セミナーレポート
314 ニュース
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2023-03-27
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 well-prepared, 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 (Gutiérrez-Ortega), sex ratio of offsprings (Hitchcock), and species co-existence/competition (Iritani). This gave rise to many interesting questions, comments and exchanges. We hope to continue conversation. Reported by Catherine Beauchemin
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2023-03-13
セミナーレポート
ABBL-iTHEMS Joint Astro Seminar by Dr. Ellis Owen on March 10, 2023
Ultra high-energy (UHE) cosmic rays (CRs) from distant sources interact with intergalactic radiation fields, leading to their spallation and attenuation through photo-hadronic processes. Their deflection and diffusion in large scale intergalactic magnetic fields (IGMFs), in particular those associated with Mpc-scale 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
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2023-03-07
セミナーレポート
iTHEMS Biology Seminar by Dr. Adrian Gonzalez-Casanova on January 19, 2023
We had the pleasure to have Dr. Adrián González-Casanova (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. González-Casanova 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 Gutiérrez-Ortega
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2023-03-03
セミナーレポートQuantum Matter Seminar by Dr. Yung-Yeh 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 Yung-Yeh Chang, a postdoctoral researcher at the National Center for Theoretical Sciences and National Yang Ming Chiao Tung University in Taiwan. Yung-Yeh 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 time-reversal symmetric superconductor in a class of Kondo lattice materials. The proposed system involves the odd-parity Kondo hybridization, which mediates ferromagnetic spin-spin coupling and leads to spin-triplet resonant-valence-bond (t-RVB) pairing between local moments. The speaker explained that spin-triplet p±p' wave topological superconductivity is reached when the Kondo effect co-exists with t-RVB. By using the mean field theory to generate an effective free fermion (BdG) Hamiltonian, the topological nature was identified by the non-trivial 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 Yung-Yeh 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 Chen-Hsuan Hsu (Academia Sinica, Taiwan) and Ching-Kai Chiu
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2023-02-20
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 well-studied one with its success in large-scale structure formations. However, as studies proceed, some problems arise in such models: observations of small-structure 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 well-described by considering FDM of m~O(1e-20) 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, core-formation time becomes longer. One possible caveat for FDM models is the so-called "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 non-linear 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, GPU-accelerated adaptive mesh code is now being intensively invented. We should see fantastic structures of FDM halos in the near future! Reported by Nagisa Hiroshima
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2023-02-16
セミナーレポート
Quantum Matter Seminar by Dr. Chang Po-Yao on February 9, 2023
Please enter the seminar report here!On February 13, 2023, Assistant Professor Po-Yao Chang of the Department of Physics at National Tsing Hua University in Taiwan gave an online seminar entitled "Entanglement in non-Hermitian quantum systems and non-unitary conformal field theories." In the seminar, Professor Chang began by discussing the motivation for studying non-Hermitian 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 non-Hermitian systems have complex eigenvalues, he focused on systems that preserve parity and time-reversal (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 non-Hermitian 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 non-Hermitian systems and showed how it could be used to correctly obtain the entanglement properties of several non-Hermitian systems, such as the non-Hermitian Su-Schrieffer-Heeger (SSH) model, the q-deformed XXZ model with imaginary boundary terms, and the Affleck-Kennedy-Lieb-Tasaki (AKLT) model, using numerically extracted central charges. In conclusion, Professor Chang's seminar provided valuable insights into the field of entanglement in non-Hermitian quantum systems and non-unitary conformal field theories. The seminar was well-received by the audience, who appreciated the clarity of the presentation and the relevance of the research topic. Reported by Chen-Hsuan Hsu (Academia Sinica, Taiwan) and Ching-Kai Chiu
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2023-02-10
セミナーレポート
Super smash problems workshop 3 on January 25-27, 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 entropy-production 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, machine-learning process, and how universe emerges. Second topic was about phase-separation. The theory of phase-separation has a rich mathematical structure: we explored methods with which we can computationally efficiently construct convex-hull of a given function. Also, because various systems exhibit phase-separation, we discussed the potential for which the method can be applied to other systems, including formation of stars. The three-day 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 Adachi-san’s introductory lecture and subsequent discussion; and of course, Adachi-san 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
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2023-02-06
セミナーレポート
Early Universe Mini-workshop was held on Jan. 31 - Feb. 2, 2023
We held Early Universe Mini-workshop at SUURI-COOL (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 in-depth 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
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2023-01-25
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 iTHEMS-AIP 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
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2023-01-24
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 Seiberg-Witten 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 non-physicists 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 non-mathematician. After reviewing the history of topology, he introduces Donaldson’s theory and Donaldson’s polynomial invariant, and Witten’s field-theoretic interpretation (topological twist of N=2 SUSY Yang-Mills theory) of the invariant. As the low energy effective theory of N=2 SUSY Yang-Mills theory, a family of gauge theories parametrized by so-called u-plane 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 Seiberg-Witten 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
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2023-01-20
セミナーレポート
ABBL-iTHEMS 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 (r-process). 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 r-process happens in the NS merger. However, the abundance pattern synthesized in this event, which is important to understand the origin of the r-process 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
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2023-01-17
セミナーレポート
ABBL-iTHEMS 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 Weibel-mediated shock waves. Shock waves relevant to astrophysical phenomena, such as supernovae and gamma-ray bursts, form via collective plasma processes. In the so-called collision-less 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, semi-analytical Monte Carlo calculations, and ab-initio Particle-In-Cell simulations to tackle this issue in a wide range of shock velocities ranging from relativistic to non-relativistic regimes. In particular, he has introduced a theoretical model that can describe electron heating through the interplay between pitch-angle 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 face-to-face conversation with him. Reported by Hirotaka Ito
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2023-01-16
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
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2023-01-16
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
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2023-01-16
セミナーレポートABBL-iTHEMS 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 highly-magnetized, rapidly-rotating 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 engine-driven supernovae. Reported by Shigehiro Nagataki
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2023-01-16
セミナーレポート
ABBL-iTHEMS 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 r-process nucleosynthesis. However, there is no observational evidence that black hole (BH)-NS mergers are r-process sites. In this talk, Dr Wanajo overviewed the latest work of nucleosynthesis based on long-term hydrodynamics simulations of NS-NS and BH-NS mergers covering early dynamical and late post-merger mass ejections. Dr. Wanajo also briefly discussed a possible constraint on nuclear equations of state. Reported by Shigehiro Nagataki
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2023-01-07
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, Himeoka-san! Reported by Gen Kurosawa
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2023-01-06
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 Sato-san on the detail of the modeling and its result. Thank you very much for a great talk, Sato-san! Reported by Hiroshi Yokota
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2022-12-20
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 geo-neutrino 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
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2022-12-20
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 well-organized presentation! Reported by Kyosuke Adachi
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2022-12-12
セミナーレポート
ABBL-iTHEMS Joint Astro Seminar by Dr. Ryo Higuchi on November 4, 2022
Telescope Array (TA) and Auger experiments reported anisotropies in the arrival direction of ultra-high-energy 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
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2022-12-12
セミナーレポート
ABBL-iTHEMS 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 core-collapse supernovae and binary neutron star mergers as driving mass-ejection, synthesizing heavy elements including r-process 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 multi-messenger astronomy. It has recently been suggested that neutrino-flavor conversion (or neutrino-oscillation) 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
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2022-12-05
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
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2022-12-05
セミナーレポートMath-Phys 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
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2022-12-05
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 large-scale 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 post-quantum 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
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2022-11-24
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 “RNA-Puzzles - 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 RNA-Puzzles 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 SARS-CoV-2. 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
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2022-11-07
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. Fermi-LAT founds extended gamma-ray 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 milli-second pulsars, which are famous gamma-ray emitters, can be expected in dSphs. However, the spectrum of milli-second 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 high-energy regime and gamma-ray emission should be interpreted with two components. The prediction of this two-component 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 cross-section is obtained from gamma-ray observations of dSphs. When we consider such investigations, usually it is assumed that astrophysical gamma-rays 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 gamma-ray 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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2022-10-27
セミナーレポート
iTHEMS Biology Seminar by Dr. Hiroyuki Ebata on October 27, 2022
On October 27th, Dr. Ebata talked about experiments and theoretical modeling of cell migration dynamics. In the introductory part, he explained the relation between fluctuations of the cell shape and migration dynamics, as well as the basics of durotaxis. After reviewing the experimental setups, he showed us the experimental results of cell migration dynamics on hydrogels with heterogeneous stiffness. He constructed models based on symmetry arguments and consistently explained the observed phenomena. We really enjoyed his clear talk with plenty of exciting movies on cell migration. Reported by Kyosuke Adachi
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2022-10-24
セミナーレポート
iTHEMS Theoretical Physics Seminar by Prof. Elisa G.M. Ferreira on October 11, 2022
In her talk, Dr. Elisa Ferreira exploited some of the intriguing models of dark matter (DM), one of the biggest mysteries in cosmology. While there are many different models to explain the nature of this elusive component, she presented a class of dark matter models: ultra-light dark matter (ULDM) or ultra-light axions (ULA). She explained that one of the most interesting features of this class of DM models is that it might condense in the interior of the halos of galaxies forming a Bose-Einstein condensate or superfluid. This interesting quantum phenomena on macroscopic scales, and the wave nature of ULDM leads to different and interesting astrophysical consequences that can be probed on small scales. She first reviewed the fuzzy dark matter model, one of the most well studied ULA models, and then introduced the DM superfluid model. Upon condensation in the interior of galaxies, DM dynamics in this model can represent that of so-called modified Newtonian dynamics on galactic scales. Dr. Ferreira showed the theoretical description of this model and its interesting phenomenology, especially on small scales. Reported by Ryo Namba
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2022-10-24
セミナーレポート
iTHEMS Seminar by Dr. Filippo Anzuini on September 27, 2022
The main focus of Dr. Filippo Anzuini's talk was on axions, which are pseudo-Goldstone bosons that provide a solution to the strong CP problem, and are prominent candidates for dark matter. In neutron stars, it has been shown recently that the potential of the QCD axion acquires finite density corrections that shift the axion field expectation value, which can be large compared to the vanishing expectation value in vacuum. Such a shift leaves an imprint on typical neutron star observables such as the redshifted thermal luminosity, which can be used to constrain the axion parameter space. In his talk, Dr. Anzuini discussed the coupling of axions with photons, which modifies Maxwell’s equations and alters the neutron star magnetic field. By performing state-of-the-art magneto-thermal simulations, he performed his calculations of the axion-induced perturbations to the neutron star’ magnetic field, and showed that they grow on relatively short time-scales. Intense electric currents then lead to enhanced ohmic dissipation, increasing the stars’ observable thermal luminosity. The activation of such mechanisms depends on the axion decay constant and the axion mass. His results indeed opened a new astrophysical avenue to constrain axions, extending significantly the parameter range that can be probed with direct axion searches. Reported by Ryo Namba
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2022-10-24
セミナーレポート
iTHEMS Theoretical Physics Seminar by Dr. Yuko Urakawa on July 27, 2022
In her talk, Prof. Yuko Urakawa discussed the generalized deltaN formalism of cosmological perturbations, which dramatically facilitates a computation of the primordial density perturbation and the primordial gravitational waves. In particular, she addressed a violation of the cosmological principle, namely a violation of the global isotropy in the Universe. A major implication of her study is that measuring the PGWs provides a powerful tool to explore a violation of the global isotropy. Such effects can potentially be searchable by the future space-based CMB polarization mission LiteBIRD. Reported by Ryo Namba
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2022-10-21
セミナーレポート
iTHEMS Biology Seminar by Mr. Keiichi Morita on October 20, 2022
I talked about my research progress about a mathematical model on how interspecific pollen transfer can affect coexistence and evolution of sex allocation. First, analytical results without evolution showed that interspecific pollen transfer had negative impacts on coexistence by preventing fertilization in the other species. Also, asymmetry of sex allocation between species promoted extinction of either species. Second, analytical results with evolution of sex allocation revealed that sex allocation always evolved into one regardless of strength of interspecific pollen transfer. Although my model is very tough to understand, thank you for your listening and giving me comments! Reported by Keiichi Morita
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2022-10-14
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iTHEMS Biology Seminar by Dr. Lazaro-Guevara Jose Miguel on October 6, 2022
On October 6th, 2022, we had the pleasure to have José Miguel Lázaro-Guevara, a postdoctoral researcher at the University of British Columbia, in our Biology seminar. His talk was related to pharmacogenomics. The idea behind the field of pharmacogenomics is that the effectiveness of drugs in medical treatments is partially determined by the genetic variation of patients, but producing genome-wide data for one patient is costly and not affordable for many patients or insurance companies. For these cases, Lázaro-Guevara proposes using an extreme-low coverage genotyping, which consists on sequencing random sections of the genome of on a patient. By doing so, it is possible to later use a background reference (the genome of other genetically related people) to apply an imputation method to infer the parts of the genome that were not directly sequenced. By showing clinical cases on patients from a population from Utah, USA, the extreme-low coverage method seems to be a reliable and effective method to detect associations between genetic variation and the effectiveness of drug treatment. Reported by José Said Gutiérrez-Ortega
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2022-10-13
セミナーレポートiTHEMS Math Seminar by Mr. Hayato Imori on July 25, 2022
On July 25, there was a math seminar by Dr. Hayato Imori. He gave a talk entitled Introduction to instanton knot homology. In the first part of his talk, the speaker explained the fundamental construction of Morse homology for finite dimensional manifolds by giving concrete examples of Morse functions. He then explained how the discussion extends to the case of infinite dimensional manifolds obtained by singular connections. Reported by Masaki Taniguchi
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2022-10-11
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ABBL-iTHEMS Joint Astro Seminar by Dr. Ryo Namba on October 7, 2022
Blazar observations have provided tantalizing evidence for the presence of magnetic fields in the extragalactic regions, where astrophysical processes may not be an efficient source for their generation. While a natural speculation is to associate the production of such large-scale magnetic fields to inflationary physics, it has been known that magnetogenesis solely from inflation is quite challenging. In this talk Dr. Ryo Namba discussed some mechanisms, successful/unsuccessful, for production of magnetic fields in the primordial universe, as well as the constraints from theoretical consistencies and observational data. Reported by Shigehiro Nagataki
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2022-09-26
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ABBL-iTHEMS Joint Astro Seminar by Dr. Filippo Anzuini on September 26, 2022
Neutron stars challenge current models of highly dense matter. Despite being the targets of numerous observational campaigns (e.g. gravitational-wave searches and X-ray observations), their equation of state is still unknown. One of the most exciting possibilities is that “unconventional” particles such as hyperons may appear in neutron star cores. Hyperons have a major impact on the observed thermal luminosity, because they accelerate the cooling rate via direct Urca processes, which copiously increase the neutrino emission from the core. Such mechanism is often considered to be a key signature of hyperon concentrations at high densities. Hyperon superfluidity plays a major role as well, because it can suppress the neutrino emissivity exponentially. The hope is that a comparison of the theoretical cooling curves against the available data of thermally-emitting neutron star can hint towards the existence of hyperons and their superfluidity. There is one ingredient, however, that is often neglected in neutron star cooling models: internal heating. The magnetic field of neutron stars decays due to the dissipation of the electric currents circulating in the crust, generating substantial Joule heating in the shallower layers. The thermal power generated by this process can counterbalance hyperon fast cooling, making it difficult to infer the presence of hyperons from the available thermal luminosity data, and complicating the link between measured thermal emission and internal composition. The speaker showed that this is the case for magnetars, because their crustal temperature is almost independent of hyperon direct Urca cooling in the core, regardless of whether hyperons are superfluid or not. Likewise, thermal luminosity data of moderately magnetized neutron stars are not suitable to extract information about the internal composition, as long as hyperons are superfluid. During/after the talks, there were some interesting questions and discussions. The seminar was done in a hybrid style. Reported by Shigehiro Nagataki
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2022-09-21
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Report of DM3 Workshop on September 15-17, 2022
Please enter the seminar report here!The study of dark matter (DM) has a long history. It starts in the 1930s from the article that Zwicky pointed out the existence of a huge invisible mass in galaxy clusters. We now know that about a quarter of the total energy density of the Universe is occupied by DM. But we still do not understand its nature, even we do not know whether or not it is a particle. We have three kinds of strategies to probe DM so-called collider, direct detection, and indirect detection experiments. By establishing a smooth connection between each other with theoretical support, we should approach a better understanding of DM. With this rationale, the iTHEMS DM working group held an international workshop "DM3- Deep insights and Multiple strategies for Deciphering the Mystery of Dark Matter" during Sep.15-17. The theme of the workshop can be summarized as just a simple question, "what is DM for you?" The workshop was composed of 18 invited talks for reviews of various DM studies and a poster session for individual presentations. The 1st day has been devoted to the discussion about DM search with astrophysical objects. On the 2nd day, we paid much attention to the particle nature of DM. Novel ideas for candidates and techniques to probe a huge parameter space of DM are exhibited. We went through the intersection between cosmic-ray study and DM search on the final day of the workshop. The latest status of the DM study was presented in posters. Throughout the workshop, attendees discussed the nature and probe for DM regarding multiple aspects. According to the follow-up questionnaire, they said that "there are differences between the view before and after the workshop" and "would like to continue studying DM". After the workshop, we reconsider the question again: "what is DM for you?" There have been so many answers to the question till now. Continuing the study of DM, we believe that we see a consensus someday. Reported by Nagisa Hiroshima
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2022-09-16
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ABBL-iTHEMS Joint Astro Seminar by Dr. Naomi Tsuji on September 16, 2022
The MeV gamma-ray domain is the only unexplored window among recent multiwavelength observations in astrophysics, often referred to as the "MeV gap". To fulfill this gap, there are several ongoing and planned projects of MeV gamma-ray telescopes. The measurement of MeV gamma rays (both continuum and line emission) would give us new insight into many topics in astrophysics, such as relativistic jets, particle acceleration, and origin of matter. In advance of the future MeV gamma-ray missions, we have been working on prediction of the MeV gamma-ray sky, which is helpful to determine what kinds of sources can be detectable with the future telescopes. In order to explore the MeV gamma-ray sources, Tsuji-san and her collaborators performed a catalog cross-matching between the hard X-ray (Swift/BAT) and GeV gamma-ray (Fermi/LAT) catalogs, resulting in 145 firmly cross-matched sources. Combined with the Galactic diffuse emission, which is calculated by GALPROP to reconcile the cosmic-ray and gamma-ray spectra with observations by AMS-02, Voyager, and Fermi-LAT, the all-sky maps in the MeV gamma-ray band can be produced. This is also used to investigate a long-standing problem in the MeV gamma-ray astrophysics: the origin of the diffuse emission from the inner Galaxy, measured by COMPTEL. Tsuji-san reported the analysis and results in detail, and introduce future missions of the MeV gamma-ray detectors. There were useful discussions among the speaker and audience during/after the talk. Reported by Shigehiro Nagataki
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2022-09-05
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ABBL-iTHEMS Joint Astro Seminar by Dr. Tomohiko Oka on September 2, 2022
Supernova remnants (SNRs) are believed to be the site of cosmic ray acceleration up to PeV (called PeVatron), but there is no conclusive observational evidence. The possible reason is that only young SNRs (t_age < 1 kyr) can accelerate CRs up to PeV, and then the particles escape at the early stage, thus, the opportunity to observe them is limited. To investigate this scenario, Oka-san and his collaborators observed and analyzed the following two SNRs. First, they focused on SNR G106.3+2.7, the most promising SNR as a PeVatron, since 100 TeV gamma rays have been detected with air shower experiments. With the gamma-ray observation results, they discussed the origin of the PeV CR in the vicinity of this middle-aged SNR (t_age = 5-10 kyr) and then obtained the following interpretation: CRs accelerated at the SNR in the past are illuminating the molecular cloud and producing gamma rays at present. Second, they analyzed the observation data around SNR HB9 and newly found gamma-ray emissions outside the SNR shell at the molecular cloud region. The gamma-ray emission can be explained by the protons accelerated and escaped from the SNR in the past. Therefore, they have attempted to measure the time evolution of the maximum acceleration energy at the SNR by comparing the gamma-ray spectra at the SNR shell and cloud regions. In this seminar, Oka-san reported the analysis results of those two SNRs. Following the seminar talk, we discussed about the SNRs and high-energy gamma-rays from them. Reported by Shigehiro Nagataki
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2022-09-05
セミナーレポート
iTHEMS-RNC Meson Science Lab. Joint Seminar by Dr. Natsuki Tomida on August 26, 2022
Natsuki Tomida (SACRA, Kyoto Univ.) gave a hybrid talk on her experimental research on the bound eta'-meson in nuclei. This is related to the topic "Mesons in Nuclei" which is one of the central subjects in modern hadron physics. Both experimentalists and theorists from Nishina Center and iTHEMS joined the seminar, and there was a hot discussion on this interesting topic. Natsuki joined iTHEMS on Aug.1, 2022 as a visiting scientist to promote collaboration between SACRA's MACS program at Kyoto Univ. and RIKEN iTHEMS. On Sept. 20-21, 2022, she will visit iTHEMS again together with 11 undergraduate and graduate students of Kyoto University. Reported by Tetsuo Hatsuda
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2022-09-02
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iTHEMS Biology Seminar by Dr. Hiroshi Yokota on September 1, 2022
In the iTHEMS biology seminar on September 1st, I, Hiroshi Yokota, talked about a theoretical model of chromosome condensation based on Langevin simulation. In this model, the twist and the writhe structures on biopolymer is quantified in a computational manner. In this seminar, I enjoyed the discussion with audiences on the computational method and the definition of the twist and the writhe. Thank you so much! Reported by Hiroshi Yokota
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2022-08-26
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ABBL-iTHEMS Joint Astro Seminar by Dr. Yosuke Mizuno on August 26, 2022
Dr. Yosuke Mizuno presented the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength 1.3 mm. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of ~50 micro-arcsecond. Using a large suite of numerical simulations, The EHT group demonstrated that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass ∼4 million solar mass, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Their model comparisons disfavor scenarios where the black hole is viewed at high inclination (i > 50 deg), as well as non-spinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way. In the seminar, Dr. Yosuke Mizuno focused on more theoretical interpretation and model comparison to understand the accretion flow properties nearby Sgr A*. Reported by Shigehiro Nagataki
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2022-08-08
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iTHEMS Math Seminar by Prof. Narutaka Ozawa on August 2, 2022
On August 2, Professor Narutaka Ozawa (RIMS, Kyoto University) gave a talk entitled "Product Replacement Algorithm, Semidefinite Programming, and Operator Algebras" in the iTHEMS Math Seminar. He elegantly explained how his recent study on Kazhdan's property (T) ties the field of functional analysis/operator algebras and that of computer sciences. Reported by Michiya Mori
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2022-08-05
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iTHEMS Math Seminar by Dr. Hokuto Konno on July 15, 2022
On July 15, there was a math seminar by Professor Konno. He gave an introductory talk on the Seiberg-Witten Floer homotopy type. Reported by Keita Mikami
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2022-08-04
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Seminar by Dr. Xavier Roca-Maza on August 3, 2022
As a part of the RCNP domestic workshop on low-energy nuclear physics and high-energy astrophysics (RCNP研究会「低エネルギー核物理と高エネルギー天文学で読み解く中性子星」), the special seminar entitled "How does subatomic matter organize itself? A low-energy nuclear physics perspective" was given by Prof. Xavier Roca-Maza in U. Milan. This seminar is supported by Gravitational Wave and Equation of State Working Group (GW-EOS WG), RIKEN iTHEMS Program. The equation of state (EoS) of nuclear matter is one of the essential things in nuclear physics. There have been many attempts to determine parameters characterizing the EoS experimentally, which have become paid attention more. He introduced various attempts and theoretical mechanisms, including cutting-edge proposals. More than 80 participants attended the seminar, including from the foreign country. Reported by Tomoya Naito
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2022-07-29
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iTHEMS Colloquium by Prof. Yasunori Nomura on July 26, 2022
Prof. Yasunori Nomura, the director of the Berkeley Center for Theoretical Physics, the University of California, Berkeley, visited iTHEMS and gave a colloquium entitled “From the Black Hole Conundrum to the Structure of Quantum Gravity” on July 26th. Prof. Nomura started the colloquium by explaining that the two pillars of modern physics, quantum mechanics and general relativity are actually at odds with each other, but each of them usually governs a different domain of physical phenomena, thus obscuring the incompatibility. The focus of the colloquium lies on one of the areas where both quantum mechanics and general relativity become equally important, namely quantum theory of black holes. Prof. Nomura illustrated how the famous phenomenon of black holes discovered by Stephen Hawking, Hawking radiation leads to so-called information paradox, in which the conservation the probability appears to be violated during the process of the radiation from the horizon. He went on to describe the key ingredients in solving the paradox, which are the concept of holography, the stretched horizon, and AdS/CFT correspondence. In the latter part of the colloquium, Prof. Nomura pedagogically showed the audience the most recent development in the study of the information paradox. The calculation including the contribution from “wormholes” was shown to reproduce the Page curve implying the recovery of the lost probability. The same calculation was also explained through formalism which was developed by Prof. Nomura himself. He concluded with the message that the study of the black hole conundrum is thus revealing the structure of quantum gravity, which involves with a wide range of various research fields such as high energy physics and astrophysics, quantum information science, and many-body physics. The colloquium was taken place at the 2F Large Meeting Room of RIBF Building and was attended by a limited number of audience in person due to the wide spreading of COVID-19, but more than eighty people joined through zoom. Reported by Tsukasa Tada
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2022-07-25
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iTHEMS Biology Seminar by Dr. Namiko Mitarai on July 7, 2022
Dr. Namiko Mitarai (Niels Bohr Institute) gave us an amazing talk in the biology seminar. She told us about the collaborative works with experimental biologists on a microbial world. Some viruses that infect bacteria are known to provide immunity to infection by the same virus. According to her, no-immune bacteria can be protected from infection when the ratio of immune bacteria is substantially high in the population, which reminds us of our current cases for Covid-19. Interestingly, the metabolic state of host (bacteria) also affects the virus infection. The talk was very very exciting. In the end of her seminar, she also showed us the tips for the successful collaboration with experimental biologists: (1) We (theorists) should care about them. (2) They (experimental biologists) should care about us. During and after the talk, there were lively discussion between the speaker and iTHEMS researchers. Thanks Mitarai-san!! Reported by Gen Kurosawa
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2022-07-15
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iTHEMS Biology Seminar by Dr. Jun-nosuke Teramae on July 14, 2022
In this week’s biology seminar, we were very happy to have Dr. Jun-nosuke Teramae from Kyoto University to tell us about the mysterious stochastic behavior of neurons and synapses in the brain. Many biological experimental observations are reported. However, how this stochasticity is beneficial for computation and learning in the brain remains largely unknown. Dr. Teramae presented his work on developing an efficient learning algorithm inspired by this brain behavior. The algorithm is based on Gibbs-sampling which allow us to efficiently obtain high-dimensional sampling results. The algorithm shows similar stochastic behavior of the brain, which other machine leaning algorithms doesn’t show. In the end, Dr. Teramae briefly showed us the algorithm enables us to reproduce the recently discovered efficient power-law coding in the cortex. Even the seminar time is ended, the discussion continued for a long while. The seminar inspired many open questions on brain behavior and learning algorithms, both for the speaker and the audiences. We look forward to further development on the subjects. We thank Dr. Jun-nosuke Teramae and everyone joined the seminar. Reported by Yingying Xu
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2022-07-15
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Quantum Matter Seminar by Dr. Ken Shiozaki on July 12, 2022
Prof. Ken Shiozaki gave a seminar about adiabatic cycles of quantum spin systems. Topological phases of matter without ground state degeneracy are known as inevitable phases. In the literature, their topological properties have been well-studied in free-fermion and many-body systems. The speaker started with the transverse-field Ising model and the Rice-Mele model to demonstrate the pumping of the 1D chain in an adiabatic cycle. He then generalized the concept to cover broader systems, including general spatial dimensions and generic models with any onsite symmetry, such as time-reversal, Z2 Ising, and U(1). He demonstrated that one can classify adiabatic cycles of a spin model, which can be characterized by a Z2 topological invariant. This talk showed that symmetry-protected topological phases emerge by performing an adiabatic cycle. Reported by Chen-Hsuan Hsu (YITP, Kyoto University)
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2022-07-13
セミナーレポートiTHEMS Theoretical Physics Seminar by Prof. Hiroshi Suzuki on July 5, 2022
The iTHEMS-phys intensive lecture was held on July 5 and 6, 2022. The speaker is Prof. Hiroshi Suzuki at Kyushu University. The title is “Gradient flow exact renormalization group.” Wilson’s exact renormalization group (ERG), which tells how a system changes under the scale transformation, provides a fundamental framework to define quantum field theory even beyond the perturbation theory. It has, however, been known that it is difficult to preserve a manifest gauge symmetry in ERG because of the usage of the momentum cutoff in ERG. Recently, he has proposed a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gauge-covariant diffusion equation. He has explained the basic idea and properties of GFERG. He has also presented a possible application of GFERG to the consideration of the axial anomaly. The lecture was held via Zoom. There were about 30 participants from iTHEMS and other universities. The participants enjoyed fruitful discussions throughout the lecture. Reported by Kengo Kikuchi
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