Seminar

Quantum groups and cohomology theories

February 15 (Wed) at 14:00 - 16:00, 2023

Dr. Yaping Yang (Senior Lecturer, University of Melbourne, Australia)

In the first half of my talk, I will review quantum groups at roots of unity and their representation theory. In the second half, I will explain a construction of new quantum groups using cohomology theories from topology. The construction uses the so-called cohomological Hall algebra associated to a quiver and an oriented cohomology theory. In examples, we obtain the Yangian, quantum loop algebra and elliptic quantum group, when the cohomology theories are the cohomology, K-theory, and elliptic cohomology respectively.

Venue: Hybrid Format (Common Room 246-248 and Zoom)

Event Official Language: English

Entanglement in non-Hermitian quantum systems and non-unitary conformal field theories

February 9 (Thu) at 17:00 - 18:15, 2023

Dr. Chang Po-Yao (Assistant Professor, Department of Physics, National Tsing Hua University, Taiwan)

Time: 5pm ~ 6:15pm (JST); 9am ~ 10:15am (CET); 4pm ~ 5:15pm (Taiwan) Entanglement is a powerful tool to diagnose many-body quantum systems. One example is the critical system where the low energy property can be described by conformal field theories (CFTs), and the central charge which uniquely characterizes the CFT can be perfectly extracted from the entanglement entropy. However, the entanglement properties for non-unitary CFTs are not well understood. Moreover, the entanglement properties in many-body microscopic models which can be described by non-unitary CFTs have not been explored. In this talk, I would like to demonstrate several non-Hermitian systems which can be described by non-unitary CFTs, and show their entanglement properties can be correctly obtained by the proposed generic entanglement entropy. Field: Condensed Matter Physics Keywords: non-Hermitian systems, conformal field theory, many-body systems, entanglement entropy

Venue: via Webex

Event Official Language: English

Elasticities of population growth and their significance to evolutionary biology

February 9 (Thu) at 16:00 - 17:00, 2023

Dr. Stefano Giaimo (Postdoc, Department for Evolutionary Theory, Max Planck Institute for Evolutionary Biology, Germany)

The elasticity of population growth to a demographic parameter quantifies the proportional sensitivity of population growth to such parameter. In this talk, I will illustrate some cases where elasticities of population growth to demographic parameters acquire a special importance to evolutionary biology. In particular, I will discuss the relevance of these elasticities in studying the evolution of aging, their role in the computation of the generation time and their relationship to some trade-offs organisms may face as they optimise their fitness.

Venue: via Zoom

Event Official Language: English

Boltzmann or Bogoliubov? A Case of Gravitational Particle Production

February 9 (Thu) at 13:30 - 15:00, 2023

Dr. Kunio Kaneta (Lecturer, Graduate School of Science, Tokyo Woman's Christian University)

Despite its weakness, gravity is the primordial source of particle production in the early Universe. All the particles, including dark matter, can inevitably be created after the end of inflation through gravity. To study this production channel, two different approaches have commonly been considered, one of which is based on the Boltzmann equation, and the other is based on the Bogoliubov transformation. The former approach has widely been used in phenomenological studies of dark matter, while the latter has been developed to describe particle production in curved spacetime. I will discuss when these two approaches are equivalent and when they are not by considering the pure gravitational production of a scalar particle.

Venue: Hybrid Format (Common Room 246-248 and Zoom)

Event Official Language: English

Fuzzy DM simulation (TBA)

February 9 (Thu) at 11:00 - 12:00, 2023

Dr. Jowett Chan (Postdoc, Physics Division, National Center for Theoretical Sciences, Taiwan)

Venue: via Zoom

Event Official Language: English

Thermodynamic inequalities: motivation, foundations, and applications

February 7 (Tue) at 13:30 - 15:00, 2023

Prof. Andreas Dechant (Lecturer, Graduate School of Science, Kyoto University)

In this talk, I will introduce the topic of thermodynamic inequalities. One motivation for studying inequalities is that they can provide universal constraints on what can and cannot happen in physical systems. From a more practical point of view, they can be used to estimate physical observables even in situations where no equality is available. I will highlight a few recent examples of thermodynamic inequalities in the form of uncertainty relations and speed limits. In the main part of the talk, I will explain a general technique for deriving new inequalities, by starting from information-theoretic bounds and considering “virtual perturbations” of a physical system. I will show how this method can be used to derive and generalize the so-called “thermodynamic uncertainty relation”. An interesting application of such uncertainty relations is to estimate the dissipation in biological systems such as molecular motors. The second main topic is how to relate inequalities to equalities. When using inequalities to estimate physical quantities, it is crucial to understand the conditions under which the inequality can be tight. One way to achieve this is to “promote” the inequality into an equality via a variational principle. On the one hand, this provides conditions for obtaining a tight bound. On the other hand, variational expressions can also serve as a starting point to derive new inequalities.

Venue: via Zoom

Event Official Language: English

Universal Biology in Adaptation and Evolution: Dimensional Reduction and Fluctuation-Response Relationship

February 2 (Thu) at 16:00 - 17:00, 2023

Prof. Kunihiko Kaneko (Professor, Niels Bohr Institute, University of Copenhagen, Denmark)

A macroscopic theory for adaptive changes of cells is presented, based on consistency between cellular growth and molecular replication, as well as robustness of fitted phenotypes against perturbations. Adaptive changes in high-dimensional phenotypes are shown to be restricted within a low-dimensional slow manifold, from which a macroscopic law for cellular states is derived, as is confirmed by adaptation experiments of bacteria under stress. The theory is extended to phenotypic evolution, leading to proportionality between phenotypic responses against genetic evolution and by environmental adaptation, which also explains the evolutionary fluctuation-response relationship previously uncovered. Relevance of statistical-physics and dynamical-systems approach is discussed.

Venue: via Zoom

Event Official Language: English

Physics-informed deep learning approach for modeling crustal deformation

January 23 (Mon) at 10:30 - 11:30, 2023

Dr. Naonori Ueda (Deputy Director, RIKEN Center for Advanced Intelligence Project (AIP))

The movement and deformation of the Earth’s crust and upper mantle provide critical insights into the evolution of earthquake processes and future earthquake potentials. Crustal deformation can be modeled by dislocation models that represent earthquake faults in the crust as defects in a continuum medium. In this study, we propose a physics-informed deep learning approach to model crustal deformation due to earthquakes. Neural networks can represent continuous displacement fields in arbitrary geometrical structures and mechanical properties of rocks by incorporating governing equations and boundary conditions into a loss function. The polar coordinate system is introduced to accurately model the displacement discontinuity on a fault as a boundary condition. We illustrate the validity and usefulness of this approach through example problems with strike-slip faults. This approach has a potential advantage over conventional approaches in that it could be straightforwardly extended to high dimensional, anelastic, nonlinear, and inverse problems.

Venue: via Zoom

Event Official Language: English

Math and Physics of Seiberg-Witten theory

January 20 (Fri) at 16:00 - 18:10, 2023

Dr. Nobuo Iida (JSPS Research Fellow PD, School of Science, Tokyo Institute of Technology)

Math and physics have developed through interactions with each other. For example, classical mechanics and calculous were born together. Einstein's theory of gravitation is written in the language of pseudo-Riemann geometry. Since the late 20th century, physicists centering on Edward Witten have revolutionized modern geometry. Seiberg-Witten theory is one of such breakthroughs, for both mathematicians and physicists. In physics it is regarded as a theory describing strong coupling (i.e. low energy) behavior of some supersymmetric gauge theories. It showes confinement (by a mechanism similar to superconductivity) and electric magnetic duality. Even though this story has not been mathematically justified yet, it is regarded as an important trigger of developments in understanding non perturbative aspects of quantum field theory and string theory, and stimulates broad fields of physics and math. In math, Seiberg-Witten theory is regarded as a fundamental tool to study 3 and 4-dimensional geometry. This is based on a PDE called Seiberg-Witten equation, which originates from the "electric magnetic dual description" of monopoles, but people can use it as a tool to study geometry without knowing such a physical origin. In this talk, developments of Seiberg-Witten theory from both viewpoints will be reviewed and if the time permits, works in math by the speaker and collaborators will be discussed. The speaker thinks it is unusual for a mathematician to talk about something that has not been mathematically justified yet, but hopes this talk will lead to new interactions between math and physics.

Venue: Hybrid Format (Common Room 246-248 and Zoom)

Event Official Language: English

Understanding kilonova spectra and identification of r-process elements

January 20 (Fri) at 14:00 - 15:00, 2023

Dr. Nanae Domoto (Ph.D. Student, Department of Astronomy, Graduate School of Science, Tohoku University)

Binary neutron star (NS) merger is a promising site for the rapid neutron capture nucleosynthesis (r-process). 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 r-process happens in the NS merger. However, the abundance pattern synthesized in this event, which is important to understand the origin of the r-process elements, is not yet clear. In this talk, I will first introduce an overview and current understanding of kilonova. Then, I will discuss our recent findings of elemental features in photospheric spectra of kilonova toward identification of elements.

Venue: via Zoom

Event Official Language: English

Mathematical models inspired by the Lenski experiment

January 19 (Thu) at 10:00 - 11:00, 2023

Dr. Adrian Gonzalez-Casanova (Neyman Visiting Assistant Professor, The University of California, Berkeley, USA / Associate Professor, National Autonomous University of Mexico, Mexico)

We will discuss the basic models of mathematical population genetics and see how to apply them to the study of the Lenski experiment. Furthermore, we will describe novel models that are capable of providing a parsimonious explanation of the deceleration of the relative fitness and can be used to attack questions such as, is it advantageous to be efficient? If time permits, we will also discuss examples of mathematical modelling beyond the Lenski experiment, including the study of populations of bacteria carrying plasmids.

Venue: via Zoom

Event Official Language: English

Tetra-neutron system studied by RI-beam experiments

January 17 (Tue) at 13:30 - 15:00, 2023

Prof. Susumu Shimoura (Research Scientist, Spin isospin Laboratory, RIKEN Cluster for Pioneering Research (CPR))

Multi-neutron systems have attracted a long-standing attention in nuclear physics. In several decades, experimental attempts have been made with a particular focus on the tetra-neutron system. Among them, the two different experiments, the double-charge exchange reaction on 4He and the alpha-particle knockout reaction from the 8He, show a sharp peak just above the threshold in the four-neutron spectra, which could be a signature of a "resonant state", separate from a broad bump structure at higher excitation energy regions. Both the experiments have been realized by using the 8He beam above 150 A MeV at the RIKEN RI Beam Factory. Details of the two experiments including basic idea, experimental techniques, and analysis are presented as well as a historical review of previous experimental attempts. Emphasis is made for the experimental conditions for populating a kinematically isolated tetra-neutron system with very small momentum transfer. The spectral shape is discussed by means of reaction processes and correlations in the final tetra-neutron system with several recent theoretical studies.

Venue: Common Room #246-248 (Main Venue) / via Zoom

Event Official Language: English

Mergers of neutron star-neutron star (or black hole) binaries as r-process sites

January 13 (Fri) at 14:00 - 15:00, 2023

Dr. Shinya Wanajo (Senior Scientist, Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Germany)

The discovery of an electromagnetic counterpart (kilonova) associated with GW170817 confirms that binary neutron star (NS) mergers are at least one of sites of r-process nucleosynthesis. However, there is no observational evidence that black hole (BH)-NS mergers are r-process sites. In this talk, we overview the latest work of nucleosynthesis based on long-term hydrodynamics simulations of NS-NS and BH-NS mergers covering early dynamical and late post-merger mass ejections. We also briefly discuss a possible constraint on nuclear equations of state.

Venue: via Zoom / Common Room #246-248

Event Official Language: English

Basic of microbial ecology and applicability of your life and research

January 12 (Thu) at 16:00 - 17:00, 2023

Mr. Daiki Kumakura (Ph.D. Student, Graduate School of Life Science, Hokkaido University)

Microbial ecology is a fascinating field that examines the various environments in which microbes can thrive and their potential applications to human life. In this seminar, I will delve into four main topics:

Venue: via Zoom

Event Official Language: English

Searching for high-freqeuncy gravitational waves with axion detectors

January 12 (Thu) at 14:00 - 15:30, 2023

Dr. Valerie Domcke (Senior Faculty, Department of Theoretical Physics, CERN, Switzerland)

Current gravitational wave (GW) experiments cover a large frequency range from nHz to kHz. Beyond that, the regime of high frequency GWs is both extremely challenging challenging, and highly motivated as a unique window to the very early Universe. In this talk I will discuss a proposal for a new type of electromagnetic GW detector which makes use of the observation that GWs generate oscillating electromagnetic effects in the vicinity of external electric and magnetic fields. This is in close analogy to the interaction of the axion with electromagnetic fields. I will discuss how existing bounds from axion searches can be recast for GWs, as well as implications for future axion searches such as the DMRadio program.

Venue: Hybrid Format (Common Room 246-248 and Zoom)

Event Official Language: English

A cell membrane model that reproduces cortical flow-driven cell migration and collective movement

January 5 (Thu) at 16:00 - 17:00, 2023

Dr. Katsuhiko Sato (Associate Professor, Research Institute for Electronic Science, Hokkaido University)

Cellular migration is a key component of numerous biological processes, including the morphogenesis of multicellular organisms, wound healing, and cancer metastasis, where cells adhere to each other to form a cluster and collectively migrate. Although the mechanisms controlling single-cell migration are relatively well understood, those underlying multiple-cell migration still remain unclear. A key reason for this knowledge gap is the so-called many-body problem. That is, many forces—including contraction forces from actomyosin networks, hydrostatic pressure from the cytosol, frictional forces from the substrate, and forces from adjacent cells—contribute to cell cluster movement, making it challenging to model, and ultimately elucidate, the final result of these forces. In this talk, I provide a two-dimensional cell membrane model that represents cells on a substrate with polygons and expresses various mechanical forces on the cell surface, keeping these forces balanced at all times by neglecting cell inertia. The model is discrete but equivalent to a continuous model if appropriate replacement rules for cell surface segments are chosen. When cells are given a polarity, expressed by a direction-dependent surface tension reflecting the location dependence of contraction and adhesion on a cell boundary, the cell surface begins to flow from front to rear as a result of force balance. This flow produces unidirectional cell movement, not only for a single cell but also for multiple cells in a cluster, with migration speeds that coincide with analytical results from a continuous model. Further, if the direction of cell polarity is tilted with respect to the cluster center, surface flow induces cell cluster rotation. The reason why this model moves while keeping force balance on cell surface (i.e., under no net forces from outside) is because of the implicit inflow and outflow of cell surface components through the inside of the cell. I provide an analytical formula connecting cell migration speed and turnover rate of cell surface components.

Venue: via Zoom

Event Official Language: English

How to infer evolutionary history

December 22 (Thu) at 16:00 - 17:00, 2022

Dr. Jeffrey Fawcett (Senior Research Scientist, iTHEMS)

One main goal of evolutionary studies is to infer the evolutionary that explains the current diversity. We want to infer the ancestral state and what kind of changes occurred from the previous ancestral state to the current state. In other words, we want to infer the phylogenetic relationship that explains the branching pattern that leads to the current diversity and infer the state at each node and the changes that occurred in each branch of the phylogeny. In this talk, I will introduce some basic concepts that are used in evolutionary biology to tackle these questions, especially how molecular data, i.e., DNA and protein sequence data, can be utilized. This talk will be introductory and aimed at non-experts including non-biologists.

Venue: via Zoom

Event Official Language: English

Modelling Optical Signals from Magnetar-Driven Supernovae

December 20 (Tue) at 14:00 - 15:00, 2022

Dr. Conor Omand (Postdoctoral Researcher, Department of Astronomy, Stockholm University, Sweden)

Many energetic supernovae are thought to be powered by the rotational energy of a highly-magnetized, rapidly-rotating 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. I will present 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 engine-driven supernovae.

Venue: Common Room #246-248 / via Zoom

Event Official Language: English

The ANDES Deep Underground Laboratory in South America: status and prospects

December 19 (Mon) at 12:30 - 13:30, 2022

Dr. Maria Manuela Saez (Postdoctoral Researcher, iTHEMS)

The construction of the Agua Negra tunnels that will link Argentina and Chile under the Andes mountains opens the possibility of building a deep underground laboratory in the Southern Hemisphere. Dark Matter particles can be detected directly via their elastic scattering with nuclei, and next-generation experiments can eventually find physical evidence about dark matter candidates. I will show you our predictions for the expected direct dark matter signal and the ANDES site laboratory, whose location in the Southern Hemisphere should play a significant role in understanding dark matter modulation signals. Additionally, since planned next-generation large-scale direct detection experiments will measure the coherent elastic scattering of neutrinos on protons and nuclei, we have calculated the SN neutrino signal expected for the location. Finally, to study the background, we have calculated the contributions to the neutrino floor by considering the reactor’s neutrinos and geoneutrinos at the laboratory site. We hope these studies might contribute to dark matter detection strategies that maximize the future ANDES laboratory detection capabilities.

Venue: via Zoom

Event Official Language: English

CM minimization and special K-stability

December 16 (Fri) at 14:00 - 16:30, 2022

Mr. Masafumi Hattori (Ph.D. Students, Department of Mathematics, Graduate School of Science, Kyoto University)

Odaka proposed a conjecture predicting that the degrees of CM line bundles for families with fixed general fibers are strictly minimized if the special fibers are K-stable. This conjecture is called CM minimization and a quantitative strengthening of the conjecture of separatedness of moduli spaces of K-stable varieties (K-moduli). This conjecture was already shown for K-ample (Wang-Xu), Calabi-Yau (Odaka) and Fano varieties (Blum-Xu). In this talk, we introduce a new class, special K-stable varieties, and settle CM minimization for them, which is a generalization of the above results. In addition, we would like to explain an important application of this, construction of moduli spaces of uniformly adiabatically K-stable klt trivial fibrations over curves as a separated Deligne-Mumford stack in a joint work with Kenta Hashizume to appear. This is based on arXiv:2211.03108.

Venue: via Zoom

Event Official Language: English