Pebbles in Planet Formation

February 10 (Mon) - 13 (Thu), 2025

Research on planet formation involves various approaches, including explorations of small solar system bodies, observations of protoplanetary disks, dust experiments, simulations, and theoretical studies. One of the primary objectives in this field is to develop a comprehensive theory that explains how kilometer-sized planetesimals form from micrometer-sized dust grains, drawing upon findings from these diverse research methods. This workshop will focus on the concept of pebbles, which play a crucial role in the planet formation process. Pebbles — typically defined as solids ranging from millimeter to centimeter in size — are intermediate building blocks in planet formation, though their definition varies depending on the context. Assuming pebbles has led to theoretical advances in mechanisms such as streaming instability and pebble accretion, which promote the formation and growth of planetesimals. Additionally, pebbles have been linked to barriers against dust growth, such as the bouncing barrier. Furthermore, observations of protoplanetary disks have revealed the size distribution and porosity of solids, while the strength and thermal conductivity of comets obtained by the Rosetta mission suggest the accumulation of pebbles due to disk instabilities. However, inconsistencies have been pointed out between pebble formation and theories of dust growth. This workshop aims to revisit and refine our understanding of solid materials implicated in planet formation, particularly in light of findings from solar system explorations and protoplanetary disk observations. We aim to reevaluate the definition and role of pebbles in the broader context of planet formation, with a special focus on the current challenges and open questions in the field. The workshop will include discussions of experiments and simulations of dust growth and collisions, and planetesimal formation mechanisms such as streaming instability. The workshop features keynote talks from the perspectives of explorations, observations, experiments, simulations, and theories, and we also call for presentations on related topics.

Venue: National Astronomical Observatory of Japan (Mitaka Campus) (Main Venue) / via Zoom

Event Official Language: English

Mathematical Studies on Human Cooperation

February 12 (Wed) at 15:00 - 17:00, 2025

Yohsuke Murase (Research Scientist, Discrete Event Simulation Research Team, RIKEN Center for Computational Science (R-CCS))

Cooperation is a fundamental part of human society. But from an evolutionary perspective, it remains a puzzle—why do people help others even when it costs them? In theory, selfish individuals should have an advantage over cooperators. To explain how cooperative behaviors evolved, researchers have proposed several mechanisms, among which direct and indirect reciprocity play key roles in human interactions. In this talk, I will present my research on the evolution of cooperation, focusing on these two mechanisms. I will begin with an introduction to game theory and evolutionary game theory, which help us understand how people make decisions in strategic situations. Then, I will discuss my study on the repeated Prisoner’s Dilemma, where we discovered a new class of strategies through mathematical analysis and large-scale computations [1]. Finally, I will talk about my research on indirect reciprocity, a process where people cooperate based on reputation [2].

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Application of genetics and genomics to breeding

February 13 (Thu) at 16:00 - 17:30, 2025

Jeffrey Fawcett (Chief Scientist, Regional Fish Institute, Ltd.)

Humans have domesticated and modified several plants and animals over the course of history to achieve food security. However, drastic changes are required in order to meet the needs of a growing population while facing global warming. In particular, utilizing and improving the productivity of unutilized or underutilized resources such as minor crops, aquatic species, and insects are thought to be essential. Here, I will provide an overview of how humans have been modifying organisms by selective breeding, the role of genetics and genomics in modern selective breeding, and the challenges we are currently facing. This talk will be aimed at non-experts/non-biologists and will cover the basics of genetics.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Linking quantum error correction and gauge theories with quantum reference frames

February 14 (Fri) at 10:30 - 11:30, 2025

Philipp Hoehn (Assistant Professor, Okinawa Institute of Science and Technology Graduate University (OIST))

Redundancy is the hallmark of both quantum error correction and gauge theories. In this talk, I will show that this analogy is not merely a coincidence but that there is a deeper underlying structural relationship. The key ingredient to this observation is quantum reference frames (QRFs), which constitute a universal tool for dealing with symmetries in quantum systems. They define a split between redundant and physical information in gauge systems, thereby establishing a notion of encoding in that context. This leads to an exact dictionary between (group-based) quantum error correcting codes and QRF setups. In stabilizer codes, this uncovers a correspondence between errors and QRFs: every maximal set of correctable errors generates a unique QRF, and each QRF is associated with a unique class of correctable errors. This allows for a reinterpretation of the Knill-Laflamme condition and novel insights into the relation between correctability and redundancy. The dictionary also reveals a novel error duality, based on Pontryagin duality, and somewhat akin to electromagnetic duality. Time permitting, I will illustrate these findings in surface codes, which can be understood as both codes and lattice gauge theories. These findings may find use in code design and quantum simulations of gauge theories.

Venue: #345-347, 3F, Main Research Building

Event Official Language: English

Operator-algebraic approach to point processes

February 14 (Fri) at 15:00 - 17:00, 2025

Ryosuke Sato (JSPS Postdoctoral Research Fellow, Faculty of Science and Engineering, Chuo University)

A point process is a mathematical description of a particle system with random interactions, and it naturally appears in various areas of mathematical physics and mathematics, including statistical mechanics, random matrix theory, combinatorics, and representation theory. In particular, a random particle system with repulsive interactions is associated with a determinantal point process, in which the correlation of any number of particles is expressed in terms of the two-particle correlation via a determinant. Furthermore, this determinantal structure enables an algebraic analysis using CAR algebras, which are operator algebras determined by canonical anti-commutation relations. In the first half of the talk, we will review the relationship between determinantal point processes and operator algebras, with a focus on why operator algebras naturally lend themselves to analyses in probability theory and statistical mechanics. In the second half, based on recent work, we will examine the dynamic relationship between point processes and operator algebras, discussing how dynamics on CAR algebras give rise to stochastic processes on determinantal point processes.

Venue: #359, 3F, Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

MACS 10th Anniversary Colloquium & 2024 MACS Achievement Report Meeting

February 19 (Wed) at 14:45 - 18:30, 2025

Hiroshi Kokubu (Executive Vice-President, Kyoto University)
Yoshiko Takahashi (Professor, Division of Biological Sciences, Graduate School of Science, Kyoto University)

14:45-15:00 Teatime discussion [15:00-16:30 First part: MACS 10th Anniversary Colloquium] 15:05-15:05 Opening 15:05-15:30 Talk by Prof. Hiroshi KOKUBU Title: How did MACS begin? Abstract: As the MACS program, which began with a kick-off symposium in May 2016, enters its 10th year in the academic year 2025, I would like to look it back and talk about how it started, what thoughts shared by people involved at the time led to the spirit of MACS. I’d also like to share ideas and experiences in the history of MACS over the past 10 years, including what we wanted to do with MACS in the beginning but could not, or how MACS have collaborated with other subsequent activities of Kyodai RIGAKU (Kyoto U Science). 15:30-15:55 Talk by Prof. Yoshiko TAKAHASHI Title: Excitement through the MACS program Abstract: When the MACS program was launched, a research article was published by Harvard University, in which the gut looping during vertebrate development was beautifully explained by inter-disciplined science with experimental biology, physics, and mathematics. I was very impressed and motivated by this paper, and aimed at similar new waves through the MACS program. I have been running a study group, in which graduate- and undergrad students of not only life science but also physics and mathematics joined, and we enjoyed discussion and looking at real chicken embryos. Such experiences are not what we can easily obtain in conventional education program in campus life. 15:55-16:20 Discussion 16:20-16:30 Break [16:30-18:30 Second part: 2024 MACS Achievement Report Meeting] 16:30-17:30 Flash Talks to report results 17:30-18:30 Poster Session by SG participating students

Venue: Science Seminar House (Map 9), Kyoto University

Event Official Language: Japanese

The Topology, Geometry and Physics of non-Hausdorff manifolds

February 19 (Wed) at 15:00 - 17:00, 2025

O'Connell David (Ph.D. Student, Okinawa Institute of Science and Technology Graduate University (OIST))

Non-Hausdorff manifolds are manifolds containing "doubled points" that cannot be separated by disjoint open sets. In this talk we will survey some mathematical and physical results surrounding these unusual spaces. As a theme, we will start with their fundamental description as a topological space, and slowly add in more and more structure of interest until we can meaningfully phrase questions of physics. On the mathematical side, we will see descriptions of non- Hausdorff manifolds as colimits of ordinary manifolds, which allows us to describe their geometric features without appealing to arbitrarily- existent partitions of unity. On the physical side, we will consider the inclusion of non-Hausdorff manifolds in a naïve 2d Lorentzian path integral for gravity, and (time permitting) explain how construct quantum fields on a non-Hausdorff background. Ultimately, we will see that these latter two arguments suggest that non-Hausdorff manifolds may be more appropriate than the standard "Trousers space" for the modelling of topology change in Lorentzian signature.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

How to define a Majorana fermion?

February 20 (Thu) at 13:00 - 14:30, 2025

Kazuo Fujikawa (Professor Emeritus, The University of Tokyo)

It is fundamental in particle physics if the neutrino is a Dirac fermion or a Majorana fermion, and the seesaw model gives naturally a Majorana neutrino in an extension of the Standard Model. However, the commonly used chirality changing \(pseudo-C symmetry \) \(\nu^{\tilde C}_L=C\overline{\nu_L}^T\) of a chiral fermion is not defined in Lagrangian field theory. Precisely speaking, the neutrinoless double beta decay is not described by the pseudo-C symmetry. The Majorana neutrino obtained after a Bogoliubov-type canonical transformation, which is the one originally defined by Majorana using a Dirac-type fermion, describes consistently all the properties expected for the Majorana neutrino. Physical implication of this fact is briefly discussed.

Venue: #359, 3F, Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Exploring the evolutionary fate of a mutualistic community using automated microbial culture system

February 20 (Thu) at 16:00 - 17:00, 2025

Junya Sunagawa (Ph.D. Student, Graduate School of Life Science, Hokkaido University)

Microbes are ubiquitous around the world, forming systems where they interact through competition or cooperation. Especially in the form of cooperation, exchange of essential metabolites, known as metabolic cross-feeding, plays a fundamental role in the assembly of microbial communities. An extreme case of metabolic cross-feeding is an obligate mutualism, where one organism can only grow with the help of a partner supplying metabolites (e.g., amino acid). When they face environmental stresses such as antibiotics, it is unclear whether the benefit that causes the formation of obligate ecological mutualism may benefit (or cost) the members to increases (inhibits) resistance through interactions at the evolutionary scale. Another fascinating question is whether an additional benefit (e.g., an enzyme that helps the community persistence against environmental change) will select the community to increase the resistance. Here, I will report my ongoing research progress of obligate cross-feedings involving β-lactamase and discuss the conditions where the benefit can overcome the cost of the obligate interaction. I have started to address this issue by conducting laboratory evolution experiments with an automated culture system which can automatically adjust the strength of the stress (i.e., concentration of the antibiotics), so that the focal microbes have to get evolved. I will also share my story about building this automated culture system.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Ubiquity of geometric Brascamp--Lieb data

February 21 (Fri) at 15:00 - 17:00, 2025

Hiroshi Tuji (JSPS Research Fellow PD, Graduate School of Science and Engineering, Saitama University)

This talk is based on a joint work with Neal Bez (Nagoya university) and Anthony Gauvan (Saitama university). The Brascamp--Lieb inequality is a futher general inequality involving some data (we call it the Brascamp--Lieb datum), which has been studied in harmonic analysis and convex geometry. For instance, the Hölder inequality and the Young convolution inequality are particular cases. In this talk, we have an interest in geometric Brascamp--Lieb data, which are specific data satisfying nice properties, for which the best constant of the Brascamp--Lieb inequality is well-understood. Our goal in this talk is to show that geomtric Brascamp--Lieb data are dense in general Brascamp--Lieb data in certain sence. Our result substantially follows from the work by Garg, Gurvits, Oliveira and Wigderson.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Asymptotics in astrophysics iTHEMS workshop

February 25 (Tue) - 28 (Fri), 2025

This workshop will include overview talks of application of asymptotics and perturbation theory techniques in (wave transport or oscillation related) astrophysics and cosmology eigenvalue problems. In addition, there will be introductory talks about fundamental asymptotics and perturbation theory techniques used in theoretical physics. The purpose of this interdisciplinary workshop is to identify problems in astrophysics and related fields including, but not limited to, stellar structure and evolution, black holes and high-energy physics which can be solved using existing asymptotics and perturbation theory methods in theoretical physics problems (e.g. quantum field theory, gravity), and vice versa.

Venue: 8F, Integrated Innovation Building (IIB)

Event Official Language: English

Genome and Sex Chromosome Analyses of Japanese Frogs Carrying Both XY and ZW Chromosomes Within the Same Species

February 27 (Thu) at 16:00 - 17:00, 2025

Yukako Katsura (Assistant Professor, Center for the Evolutionary Origins of Human Behavior, Kyoto University)

The evolution of sex chromosomes, particularly sex chromosome turnover, is a complex and fascinating topic in genetics and evolutionary biology. Sex chromosome turnover refers to the process in which the sex chromosome system changes from XY to ZW (or vice versa), or in which sex chromosomes with different evolutionary origins emerge within the same system (e.g., from one XY system to another XY system). To study sex chromosome turnover, we focus on the Japanese frog (Glandirana rugosa), which possesses both XY and ZW sex chromosomes within the same species, and investigate the molecular mechanisms behind the turnover in the frog (Review: Hayashi et al. JB 2024). Previously, we sequenced the nuclear genome of the ZZ frog (Katsura et al. LSA 2021) and identified sex-linked genes in two populations of the XY and ZW frogs (Miura et al. Mol Ecol 2022). It has been suggested that sex chromosomes originating from at least three different chromosomal lineages have independently emerged within this species. The frogs have a total of 13 chromosomes, and in two populations (Tokai/Eastern Central Japan and Hokuriku-Tohoku/North-Western Japan), chromosome 7 has morphologically differentiated into both ZW and XY chromosomes. However, in other populations, sex chromosomes do not show any morphological differentiation. In this seminar, I introduce the background of our sex chromosome study and present the results of sequence comparisons of morphologically differentiated XY and ZW chromosomes, as well as findings from our analyses of populations, genome, and transcriptome.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

RIKEN-Nara Women's University Joint Diversity Promotion Workshop 2025

March 3 (Mon) - 4 (Tue), 2025

The RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) and the Faculty of Science at Nara Women's University are promoting a project to foster female researchers under the auspices of the RIKEN Diversity Promotion Office. As part of the program, 19 undergraduate and graduate students from Nara Women's University will visit several laboratories on the RIKEN Wako campus to ask questions about their research and hold workshops/presentations with iTHEMS researchers. Organizers: RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program Faculty of Science, Nara Women's University Program: TBD

Venue: via Zoom

iTHEMS Cosmology Forum 3 - (P)reheating the primordial Universe

March 4 (Tue) - 5 (Wed), 2025

Seishi Enomoto (Postdoctoral Researcher, College of Engineering Science, Yokohama National University)
John T. Giblin (Professor, Department of Physics, Kenyon College, USA)
Kyohei Mukaida (Assistant Professor, Theory Center, High Energy Accelerator Research Organization (KEK))

iTHEMS Cosmology Forum Workshop is a series of short workshops, each focusing on an emerging topics in cosmology. The target audience is cosmologists, high-energy physicists and astronomers interested in learning about the subject, not just those who have already worked on the topic. The goal of the workshop is to provide working knowledge of the topic and leave dedicated time for discussions to encourage mutual interactions among participants. The third workshop is devoted to the 'reheating' phase of the early Universe. Reheating bridges the gap between the (almost) empty universe at the end of cosmic inflation and the thermal state of particles, required for Big-Bang nucleosynthesis, and the events of the hot Big-Bang model as a whole, to unfold. It is expected to proceed in different stages starting with a violent parametric resonant creation of particles, dubbed preheating, followed by a redistribution of energy leading to a thermal state. This phase potentially hosts rich phenomenology such as the formation of topoligical defects e.g. solitons, generation of gravitiational wave, and so on. Yet, the very non-linear nature of reheating makes it notoriously hard to describe analytically, and even numerical simulations struggle to follow the whole sequence of events in a given model. Reheating studies have thus yet to reach the degree of compherensiveness and universality that the understanding of cosmic inflation has achieved. This forum will consist of two events. The first, on March 4th, will be in conference format comprising scientific talks on research trends in (P)Reheating. The second, on March 5th, will be a tutorial on numerical aspects of reheating (both theory and hands-on with code) hosted by Tom Giblin of Kenyon College. The workshop will be in English. The workshops are organised by the iTHEMS Cosmology Forum working group, which is the successor of the Dark Matter Working Group at RIKEN iTHEMS. Important dates: Feb. 25th - Registration deadline March 4th - Workshop Day (Room #435-437, Main Research Building 4F) March 5th - Tutorial Day (Room #445-447, Main Research Building 4F) Invited Speakers: John T. Giblin - Kenyon College Kyohei Mukaida - KEK Seishi Enomoto - Yokohama National University Organisers: Kohei Hayashi, Nagisa Hiroshima, Derek Inman, Amaury Micheli, Ryo Namba

Venue: #435-437, 4F, Main Research Building / #445-447, 4F, Main Research Building

Event Official Language: English

Smart heuristics of a single-celled organism

March 7 (Fri) at 14:00 - 15:30, 2025

Toshiyuki Nakagaki (Professor, Research Institute for Electronic Science, Hokkaido University)

Although we rarely question how smart unicellular organisms are, it has become clear that unicellular organisms are smarter than we expected. In fact, various protozoa (unicellular eukaryotes) can take actions that are advantageous for their survival even in complex environments in the wild environments. In this talk, I will introduce some typical examples of smart behaviors in a protozoan amoeba (the plasmodium of Physarum polycephalum): (1) maze-solving, (2) formation of multi-functional transport network that mimics public transportation network among cities in Tokyo region, and so on. We will propose a mathematical model of these behaviors and extract the heuristics (simple rules of behavior) that give rise to their smartness. In general, we will discuss the future potential of research into the behavioral intelligence of protozoa.

Venue: Okochi Hall (Main Venue) / via Zoom

Event Official Language: English

Third Workshop on Density Functional Theory: Fundamentals, Developments, and Applications (DFT2025)

March 25 (Tue) - 27 (Thu), 2025

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, is still ongoing. 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 interdisciplinary discussions and collaborations were started. On February 2024, we had the second workshop on this series (DFT2024) at RIKEN Kobe Campus, and more stimulated discussion occured. To keep and extend collaborations, we organize the third workshop. Since the third workshop, we extend the scope of the workshop to the development and application of DFT as well. 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 sessions composed of contributed talks are also planned.

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

Event Official Language: English

Stability of nonsingular black holes

March 27 (Thu) at 15:00 - 16:30, 2025

Shinji Tsujikawa (Professor, Graduate School of Advanced Science and Engineering, Faculty of Science and Engineering, Waseda University)

We show that nonsingular black holes (BHs) realized in nonlinear electrodynamics are always prone to Laplacian instability around the center because of a negative squared sound speed in the angular direction. This is the case for both electric and magnetic BHs, where the instability of one of the vector-field perturbations leads to enhancing a dynamical gravitational perturbation in the even-parity sector. Thus, the background regular metric is no longer maintained in a steady state. We also generalize our analysis to the case in which a scalar field is present besides the U(1) gauge field and find no explicit examples of linearly stable nonsingular BHs. Our results suggest that the construction of regular BHs without instabilities is generally challenging within the scheme of classical field theories.

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

Event Official Language: English