This seminar investigates the Urca cooling strength of the 63Fe-63Mn pair, which varies due to uncertainties in the spin-parity of 63Fe, relevant to the Island of Inversion at N = 40. We present simulations that analyze the impact of this cooling mechanism on the thermal evolution of neutron star crusts, focusing on superburst ignition and anomalous hot quiescent phase cooling of MAXI J0556-332. Additionally, we explore the potential crust Urca process through the anomalous cooling curve of MAXI J0556-332, fitting observational data to determine neutron star mass and radius preferences. Preliminary results suggest that neutron stars with a crust Urca process tend to have smaller masses and larger radii, highlighting the need for precise β-decay measurements to further understand these phenomena.

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.

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].

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.

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.

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

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.

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.

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.

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.

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 (iTHEMS)
Faculty of Science, Nara Women's University

Program:
13:50-15:15
RIBF Facility, RIKEN Nishina Center (RNC) (E01, Nishina RIBF Building)

15:30-16:30
RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) (C01, Main Research Building, #359)
Introduction to iTHEMS: Tetsuo Hatsuda (iTHEMS Director)
Lecture and Q&A: Nagisa Hiroshima (iTHEMS)

16:45-18:00
RIKEN Center for Brain Science (CBS) (C56, Ikenohata Research Building, #316)
Laboratory for Sensorimotor Integration (Fumi Kubo, Team Leader)

18:30-21:00
Networking Session (C01, Research Building 3F)

9:15-10:30
RIKEN Center for Advanced Photonics (RAP) (C32, Laser Research Building, Mid Conference Room A)
Photonics Control Technology Team (Satoshi Wada, Team Leader)

10:45-12:00
RIKEN Center for Sustainable Resource Science (CSRS) (S01, Biological Science Research Building, S311)
Molecular Bioregulation Research Team (Shinya Hagihara, Team Leader)

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

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.

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.

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.