Seminar
385 events

Mathematical modeling of understanding how adaptive evolution of sexual traits can affect coexistence
June 23 (Thu) at 16:00  17:00, 2022
Mr. Keiichi Morita (Ph.D. Student, School of Advanced Sciences Department of Evolutionary Studies of Biosystems, SOKENDAI, the Graduate University for Advanced Studies)
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., ecoevolutionary 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 ecoevolutionary 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.
Venue: via Zoom
Event Official Language: English

Seminar
Dress code for infrared safe Smatrix in QED
June 22 (Wed) at 13:30  15:00, 2022
Dr. Sotaro Sugishita (Designated Assistant Professor, Institute for Advanced Research (IAR), Nagoya University)
We consider the infrared (IR) aspects of the gauge invariant Smatrix in QED. I will review the problem of IR divergences in QED, and introduce the dressed state formalism to obtain IRsafe Smatrix elements. I will show a condition for dressed states to obtain IRsafe Smatrix 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 crosssection summing over soft photons.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Seminar
Topological aspects of nonHermitian physics
June 21 (Tue) at 16:00  17:15, 2022
Dr. Nobuyuki Okuma (Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
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 bulkboundary 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 nonHermitian Hamiltonians, whose eigenvalues can be complex. Besides the topology, nonHermiticity can also cause a boundary phenomenon called the nonHermitian skin effect, which is an extreme sensitivity of the spectrum to the boundary condition. In this talk, I will explain recent developments in nonHermitian topological physics by focusing mainly on the boundary problem. As well as the competition between nonHermitian and topological boundary phenomena, I will discuss the topological nature inherent in nonHermiticity itself. Field: condensed matter physics Keywords: topological materials, nonHermitian systems, skin effect, bulkboundary correspondence
Venue: via Zoom
Event Official Language: English

Seminar
Selforganisation of a dynamic meshwork structure in the mesoderm during the development of a chick embryo and its characterisation using persistent homology
June 16 (Thu) at 16:00  17:00, 2022
Dr. Mitsusuke Tarama (Research Scientist, Laboratory for Physical Biology, RIKEN Center for Biosystems Dynamics Research (BDR))
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 selforganisation 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 agentbased mechanical model of cells that interact through a shortrange 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.
Venue: via Zoom
Event Official Language: English

Seminar
Implications of singularity theorem for nonsingular universe
June 16 (Thu) at 13:30  15:00, 2022
Dr. Daisuke Yoshida (Designated Assistant Professor, Graduate School of Mathematics, Nagoya University)
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 nonsingular. In this talk, we will discuss general properties that a nonsingular 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.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Seminar
NonAbelian vortices in twoflavor dense QCD
June 15 (Wed) at 13:30  15:00, 2022
Dr. Yuki Fujimoto (Postdoctoral Scholars, Department of Physics, University of Washington, USA)
Recently, the phase of the twoflavor 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 "nonAbelian 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 wellestablished CFL vortices in threeflavor symmetric setup, by putting some emphasis on their peculiarity: the nonAbelian 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].
Venue: via Zoom
Event Official Language: English

Introduction to Topological Insulators: The Tenfold Classification of Topological Insulators and Superconductors Part.2
June 13 (Mon) at 14:00  15:30, 2022
Dr. ChingKai Chiu (Senior Research Scientist, iTHEMS)
Venue: via Zoom
Event Official Language: English

Algebraic geometry in mixed characteristic
June 10 (Fri) at 14:00  16:30, 2022
Dr. Shou Yoshikawa (Special Postdoctoral Researcher, iTHEMS)
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.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Seminar
Mathematical Model on Evolution of Selfsustained Circadian Rhythms
June 9 (Thu) at 16:00  17:00, 2022
Dr. Motohide Seki (Assistant Professor, Department of Design Futures, Faculty of Design, Kyushu University)
Selfsustained oscillation is a fundamental property of circadian clocks found in many organisms. However, evolutionary advantage of the selfsustainability 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 selfsustained circadian clock, which was consistent with empirical records.
Venue: via Zoom
Event Official Language: English

Seminar
Cosmological phenomena with sterile neutrino
June 6 (Mon) at 16:30  18:00, 2022
Dr. Shintaro Eijima (Institute for Cosmic Ray Research (ICRR), The University of Tokyo)
Event Official Language: English

Seminar
Corecollapse Supernova Models with Heavy Axionlike Particles
June 3 (Fri) at 14:00  15:00, 2022
Dr. Kanji Mori (Research Institute of Stellar Explosive Phenomena (REISEP), Fukuoka University)
Axionlike particles (ALPs) are a class of hypothetical bosons which feebly interact with ordinary matter. The hot plasma of stars and corecollapse 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 corecollapse 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 40400 MeV.
Venue: via Zoom
Event Official Language: English

Do the mechanisms of speciation vary with latitude? Empirical case study 1: evolution of the plant cycad genus Ceratozamia from Mexico
June 2 (Thu) at 16:00  17:00, 2022
Dr. José Said GutiérrezOrtega (Special Postdoctoral Researcher, iTHEMS)
“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 latitudeassociation 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.
Venue: via Zoom
Event Official Language: English

Equilibrium or not? Mathematical differences between acute & chronic virus infections
May 25 (Wed) at 13:30  15:00, 2022
Prof. Catherine Beauchemin (Deputy Program Director, iTHEMS)
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 COVID19 [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)
Venue: via Zoom
Event Official Language: English

Introduction to Topological Insulators: The Tenfold Classification of Topological Insulators and Superconductors Part.1
May 24 (Tue) at 14:00  15:30, 2022
Dr. ChingKai Chiu (Senior Research Scientist, iTHEMS)
Venue: via Zoom
Event Official Language: English

A mathematical formulation of twodimensional conformal field theory
May 23 (Mon) at 14:00  16:30, 2022
Dr. Yuto Moriwaki (Special Postdoctoral Researcher, iTHEMS)
The mathematical construction of nontrivial quantum field theory in four dimensions, known as the "YangMills 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, twodimensional 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.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Seminar
The Hunt for Extraterrestrial Neutrino Counterparts
May 20 (Fri) at 16:00  17:00, 2022
Dr. Yannis Liodakis (Postdoctoral Researcher, University of Turku, Finland)
The origin of highenergy 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 AGNjets with highenergy 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 AGNjets are neutrino emitters.
Venue: via Zoom
Event Official Language: English

Seminar
Deviations from the Standard Model Predictions and New Physics Interpretations
May 20 (Fri) at 13:30  15:00, 2022
Dr. Teppei Kitahara (Assistant Professor, KobayashiMaskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University)
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 crosschecked 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 g2 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.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Seminar
More Data, More Problems: Big Data in Correlative Ecology
May 19 (Thu) at 16:00  17:00, 2022
Dr. Dan Warren (Staff Scientist, Biodiversity and Biocomplexity Unit, Okinawa Institute of Science and Technology Graduate University (OIST))
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.
Venue: via Zoom
Event Official Language: English

Seminar
Recent Progress in the Swampland Program
May 19 (Thu) at 14:00  15:30, 2022
Dr. Toshifumi Noumi (Associate Professor, Institute of Cosmophysics, Department of Physics, Graduate School of Science, Kobe University)
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.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Khovanov homology theory  an introduction to categorification
May 13 (Fri) at 14:00  16:30, 2022
Dr. Taketo Sano (Special Postdoctoral Researcher, iTHEMS)
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 lowdimensional 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.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English
385 events
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