Seminar

Reproductive interference can affect trait diversity of closely related animal species

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

Keiichi Morita (Ph.D. Student, School of Advanced Sciences Department of Evolutionary Studies of Biosystems, The Graduate University for Advanced Studies (SOKENDAI))

Previous theoretical studies have considered that evolution driven by resource competition is important for the creation and maintenance of biodiversity. Recently, reproductive interference caused by misrecognition of sexual traits such as calling between closely related species has been increasingly important for the creation and maintenance of diversity, but the impact of reproductive interference on trait diversity between closely related species remains unresolved. In this study, we combined population dynamics model with reproductive interference in two closely related species with an evolutionary model of traits related to reproduction to examine the impact of reproductive interference on the evolutionary consequences of reproductive traits in the two closely related species. The model assumed a trade-off in which reproductive interference weakens as reproductive traits diverge between the two species, but predation pressure increases as the reproductive traits diverge from their optimum traits in their habitat. For simplicity, we assumed that only one species evolves. Our model analysis revealed that convergence and divergence of traits of two closely related species occurs depending on initial trait divergence. Also, under the parameter condition where trait convergence occurs, large mutation makes trait divergence possible. Our model will provide a new framework for understanding evolutionary dynamics in ecological communities containing closely related species.

Venue: via Zoom

Event Official Language: English

Topological Kondo superconductors

March 2 (Thu) at 17:00 - 18:15, 2023

Yung-Yeh Chang (Postdoctoral Researcher, National Center for Theoretical Sciences & National Chiao Tung University, Taiwan)

Spin-triplet p-wave superconductors are promising candidates for topological superconductors. They have been proposed in various heterostructures where a material with strong spin-orbit interaction is coupled to a conventional s-wave superconductor by proximity effect. However, topological superconductors existing in nature and driven purely by strong electron correlations are yet to be studied. Here we propose a realization of such a system in a class of Kondo lattice materials in the absence of proximity effect. Therein, the odd-parity Kondo hybridization mediates ferromagnetic spin-spin coupling and leads to spin-triplet resonant-valence-bond (t-RVB) pairing between local moments. Spin-triplet p±p’ wave topological superconductivity is reached when Kondo effect co-exists with t-RVB [1]. We identify the topological nature by the non-trivial topological invariant and the Majorana zero modes at edges. Our results on the superconducting transition temperature, Kondo coherent scale, and onset temperature of Kondo hybridization not only qualitatively but also quantitatively agree with the observations for UTe2, a U-based ferromagnetic heavy-electron superconductor. *This work is supported by the National Science and Technology Council, Taiwan. Field: condensed matter physics Keywords: strongly correlated systems, topological superconductor, Kondo effect, resonant valence bond, heavy-fermion compounds

Venue: via Webex

Event Official Language: English

How to sit Maxwell and Higgs on the boundary of AdS

February 28 (Tue) at 13:30 - 15:00, 2023

Matteo Baggioli (Associate Professor, School of Physics and Astronomy, Shanghai Jiao Tong University, China)

Within the holographic correspondence, boundary conditions play a fundamental role in determining the nature of the dual field theory. In this talk, I will show how to exploit mixed boundary conditions to obtain dynamical electromagnetism in the boundary theory. This is necessary to apply AdS-CFT to many real-world applications, e.g., magnetohydrodynamics, plasma physics, superconductors, etc. where dynamical gauge fields and Coulomb interactions are fundamental. As a proof of concept, I will show two emblematic cases. First, I will prove that the results from the 4-dimensional Einstein-Maxwell bulk theory with these deformed boundary conditions are in perfect agreement with relativistic magneto-hydrodynamics in 2+1 dimensions. Second, I will discuss the collective excitations of a bona-fide holographic superconductor and prove the existence of the Anderson-Higgs mechanism therein.

Venue: Room 6209, Korakuen Campus, Chuo University (Main Venue) / via Zoom

Event Official Language: English

Algebra of symmetry in BF-like models in 3d and 4d

February 22 (Wed) at 14:00 - 15:30, 2023

Christophe Goeller (Humboldt Fellow, Ludwig-Maximilians-Universität München, Germany)

In this talk, I will discuss the construction of the boundary symmetry algebra for BF-like theories in 3D and 4D. In the 3D case, the theory corresponds to (an extension of) 3D gravity allowing for a source of curvature and torsion. I will show how the study of the current algebra and its associated Sugawara construction allows for two notions of quadratic charges (the usual diffeomorphism and its "dual") independently of boundary conditions. I will discuss their resulting algebra and its relation with the usual construction of the asymptotic boundary algebra. In the 4D case, a similar yet fundamentally different construction is possible, similarly resulting in multiple quadratic charges. I will discuss their constructions and their possible relations to 4D gravity.

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

Event Official Language: English

Coherent sheaves, quivers, and quantum groups

February 17 (Fri) at 14:00 - 16:00, 2023

Gufang Zhao (Senior Lecturer, University of Melbourne, Australia)

This talk aims to illustrate symmetries in geometry. The first half surveys a few examples of parametrizing coherent sheaves on a variety and how quantum groups control the symmetry of parametrization space. The second half aims to illustrate some special cases when the variety is a local toric 3-Calabi-Yau.

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

Event Official Language: English

String theory, N=4 SYM and Riemann hypothesis

February 16 (Thu) at 14:00 - 16:10, 2023

Masazumi Honda (Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)

We discuss new relations among string theory, four-dimensional N=4 supersymmetric Yang-Mills theory (SYM) and the Riemann hypothesis. It is known that the Riemann hypothesis is equivalent to an inequality for the sum of divisors function σ(n). Based on previous results in literature, we focus on the fact that σ(n) appears in a problem of counting supersymmetric states in the N=4 SYM with SU(3) gauge group: the Schur limit of the superconformal index plays a role of a generating function of σ(n). Then assuming the Riemann hypothesis gives bounds on information on the 1/8-BPS states in the N=4 SYM. The AdS/CFT correspondence further connects the Riemann hypothesis to the type IIB superstring theory on AdS5×S5. In particular, the Riemann hypothesis implies a miraculous cancellation among Kaluza-Klein modes of the supergravity multiplet and D3-branes wrapping supersymmetric cycles in the string theory. We also discuss possibilities to gain new insights on the Riemann hypothesis from the physics side. This talk is based on a collaboration with Takuya Yoda (arXiv:220317091).

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

Event Official Language: English

Quantum groups and cohomology theories

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

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

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

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

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

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

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

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

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

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

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

Adrian Gonzalez-Casanova (Neyman Visiting Assistant Professor, 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

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

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

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