セミナー
625 イベント

Early Formation of Dark Matter Halos
2023年11月24日(金) 14:00  15:15
デリック・ビーティ―・インマン (数理創造プログラム 研究員)
Cosmological observations have led to an extremely precise understanding of the largescale structure of the Universe. A common assumption is to extrapolate largescale properties to smaller scales; however, whether this is correct or not is unknown and many wellmotivated early Universe scenarios predict substantially different structure formation histories. In this seminar I will discuss two scenarios where nonlinear structures form much earlier than is typically assumed. In the first case, the initial fluctuations are enhanced on small scales leading to either primordial black holes clusters or WIMP minihalos right after matterradiation equality. In the second, I will show that an additional attractive dark force leads to structure formation even in the radiation dominated Universe. I will furthermore discuss possible observations of such early structure formation including changes to the cosmic microwave background, dark matter annihilation, and when the first galaxies form.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語

セミナー
Volume complexity of de Sitter bubbles
2023年11月22日(水) 16:00  17:30
Nicolò Zenoni (大阪大学 大学院理学研究科 特任研究員)
Holographic complexity is conjectured to probe the evolution of spacetime. For black holes in antide Sitter (AdS) spacetime the growth rate of complexity approaches a constant value at late times, while in de Sitter (dS) spacetime it diverges at a finite critical time. In this talk, we consider geometries interpolating between AdS and dS. In particular, we discuss the evolution of volume complexity in a class of threedimensional asymptotically antide Sitter geometries including dynamical bubbles of de Sitter in their interior. According to the dynamics of the bubble, complexity qualitatively behaves either as in the AdS black hole or as in the dS case. We conclude with some remarks about the possible dual interpretation.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語

X's Fast and Slow
2023年11月21日(火) 16:00  17:00
トーマス・ヒッチコック (数理創造プログラム 基礎科学特別研究員)
Sex chromosomes have long been suggested to undergo distinct evolutionary dynamics to the rest of the genome. Their distinct ploidy and transmission genetics may result in differing strengths of selection, magnitude of drift, and mutation rates to the autosomes, particularly if there are sex differences. Consequently, a body of theory and empirical work has developed investigating such differences, and how they might manifest in the rates of change between populations, and the diversity observed within populations. I will briefly review the theoretical basis of these comparisons, how we can infer rates of evolutionary change from genetic data, and what we can learn from nonmodel systems, particularly focusing on fungus gnats and pea aphids.
会場: via Zoom
イベント公式言語: 英語

セミナー
Introduction and prospects of topological recursion
2023年11月17日(金) 15:00  17:00
大須賀 けん斗 (東京大学 大学院数理科学研究科 日本学術振興会 特別研究員 PD)
Topological recursion is a universal recursive formalism that connects many branches in mathematical physics, such as enumerative geometry, algebraic geometry, integrable hierarchy, matrix models, 2d gravity, and more. In the first half of this talk, I will give a pedagogical overview of topological recursion and present simple examples from which we learn how topological recursion works. Then in the second half, I will present some ongoing research projects as well as a few future directions in topological recursion.
会場: セミナー室 (359号室)
イベント公式言語: 英語

セミナー
Geometry of special nilpotent orbits
2023年11月15日(水) 14:00  15:30
Baohua Fu (Professor, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, China)
Special nilpotent orbits play a key role in representation theory, but their geometry is little understood. I'll first report a joint work with Yongbin Ruan and Yaoxiong Wen proposing a mirror symmetry conjecture for special nilpotent orbits and then a joint work with Daniel Juteau, Paul Levy and Eric Sommers on the proof of sliced version of Lusztig's conjecture on special pieces.
会場: via Zoom
イベント公式言語: 英語

セミナー
Vortex Reconnection in Classical and Quantum Fluids
2023年11月10日(金) 15:00  16:30
木村 芳文 (名古屋大学 大学院多元数理科学研究科 特任教授)
As a fundamental process in turbulence, vortex reconnection has been studied widely not only in classical fluids but also in quantum fluids. For the latter, the first real observation of vortex reconnection was rather recent, and since then active analyses have been continued. On the other hand, vortex reconnection in the former has a long history, and it is now studied intensively as a candidate for a solution to the problem of the regularity/Singularity of the NavierStokes equations, which is one of the seven millennium prize problems of the Clay Mathematical Institute. In this talk, after introducing the problem, we will present some results of analysis and simulations of the dynamical system which has been proposed to describe a vortex reconnection of two vortex rings located symmetrically on two tilted planes [1], [2], [3]. Then it will be shown that this dynamical system can be written in noncanonical Hamiltonian form with Hamiltonian, H, and a Casimir invariant, C in the limit of zero viscosity [4].
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語

Patterns of fern community assembly throughout the American continent: Do the mechanisms of species diversification also vary with latitude?
2023年11月7日(火) 16:00  17:00
ホセ サイード・グティエレス オルテガ (数理創造プログラム 基礎科学特別研究員)
The global latitudinal gradient of biodiversity, a pattern suggesting that the lowlatitude (tropical) areas have more species than the highlatitude (temperate) areas, represents the most conspicuous pattern of correlation between the environmental/geographic variation and biodiversity distribution. Yet, the relative roles of all ecological, geographic, and historical variables that can explain the gradient are unclear. Specifically, it is because we do not have a clear link between latitude and the underlying mechanisms that originate and extinct species throughout the gradient. In other words, we lack a connection between the “macroevolutionary patterns" and “microevolutionary processes”. I am researching the community assembly of ferns from the American continent, as it seems to be a group that can give some answers to what causes the latitudinal gradient of biodiversity and how the gradient is related to the processes of speciation and extinction. Regarding the community assembly, as expected, I found that the fern community clearly follows the latitudinal gradient: the number of species and localities colonized by ferns decrease with latitude. Also, this pattern is associated to a strong phylogenetic structure: the community at each latitudinal area is dependent of the previously colonizing genera (in other words, genera tend to diversify within specific latitudinal spans; most of them are restricted to the tropics). These results suggest that the fern community from the American continent follows the latitudinal gradient, and that it is a good representer of this pattern. Then, using linear regressions, I tested some classical hypotheses that have been proposed to explain the latitudinal gradient (e.g., that tropical environments, being more thermodynamically active, promote higher speciation rates). However, my results so far, suggest that none of the previously proposed hypotheses give a satisfactory explanation: there is no a single factor that can link the gradient with the processes of speciation or extinction. Rather, my data suggest that to promote speciation, the relative roles of environmental differentiation, geographic isolation, niche divergence, and time since divergence between sister species pairs vary with latitude. For example, to become new species, species near the equator did not need much geographic isolation or niche divergence from their sister counterparts (i.e., near the equator, species pairs tend to be more sympatric and present higher niche overlap). I hope my talk can stimulate some discussion about how to approach and treat the data that I have compiled, and that we can create opportunities for further collaboration.
会場: via Zoom
イベント公式言語: 英語

セミナー
Compact Star Solutions Beyond General Relativity
2023年11月7日(火) 13:30  15:00
沼尻 光太 (名古屋大学 大学院理学研究科 博士課程)
The neutron star solutions have been gathering attention. Their high compactness enables us to observationally access the information about extreme regimes of hadron physics. On the other hand, their strong gravity features bring up another possibility, gravity beyond general relativity (GR). Although GR has been a great success until now, the present scenario for our universe still has several problems, such as dark sectors and the quantum description of gravity. To tackle these problems, the modified gravity theories have been discussed for decades. Their modifications are expected to become noticeable in strong gravity regimes like compact stars. In this talk, I will discuss the configuration of the compact star solution under the F(R) gravity, one of the most popular and simplest modifications of GR. The background hydrostatic solutions are calculated with some F(R) models, which show nontrivial influences from the additional scalar DOF in this theory. The tidal deformation phenomenon is also considered to focus on another observable, tidal deformability. I will comment on how to utilize obtained observables to determine the gravity theory and the unknown equation of state simultaneously.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語

Mathematical modelling of the host response to inhalational anthrax across different scales
2023年10月31日(火) 16:00  17:00
ビバリン・ウイリアムス (Postdoctoral Fellow, School of Mathematics, University of Leeds, UK)
Inhalational anthrax, caused by the bacterium Bacillus anthracis, is a disease with very high fatality rates. Due to the significant risk posed if the bacterium was to be intentionally used as a bioweapon, it is important to be able to defend against such an attack and to make optimal decisions about treatment strategies. Mechanistic mathematical models can help to quantify and improve understanding of the underlying mechanisms of the infection. In this talk, I will present a multiscale mathematical model for the infection dynamics of inhalational anthrax. This approach involves constructing individual models for the intracellular, withinhost, and populationlevel infection dynamics, to define key quantities characterising infection at each level, which can be used to link dynamics across scales. I will begin by introducing a model for the intracellular infection dynamics of B. anthracis, which describes the interaction between B. anthracis spores and host cells. The model can be used to predict the distribution of outcomes from this hostpathogen interaction. For example, it can be used to estimate the number of bacteria released upon rupture of an infected phagocyte, as well as the timing of phagocyte rupture and bacterial release. Next, I will show how these key outputs can be used to connect the intracellular model to a model of the infection at the withinhost scale. The withinhost model aims to provide an overall understanding of the early progression of the infection, and is parametrised with infection data from studies of rabbits and guinea pigs. Furthermore, this model allows the probability of infection and the time to infection to be calculated. Building a model that offers a realistic mechanistic description of these different animal responses to the inhalation of B. anthracis spores is an important step towards eventually extrapolating the model to describe the dynamics of human infection. This would enable predictions of how many individuals would become infected in different exposure scenarios and also on what timescale this would occur.
会場: via Zoom / 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語

セミナー
Searching for dark neutrinos through exotic Higgs decays at the ILC
2023年10月24日(火) 16:30  17:30
Simon Thor (Ph.D. Student, KTH Royal Institute of Technology, Sweden)
In this study we investigate the feasibility of detecting heavy dark neutrinos ($N_d$) through exotic Higgs decays at the proposed International Linear Collider (ILC), specifically in the channel of $e^+ e^ \to qq~ H$ with $H\to \nu N_d \to \nu~lW \to \nu l~qq$. Analyses based on full detector simulations of the ILD are performed at the centerofmass energy of 250 GeV for two different beam polarization schemes with a total integrated luminosity of 2 $\mathrm{ab}^{1}$. A range of dark neutrino masses between the $Z$ boson and Higgs boson masses are studied. The $2\sigma$ significance reach for the joint branching ratio of $BR(H\to\nu N_d)\cdot BR(N_d\to lW)$ is about 0.1\%, nearly independent of the dark neutrino masses, while the $5\sigma$ discovery is possible at a branching ratio of $0.3\%$. Interpreting these results in terms of constraints on the mixing parameters $\varepsilon_{id}^2$ between SM neutrinos and the dark neutrino, it is expected to have a factor of 10 improvement from current constraints.
会場: via Zoom
イベント公式言語: 英語

セミナー
Topological Aspect of Adsorption Site Selectivity on Metal Surfaces
2023年10月24日(火) 13:30  15:00
辻 雄太 (九州大学 総合理工学研究院 准教授)
In this talk, the presenter will discuss which adsorption structure is preferred in the adsorption of atoms and molecules on metal surfaces based on the topology of the adsorption structures. The method of moments is used to analyze the electronic density of states of the surface. The thirdorder moment, which characterizes the skewness of the distribution of the electronic density of states, is related to the topology of the triangles at the adsorption interface. By further relating this to the change in energy of the system with the change in electron occupancy of the states, it is shown that it is possible to discuss the relationship between the type of metal and the topological features of the energetically stable adsorption structure.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語

セミナー
A cluster algebra structure in the quantum cohomology ring of a quiver variety
2023年10月24日(火) 10:00  11:30
Yingchun Zhang (Postdoctoral Researcher, Institute for Advanced Study in Mathematics, Zhejiang University, China)
The GromovWitten theory of a quiver variety is expected to be preserved by quiver mutation according to Seiberg duality, which has been proved to be true for Atype and starshaped quivers. Cluster algebra can be constructed for a given quiver via quiver mutation. The two subjects GromovWitten and cluster algebra seem to differ a lot. Howerver, when we move to the quantum cohomology ring of a quiver variety, BeniniParkZhao’s work “indicates” that there should be a cluster algebra structure in the quantum cohomology ring of the quiver variety. In this talk, I will introduce our recent work about the construction of such a cluster algebra structure in the quantum cohomology of a quiver variety. In particular, we will give a proof of the construction for Atype cluster algebra in quantum cohomology of a flag variety. This is a joint work with Weiqiang He.
会場: セミナー室 (359号室)
イベント公式言語: 英語

Toward inferring the equation of state from gravitationalwave astronomy
2023年10月18日(水) 14:30  16:00
久德 浩太郎 (京都大学 大学院理学研究科 准教授)
The property of supranucleardensity matter is an important question to be answered in QCD. One promising avenue is to study neutron stars with astronomical observations. For this purpose, gravitational waves have become an important tool after GW170817 that delivered information about the matter at a few times the saturation density. If future detectors improve the sensitivity at high frequency, we may be able to investigate the phase structure at further higher density via observations of postmerger gravitational waves or the absence thereof. In this talk, I will review the current understanding of the neutronstar equation of state and then discuss possible future directions based on our binary merger simulation. This seminar is a part of UKAKUREN seminar and jointly held by GWEOS WG in iTHEMS.
会場: via Zoom / セミナー室 (359号室)
イベント公式言語: 英語

セミナー
Population genetics in microchannels
2023年10月17日(火) 16:00  17:00
Anzhelika Koldaeva (沖縄科学技術大学院大学 (OIST) 生物複雑性ユニット 研究員)
Spatial constraints, such as rigid barriers, affect the dynamics of cell populations, potentially altering the course of natural evolution. In this paper, we investigate the population genetics of Escherichia coli proliferating in microchannels with open ends. Our analysis is based on a population model, in which reproducing cells shift entire lanes of cells toward the open ends of the channel. The model predicts that diversity is lost very rapidly within lanes but at a much slower pace among lanes. As a consequence, two mixed, neutral E. coli strains competing in a microchannel must organize into an ordered regular stripe pattern in the course of a few generations. These predictions are in quantitative agreement with our experiments. We also demonstrate that random mutations appearing in the middle of the channel are much more likely to reach fixation than those occurring elsewhere. Our results illustrate fundamental mechanisms of microbial evolution in spatially confined space.
会場: via Zoom
イベント公式言語: 英語

セミナー
Do higherorder interactions promote coexistence in diverse ecological communities?
2023年10月10日(火) 10:00  11:00
Theo Gibbs (Ph.D. Student, LewisSigler Institute for Integrative Genomics, Princeton University, USA)
A central assumption in most ecological models is that the interactions in a community operate only between pairs of species. However, two species may interactively affect the growth of a focal species. Although interactions among three or more species, called higherorder interactions, have the potential to modify our theoretical understanding of coexistence, ecologists lack clear expectations for how these interactions shape community structure. In this talk, I will analyze two different sets of assumptions for how higherorder interactions impact the dynamics of competing species and show that they lead to differing outcomes. When higherorder interactions are sampled from unconstrained probability distributions, they are unlikely to generate widespread coexistence. In fact, using an analytical technique from statistical physics, I will show many — though not all — of the qualitative rules derived for pairwise interactions still apply to the higherorder case. Higherorder interactions that have specific relationships with the underlying pairwise interactions, however, can stabilize coexistence in diverse communities. I will conclude by briefly discussing ongoing experimental work that seeks to determine whether or not the dynamics of annual plant communities are structured by higherorder interactions.
会場: via Zoom
イベント公式言語: 英語

セミナー
Neutrino production in AGN cores: Constraints from Kinetic Plasma Simulations
2023年10月6日(金) 14:00  15:15
Amir Levinson (Professor, Tel Aviv University, Israel)
Accreting black holes power a variety of highenergy astrophysical systems. The activation and mode of operation of these engines has been subject of intensive research. In recent years the structure of the multiflow emanating from the putative, giant black hole in the M87 galaxy was probed down to near horizon scales in unprecedented detail, shedding new light on the physics of accretion and the processes responsible for the formation and dissipation of relativistic jets by the black hole. I shall review recent progress in observational and theoretical studies of accreting black hole engines.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語

セミナー
Progenitors and Explosion Properties of Supernova Remnants Hosting Central Compact Objects
2023年10月6日(金) 10:00  11:30
チェルシー・ブラウン (Ph.D. Student, Department of Physics and Astronomy, University of Manitoba, Canada)
Presented is a systematic, global study of Galactic supernova remnants (SNRs) hosting Central Compact Objects (CCOs) aimed at addressing their explosion properties and supernova progenitors. With the Chandra and XMMNewton telescopes, a spatially resolved Xray spectroscopy study is performed on seven SNRs that show evidence of shockheated ejecta. Using an algorithm, we segmented each SNR in the sample into regions of similar surface brightness. These regions were fit with one or twocomponent plasma shock model(s) in order to separate the forwardshocked interstellar medium from the reverse shockheated ejecta which peak in the Xray bands for elements including O, Ne, Mg, Si, S, Ar, Ca, and Fe. We subsequently derived the explosion properties for each SNR in the sample and found overall low explosion energies (<10^51 erg). To address their progenitor mass, we compare the measured abundances from our spectroscopic modelling to five of the most widely used explosion models and a relatively new electroncapture supernova model. Additionally, we explore degeneracy in the explosion energy and its effects on the progenitor mass estimates. However, no explosion models match all of the measured ejecta abundances for any of the SNRs in our sample. Therefore, we present our best progenitor mass estimates and find overall low progenitor masses (<=25 solar masses) and we highlight the discrepancies between the observed data and the theoretical explosion models.
会場: via Zoom
イベント公式言語: 英語

セミナー
How is hostsymbiont specificity determined? Host’s partnerchoice mechanisms and symbiont’s motility
2023年10月3日(火) 16:00  17:00
菊池 義智 (国立研究開発法人産業技術総合研究所 (AIST) 生物プロセス研究部門北海道センター 研究グループ長)
Microbial symbiosis is omnipresent in animals and plants, playing a crucial role in the evolution of these organisms. While some organisms have developed mechanisms for vertical symbiont transmission, in most cases, these microbial partners are acquired from the surrounding environment, where the enormously diverse microorganisms inhabit. How, then, do these hosts ensure specificity with their symbiotic partners among such diverse environmental microorganisms? And how has this hostsymbiont specificity evolved? We are addressing these questions using the bean bug Riptortus pedestris as our model. The insect acquires Caballeronia insecticola from the soil and symbioses with it in the gut crypts. Recently, we revealed that the entrance to the gut symbiotic organ is a narrow tube, just a few micrometers in diameter, filled with a mucuslike matrix. This constricted region helps the host insect select the symbiotic bacterium from the many other soil microbes. Notably, to pass through the constricted region, Caballeronia shows a unique motility called “drill motility”, where the bacterium wraps its flagella around its body. In this presentation, I will introduce the evolutionary process of both host insects and symbiotic bacteria and will discuss the pivotal role played by bacterial motility in the context of hostsymbiont specificity.
会場: via Zoom
イベント公式言語: 英語

Interactions between Algebraic Topology and Representation Theory by Toric Code
2023年10月2日(月)  4日(水)
ミンキュ・キム (Research Fellow, School of Mathematics, Korea Institute for Advanced Study (KIAS), Republic of Korea)
Toric code is an error correction code designed by Kitaev in late 1990’s, which contributes to the birth of topological quantum computation. The goal of these lectures is to introduce toric code and related mathematics. We will explain an interaction between lowdimensional topology and representation of Drinfeld double. Especially, we will encode several operations (e.g. braidings) on representations into topology and geometry on surfaces. If time allows, we will give an overview of how toric code arises from chain complexes, which will be the prequel of our talk at TokyoSeoul Conference on Oct 6. These lectures will be fundamental and concrete. We hope that the audience are familiar with basic concepts of finite groups and Hopf algebras. These lectures will be held from Oct 2 to Oct 4, each from 13:30 to 15:00, for a total of 3 lectures. Oct 2 (mon) Introduction to toric code. Oct 3 (tue) Introduction to nonabelian toric code. Oct 4 (wed) Further studies on toric code.
会場: via Zoom / セミナー室 (359号室)
イベント公式言語: 英語

セミナー
Response to sounds in the cochlea of the inner ear
2023年9月26日(火) 16:00  17:00
太田 岳 (大阪大学 大学院医学系研究科薬理学講座統合薬理学 助教)
We hear sounds. The acoustic wave passes through the ear canal and oscillates the ear drum. The middle ear bones conduct the mechanical input into the cochlea, the primary sensory organ of hearing. A sensory epithelium, a sheetlike tissue inside the snaillike structure, decomposes the sound frequencies into each component along the coil. The sound stimulation evokes nanometerscale motions in the epithelium which contains hair cells. The cells expose their hair bundles to endolymph, the extracellular solution characterized by high [K+]. The epithelium vibration changes the open probability of mechanosensitive channels on the bundles and modulates the ion entering from the fluid. Inner hair cells release neurotransmitters to the auditory nerves and outer hair cells shrink and elongate their soma depending on the receptor potentials. The electromotive response amplifies the vibration of the sensory epithelium and contributes to the faint sound sensitivity and sharp frequency selectivity. With developed technique, we observed the soundevoked vibrations in the sensory epithelium. In this seminar, I will introduce the physiological background of the cochlear physics and the recent results.
会場: via Zoom
イベント公式言語: 英語
625 イベント
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