セミナー

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

チンカイ・チウ (数理創造プログラム 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 (数理創造プログラム 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 (数理創造プログラム 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 (数理創造プログラム 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

チンカイ・チウ (数理創造プログラム 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 (数理創造プログラム 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

Dr. 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

More Data, More Problems: Big Data in Correlative Ecology

2022年5月19日(木)16:00 - 17:00

Dr. Dan Warren (沖縄科学技術大学院大学 (OIST) 生物多様性・複雑性研究ユニット 研究員)

The rapidly expanding pool of large data sets on species distributions, community composition, and environmental factors has been accompanied by an increasing number of methodological approaches to analyze this data. If done correctly, this represents an unprecedented opportunity for understanding ecological processes at large scales. However, it also represents an opportunity to be wrong about those same processes at a scale that was previously not possible. In this talk, I will use examples from ecology and other fields to discuss some of the issues that arise when we take big data approaches to ecological questions.

会場: via Zoom

イベント公式言語: 英語

Recent Progress in the Swampland Program

2022年5月19日(木)14:00 - 15:30

野海 俊文 (神戸大学 大学院理学研究科 物理学専攻 宇宙論研究室 准教授)

In the past years, it has become increasingly clear that there exist nontrivial consistency conditions on symmetries in quantum gravity, that are invisible in classical gravity. The Swampland program aims at identifying such quantum gravity constraints and their implications for particle physics and cosmology, toward quantum gravity phenomenology. In this talk, I will review recent progress in this program, including my own 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

Khovanov homology theory - an introduction to categorification

2022年5月13日(金)14:00 - 16:30

佐野 岳人 (数理創造プログラム 基礎科学特別研究員)

Jones polynomial is a knot invariant discovered by V. F. R. Jones in 1984. Not only that it is a useful mathematical tool, the discovery led to opening up a new research area, quantum topology, which connects quantum mechanics and low-dimensional topology. In 2000, M. Khovanov introduced a “categorification of the Jones polynomial”, which is now called Khovanov homology, and made categorification one of the fundamental concept in knot theory. Now what does categorification mean, and what is it good for? In this talk, assuming that many of the audience are not familiar with abstract category theory, I will start from easy examples of categories and categorifications, for example categorification of natural numbers, and explain why they are something natural to think of. In the latter part, I will briefly explain the construction of Khovanov homology, and introduce several related topics.

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

Classical and Quantum Chaos

2022年5月12日(木)16:00 - 17:00

首藤 啓 (東京都立大学 大学院理学研究科 物理学専攻 教授)

Classical and quantum mechanics in multi-dimensions are qualitatively different from those in one-dimension since they are no more integrable in general and chaos appears in the dynamics. This brings a great deal of complexity or even richness both in classical and quantum dynamics. Especially in generic nonintegrable systems which are neither completely integrable nor fully chaotic, phase space becomes a mixture of regular and chaotic components. Such an aspect is a source of inexhaustible questions not only in the past but in the future. We here overview classical and quantum chaos in Hamiltonian systems.

会場: via Zoom

イベント公式言語: 英語

Introduction to Topological Insulators: Topological Superconductors and Quantum Computing

2022年5月9日(月)14:00 - 15:30

チンカイ・チウ (数理創造プログラム 上級研究員)

会場: via Zoom

イベント公式言語: 英語

Diversity of Asgardarchaota and Theoretical verification of the endosymbiotic theory

2022年4月28日(木)10:00 - 11:00

熊倉 大騎 (北海道大学 大学院生命科学院 生命科学専攻 博士課程)

How did intracellular symbiosis occur and give rise to eukaryotic ancestor? This question has been considered to the two theories as three-domain theory and eocyte theory. Here I present asgard archaea, the archaeon closest to eukaryotes. Asgard archaea is an archaeon found at a deep-sea sampling site called Loki's castle at between Greenland and Norway. So all the closely related species are named after Norse mythology (Loki-, Thor-, Odin-, Heimdall-, etc.). Unlike other archaea, asgard archaea has many eukaryotic-specific proteins and is considered to be the closest to eukaryotes. In 2020, one of the asgard archaea species was finally successfully cultured. This archaeon was cultured and found to take on a branch-like structure. It is then hypothesized that intracellular symbiosis between this archaeon and the ancestor of mitochondria resulted in the ancestor of today's eukaryotic cells. In this talk, I would like to discuss with you the explanation of how we arrived at this hypothesis and how to construct a mathematical model.

会場: via Zoom

イベント公式言語: 英語

Recurrence theorems for topological Markov chains

2022年4月22日(金)17:00 - 19:00

Dr. Cédric Ho Thanh (理化学研究所 開拓研究本部 (CPR) 三好予測科学研究室 特別研究員)

Recurrence theorems place conditions under which probabilistic systems, specifically Markov chains, are expected to visit certain states infinitely often. For example, a printer with its many moving parts and the random requests it receives, may be described as a probabilistic system, and recurrence of the "ready to print" state is desirable. Recurrence theorems in the case of finite Markov chains are widely known. In this talk, we are interested in generalization to the infinitary setting. As it turns out, some care has to be put in the definition of infinite Markov chains. Rather than simply infinite, the introduct topological Markov chains, and show how standard constructions can be naturally extended to thisframework: path spaces, cylinder sets, as well as the semantic of LTL and PCTL. With all these tools in hand, we finally state our recurrence theorems. This is work in progress in collaboration with Natsuki Urabe and Ichiro Hasuo. This seminar is hold in a hybrid style. If you want attend the seminar onsite, please contact to Keita Mikami.

会場: コモンルーム 246-248号室 とZoomのハイブリッド開催 (メイン会場)

イベント公式言語: 英語

Coherent emission from 3D relativistic shocks

2022年4月22日(金)14:00 - 15:00

岩本 昌倫 (九州大学)

The origin of fast radio bursts (FRBs; Lorimer et al. 2007) is one of the unsolved problems in astrophysics. Many observations of FRBs indicate that FRBs must be coherent emission in the sense that coherently moving electrons radiate electromagnetic waves. In relativistic shocks, it is well known that coherent electromagnetic waves are excited by synchrotron maser instability (SMI) in the shock transition (Hoshino & Arons 1991). The SMI is also known as the emission mechanism of coherent radio sources such as auroral kilometric radiation at Earth and Jovian decametric radiation. Recently, some models of fast radio burst based on the coherent emission from relativistic shock via the SMI have been proposed (e.g., Lyubarsky 2014; Beloborodov 2017; Plotnikov & Sironi 2019; Metzger et al. 2019) and the SMI in the context of relativistic shocks attracts more attention from astrophysics. In this study, by performing the world’s first three-dimensional (3D) particle-in-cell (PIC) simulation of relativistic shocks, we will demonstrate that large-amplitude electromagnetic waves are indeed excited by the SMI even in 3D and that the wave amplitude is significantly amplified and comparable to that in pair plasmas due to a positive feedback process associated with ion-electron coupling. Based on the simulation results, we will discuss the applicability of the SMI for FRBs in this talk.

会場: via Zoom

イベント公式言語: 英語

Neurons are potential statisticians

2022年4月21日(木)10:00 - 11:00

磯村 拓哉 (理化学研究所 脳神経科学研究センター (CBS) 脳型知能理論研究ユニット ユニットリーダー)

Humans and animals can predict what will happen in the future and act appropriately by inferring how the sensory inputs were generated from underlying hidden causes. The free-energy principle is a theory of the brain that can explain how these processes occur in a unified way. However, how the fundamental units of the brain, such as the neurons and synapses, implement this principle has yet to be fully established. Here, we have mathematically shown that neural networks that minimise a cost function implicitly follow the free-energy principle and actively perform statistical inference. We have reconstructed a biologically plausible cost function for neural networks based on the equation of neural activity and shown that the reconstructed cost function is identical to variational free energy, which is the cost function of the free-energy principle. This equivalence speaks to the free-energy principle as a universal characterisation of neural networks, implying that even at the level of the neurons and synapses, the neural networks can autonomously infer the underlying causes from the observed data, just as a statistician would. The proposed theory will advance our understanding of the neuronal basis of the free-energy principle, leading to future applications in the early diagnosis and treatment of psychiatric disorders, and in the development of brain-inspired artificial intelligence that can learn like humans.

会場: via Zoom

イベント公式言語: 英語