セミナー

Long-term evolution of a supernova remnant hosting a double neutron star binary

2022年7月1日(金) 14:00 - 15:00

松岡 知紀 (京都大学 大学院理学研究科 博士課程)

Stellar mass loss is one of the crucial elements which determine the fate of progenitors of core-collapse supernovae (SNe). Since the material released from the progenitor will be distributed as circumstellar medium (CSM), it can also have an influence on 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, we investigate the dynamical evolution of an ultra-stripped supernova remnant (USSNR), originated from a type of core-collapse SN explosion proposed to be a candidate formation site of a double neutron star binary. By accounting for the mass-loss history of the progenitor binary using a model developed by a previous study, we construct the large-scale structure of the CSM up to a radius ∼100 pc, and simulate the explosion and subsequent evolution of a USSN surrounded by such a CSM environment. We find that the CSM encompasses an extended 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 I will talk about the background of the connection between the models for stellar evolution and SNRs, the details of our methods, and future prospects.

会場: via Zoom

イベント公式言語: 英語

Topological quantum effects in low-dimensional spin systems - The power of the boundary

2022年6月30日(木) 17:00 - 18:15

Thore Posske (Group Leader, I. Institute for Theoretical Physics, University of Hamburg, Germany)

Manipulating the boundary of low-dimensional magnetic structures could grant control about topological magnetic quantum sates. I will discuss the creation of one- and two-dimensional topological quantum magnets by manipulating the boundary magnetization, address their stability against external perturbations, and discuss their possible application to quantum information processing.

会場: via Zoom

イベント公式言語: 英語

Predicting local patterns of diversity: coexistence models, networks and wildflowers

2022年6月30日(木) 10:00 - 11:30

Margie Mayfield (Professor, University of Melbourne, Australia)

The question of how species coexist in diverse natural communities has challenged ecologists for generations. Theoretical models of species coexistence have been developed, but primarily as proof of concept for specific coexistence theories. These theories and associated models focus on coexistence between species pairs and ignore the great complexity of interactions found in most natural systems. Though useful for advancing ecological theory, these models are often of limited use for understanding and predicting diversity in real natural communities. In this talk, I explore the three main assumptions made by coexistence models developed under the framework of Modern Coexistence Theory (MCT): that only direct competition is important, that demographic variation is noise, not valuable biological information, and that only the average environment matters. Using Bayesian statistical approaches with population growth models applied to field data from the annual plant communities of the York gum woodlands of SW Western Australia, I illustrate the issues with these assumptions in predicting coexistence in diverse systems. I show how these Bayesian approaches to MCT can improve on frequentist approaches and discuss the potential value of interaction networks for studying coexistence dynamics in diverse natural systems.

会場: 大河内記念ホール (メイン会場) / via Zoom

イベント公式言語: 英語

Mathematical modeling of understanding how adaptive evolution of sexual traits can affect coexistence

2022年6月23日(木) 16:00 - 17:00

森田 慶一 (総合研究大学院大学 先導科学研究科 生命共生体進化学専攻 博士課程)

One of the challenges in ecology is understanding the processes of species coexistence. Recent studies have underlined the importance of the interaction between rapid adaptation and population dynamics (i.e., eco-evolutionary feedbacks) in coexistence. Reproductive interference may reduce population growth rate due to costs of hybridization by incomplete recognition of sexual traits such as ornaments and songs in birds. Recent theoretical studies have suggested that eco-evolutionary feedbacks in sexual traits can affect coexistence. I will present mathematical modeling for investigating how reproductive interference can affect coexistence. Furthermore, I will present an analytical method, adaptive dynamics for understanding how evolution of sexual traits can affect coexistence.

会場: via Zoom

イベント公式言語: 英語

Dress code for infrared safe S-matrix in QED

2022年6月22日(水) 13:30 - 15:00

杉下 宗太郎 (名古屋大学 高等研究院 (IAR) 特任助教)

We consider the infrared (IR) aspects of the gauge invariant S-matrix in QED. I will review the problem of IR divergences in QED, and introduce the dressed state formalism to obtain IR-safe S-matrix elements. I will show a condition for dressed states to obtain IR-safe S-matrix elements, and explain that this condition can be interpreted as the memory effect and is related to asymptotic symmetry. I also explain that IR divergences are necessary to prohibit the violation of asymptotic symmetry. We also argue that the difference between dressed and undressed states can be observed, even if we are able to observe an inclusive cross-section summing over soft photons.

会場: コモンルーム 246-248号室 とZoomのハイブリッド開催

イベント公式言語: 英語

Topological aspects of non-Hermitian physics

2022年6月21日(火) 16:00 - 17:15

大熊 信之 (京都大学 基礎物理学研究所 助教)

The past decades have witnessed an explosion of interest in topological materials, and a lot of mathematical concepts have been introduced in condensed matter physics. Among them, the bulk-boundary correspondence is the central topic in topological physics, which has inspired researchers to focus on boundary physics. Recently, the concepts of topological phases have been extended to non-Hermitian Hamiltonians, whose eigenvalues can be complex. Besides the topology, non-Hermiticity can also cause a boundary phenomenon called the non-Hermitian skin effect, which is an extreme sensitivity of the spectrum to the boundary condition. In this talk, I will explain recent developments in non-Hermitian topological physics by focusing mainly on the boundary problem. As well as the competition between non-Hermitian and topological boundary phenomena, I will discuss the topological nature inherent in non-Hermiticity itself. Field: condensed matter physics Keywords: topological materials, non-Hermitian systems, skin effect, bulk-boundary correspondence

会場: via Zoom

イベント公式言語: 英語

Self-organisation of a dynamic meshwork structure in the mesoderm during the development of a chick embryo and its characterisation using persistent homology

2022年6月16日(木) 16:00 - 17:00

多羅間 充輔 (理化学研究所 生命機能科学研究センター (BDR) フィジカルバイオロジー研究チーム 研究員)

Morphogenesis is a fundamental process of development. Appropriate morphogenesis of tissues is achieved by coordinated motion of individual cells. To elucidate the mechanism behind this self-organisation of cells, one needs to develop a theoretical model based on experimental observations. In our recent study, our experimental colleague found that the mesoderm cells in early chick embryo organise into a meshwork structure, which changes dynamically. To understand the mechanism behind this dynamic meshwork structure formation, we developed an agent-based mechanical model of cells that interact through a short-range attractive interaction. To compare the simulation results with the experiment, we utilized persistent homology, a method of topological data analysis that allows to systematically characterise irregular structures. In this seminar, we will talk about the mechanical mechanism behind the mesoderm structure formation during the development of the early chick embryo, and how the persistent homology analysis is applied to our biological system.

会場: via Zoom

イベント公式言語: 英語

Implications of singularity theorem for non-singular universe

2022年6月16日(木) 13:30 - 15:00

吉田 大介 (名古屋大学 大学院多元数理科学研究科 特任助教)

The singularity theorem by Penrose shows that a spacetime singularity arises in certain universal situations. The existence of a spacetime singularity is thought to represent a breakdown in the validity of theories such as general relativity and the phenomenological models of the universe. Thus, if we could build a correct model that describes the beginning of the universe, the universe predicted by that model should be non-singular. In this talk, we will discuss general properties that a non-singular universe must satisfy in order to avoid the singularity theorem. In particular, we will see that the universe must be, in some sense, smaller than the corresponding closed de Sitter spacetime.

会場: コモンルーム 246-248号室 とZoomのハイブリッド開催

イベント公式言語: 英語

Non-Abelian vortices in two-flavor dense QCD

2022年6月15日(水) 13:30 - 15:00

藤本 悠輝 (Postdoctoral Scholars, Department of Physics, University of Washington, USA)

Recently, the phase of the two-flavor quark matter with the new pattern of color superconductivity was proposed so that the continuous crossover from the hadronic to the quark phase is realized [1]; it is in consonance with the recent observation of neutron stars. In this talk, I will show the classification of the topological vortices in this phase. We found that the stable vortices are what we call the "non-Abelian Alice strings" [2]. They are superfluid vortices carrying 1/3 quantized circulation and color magnetic fluxes. I will discuss their properties in comparison to the well-established CFL vortices in three-flavor symmetric setup, by putting some emphasis on their peculiarity: the non-Abelian generalization of the Alice property. I will then discuss in detail the possibility that these vortices are confined as well as how the vortices in the quark phase can be connected to those in the hadronic phase [3]. [1] Y. Fujimoto, K. Fukushima, W. Weise, PRD 101, 094009 (2020) [1908.09360]. [2] Y. Fujimoto, M. Nitta, PRD 103, 054002 (2021) [2011.09947]; JHEP 09 (2021) 192 [2103.15185]. [3] Y. Fujimoto, M. Nitta, PRD 103, 114003 (2021) [2102.12928].

会場: via Zoom

イベント公式言語: 英語

Introduction to Topological Insulators: The Ten-fold Classification of Topological Insulators and Superconductors Part.2

2022年6月13日(月) 14:00 - 15:30

邱 靖凱 (理化学研究所 数理創造プログラム (iTHEMS) 上級研究員)

会場: via Zoom

イベント公式言語: 英語

Algebraic geometry in mixed characteristic

2022年6月10日(金) 14:00 - 16:30

吉川 翔 (理化学研究所 数理創造プログラム (iTHEMS) 基礎科学特別研究員)

In algebraic geometry, we study the geometry of algebraic varieties, which are sets defined by algebraic equations. There are two types of algebraic varieties, they are varieties over characteristic zero and varieties over positive characteristic. Algebraic geometry in characteristic zero is similar to analytic geometry, so it is related to many other subjects. In this talk, I will introduce the notion of algebraic geometry in positive characteristic and relationships between positive characteristic and characteristic zero. In order to study it, we consider families consisting of varieties over characteristic zero and varieties over positive characteristic, called mixed characteristic.

会場: コモンルーム 246-248号室 とZoomのハイブリッド開催

イベント公式言語: 英語

Mathematical Model on Evolution of Self-sustained Circadian Rhythms

2022年6月9日(木) 16:00 - 17:00

関 元秀 (九州大学 大学院芸術工学研究院 未来共生デザイン部門 助教)

Self-sustained oscillation is a fundamental property of circadian clocks found in many organisms. However, evolutionary advantage of the self-sustainability has been only speculatively discussed. In this seminar, I will present a simulation result of our mathematical model indicating that seasonality facilitates the evolution of the self-sustained circadian clock, which was consistent with empirical records.

会場: via Zoom

イベント公式言語: 英語

Cosmological phenomena with sterile neutrino

2022年6月6日(月) 16:30 - 18:00

永島 伸多郎 (東京大学 宇宙線研究所 (ICRR) 博士研究員)

イベント公式言語: 英語

Core-collapse Supernova Models with Heavy Axion-like Particles

2022年6月3日(金) 14:00 - 15:00

森 寛治 (福岡大学 基盤研究機関 爆発天体研究所)

Axion-like particles (ALPs) are a class of hypothetical bosons which feebly interact with ordinary matter. The hot plasma of stars and core-collapse supernovae is a possible laboratory to explore physics beyond the standard model including ALPs. Once produced in a supernova, some of the ALPs can be absorbed by the supernova matter and affect energy transfer. We recently calculated the ALP emission in core-collapse supernovae and the backreaction on supernova dynamics consistently. It is found that the stalled bounce shock can be revived if the coupling between ALPs and photons is as high as $g_{a\gamma}\sim 10^{-9}$ GeV$^{-1}$ and the ALP mass is 40-400 MeV.

会場: via Zoom

イベント公式言語: 英語

Do the mechanisms of speciation vary with latitude? Empirical case study 1: evolution of the plant cycad genus Ceratozamia from Mexico

2022年6月2日(木) 16:00 - 17:00

ホセ サイード・グティエレス オルテガ (理化学研究所 数理創造プログラム (iTHEMS) 基礎科学特別研究員)

“Species” form biodiversity, and “speciation” is the evolutionary process that originate them. Speciation can occur by stochastic processes —neutral theory— or through the influence of ecological factors —selection theory—. They are not competing theories, but rather explain different facets of speciation. But the mechanisms of speciation seem quite to depend on the group of study and its underlying spatial and temporal factors. Why do in some groups species are more prone to evolve via selection or stochastically than others? It does not exist a unified theory that can explain and predict events of speciation at the global level. However, I hypothesize that there is a latitude-association between two main mechanisms of speciation: 1) “allopatric speciation by means of niche conservatism” and 2) “ecological speciation by means of niche divergence”. The first is hypothetically more common at low latitudes, and the second is more common at high latitudes. In this context, I will use the recent results of my own empirical research on the plant cycad genus Ceratozamia from Mexico as an example to show how mechanisms of speciation seem to covariate with latitude. Hopefully, you can help me to formulate a theory that can explain where and under what factors speciation can occur.

会場: via Zoom

イベント公式言語: 英語

Equilibrium or not? Mathematical differences between acute & chronic virus infections

2022年5月25日(水) 13:30 - 15:00

カトゥリン・ボシゥメン (理化学研究所 数理創造プログラム (iTHEMS) 副プログラムディレクター)

The widely acclaimed 1995/1996 papers by Ho, Perelson and others [1,2] demonstrated the important insights that come from mathematical modelling of virus infection kinetics within a person. But there are key dynamical differences between chronic and acute infections, namely whether the infection reaches or maintains some equilibrium or not. In this talk, I will introduce the equations used to describe a virus infection within a person. I will show some of the tricks used by mathematical modellers to extract important rate estimates from measurements in patients infected with chronic diseases, like HIV or Hepatitis C virus. I will explain why it is difficult to extract meaningful information from measurements in patients with an acute infection, like influenza or possibly COVID-19 [3]. I hope to hear from the audience if they have any thoughts about overcoming the issue to extract better rate information from limited data in patients with acute infections. (This seminar is a joint seminar between Nonequilibrium working group and Biology study group)

会場: via Zoom

イベント公式言語: 英語

Introduction to Topological Insulators: The Ten-fold Classification of Topological Insulators and Superconductors Part.1

2022年5月24日(火) 14:00 - 15:30

邱 靖凱 (理化学研究所 数理創造プログラム (iTHEMS) 上級研究員)

会場: via Zoom

イベント公式言語: 英語

A mathematical formulation of two-dimensional conformal field theory

2022年5月23日(月) 14:00 - 16:30

森脇 湧登 (理化学研究所 数理創造プログラム (iTHEMS) 基礎科学特別研究員)

The mathematical construction of non-trivial quantum field theory in four dimensions, known as the "Yang-Mills existence and mass gap problem", is a very important issue in mathematical sciences. There are many examples of rigorous quantum field theories in two dimensions, although the four dimensions have not yet been solved. In particular, two-dimensional conformal field theory, which is a quantum field theory with conformal symmetry, has good properties and can be formulated mathematically using algebraic structures formed by "products of a field and a field" (operator product expansion). In this talk, this algebraic formulation (full vertex algebra) will be explained. Various construction methods and concrete examples (construction using codes, construction from quantum groups, and construction by deformation) will then be discussed. All the talk here is mathematical, but I will try to speak in a way that is motivated by physics as much as possible throughout the talk. I hope to receive various comments from the viewpoints of other fields.

会場: コモンルーム 246-248号室 とZoomのハイブリッド開催

イベント公式言語: 英語

The Hunt for Extraterrestrial Neutrino Counterparts

2022年5月20日(金) 16:00 - 17:00

Yannis Liodakis (Postdoctoral Researcher, University of Turku, Finland)

The origin of high-energy neutrinos is fundamental to our understanding of the Universe. Apart from the technical challenges of operating detectors deep below ice, oceans, and lakes, the phenomenological challenges are even greater. The sources are unknown, unpredictable, and we lack clear signatures. Neutrino astronomy therefore represents the greatest challenge faced by the astronomy and physics communities thus far. The possible neutrino sources range from accretion disks and tidal disruption events, through relativistic jets to galaxy clusters with blazar TXS 0506+056 the most compelling association thus far. Since then, immense effort has been put into associating AGN-jets with high-energy neutrinos, but to no avail. I will discuss our current efforts in understanding the multimessenger processes in the Universe, and once and for all proving or disproving if AGN-jets are neutrino emitters.

会場: via Zoom

イベント公式言語: 英語

Deviations from the Standard Model Predictions and New Physics Interpretations

2022年5月20日(金) 13:30 - 15:00

北原 鉄平 (名古屋大学 素粒子宇宙起源研究所 (KMI) 特任助教)

Continuous development of experiments in recent years has revealed a large number of experimental anomalies which the Standard Model cannot explain. It is statistically obvious that as the number of experiments increases, one encounters a new anomaly due to the statistical fluctuation. But interestingly, some of the anomalies have been cross-checked by different experiments. These would be hints for physics beyond the Standard model. In this talk, I will review the flavor anomalies (also known as lepton flavor universality violation), the muon g-2 anomaly, and recently measured the W boson mass anomaly. I will also discuss these implications for the new physics, and introduce several of our works.

会場: コモンルーム 246-248号室 とZoomのハイブリッド開催

イベント公式言語: 英語