participants. We extend our gratitude to Dr. Ashley Cook for her illuminating and thoughtprovoking contribution. Reported by ChingKai Chiu (iTHEMS) and Thore Posske (University of Hamburg, Germany)

20230905
セミナーレポートLabTheory Standing Talk #2 by Yusaku Nishimiya on September 5, 2023
At this LabTheory Standing Talks, taken place at the third floor open space, Yusaku Nishimiya explained the effect of heavyion beam on yeast. Reported by Tsukasa Tada

20230825
セミナーレポートExploring 2D Quantum Spacetime Based on Causal Dynamical Triangulations by Yuki Sato on August 21, 2023
The fourth set of intensive lectures organised by the iTHEMS Quantum Gravity Gatherings study group has now concluded. Approximately 15 participants joined this three day event in which we were given a comprehensive overview of the causal dynamical triangulations (CDT) approach to 2D quantum spacetime. Leading affairs was Dr Yuki Sato of the National Institute of Technology, Tokuyama College, who presented in a tightly organised and very pedagogical manner. Following some brief motivations for the CDT approach to quantum gravity and a summary of the numerical understanding of the theory in 4D, Satosan began with an overview of discrete geometry in Lorentzian spaces and used this to introduce Lorentzian Regge calculus. The fundamental idea here is to realise curvature as a conical defect at certain codimension 2 regions of piecewiseflat manifolds. We concluded the first day by using this to construct the Lorentzian EinsteinRegge action in arbitrary dimension before specialising to the 2D case. We began the second day by explicitly quantising this 2D action and then proceeded to take its continuum limit, allowing for the deduction of the quantum Hamiltonian of the theory. We then briefly covered the formalism of 2D projectable Hořava–Lifshitz (PHL) gravity and demonstrated the equivalence of this theory to 2D CDT by showing that PHL gravity is described by the same Hamiltonian as in the CDT case. On the third day we learnt about a generalisation of the 2D CDT model allowing for topology change to occur, employing ideas from string field theory in the process; we studied a dual matrix model representation of the theory and derived an effective quantum Hamiltonian including the contribution of such wormhole configurations. Finally we saw how topology change in 2D generalised CDT could be realised in terms of stochastic timedependent fluctuations of the cosmological constant in line with the socalled Coleman mechanism. In addition to the scientific activities above we had a number of short talks on the first and second days of the event by participants as well as a banquet on the first day where we were joined by several iTHEMS members. The intimate nature of the event lead to the active participation of attendees and overall a very lively and productive learning environment. Reported by Christy Koji Kelly

20230816
セミナーレポート3rd QGG Intensive Lectures: Spinfoam path integrals for Quantum Gravity by Etera Livine on July 26, 2023
The 3rd Intensive Lecture by iTHEMS’ Quantum Gravity Gatherings concluded with resounding success. Around 30 enthusiasts, including students, junior and senior researchers from various disciplines, convened at the RIKEN Wako Campus to learn and discuss spinfoam quantum gravity. Prof. Etera Livine from ENS Lyon, our distinguished lecturer this time, delivered a fantastic 3day lecture about the spinfoam approach to quantum gravity (QG). He began with a wonderful introduction explaining why physicists have long sought the theory of quantum gravity: the ultimate theory that unifies physics at both macroscopic and subatomic scales. Prof. Livine highlighted various existing candidates for quantum gravity theory and forged connections among these diverse approaches. Regarding the main topic, he started with the basics of loop quantum gravity and clearly explained the origin of the fundamental discreteness of spacetime. In the latter half of his lecture, he detailed how to construct the spinfoam path integral for QG in 3D before moving on to the 4D case. He concluded his lecture by discussing the limitations of this approach and outlining future directions. Throughout his lecture, he consistently elaborated on the mathematical similarities between these QG approaches and other areas of physics, such as condensed matter physics. This allowed the audience to grasp the current advancements in the field, recognizing how their areas of expertise, seemingly distant from quantum gravity, could intricately interlace with it. This event presented a great opportunity for fostering interdisciplinary research, as it brought together people with various interests, including physicists working on highenergy physics, gravity, cosmology, and condensed matter systems, as well as pure mathematicians. Everyone exhibited keen enthusiasm for quantum gravity, creating an atmosphere of unity and togetherness that permeated the room. Many interesting questions were posed during the lecture, and participants enthusiastically engaged in discussions during coffee breaks. Some of them also shared their stories and work during the short talk sessions, and everyone enjoyed the banquet on the second day. Overall, this event provided a relaxed and active platform for learning, offering an exceptional opportunity to strengthen connections and friendships among participants, particularly those in the early stages of their research careers. Reported by Puttarak Jaiakson

20230811
セミナーレポートHigher Algebra in Geometry by Hiro Lee Tanaka on July 31, 2023
8 days of introductory lectures on Higher Algebra (infinity categories) were given by Dr. Hiro Lee Tanaka (Texas State University). Recent developments on infinitycategory theory and their applications have received attraction from various areas of mathematics, including geometric topology, symplectic geometry, and algebraic geometry. The lectures were targeted to students and researchers interested in applications of infinitycategorical tools. The first day was devoted to nonspecialists, where Dr. Tanaka introduced the concept of associativity and homotopies, and explained how they naturally lead us to the ideas of infinitycategories. From the second day, Dr. Tanaka introduced the basic concepts of infinitycagetories together with familiar examples. In the second week, some of the works of Dr. Tanaka were given as applications of the ideas of inifitycategories. His aim was to show us that these concepts are not mere abstractions, but are accessible and usefully applicable to concrete questions of geometry. The participants also shared their own works and interests after the lectures, and lively discussions took place. Reported by Taketo Sano

20230726
セミナーレポートQuantum Matter Seminar by Xinloong Han on July 24, 2023
On July 24th, 2023, quantum matter SG hosted a seminar entitled "Electronic instabilities emerging from higherorder van Hove singularities", and the guest speaker was Xinloong Han, a Postdoctoral Fellow at the Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, China. Xinloong Han started by introducing van Hove singularity (VHS). Building on the conventional understanding of VHS points, Han introduced the concept of higherorder VHSs, which have recently been explored in ABCstacked trilayer graphene and twisted bilayer graphene. He elucidated the differences between conventional VHSs and higherorder VHSs, paving the way for a discussion on the enhanced nematicity driven by large flavor number with higherorder VHSs on the square and Kagome lattices. Towards the conclusion of his talk, Han shed light on the possibility of robust topological superconductivity emerging on the square lattice due to the interplay of spinorbital coupling and higherorder VHSs. This revelation presented a captivating insight into the advancements in the study of topological superconductors. Reported by ChingKai Chiu

20230720
セミナーレポートDMWG Seminar by Slivia Manconi on July 10, 2023
As a nature of dark matter that feels gravity, dark matter in our Universe forms halos, which are gravitationallybounded macroscopic structures. The halo structure is highly hierarchical and the halo of our Milky Way, for example, hosts many subhalos inside. However, smaller halos below a certain scale could not be visible because they cannot host galaxies. If we look at the sky in gammaray wavelength, there are lots numbers of bright sources. Most of them are socalled active galactic nuclei (AGN), which are related to the powerful jet activities of black holes. A certain portion of point sources are not categorized yet. They could be AGNs, while it is also possible that they are bright due to DM annihilation occurring in compact and small subhalos in our Galaxy. Neural networks, which are tools we have obtained in this era, powerfully help us to obtain insights into the properties of unknown gammaray sources. Properties of known sources such as spectrum and population serve as data for the supervision of the neural network. The trained network is used to look for outliers in the gammaray unknown sources which can be candidates for subhalos emitting gammarays by DM annihilations. In this way, a conservative upper limit on the annihilation crosssection of DM is derived. The scheme is highly flexible and has many possibilities for extensions. In the near future, a huge amount of data, which is far beyond human ability to analyze all, from experiments in multiple wavelengths and probes should appear. The future of DM study assisted with machine learning should be bright. Reported by Nagisa Hiroshima

20230707
セミナーレポートABBLiTHEMS Joint Astro Seminar by Takatoshi Ko on July 7, 2023
Iras 00500+6713 is a bright nebula in the infrared, and Xray observations show it consists of diffuse region and strong illuminated central region. In addition, optical spectral observations have recently revealed that fast wind with about 15,000 km/s is blowing from the massive white dwarf at the center. The properties of this nebula and white dwarf are very similar to those theoretically predicted by the binary white dwarf merger. In addition, its position on the celestial sphere and the extent make it a prime candidate for the remnant of SN 1181, a historical supernova. In this seminar, Mr. Takatoshi Ko proposed that such a multilayered structure is formed by the collision between the remnant of SN 1181 and the stellar wind blowing from the central white dwarf, and succeeded in constructing a model that is consistent with the multiwavelength observations. The results show that the progenitor of SN 1181 is a binary white dwarf with 1.31.9 solar mass and that their merger triggered an explosion that ejected mass with 0.20.6 solar mass to form the present object. The extent of the Xray source concentrated in the center reveals that these winds began blowing within the last 30 years, and Mr. Takatoshi Ko discussed this property as well. Reported by Shigehiro Nagataki

20230619
セミナーレポートiTHEMS Biology Seminar by Dr. Yu Okamura on May 25, 2023
We had the pleasure to have Dr. Yu Okamura (The University of Tokyo) as an invited speaker of our Biology seminar of May 25th, 2023. Dr. Okamura introduced us to the mechanism that allow herbivory of Pieris butterflies on Brassicaceae plants (plants of the group of the mustard). Brassicaceae, as well as most plants, will defend from herbivores by producing chemical compounds that can be lethal, but at the same time, insects will need to evolve strategies to elude the chemical defenses of the plants. This relationship leads to an interesting coevolutionary pathway that has not been widely explored from the genomic perspective. In his study system, Dr. Okamura has performed experiments to research how the toxic chemical compounds derived from glucosinolates of plants are eluted by their butterfly herbivores thanks to the expression of two specific genes that produce proteins that decompose the glocusinolates into nonlethal metabolites. One of the two genes (NSP gene) is known to be expressed in most Pieris butterflies that feed on Brassicaceae plants, but in his research, Dr. Okamura found that another gene (MA gene) is complementary of the effect of the NSP gene. Using genome editing techniques (CRISPR/Cas9), Dr. Okamura showed that the absence of NSP or MA genes can be lethal for herbivores. It is concluded that, in combination, NSP and MA genes are necessary for Pieris butterflies to maintain herbivory on a wide variety of plants in the Brassicacae family. Reported by José Said GutiérrezOrtega

20230613
セミナーレポートiTHEMS Math Seminar by Mr. Kan Kitamura on June 7, 2023
In iTHEMS Math Seminar on June 7, 2023, Kan Kitamura gave us a talk on his recent research on quantum groups. In the first half of the talk, he introduced the definition of C*algebras and compact quantum groups. In the latter half of the talk, he explained his theorem on the classification of the discrete quantum subgroups of the quantum double of qdeformed simple Lie groups. The talk was highly clear and stimulating. Reported by Mizuki Oikawa

20230601
セミナーレポートQuantum uncertainty of fields and its effect on entanglement generation in quantum particles by Mr. Yuki Sugiyama on May 31, 2023
The unification of gravity and quantum mechanics is one of the important problems. To elucidate the theory of quantum gravity, it is becoming more and more important to get any hint of the quantum nature of gravity. In particular, the quantumgravityinducedentanglement of masses (QGEM) scenario, which is expected to observe the quantum nature of nonrelativistic gravity, has recently attracted great attention. In this talk, Sugiyamasan showed the effect of relativistic fields on entanglement generation based on quantum field theory. We also discussed the relationship between the entanglement generation and quantum uncertainty of the fields. Reported by Shigehiro Nagataki

20230531
セミナーレポートiTHEMS Theoretical Physics Seminar by Dr. Masaki Tezuka on May 30, 2023
On May 30, Dr. Masaki Tezuka gave a talk on Spectral correlations and scrambling dynamics in SachdevYeKitaev(SYK) type models. He explained his recent studies on quantum chaotic features, quantum scrambling, and connections to holography and quantum error corrections in the SYKtype models. Reported by Yuta Sekino

20230528
セミナーレポートExploring GPT’s Influence on Natural Science and Mathematics on May 17, 2023
The emergence of ChatGPT has shocked the world. Its influence on our society is inestimable, both for its possibility and its potential risk. Together with MLPhys (Foundation of “Machine Learning Physics”), we held a workshop “Exploring GPT’s Influence on Natural Science and Mathematics” on 17th May, to discuss the influence of GPT particularly on natural science and mathematics. An introductory lecture on GPT (generative pretrained transformer) and LLM (large language model) was given by Mr. Shota Imai (The University of Tokyo), and an introductory lecture on proof assistant system (automated theorem proving) was given by Dr. Yoshihiro Mizoguchi (Kyushu University). Around 30 people attended in place, and over 400 people attended the workshop online. Lively discussion took place among specialists of Mathematics, Physics and Computer science. Reported by Taketo Sano (iTHEMS, RIKEN)

20230526
セミナーレポートMathPhys Seminar by Dr. Masazumi Honda on February 16, 2023
On Febururary 16, Masazumi Honda gave a talk. He explained his recent results on the relationship between Riemann hypothesis and fourdimensional N=4 supersymmetric YangMills theory. Reported by Keita Mikami

20230525
セミナーレポートiTHEMS Math Seminar by Dr. Kohei Hayashi on May 24, 2023
On May 24, there was a math seminar by Kohei Hayashi. In the first part of his talk, he start by explaining the idea of the hydrodynamic limit and the fluctuating hydro dynamic limit. He then explained Markov chain and how to obtain the diffusion equation. In the second part, he explained KPZ equation and its universality. Reported by Keita Mikami

20230522
セミナーレポートABBLiTHEMS Joint Astro Seminar by Mr. Vincenzo Sapienza on May 19, 2023
Synchrotron Xray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high energy electrons accelerated at the shock front. Mr. Sapienza and his collaborators performed a spatially resolved spectral analysis of the young Kepler's SNR, where they identify two different regimes of particle acceleration. In the north, where the shock interacts with a dense circumstellar medium (CSM), they found a more efficient acceleration than in the south, where the shock velocity is higher and there are no signs of shock interaction with dense CSM. They also studied the temporal evolution of the synchrotron flux, from 2006 to 2014. A number of regions show a steady synchrotron flux and equal cooling and acceleration times. However, they found some regions where they measured a significant decrease in flux from 2006 to 2014. Our results display a coherent picture of the different regimes of electron acceleration observed in Kepler's SNR. Also Mr. Sapienza presented some preliminary results on the SN 1987A project. Reported by Shigehiro Nagataki

20230515
セミナーレポートSpring Workshop on Quantum Gravity on April 26, 2023
Spring Workshop on Quantum Gravity, the first one in the lecture series Quantum Gravity Gatherings and cosponsored by NCTS, was a great success with about 50 participants, including some from Taiwan. First, Prof. Kawai's intensive lecture on quantum gravity was wonderful. In the basic part of the first half, he explained the physical aspects of the ordinary formulas found in textbooks on general relativity, from a quantum theoretical standpoint, and transformed the equations consistently, to arrive at physically clear results about quantum gravitational fields. In the latter part, he described the features of fieldtheoretic quantum gravity and its limitations. Through these, he showed us the importance of researching quantum gravity step by step from a fundamental point of view. All participants were interested in quantum gravity, and there was an atmosphere of togetherness in the room. During the lecture, a variety of questions, from the simple to the fundamental, were raised. During breaks, small discussions spontaneously occurred here and there in the common space. And in the short talk sessions, we were able to share each other's research and interests. The banquet on the first day of the event was a great opportunity to deepen friendship. Thus, this event provided many opportunities for learning, research, and exchange for the younger generation. Reported by Yuki Yokokura

20230512
セミナーレポートDMWG Seminar: DMline search in the Galactic Center with MAGIC telescope
Among kinds of dark matter (DM) candidates, weakly interacting massive particles (WIMPs) are the most intensively studied ones along their theoretical background and expectations for the signals in onEarth experiments. However, up to now, our understanding of the regime of m>O(1) TeV is still limited since we cannot produce them at colliders and cannot expect a sufficient interaction rate at underground recoil detectors. Highenergy astrophysical observations are powerful in probing that regime and projects all over the world are now searching for corresponding signals. When we look for signatures of DM from astrophysical data, it is necessary to consider contributions from astrophysics very carefully. The key signatures could be the morphology of the emission, the spectrum, and correlating signals in other kinds of observations, variabilities, and so on. If DM particles annihilate to produce photon pairs, the spectrum should show a monochromatic peak corresponding to the mass of DM, hence it is distinctive against the astrophysical emissions. MAGIC telescope, which locates in the Northern Hemisphere, only considers target objects in the northern sky previously. However, it actually can see the Galactic Center in a large inclination. For this case, the threshold of the analysis is worsened but the effective area is improved, then it can achieve a good sensitivity to highenergy emissions. Using 223h of observation at the Galactic Center with MAGIC, the line emission search is carefully performed. The determination of the "off" takes an important role in not overestimating the sensitivity and the sliding window technique is adopted regarding this point. The uncertainty of the DM density of the region of interest is also carefully discussed by performing the analysis applying both the cuspy and cored profiles. No signatures of the monochromatic gammaray from DM annihilation are found in this analysis hence we obtain upper limits of the annihilation crosssection. The sensitivity is comparable to the flux level of a wellmotivated Wino DM model which should exhibit annihilation lines around E~3TeV. This means that we are now approaching the era that to probe detailed particle models of DM with astrophysical observations. In the near future, observations with the Cherenkov Telescope Array will start operations and we can look into the detail of the models in combination with particle physics communities! Reported by Nagisa Hiroshima

20230427
セミナーレポートiTHEMS Biology Seminar by Mr. Naoki Konno on April 20, 2023
In April 20, Mr Naoki Konno (University of Tokyo) gave a fantastic talk about the machine leaning method for the prediction of evolution. The talk was entitled, “Machine learning predicts biological system evolution by gene gains and losses”. To my knowledge, this study using genome data of ~3000 species is one of few seminal attempts to theoretically predict longterm and systemlevel evolution. The seminar by Konno san was very clear and we understood the predictability of the proposed framework, called “Evodictor”. In the beginning of the talk, he kindly explained the theoretical basis about phylogenetic tree estimation and machine learning for nonspecialists for which we could enjoy and learn from his seminar a lot. Thank you, Konnosan for the great talk!! Reported by Gen Kurosawa

20230424
セミナーレポートABBLiTHEMS Joint Astro Seminar by Dr. Kumiko Kotera on April 18, 2023
We are living exciting times: we are now able to probe the most violent events of the Universe with diverse messengers (cosmic rays, neutrinos, photons and gravitational waves). One challenge to complete the multimessenger picture resides in the highest energies, as no ultrahigh energy neutrinos have been observed yet. This challenge could be undertaken by the GRAND (Giant Radio Array for Neutrino Detection) project, which aims at detecting ultrahigh energy particles, with a colossal array of 200'000 antennas over 200'000 km2, split into ~20 subarrays of ~10'000 km2 deployed worldwide. In this talk, Kumiko Kotera presented preliminary designs and simulation results, plans for the ongoing, staged approach to construction, and the rich research program made possible by the proposed sensitivity and angular resolution. Reported by Shigehiro Nagataki

20230413
セミナーレポートSeminar, "Introduction to the Renormalization group method as a powerful reduction method of dynamics" by Dr. Teiji Kunihiro on April 10, 2023
In April 10, Dr Teiji Kunihiro (Prof Emeritus, Kyoto Univ) gave an introductory talk about the renormalization group method, entitled “Introduction to the Renormalization group method as a powerful reduction method of dynamics.” In fact, this talk was the first seminar at our new seminar room #359 with the splendid blackboard in RIKEN Wako Campus. The talk by Kunihirosan using the blackboard was very very clear, and we can understand the power of the Renormalization group method and its applicability [1]. The talk was also delivered via Zoom (i.e. ~35 participants in total), and there were lively discussions between the lecturer and the audience. After the talk, he kindly shared his lecture note with us so that we can take advantage of it. Thank you, Kunihirosan for the wonderful talk!! Reported by Gen Kurosawa

20230411
セミナーレポートLabTheory Standing Talks #1 by Dr. Hideshi Ooka on March 16, 2023
The first LabTheory standing talk took place on March 16th, 2023, inviting Hideshi Ooka from CSRS (Riken Center for Sustainable Resource Science). He picked up the chemical process of making hydrogen from water as the subject. By design, the event is organized in a very informal setting."I was glad that the speaker prepared very few slides and all the slides were simple because it gave the audience an opportunity to ask many random questions in all sorts of direction," one of the participants, Catherine Beauchemin says. As she says, "in this light and flexible format, it is the audience that can decide what aspects are more interesting for them and ask more questions about it," there have been many questions asked and discussions followed. The event appears to be fruitful for the speaker too; "I will share the comment with my colleagues, as I believe it is a chance to advance the level of chemistry in our lab, " Hideshi Ooka concludes. Reported by Tsukasa Tada

20230407
セミナーレポートiTHEMS Biology Seminar by Dr. Yohei Nakayama on March 30, 2023
On March 30th, Dr. Nakayama talked about F1ATPase from both experimental and theoretical aspects. In the introduction, he reviewed biological molecular motors and experimental facts. Then he introduced a Langevin model for the kinetics of F1 and explained how a specific case of the model fits the previous experiments. In the main part, he told us about new experimental results, relation to the theoretical model, and theoretical prediction based on the model. We thank Dr. Nakayama for giving us an exciting presentation. Reported by Kyosuke Adachi

20230327
セミナーレポートiTHEMS Biology Seminar by Dr. Midori Tuda on March 23, 2023
Dr. Tuda gave us a very wellprepared, clear and interesting presentation about her group's current research. Her work is primarily experimental, while iTHEMS Biology members' work is primarily theoretical, which could create interesting opportunities. We found many common interest between her research and that of iTHEMS Biology members, such as niche divergence under a changing climate (GutiérrezOrtega), sex ratio of offsprings (Hitchcock), and species coexistence/competition (Iritani). This gave rise to many interesting questions, comments and exchanges. We hope to continue conversation. Reported by Catherine Beauchemin

20230313
セミナーレポートABBLiTHEMS Joint Astro Seminar by Dr. Ellis Owen on March 10, 2023
Ultra highenergy (UHE) cosmic rays (CRs) from distant sources interact with intergalactic radiation fields, leading to their spallation and attenuation through photohadronic processes. Their deflection and diffusion in large scale intergalactic magnetic fields (IGMFs), in particular those associated with Mpcscale structures, alter the cumulative cooling and interactions of a CR ensemble to modify their spectral shape and composition observed on Earth. In this talk, Ellis Owen demonstrated the extent to which IGMFs can affect observed UHE CRs, and showed that source population models are degenerate with IGMF properties. Interpretation of observations, including the endorsement or rejection of any particular UHE CR source classes, needs careful consideration of the structural properties and evolution of IGMFs. Future observations providing tighter constraints on IGMF properties will significantly improve confidence in assessing UHE CR sources and their intrinsic CR production properties. Reported by Shigehiro Nagataki

20230307
セミナーレポートiTHEMS Biology Seminar by Dr. Adrian GonzalezCasanova on January 19, 2023
We had the pleasure to have Dr. Adrián GonzálezCasanova (Neyman Visiting Assistant Professor, The University of California, Berkeley, USA / Associate Professor, National Autonomous University of Mexico, Mexico) in our Biology seminar of January 19th, 2023. He presented us a talk consisting of two sections. First, he explained to us the basis of the coalescent theory: a model that depicts how alleles within a population relate each other until reaching a common ancestor. Second, he presented us how the coalescent theory can be used to explain and predict the behavior of one of the most intriguing experiments in evolutionary biology: the Lenski experiment. The Lenski experiment consists of a daily cultivation of E. coli; each day's culture is grown from a population cultivated the previous day. This, way, after thousand generations, the experiment has shown that the fitness increase of individuals is decelerating, but it doesn't decrease or even reach a plateau. Dr. GonzálezCasanova presented us some ideas of how we can model the underlying biological processes behind the experiment while considering other noisy processes such as epistasis or clonal interference, and thus better understand how evolution occurs. Reported by José Said GutiérrezOrtega

20230303
セミナーレポートQuantum Matter Seminar by Dr. YungYeh Chang on March 2, 2023
On March 2nd, 2023, the iTHEMS Quantum Matter Seminar was held online, featuring a talk on "Topological Kondo Superconductors" by YungYeh Chang, a postdoctoral researcher at the National Center for Theoretical Sciences and National Yang Ming Chiao Tung University in Taiwan. YungYeh Chang began by introducing Kondo lattice and heavy fermion compound. Interestingly, superconductivity can emerge in this compound. Then, including topology, he proposed a realization of a 2D timereversal symmetric superconductor in a class of Kondo lattice materials. The proposed system involves the oddparity Kondo hybridization, which mediates ferromagnetic spinspin coupling and leads to spintriplet resonantvalencebond (tRVB) pairing between local moments. The speaker explained that spintriplet p±p' wave topological superconductivity is reached when the Kondo effect coexists with tRVB. By using the mean field theory to generate an effective free fermion (BdG) Hamiltonian, the topological nature was identified by the nontrivial topological invariant and the chiral Majorana modes at edges. The results on the superconducting transition temperature, Kondo coherent scale, and onset temperature of Kondo hybridization were discussed, which not only qualitatively but also quantitatively agree with the observations for UTe2. In summary, the iTHEMS Quantum Matter Seminar on "Topological Kondo Superconductors," presented by YungYeh Chang, provided an insightful discussion on the study of topological superconductors in Kondo lattice materials. The attendees had the opportunity to ask questions and engage in discussions with the speaker, making it an interactive and informative seminar. Reported by ChenHsuan Hsu (Academia Sinica, Taiwan) and ChingKai Chiu

20230220
セミナーレポートDMWG Seminar by Dr. Jowett Chan on February 9, 2023
Dark matter (DM) of our Universe could be categorized into three types: cold DM (CDM), warm DM (WDM), or fuzzy DM (FDM) depending on its mass. CDM is the most wellstudied one with its success in largescale structure formations. However, as studies proceed, some problems arise in such models: observations of smallstructure would not match the predictions of CDM structures in simulations. For example, observations of Milky Way satellites indicate the existence of the central core while simulations predict cuspy structures at the center. The feature could be welldescribed by considering FDM of m~O(1e20) eV or below. The unique point of FDM is that the mass of the particle becomes a unique parameter for calculation. In numerical simulations of FDM halos, we can see the formation of cores in the Hubble time (i.e. the age of the Universe) and relaxations of radial structures. As the test particle mass gets larger, coreformation time becomes longer. One possible caveat for FDM models is the socalled "diversity problem". Our satellite galaxies show diversity in their core structures, while FDM predicts a single scale for core size which is determined by the particle mass. It can be understood by considering nonlinear processes of mergers, the diversity could be generated. Mergers could also be responsible for structures at outer radii, such as the density profile proportional to the inverse cubic of the radius. In order to overcome the numerical difficulties and proceed, GPUaccelerated adaptive mesh code is now being intensively invented. We should see fantastic structures of FDM halos in the near future! Reported by Nagisa Hiroshima

20230216
セミナーレポートQuantum Matter Seminar by Dr. Chang PoYao on February 9, 2023
Please enter the seminar report here!On February 13, 2023, Assistant Professor PoYao Chang of the Department of Physics at National Tsing Hua University in Taiwan gave an online seminar entitled "Entanglement in nonHermitian quantum systems and nonunitary conformal field theories." In the seminar, Professor Chang began by discussing the motivation for studying nonHermitian systems, such as open quantum systems and those with imaginary self energy induced by interaction or disorder. He then introduced the basic concepts of entanglement entropy, arguing that while the quantity is defined through the ground state, it can be used to characterize the entire system similarly to how Boltzmann's thermal entropy characterizes a classical system. In particular, it can be used to characterize topological systems with anyons. Although general nonHermitian systems have complex eigenvalues, he focused on systems that preserve parity and timereversal (PT) symmetry, so that all of the eigenvalues must be real in order to determine the ground state and the entanglement entropy. He showed that in a nonHermitian model, the entropy is negative and corresponds to the negative central charge, which uniquely characterizes conformal field theories (CFTs). As the main result of his recent work, Professor Chang proposed a generic entanglement entropy to characterize nonHermitian systems and showed how it could be used to correctly obtain the entanglement properties of several nonHermitian systems, such as the nonHermitian SuSchriefferHeeger (SSH) model, the qdeformed XXZ model with imaginary boundary terms, and the AffleckKennedyLiebTasaki (AKLT) model, using numerically extracted central charges. In conclusion, Professor Chang's seminar provided valuable insights into the field of entanglement in nonHermitian quantum systems and nonunitary conformal field theories. The seminar was wellreceived by the audience, who appreciated the clarity of the presentation and the relevance of the research topic. Reported by ChenHsuan Hsu (Academia Sinica, Taiwan) and ChingKai Chiu

20230210
セミナーレポートSuper smash problems workshop 3 on January 2527, 2023
From January 25th to 27th, we organized the third Super Smash Problems (SSP) workshop in Kobe. This time we had Kyosuke Adachi (BDR/iTHEMS SPDR) presenting challenging problems he faced in his work. Two main topics were intensively discussed in the workshop. One of them was concerning the generalization of entropyproduction in information thermodynamics. Entropy production can be regarded as a measure of irreversibility of stochastic processes. In other words, irreversibility necessarily comes with positive entropy production. We discussed various systems in biology, physics, and astrophysics that may be relevant to irreversible stochastic systems, like cell growth, formation of phylogenetic trees, machinelearning process, and how universe emerges. Second topic was about phaseseparation. The theory of phaseseparation has a rich mathematical structure: we explored methods with which we can computationally efficiently construct convexhull of a given function. Also, because various systems exhibit phaseseparation, we discussed the potential for which the method can be applied to other systems, including formation of stars. The threeday discussion did not allow us to reach solid conclusion though, we found it very fun and stimulating that mathematics can explain parts of our world that are seemingly totally different. We will continue discussing the problems and hopefully provide you all an update for something resulting. We the organizers sincerely appreciate the audience who attended Adachisan’s introductory lecture and subsequent discussion; and of course, Adachisan for the effort, time, and passion for the SSP workshop. We believe this was a short but very inspiring opportunity. Thank you so much! On behalf, Ryosuke Iritani Reported by Ryosuke Iritani

20230206
セミナーレポートEarly Universe Miniworkshop was held on Jan. 31  Feb. 2, 2023
We held Early Universe Miniworkshop at SUURICOOL (Kobe) on Jan. 31  Feb. 2, 2023. The aim of the workshop was to gather researchers in cosmology and neighboring areas, from students to professors, and discuss future directions towards the understanding of the early Universe and related fundamental issues. In order to stimulate indepth discussions and future collaborations, we organized the workshop in the way that the participants have ample time to interact with each other. Total 22 people attended the workshop on site, as well as over 30 people registered for online participation. The backgrounds of the participants were diverse in terms of nationality, gender and expertise. The topics of the talks at the workshop also range wide, albeit all on the early Universe cosmology in a broad sense, from observational aspects to formal ones. Reported by Ryo Namba

20230125
セミナーレポートiTHEMS Colloquium by Dr. Gabriel Peyré on January 24, 2023
Prof. Gabriel Peyré, a CNRS research director and professor at Ecole Normale Supérieure (France) gave an iTHEMSAIP joint colloquium entitled "Scaling Optimal Transport for High dimensional Learning" on January 24th. He started his talk with the old Monge's problem and moved to modern concept of the optimal transport by Kantorovich with historical stories behind it. He showed us that there have been many efforts of various mathematicians, economists, and physicists behind the developments of the optimal transport theory. In the later part of his talk, Prof. Gabriel Peyré focused on optimal transport problems in extremely high dimensions looking ahead various potential scientific applications like imaging, natural language processing, and biology. He introduced the key concept, entoropic term, with the historical quotation from Schrödinger, and showed us how it enables approximately solving optimal transport problems in high dimensions. He made his talk with a lot of beautiful figures and detailed explanations. We have many discussions during/after the talk, and enjoyed the colloquium. Reported by Akinori Tanaka

20230124
セミナーレポートiTHEMS Math Seminar by Dr. Nobuo Iida on January 20, 2023
On January 20, Nobuo Iida from the Tokyo Institute of Technology gave a talk titled “Math and Physics of SeibergWitten theory” at the iTHEMS math seminar. He started by explaining a wide range of reviews in physics such as classical theory, relativity, quantum mechanics, and quantum field theory. Specially, these explanations were prepared for nonphysicists and stimulated discussions. Also, his explanation of these theories contained many instructive examples of such theories which enable us to understand his talk easily. At the end of the first part, he focused on three kinds of QFTs: free theory, perturbative theory, and more general QFT, and introduced renormalization which gives interactions between high energy theory and low energy theory. Secondly, he started to explain general motivational questions in geometry on the mathematical side. This part is also prepared for nonmathematician. After reviewing the history of topology, he introduces Donaldson’s theory and Donaldson’s polynomial invariant, and Witten’s fieldtheoretic interpretation (topological twist of N=2 SUSY YangMills theory) of the invariant. As the low energy effective theory of N=2 SUSY YangMills theory, a family of gauge theories parametrized by socalled uplane was introduced. By analyzing the family and using duality and topological twist, an idea of the Witten conjecture was shared, which relates Donaldson’s polynomial invariant with the SeibergWitten invariant on the mathematical side. 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

20230120
セミナーレポートABBLiTHEMS Joint Astro Seminar by Dr. Nanae Domoto on January 20, 2023
Binary neutron star (NS) merger is a promising site for the rapid neutron capture nucleosynthesis (rprocess). The radioactive decay of newly synthesized elements powers electromagnetic radiation, as called kilonova. The detection of gravitational wave from a NS merger GW170817 and the observation of the associated kilonova AT2017gfo have provided with us the evidence that rprocess happens in the NS merger. However, the abundance pattern synthesized in this event, which is important to understand the origin of the rprocess elements, is not yet clear. In this talk, Ms. Domoto first introduced an overview and current understanding of kilonova. Then, she discussed her recent findings of elemental features in photospheric spectra of kilonova toward identification of elements. Reported by Shigehiro Nagataki

20230117
セミナーレポートABBLiTHEMS Joint Astro Seminar by Dr. Arno Vanthieghem on November 24, 2022
On November 24th, Dr. Arno Vanthieghem (Princeton University) gave a talk about the energy equipartition in Weibelmediated shock waves. Shock waves relevant to astrophysical phenomena, such as supernovae and gammaray bursts, form via collective plasma processes. In the socalled collisionless shock waves, how exactly the different plasma species (thermal and suprathermal ions and electrons) share energy through dissipation is an open question. In the talk, he gave a broad overview and described the current understanding of this issue based on his recent studies. He carried out analytical kinetic estimates, semianalytical Monte Carlo calculations, and abinitio ParticleInCell simulations to tackle this issue in a wide range of shock velocities ranging from relativistic to nonrelativistic regimes. In particular, he has introduced a theoretical model that can describe electron heating through the interplay between pitchangle scattering in the microturbulence and the coherent electrostatic field induced by the difference in inertia between species. He has shown how successfully the model can be applied to unmagnetized shocks (shocks formed in a plasma without a background magnetic field). During and after the seminar, we had very fruitful discussions. We are grateful for the excellent talk and the great opportunity to have a facetoface conversation with him. Reported by Hirotaka Ito

20230116
セミナーレポートiTHEMS Biology Seminar by Dr. Tetsuya Kobayashi on September 8, 2022
On September 8th, I invited Dr. Testuya Kobayashi, and he talked about hessian geometric structure of equilibrium and nonequilibrium chemical reaction newtworks. He offered a topic on chemical reaction networks. He discussed central issues in biophysics and quantitative biology with recent work from their laboratory. This seminar had a special focus on researchers in the physical and mathematical sciences. However, it was also accessible to biological researchers. In particular, the discussion on the landscape was in line with each biological field. Reported by Daiki Kumakura

20230116
セミナーレポートiTHEMS Biology Seminar by Mr. Daiki Kumakura on January 12, 2023
On January 12, I spoke about the basics of microbial ecology and the application of our field of research and life. First, I gave an introduction of where microbes can live. Then I talked about the application of enzymes of different microbes. And then, I talked about how to study microbiomes, especially metagenomic analysis. Finally, I talked about our project, the hot springs microbiome project. Our project is proceeding in several steps, so I talked about the perspective of our analysis. In this seminar, I focused on the researchers who are not familiar with microbial ecology. This allowed me to share my interest in microbial ecology. Reported by Daiki Kumakura

20230116
セミナーレポートABBLiTHEMS Joint Astro Seminar by Dr. Conor Omand on December 20, 2022
Many energetic supernovae are thought to be powered by the rotational energy of a highlymagnetized, rapidlyrotating neutron star. The emission from the associated luminous pulsar wind nebula (PWN) can affect the system in different ways, including accelerating the ejecta, ionizing the ejecta, and breaking the spherical symmetry through hydrodynamic instabilities or large scale asymmetries. Modeling the observables from these processes; the light curves, spectrum, and polarization; is essential from understanding the nature of the central engine. Dr. Ommand presented the results of a radiative transfer study looking at the effects of a PWN on the supernova nebular spectrum, and the preliminary results from a more physically motivated light curve model for parameter inference, and a study examining the polarization that arises due to hydrodynamic instabilities in the ejecta of enginedriven supernovae. Reported by Shigehiro Nagataki

20230116
セミナーレポートABBLiTHEMS Joint Astro Seminar by Dr. Shinya Wanajo on January 13, 2023
The discovery of an electromagnetic counterpart (kilonova) associated with GW170817 confirms that binary neutron star (NS) mergers are at least one of sites of rprocess nucleosynthesis. However, there is no observational evidence that black hole (BH)NS mergers are rprocess sites. In this talk, Dr Wanajo overviewed the latest work of nucleosynthesis based on longterm hydrodynamics simulations of NSNS and BHNS mergers covering early dynamical and late postmerger mass ejections. Dr. Wanajo also briefly discussed a possible constraint on nuclear equations of state. Reported by Shigehiro Nagataki

20230107
セミナーレポートiTHEMS Biology Seminar by Dr. Yusuke Himeoka on November 17, 2022
On last November, Dr. Yusuke Himeoka at the University of Tokyo told us about a mysterious phenomena of bacterial cells, called "dormancy". The title of his talk was "Emergence of growth and dormancy from a kinetic model of the Escherichia coli central carbon metabolism". Starting from a network model of metabolism, he theoretically discussed how dormancy emerges at bacterial cells. During and after the talk, there were lively discussions. Thank you so much, Himeokasan! Reported by Gen Kurosawa

20230106
セミナーレポートiTHEMS Biology Seminar by Dr. Katsuhiko Sato on January 5, 2023
In iTHEMS biology seminar on January 5, Katsuhiko Sato (Hokkaido University) talked about a theoretical model of cell migration. First, he gave us the overview about cell migration. The dominant forces for the cell migrations are believed to the hydrostatic pressure in the cell, the contraction force by actomyosins and the frictions. Next, he constructed a mechanical model of the cell migration in an elegant manner. In this mechanical model, the cell migration dynamics is described by the balance between the energy and the dissipation. The dissipation describes the frictions. The energy includes the hydrostatic pressure, the contraction force, bending energy and the surface tension. Then, he introduced the cell polarization into the surface tension. By using this mechanical model, he demonstrated the unidirectional movement and the rotation of the cell cluster. We enjoyed the discussion with Satosan on the detail of the modeling and its result. Thank you very much for a great talk, Satosan! Reported by Hiroshi Yokota

20221220
セミナーレポートDMWG Seminar by Dr. Maria Manuela Saez on December 19, 2022
Please enter the seminar report here!There are many ongoing experiments searching for direct scattering between DM and nuclei all over the world. Of course, the material, location, and detailed setups are different among projects. One of them, the DAMA/LIBRA collaboration has long been reported for the continuous detection of the annual modulation of signals which should be attributed to DM interactions. However, the reports are in tension with all other experiments. In order for testing the origin of the reported signals, we need further investigations with independent experiments. ANDES (Agua Negra Deep Experiment Site) provides us with such an opportunity. The experiment is planned to be built deep underground in the Andes Mountains at the border between Argentina and Chile. It should prove not only the DM interactions, but also various neutrino physics, nuclear astrophysics, and biological topics. The One important feature of the experiment is that it is built in the Southern hemisphere and close to the equator compared to other experiments. We can predict a higher amplitude of the annual modulation signals corresponding to DM interactions with these setups. Also, there are no nearby nuclear power plants hence we can expect a lower neutrino background which means better sensitivity. On the other hand, we might have to be careful about the geoneutrino background at a lower energy regime. The project is now under construction and investigating the best target materials and realistic equipment. It should start operations in not the far future. Stay tuned for various new insights! Reported by Nagisa Hiroshima

20221220
セミナーレポートInformation Theory SG Seminar by Mr. Kohei Yoshimura on December 16, 2022
On December 16th, Mr. Yoshimura gave us a talk about the decomposition of entropy production in stochastic and chemical systems. In the introductory part, he explained the two aspects of entropy production, nonstationarity and breaking of the detailed balance, as well as the strategy to decompose it. He first introduced important concepts such as detailed balance and cycle using an example of a simple Markov jump process. He then generalized the concepts to nonlinear kinetics including chemical reaction network systems. Lastly, he explained how we can decompose entropy production into excess and housekeeping parts, providing explicit simulation results. We are very grateful to him for the wellorganized presentation! Reported by Kyosuke Adachi

20221212
セミナーレポートABBLiTHEMS Joint Astro Seminar by Dr. Ryo Higuchi on November 4, 2022
Telescope Array (TA) and Auger experiments reported anisotropies in the arrival direction of ultrahighenergy cosmic rays (UHECRs). In the current correlation studies between UHECRs and source candidates, the Auger experiment reported a correlation between the flux model of assumed sources and UHECR events and suggested a 10% contribution of starburst galaxies (SBGs) to the anisotropy of UHECRs. However, they do not consider the effect of coherent deflection by the galactic magnetic field (GMF), and they should significantly affect the results of the correlation studies. In this talk, Dr. Ryo Higuchi introduced a current study of UHECR anisotropy and the effect of GMF on them. Reported by Shigehiro Nagataki

20221212
セミナーレポートABBLiTHEMS Joint Astro Seminar by Dr. Hiroki Nagakura on December 9, 2022
Neutrinos are the most mysterious and elusive particles in the standard model of particle physics. They play important roles in corecollapse supernovae and binary neutron star mergers as driving massejection, synthesizing heavy elements including rprocess nuclei, and neutrino signals from these sources. This exhibits the importance of accurate modeling of neutrino radiation field in these phenomena, which will be used to connect neutrino physics to multimessenger astronomy. It has recently been suggested that neutrinoflavor conversion (or neutrinooscillation) can ubiquitously occur in these astrophysical environments, exhibiting the requirement of quantum kinetic treatments in the modeling of neutrino transport. In this seminar, Dr. Hiroki Nagakura gave an overview of the quantum kinetics neutrino transport and then introduced its recent progress, paying a special attention to the connection to astrophysics. Dr. Hiroki Nagakura also presented the latest results of our numerical simulations of collective neutrino oscillations, which can be properly accounted for only by quantum kinetic framework. Reported by Shigehiro Nagataki

20221205
セミナーレポートiTHEMS Math Seminar by Dr. Yosuke Matsuzawa on November 11, 2022
On November 11, there was a math seminar by professor Matsuzawa. He gave an introductory talk on the arithmetic dynamical system. He started from simple and interesting examples to some conjectures. Reported by Keita Mikami

20221205
セミナーレポートMathPhys Seminar by Dr. Christy Koji Kelly on October 14, 2022
On October 14, there was a joint seminar by Christy Koji Kelly. He gave an introductory talk on the rough geometry. Reported by Keita Mikami

20221205
セミナーレポートiTHEMS Math Seminar by Dr. Yusuke Aikawa on November 18, 2022
On November 18th, Yusuke Aikawa, from Information Technology R&D Center, Mitsubishi Electric Corporation, gave a talk in Math Seminar. In the first part of the talk, he made a general introduction to the public key cryptography and its historical development. In particular, he explained that a largescale quantum computer can break today’s public key security systems. In the second part, he explained the recent attempts to create public key systems which are not easily breakable by quantum computers (so called postquantum cryptography), with an emphasis on the methods which use elliptic curves. An elliptic curve is an algebraic curve which admits a group structure, and one can form a cryptography by using this group structure. The speaker also explained his recent joint work on a generalized methods which uses abelian varieties, which are higher dimensional algebraic varieties admitting group structure. Reported by Hiroyasu Miyazaki

20221124
セミナーレポートiTHEMS Biology Seminar by Prof. Zhichao (Chichau) Miao on November 24, 2022
In this week’s biology seminar, we have invited Prof. Zhichao Miao (Guangzhou Laboratory, China) to tell us about “RNAPuzzles  the evaluation and automation of RNA 3D structure”. He introduced the development history and current situation of the RNA 3D structure prediction problem. With agreement from crystallographers, the RNA structures are predicted by various groups before the publication of the crystal structures. Systematic protocols for comparing models and crystal structures are described and analyzed. The technic is becoming routine and accurate. However, we are surprised that even with the great success of AlphaFold for protein structure prediction, the lack of information of RNA structure is still holding back the use of advanced supervised machine learning technics. The RNAPuzzles project is working hard to open the great possibilities in this task. He also presented the results of predicting the viral RNA structures, including the SARSCoV2. We are looking forward to see the further development. In the seminar, we had many insightful questions and discussions. We are very thankful for Prof. Miao’s talk and this great communication opportunity. Reported by Yingying Xu

20221107
セミナーレポートDMWG Seminar by Dr. Oscar Macias on October 28, 2022
Dark matter (DM) is only a part of the mysterious phenomena in our Universe. As our exploration of the Universe proceeds, we frequently meet new mysteries. The Fermi bubble is such an example. FermiLAT founds extended gammaray emissions in the vertical direction from the Galactic Center and the origin is still unknown. Observations in other wavelengths could give some hints about its interpretation. The Saggitarius stellar stream, which is believed to be a dwarf spheroidal galaxy (dSph) being disrupted, seems to overlap with the Fermi Bubble region. Old star populations including millisecond pulsars, which are famous gammaray emitters, can be expected in dSphs. However, the spectrum of millisecond pulsars is different from that of the Fermi Bubble and the interpretation cannot be possible in a straightforward way. Another key ingredient for this consideration is the gas component of the Saggitarius stream. In such environments, inverse Compton emission should contribute to the highenergy regime and gammaray emission should be interpreted with two components. The prediction of this twocomponent model fairly matches the observed properties of the Fermi Bubble. This fact, at this stage, leads to another hint to DM study. Currently, one of the tightest constraints of the DM annihilation crosssection is obtained from gammaray observations of dSphs. When we consider such investigations, usually it is assumed that astrophysical gammarays are subtle enough. However, regarding the fact that the tidally disrupted dSph of Saggitarius emits gamma rays from interactions of baryonic components, we must be careful about the target selection of dSphs for future observations. It is suggested in the talk that the ordering of the promising dSphs for the future gammaray search of DM could be different. Interaction between visible and invisible sectors in our Universe always brings us fruitful insights. We will meet further indications in this era by boosting astrophysical studies. Reported by Nagisa Hiroshima
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