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iTHEMS x academist Online Event "World of Mathematical Sciences 2024"

April 21 (Sun) 10:00 - 15:30, 2024

Shingo Gibo (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Taketo Sano (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Misako Tatsuuma (Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Tomoya Naito (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

Venue: via Zoom

Event Official Language: Japanese

Zooming into the ancient world by reconstructing the joint genealogies of modern and ancient humans

April 18 (Thu) 16:00 - 18:00, 2024

Leo Speidel (Senior Research Fellow, Genetics Institute, University College London, UK)

In recent years, we have gone from databases that store the genetic differences observed between hundreds of thousands of sequenced people to using this information to build the actual genetic trees that relate individuals through their shared ancestors back in time. These genetic trees describe how our genomes have evolved up to millions of years into the past. Additionally, sequencing of DNA from ancient human bone has enabled the direct observation of genomic change over past millennia and has unlocked numerous previously hidden genetic histories. In this talk, I will illustrate how we can unearth the human past from these data, ranging from ancient migrations out of Africa and subsequent mixtures with now extinct Neanderthals to waves of ancestry transformations in a nation’s recent past.

Venue: via Zoom

Event Official Language: English

Quantum Fine-Grained Complexity

April 18 (Thu) 10:30 - 12:00, 2024

Harry Buhrman (Chief Scientist for Algorithms and Innovation, Quantinuum, UK)

(The speaker is also a professor at University of Amsterdam & QuSoft. This is a joint seminar with the iTHEMS Quantum Computation Study Group.) One of the major challenges in computer science is to establish lower bounds on the resources, typically time, that are needed to solve computational problems, especially those encountered in practice. A promising approach to this challenge is the study of fine-grained complexity, which employs special reductions to prove time lower bounds for many diverse problems based on the conjectured hardness of key problems. For instance, the problem of computing the edit distance between two strings, which is of practical interest for determining the genetic distance between species based on their DNA, has an algorithm that takes O(n^2) time. Through a fine-grained reduction, it can be demonstrated that a faster algorithm for edit distance would imply a faster algorithm for the Boolean Satisfiability (SAT) problem. Since faster algorithms for SAT are generally considered unlikely to exist, this implies that faster algorithms for the edit distance problem are also unlikely to exist. Other problems used for such reductions include the 3SUM problem and the All Pairs Shortest Path (APSP) problem. The quantum regime presents similar challenges; almost all known lower bounds for quantum algorithms are defined in terms of query complexity, which offers limited insight for problems where the best-known algorithms take super-linear time. Employing fine-grained reductions in the quantum setting, therefore, represents a natural progression. However, directly translating classical fine-grained reductions to the quantum regime poses various challenges. In this talk, I will present recent results in which we overcome these challenges and prove quantum time lower bounds for certain problems in BQP, conditioned on the conjectured quantum hardness of, for example, SAT (and its variants), the 3SUM problem, and the APSP problem. This presentation is based on joint works with Andris Ambainis, Bruno Loff, Florian Speelman, and Subhasree Patro.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Short-Lived Hawking Radiation Under Stringy Effects

April 11 (Thu) 13:30 - 15:00, 2024

Wei-Hsiang Shao (Ph.D. Student, Department of Physics, National Taiwan University, Taiwan)

A UV theory is required in order to describe the origin of late-time Hawking radiation. In this talk, I will explore Hawking radiation in a non-local model of the radiation field inspired by Witten's open string field theory. An attempt at extracting the correlators of this theory will be discussed, which leads to a space-time uncertainty relation. As a result, the characteristics of trans-Planckian field modes differ significantly from that in the standard low-energy effective theory, and I will argue that this ultimately results in the termination of Hawking radiation around the scrambling time of the black hole.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

A socio-ecological and genomic approach to mixed-species formation of African forest guenons

April 4 (Thu) 16:00 - 17:00, 2024

Haruka Kitayama (Ph.D. Student, Graduate School of Environmental Science, Hokkaido University)

While many animal groups consist of a single species, some species have been observed forming mixed-species groups (MSGs). It is thought that by forming groups with different species, animals may reduce predation risk, improve foraging efficiency, and even gain social and reproductive benefits. Red-tailed monkeys and blue monkeys, African forest guenons (Tribe Cercopithecini), are known to form MSGs in several regions in Africa, despite the large niche overlap. The underlying mechanisms driving the formation of MSGs in red-tailed monkeys and blue monkeys are still unclear. One reason is that previous studies have been limited to behavioral ecological approaches. By combining field observations with genomic analyses in the laboratory, we seek to shed light on the role of genetic factors in mediating interspecies interactions within MSGs. In this talk, I will introduce our studies on genomic introgression and gut microbiome sharing within the mixed-species population of red-tailed monkeys and blue monkeys in the Kalinzu Forest Reserve, Uganda.

Venue: via Zoom

Event Official Language: English

TadaFest 2024: Toward understanding of the Origin of Spacetime

April 2 (Tue) 14:00 - 18:00, 2024

Tsukasa Tada (Deputy Program Director, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

Program 14:00-14:05 Welcome address T. Hatsuda (RIKEN iTHEMS) 14:05-15:35 T. Tada (RIKEN iTHEMS) "Toward understanding of the origin of spacetime" (This talk is in English) 15:35-16:00 coffee break 16:00-16:30 Shin Nakamura (Chuo Univ.) "Application of gauge/gravity duality: application to non-equilibrium physics" (This talk is in Japanese) 16:30-17:00 Kinya Oda (Tokyo Woman's Chiristian Univ.) "Gaussian formalism: From Hesenberg's Uncertainty Principle to Time-Boundary Effect and Lorentz-Covariant Complete Basis for Spinors" (This talk is in Japanese) 17:00-17:30 Gen Tatara (RIKEN, CEMS) "Some topics of spintronics" (This talk is in Japanese) 17:30-18:00 Asato Tsuchiya (Shizuoka Univ.) "Recent progress in the studies of the emergence of space-time in the type IIB matrix model" (This talk is in Japanese) 18:15- informal discussion @ Common space on 3F of the main research building

Venue: Okochi Hall (Main Venue) / via Zoom

Event Official Language: English

Arrhythmic activity rhythms in ants

March 26 (Tue) 16:00 - 17:00, 2024

Haruna Fujioka (Assistant Professor, Faculty of Environmental, Life, Natural Science and Technology, Okayama University)

Most organisms exhibit a periodic activity of about 24 h. This circadian rhythm is considered to be an adaptation to the fluctuations of the environment. In social insects such as honeybees and ants, individual behavior, including activity-rest rhythms, is influenced by interactions within the colony. However, it is challenging to monitor individual activity-rest rhythms in an ant colony due to their large group size and small body size. To address this, we developed an image-based tracking system using 2D barcodes a monomorphic ant and measured the locomotor activities of all colony members under laboratory conditions. Activity-rest rhythms appeared only in isolated ants, not under colony conditions. This suggests that a mixture of social interactions, not light and temperature, induces the loss of activity-rest rhythms. These findings contribute to our understanding of the diverse patterns of circadian activity rhythms in social insects.

Venue: via Zoom

Event Official Language: English

The evolution of unusual inheritance and chromosome behaviour in flies and other critters

March 14 (Thu) 16:00 - 17:00, 2024

Laura Ross (Senior Lecturer, Institute of Evolutionary Biology, University of Edinburgh, UK)

Under Mendelian inheritance, individuals receive one set of chromosomes from each of their parents, and transmit one set of these chromosomes at random to their offspring. Yet, in thousands of animals Mendel's laws are broken and the transmission of maternal and paternal alleles becomes unequal. Why such non-Mendelian reproductive systems have evolved repeatedly across the tree of life remains unclear. My lab studies a variety of arthropod species to understand why, when and how the transmission of genes from one generation to the next deviate from Mendel’s laws. We mainly focus on species with Paternal Genome Elimination: Males transmit only those chromosomes they inherited from their mother to their offspring, while paternal chromosomes are excluded from sperm through meiotic drive. I will present recent work aimed at understanding the evolution of this unusual reproductive strategy in a clade of flies. These flies arguably have one of the most bizarre and complex chromosome systems of any insect and we use this complexity to study a range of topics including the evolution of sex chromosomes, germline-restricted chromosomes and sexual conflict.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

New horizons in immersive visualization at iTHEMS

March 14 (Thu) 14:00 - 16:00, 2024

Gilles Ferrand (Adjunct Professor, Department of Physics and Astronomy, University of Manitoba, Canada)

Visualization is an essential part of research, both to explore one’s data and to communicate one’s findings with others. Data that are 3-dimensional can be explored in a more natural way using virtual reality devices. iTHEMS recently purchased new VR headsets with advanced capabilities (Meta Quest Pro). The meeting will start with a general introduction to the current state of the VR space. Then, participants may individually experience a demonstration with the new headsets (showing research done at the ABBL on supernovae and their remnants). There will be ample time for questions and discussions. Come and discover how such tools can be used to enhance our research.

Venue: 3rd floor public space, Main Research Building

Event Official Language: English

Brane field theory with higher-form symmetry

March 12 (Tue) 14:00 - 15:30, 2024

Kiyoharu Kawana (Research Fellow, Korea Institute for Advanced Study (KIAS), Republic of Korea)

We propose field theory for branes with higher-form symmetry as a generalization of ordinary Landau theory. The field \psi[C_p^{}] becomes a functional of p-dimensional closed brane Cp embedded in a spacetime. As a natural generalization of ordinary field theory, we call this theory brane field theory. In order to construct an action that is invariant under higher-form transformation, we first generalize the concept of “derivative” for higher-dimensional objects. Then, we discuss various fundamental properties of the brane field based on the higher-form invariant action. It is shown that the classical solution exhibits the area law in the unbroken phase of U(1) p-form symmetry, while it indicates a constant behavior in the broken phase for the large volume limit of Cp. In the latter case, the low-energy effective theory is described by the p-form Maxwell theory. If time permits, we also discuss brane-field theories with a discrete higher-form symmetry and show that the low-energy effective theory becomes a BF-type topological field theory, resulting in topological order.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

Macroscopic neutrinoless double beta decay: long range quantum coherence

March 6 (Wed) 15:30 - 17:30, 2024

Gordon Baym (Professor Emeritus, University of Illinois, USA)

This talk will introduce the concept of ``macroscopic neutrinoless double beta decay" (MDBD) for Majorana neutrinos. In this process an antineutrino produced by a nucleus undergoing beta decay, $X\to Y + e^- + \bar \nu_e$, is absorbed as a neutrino by another identical $X$ nucleus via the inverse beta decay reaction, $\nu_e + X \to e^-+Y$. The distinct signature of MDBD is that the total kinetic energy of the two electrons equals twice the end-point energy of single beta decay. The amplitude for MDBD, a coherent sum over the contribution of different mass states of the intermediate neutrinos, reflects quantum coherence over macroscopic distances, and is a new macroscopic quantum effect. We discuss the similarities and differences between the MDBD and conventional neutrinoless double beta decay, as well as give estimates of the rates of MDBD and backgrounds.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building (Main Venue) / via Zoom

Event Official Language: English

Do plants have bones? Silica phytoliths and their role and fate in the development of terrestrial plants and human civilizations

March 1 (Fri) 14:00 - 15:15, 2024

Mikhail Blinnikov (Professor, St. Cloud State University, USA)

Silicon is the second most common element in the Earth’s crust. Some families of higher plants evolved mechanisms for soluble silica to be carried by xylem from groundwater and deposited as plant opal in or around plant cells as phytoliths thought to play a role in the structural support and defense against herbivores. While known since the early 19th century, phytoliths remain an intriguing class of microfossils whose formation and role in plants and their preservation in soils and sediments are a subject for a lot of active research. I outline some emerging themes in phytolith analysis including phytoliths’ role in global biogeochemical cycles, plant-herbivore interactions, and their tracing of evolution of cultural plants, especially cereals such as rice (Oryza), wild rice (Zizania), maize (Zea), wheat (Triticum) and millet (Panicum), all relevant to global archaeology. Some emerging research on phytoliths connects their changes in shapes to plant taxonomy of some families such as grasses and opens up avenues for further investigation of their active construction in the cells of some taxa by yet undiscovered genetically mediated mechanisms. New image analysis techniques and some advanced microscopy methods will allow us to further the field of phytolith study using deep machine learning algorithms and true 3D analysis of their shapes, something where contribution from other branches of science are most welcome.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Stochastic tunneling in de Sitter spacetime

February 28 (Wed) 16:00 - 17:30, 2024

Taiga Miyachi (Ph.D. Student, Institute of Cosmophysics, Department of Physics, Graduate School of Science, Kobe University)

The formulation of tunneling in real time formalism is discussed. In the case of de Sitter spacetime, there is a method called the stochastic approach, which is known to reproduce the tunneling predicted by Hawking and Moss in the imaginary time formalism. In the case of accelerated expansion of space, the short-wavelength modes are stretched and transformed into long-wavelength modes. In the stochastic approach, such UV-IR transition is incorporated as quantum noise, and the dynamics of the long-wavelength modes are described by stochastic differential equations. In this talk, we construct a Schwinger-Keldysh path integral that reproduces this stochastic differential equation and reformulate the tunneling probability. We also reproduce the Hawking-Moss tunneling probabilities by using the saddle point approximation.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Plant hackers: galling insects extend their phenotypes on the trees by novel plant organogenesis

February 27 (Tue) 16:00 - 17:00, 2024

Xin Tong (Special Postdoctoral Researcher, Cell Function Research Team, RIKEN Center for Sustainable Resource Science (CSRS))

When it comes to plant-insect interactions, insects are generally seen as pests like caterpillars eating vegetables or fruits. However, one group of insects, the galling insects can induce de novo organogenesis on the host plants which are often woody plants. Each galling insect species ‘designs’ its own gall as the extended phenotype which are so-called species-specific gall formation. Different from leaves and roots, galls represent unique plant organs swiftly formed in response to parasitic organisms, observed across diverse plant species. Yet, the precise mechanisms by which normal plant development is interrupted and redirected to form galls by galling organisms remain elusive. During the talk, I will share some discoveries and views related to aphid gall formation on the elm tree, which is the super host plant for more than 30 galling species, and further discussion about why an insect gall is not simple cell mass but well-organized structure, and how we could systematically understand insect gall formation.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

Second Workshop on Fundamentals in Density Functional Theory (DFT2024)

February 20 (Tue) - 22 (Thu) 2024

The density functional theory (DFT) is one of the powerful methods to solve quantum many-body problems, which, in principle, gives the exact energy and density of the ground state. The accuracy of DFT is, in practice, determined by the accuracy of an energy density functional (EDF) since the exact EDF is still unknown. Currently, DFT has been used in many communities, including nuclear physics, quantum chemistry, and condensed matter physics, while the fundamental study of DFT, such as the first principle derivations of an accurate EDF and methods to calculate many observables from obtained densities and excited states. However, there has been little opportunity to have interdisciplinary communication. On December 2022, we had the first workshop on this series (DFT2022) at Yukawa Institute for Theoretical Physics, Kyoto University, and several interdisiplinary discussions and collaborationd were started. To share such progresses and extend collaborations, we organize the second workshop. In this workshop, the current status and issues of each discipline will be shared towards solving these problems by meeting together among researchers in mathematics, nuclear physics, quantum chemistry, and condensed matter physics. This workshop mainly comprises lectures/seminars on cutting-edge topics and discussion, while a half-day session composed of contributed talks is also planned. This workshop is partially supported by iTHEMS-phys Study Group. This workshop is a part of the RIKEN Symposium Series. The detailed information can be found in the workshop website.

Venue: 8F, Integrated Innovation Building (IIB) (Main Venue) / via Zoom

Event Official Language: English

Cellular-level left-right asymmetry, cell chirality, induces the chiral collective rotation of multicellular colony

February 15 (Thu) 16:00 - 17:00, 2024

Tomoki Ishibashi (Special Postdoctoral Researcher, Laboratory for Physical Biology, RIKEN Center for Biosystems Dynamics Research (BDR))
Ryohei Nishizawa (Ph.D. Student, Graduate School of Frontier Biosciences, Osaka University)

The left-right (LR) asymmetric morphology of organs is essential for the development and maintenance of their functions in various species. In recent years, it has become clear that the LR asymmetry of organs originates from cell chirality, the LR asymmetric nature at the cellular level [1]. However, it is unclear how the cell chirality generates the LR asymmetry at the multicellular level. Here we show a mechanism of LR asymmetry formation at the multicellular level based on cell chirality. We previously found that Caco-2 cells, a typical cultured epithelial cell line derived from human colon cancer, exhibit stereotypical and directional cell chirality; when Caco-2 cells are cultured as single cells, their nuclei and cytoplasm rotate in the clockwise direction at a rate of 50°/h [2]. Interestingly, when Caco-2 forms multicellular colonies, the colonies also undergo a collective clockwise rotation at 10º/h. We revealed that the actomyosin cytoskeleton is essential for the formation of the collective rotation [2]. We also found that Caco-2 cells formed lamellipodia and focal adhesions LR asymmetrically during the collective colony rotation, which may be responsible for the chiral collective motion. Interestingly, the disruption of microtubules reversed the direction of collective rotation. The LR asymmetric formation of lamellipodia and focal adhesions was also reversed by inhibition of microtubule polymerization. We will discuss the possible mechanism and the mathematical model where cell chirality induces multicellular chiral rotation depending on microtubules.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Chemical reaction network theory and the problem of reaction rate

February 8 (Thu) 16:00 - 17:00, 2024

Tomoharu Suda (Postdoctoral Researcher, Biofunctional Catalyst Research Team, RIKEN Center for Sustainable Resource Science (CSRS))

A chemical system can be described at different levels. When we focus on the population of chemical species, it is convenient to consider the system as consisting of a number of chemical reactions, which assumes the structure of a (hyper)graph together with the species. The chemical reaction network theory studies chemical systems described in such a way. It aims to elucidate the dynamics of overall chemical composition in terms of the associated graph structure. Notably, it applies not only to chemical systems but also to more general systems as long as the mathematical structure is compatible. In the first part of this talk, we will review the basic concepts and results of the theory, which mainly concern the existence and stability of the equilibrium. From the viewpoint of chemical kinetics, it is interesting to consider the rate of the overall reaction, which may be obtained by the total balance of chemical species. The second part of the talk will be devoted to this topic. Formulation of the problem and some results will be presented. In particular, chemical reaction networks with first-order reactions will be considered in detail.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

Relativistic Jet Simulations and Modeling on Horizon Scale

February 8 (Thu) 13:00 - 14:30, 2024

Yosuke Mizuno (T.D. Lee Fellow / Associate Professor, Tsung-Dao Lee Institute, Shanghai Jiao Tong University, China)

Relativistic jets are launched in the vicinity of the central black holes and emit powerful radiation across the electromagnetic spectrum. According to our current understanding, relativistic jets are launched by directly tapping the rotational energy of spinning black holes via the so-called Blandford-Znajek process. In addition to the spin of the black hole, numerical simulations showed the amount of accreted magnetized flux has a major impact on the formation of relativistic jets. We have investigated the radiative signatures of self-consistently launched relativistic jets using 3D general relativistic magneto-hydrodynamical simulations and general relativistic radiative transfer calculations in horizon scale to the connection with large-scale structure. We discuss our findings and comparison with observations.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Recent advances in nuclear Density Functional Theory and applications to the nuclear response

February 6 (Tue) 13:30 - 15:00, 2024

Gianluca Colò (Professor, Department of Physics, University of Milan, Italy / Professor, Sezione di Milano, INFN, Italy)

In this contribution, I will give an overall (and, of course, biased) view of the general status of DFT. I will stress that, in contrast to ab initio methods, DFT is the only framework that allows the study of excited states, including those lying at relatively high energy. Accordingly, I will focus on the nuclear response. After a reminder on the nuclear Giant Resonances and the link with the nuclear equation of state, I will discuss the projection methods to restore symmetries in the calculations of deformed systems. While symmetry-restored calculations are nowadays of common use in the study of ground-state properties and low-lying excitations, similar realistic investigations for the nuclear response are essentially missing in the literature. Recently, we have implemented an exact Angular Momentum Projection (AMP) on top of Skyrme-Random Phase Approximation (RPA) calculations in a projection after variation (PAV) scheme, for the first time. The results will be critically analysed in the case of the monopole response, also taking into account the experimental investigations that can be envisioned for well-deformed systems. If time allows, the nuclear response will be also discussed as a way to improve the current density functionals and ground them on ab initio nuclear theory. This seminar is co-hosted by Nuclear Many-body Theory Laboratory and Few-body Systems in Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science.

Venue: 2F Large Meeting Room, RIBF Building, RIKEN Wako Campus (Main Venue) / via Zoom

Event Official Language: English