Seminar Report
307 news

20230206
Seminar ReportEarly 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
Seminar ReportiTHEMS 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
Seminar ReportiTHEMS 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
Seminar ReportABBLiTHEMS 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
Seminar ReportABBLiTHEMS 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
Seminar ReportiTHEMS 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
Seminar ReportiTHEMS 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
Seminar ReportABBLiTHEMS 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
Seminar ReportABBLiTHEMS 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
Seminar ReportiTHEMS 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
Seminar ReportiTHEMS 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
Seminar ReportDMWG 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
Seminar ReportInformation 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
Seminar ReportABBLiTHEMS 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
Seminar ReportABBLiTHEMS 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
Seminar ReportiTHEMS 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
Seminar ReportMathPhys 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
Seminar ReportiTHEMS 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
Seminar ReportiTHEMS 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
Seminar ReportDMWG 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

20221027
Seminar ReportiTHEMS 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

20221024
Seminar ReportiTHEMS 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: ultralight dark matter (ULDM) or ultralight 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 BoseEinstein 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 socalled 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

20221024
Seminar ReportiTHEMS Seminar by Dr. Filippo Anzuini on September 27, 2022
The main focus of Dr. Filippo Anzuini's talk was on axions, which are pseudoGoldstone 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 stateoftheart magnetothermal simulations, he performed his calculations of the axioninduced perturbations to the neutron star’ magnetic field, and showed that they grow on relatively short timescales. 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

20221024
Seminar ReportiTHEMS 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 spacebased CMB polarization mission LiteBIRD. Reported by Ryo Namba

20221021
Seminar ReportiTHEMS 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

20221014
Seminar ReportiTHEMS Biology Seminar by Dr. LazaroGuevara Jose Miguel on October 6, 2022
On October 6th, 2022, we had the pleasure to have José Miguel LázaroGuevara, 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 genomewide data for one patient is costly and not affordable for many patients or insurance companies. For these cases, LázaroGuevara proposes using an extremelow 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 extremelow 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 GutiérrezOrtega

20221013
Seminar ReportiTHEMS 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

20221011
Seminar ReportABBLiTHEMS 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 largescale 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

20220926
Seminar ReportABBLiTHEMS 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. gravitationalwave searches and Xray 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 thermallyemitting 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

20220921
Seminar ReportReport of DM3 Workshop on September 1517, 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 socalled 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.1517. 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 cosmicray 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 followup 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

20220916
Seminar ReportABBLiTHEMS Joint Astro Seminar by Dr. Naomi Tsuji on September 16, 2022
The MeV gammaray 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 gammaray 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 gammaray missions, we have been working on prediction of the MeV gammaray sky, which is helpful to determine what kinds of sources can be detectable with the future telescopes. In order to explore the MeV gammaray sources, Tsujisan and her collaborators performed a catalog crossmatching between the hard Xray (Swift/BAT) and GeV gammaray (Fermi/LAT) catalogs, resulting in 145 firmly crossmatched sources. Combined with the Galactic diffuse emission, which is calculated by GALPROP to reconcile the cosmicray and gammaray spectra with observations by AMS02, Voyager, and FermiLAT, the allsky maps in the MeV gammaray band can be produced. This is also used to investigate a longstanding problem in the MeV gammaray astrophysics: the origin of the diffuse emission from the inner Galaxy, measured by COMPTEL. Tsujisan reported the analysis and results in detail, and introduce future missions of the MeV gammaray detectors. There were useful discussions among the speaker and audience during/after the talk. Reported by Shigehiro Nagataki

20220905
Seminar ReportABBLiTHEMS 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, Okasan 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 gammaray observation results, they discussed the origin of the PeV CR in the vicinity of this middleaged SNR (t_age = 510 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 gammaray emissions outside the SNR shell at the molecular cloud region. The gammaray 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 gammaray spectra at the SNR shell and cloud regions. In this seminar, Okasan reported the analysis results of those two SNRs. Following the seminar talk, we discussed about the SNRs and highenergy gammarays from them. Reported by Shigehiro Nagataki

20220905
Seminar ReportiTHEMSRNC 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. 2021, 2022, she will visit iTHEMS again together with 11 undergraduate and graduate students of Kyoto University. Reported by Tetsuo Hatsuda

20220902
Seminar ReportiTHEMS 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

20220826
Seminar ReportABBLiTHEMS 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 microarcsecond. 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 propermotion studies. Their model comparisons disfavor scenarios where the black hole is viewed at high inclination (i > 50 deg), as well as nonspinning 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

20220808
Seminar ReportiTHEMS 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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Seminar ReportiTHEMS 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 SeibergWitten Floer homotopy type. Reported by Keita Mikami

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Seminar ReportSeminar by Dr. Xavier RocaMaza on August 3, 2022
As a part of the RCNP domestic workshop on lowenergy nuclear physics and highenergy 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 lowenergy nuclear physics perspective" was given by Prof. Xavier RocaMaza in U. Milan. This seminar is supported by Gravitational Wave and Equation of State Working Group (GWEOS 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 cuttingedge proposals. More than 80 participants attended the seminar, including from the foreign country. Reported by Tomoya Naito

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Seminar ReportiTHEMS 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 socalled 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 manybody 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 COVID19, but more than eighty people joined through zoom. Reported by Tsukasa Tada

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Seminar ReportiTHEMS 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, noimmune 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 Covid19. 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 Mitaraisan!! Reported by Gen Kurosawa

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Seminar ReportiTHEMS Biology Seminar by Dr. Junnosuke Teramae on July 14, 2022
In this week’s biology seminar, we were very happy to have Dr. Junnosuke 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 Gibbssampling which allow us to efficiently obtain highdimensional 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 powerlaw 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. Junnosuke Teramae and everyone joined the seminar. Reported by Yingying Xu

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Seminar ReportQuantum 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 wellstudied in freefermion and manybody systems. The speaker started with the transversefield Ising model and the RiceMele 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 timereversal, 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 symmetryprotected topological phases emerge by performing an adiabatic cycle. Reported by ChenHsuan Hsu (YITP, Kyoto University)

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Seminar ReportiTHEMS Theoretical Physics Seminar by Prof. Hiroshi Suzuki on July 5, 2022
The iTHEMSphys 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 gaugecovariant 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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Seminar ReportiTHEMS Biology Seminar by Mr. Keiichi Morita on June 23, 2022
I talk about how evolution of sexual traits such as ornaments of guppies can affect coexistence of two closely related species. First, I introduce "reproductive interference," sexual interaction driving evolution of sexual traits. Second, I show how to formulate population dynamics of two closely related species with reproductive interference. Next, I introduce mathematical modeling of quantitative genetics in order to formulate trait evolution. Finally, I show results of analysis and simulation by combining population dynamics and evolution (i.e., ecoevolutionary feedbacks). In future works, I should the effect of costs of evolution or the other species. Thank you for your listening and giving me comments! Reported by Keiichi Morita

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Seminar ReportQuantum Matter Seminar by Dr. Thore Posske on June 30, 2022
Dr. Thore Posske from the University of Hamburg gave an online seminar about controlling topological quantum effect in spin systems by manipulating the boundary. He first introduced the idea that topology can connect multiple subfields in physics and then showed how a 1D spin chain can be controlled to form a helix or the ground state by manipulating the evolution of the two chain ends. Since the different quantum states can be controlled by the boundary, this is a potential platform for quantum computing to generate distinct quantum states. Furthermore, the boundary idea was extended to 2D spin systems. By properly changing the spins on the edges, a skyrmion can emerge. In the end, the speaker talked about an experimental approach to distinguishing the topological phases in systems with periodic boundary conditions by multipulse spectroscopy, and applied these ideas to 1D topological superconductors. Reported by Thore Posske (University of Hamburg) and ChingKai Chiu

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Seminar ReportABBLiTHEMS Joint Astro Seminar by Mr. Tomoki Matsuoka on July 1, 2022
Mr. Tomoki Matsuoka gave an excellent talk on the longterm evolution of a supernova remnant hosting a double neutron star binary. He presented that stellar mass loss is one of the crucial elements determining the fate of corecollapse supernovae progenitors (SNe). Since the material released from the progenitor will be distributed as circumstellar medium (CSM), it can also influence the subsequent evolution of the SN or supernova remnant (SNR). Despite its importance, mass loss histories predicted by stellar evolution models have not been incorporated with modeling for SNRs. As a first step, he investigated the dynamical evolution of an ultrastripped supernova remnant (USSNR), which originated from a corecollapse SN explosion proposed to be a candidate formation site of a double neutron star binary. By accounting for the massloss history of the progenitor binary using a model developed by a previous study, he constructed the largescale structure of the CSM up to a radius ∼100 pc. Then, he simulated the explosion and subsequent evolution of a USSN surrounded by such a CSM environment. He found that the CSM encompasses a vast region characterized by a hot plasma with a temperature ∼10^8 K located around the termination shock of the wind from the progenitor binary (∼10 pc), and the USSNR blast wave is drastically weakened while penetrating through this hot plasma. Radio continuum emission from a young USSNR is sufficiently bright to be detectable if it inhabits our galaxy but faint compared to the observed Galactic SNRs. In this seminar, he talked about the background of the connection between the models for stellar evolution and SNRs, the details of his methods, and future prospects very well. Reported by Shigehiro Nagataki

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Seminar ReportiTHEMS Biology Seminar by Dr. Margie Mayfield on June 30, 2022
Dr. Margie Mayfield (University of Melbourne) gave us a fantastic talk in the special biology seminar, held in a hybrid style at Okouchi Hall. She told us about comparative work on theoretical models and data in wild flowers. We really thank Margie on her great talk, especially despite her very tight schedule in Japan. Thank you Margie! I look forward to seeing you soon in person! Reported by Ryosuke Iritani

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Seminar ReportiTHEMS Math Seminar by Dr. Shou Yoshikawa on June 10, 2022
On June 10, Shou Yoshikawa gave an introductory talk on his research field. He started his talk by explaining what is an algebraic geometry in mixed characteristic. He then explained some recent results on this subject. Reported by Keita Mikami

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Seminar ReportQuantum Matter Seminar by Dr. Nobuyuki Okuma on June 21, 2022
Quantum Matter Study Group invited Prof. Nobuyuki Okuma to give an online seminar about nonHermitian topological phases. The seminar started with a succinct introduction to nonHermitian matrices. Different from Hermitian systems, the energy spectra now become complex numbers, the bra and ket states become inequivalent, and the Hamiltonians are not always diagonalizable, leading to the emergence of exceptional points. Taking the HatanoNelson model as an example, the speaker studied the 1D chain with the imaginary gauge transformation and showed that the spectra strongly depend on the boundary conditions (being periodic or open). Furthermore, distinct from end modes in Hermitian topological insulators, skin effect arises in nonHermitian systems, with skin modes accumulating in one end of the chain. He further showed that this skin effect also exhibits topological nature and can be generalized to either higherdimensional systems or to other nonHermitian systems with Z2 topological invariants. Reported by ChenHsuan Hsu (YITP) and ChingKai Chiu

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Seminar ReportiTHEMS Biology Seminar by Dr. Mitsusuke Tarama on June 16, 2022
On June 16th, Dr. Tarama gave us an interesting talk about the physical modeling of selforganization in the chick embryo. He first introduced several beautiful patterns in biology such as stripes of pigment cells of Zebrafish. He then explained a recent observation of the dynamical meshwork structure of chick mesodermal cells, which is the direct motivation of his theoretical work. He showed how the intercellular interactions and shape deformation of cells can produce the dynamical meshwork structure, by physical modeling and application of the persistent homology as a useful tool. We are really grateful to Dr. Tarama for his comprehensive talk from both experimental and theoretical sides. Reported by Kyosuke Adachi
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