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

Investigating the Crust Urca Process in Accretion Neutron Stars: Implications for Superburst Ignition and Hot Cooling Curve of MAXI J0556-332

February 7 (Fri) at 16:00 - 17:15, 2025

Hao Huang (Ph.D. Student, Institute of Modern Physics, China)

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.

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

Event Official Language: English

Fireworks in the cosmos: The Hidden Power of Nuclear Reactions

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

Irin Sultana (Ph.D. Student, Department of Physics, Central Michigan University, USA)

Neutron stars in low-mass X-ray binaries, accreting hydrogen- or helium-rich material from a companion star, frequently exhibit thermonuclear runaways on their surfaces known as Type-I X-ray bursts (XRBs). These bursts are powered by nuclear processes, such as the triple-$\alpha$ process, the $\alpha p$ process, and the rapid proton capture process, which play a critical role in model-observation comparisons. In this study, we investigate the impact of nuclear reaction uncertainties on XRBs using the ONEZONE model (Cyburt et al., 2016), considering different accreted compositions and accretion rates for the binary systems that are within the range of observed burst sources. The study is carried out in two stages. First, we determine the burst ignition conditions by simulating the settling of the accreted material with a full reaction network and a semi-analytical model. Second, we perform a sensitivity analysis by varying proton- and alpha-induced reaction rates in JINA REACLIBV2.2 within their estimated uncertainties. We explore the influence of these reactions on the XRBs light curve and the final abundances. The findings highlight key nuclear reactions that significantly affect XRB observables and the final abundances produced, offering guidance for future experimental efforts to improve our understanding of the uncertainties in the reaction rates involved in XRBs.

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

Event Official Language: English

A coarse-grained model of disordered RNA for simulations of biomolecular condensates

February 6 (Thu) at 16:00 - 17:00, 2025

Ikki Yasuda (Ph.D. Student, Graduate School of Science and Technology, Keio University)

Protein-RNA condensates are involved in a range of cellular activities. Coarse-grained molecular models of intrinsically disordered proteins have been developed to shed light on and predict single-chain properties and phase separation. An RNA model compatible with such models for disordered proteins would enable the study of complex biomolecular mixtures involving RNA. Here, we present a sequence-independent coarse-grained, two-bead-per-nucleotide model of disordered, flexible RNA based on a hydropathy scale. We parameterize the model, which we term CALVADOS-RNA, using a combination of bottom-up and top-down approaches to reproduce local RNA geometry and intramolecular interactions based on atomistic simulations and in vitro experiments. The model semi-quantitatively captures several aspects of RNA-RNA and RNA-protein interactions. We examined RNA-RNA interactions by comparing calculated and experimental virial coefficients, and non-specific RNA-protein interaction by studying reentrant phase behavior of protein-RNA mixtures. We demonstrate the utility of the model by simulating the formation of mixed condensates consisting of the disordered region of MED1 and RNA chains, and the selective partitioning of disordered regions from transcription factors into these, and compare the results to experiments. Despite the simplicity of our model we show that it captures several key aspects of protein-RNA interactions and may therefore be used as a baseline model to study several aspects of the biophysics and biology of protein-RNA condensates.

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

Event Official Language: English

Mathematics of the Future, Science of the Future: Large Language Models and Their Applications

February 6 (Thu) at 14:00 - 16:00, 2025

Akiyoshi Sannai (Program-Specific Associate Professor, Graduate School of Science, Kyoto University)

In recent years, the rapid development of large language models (LLMs) such as ChatGPT has given many researchers a strong impression that these systems truly exhibit “intelligence.” In this presentation, we first review the evolution of AI research, explaining how large language models go beyond conventional machine learning by enabling more “general” forms of learning. We then highlight the importance of “sensors” and “mathematical capability” as key factors that allow AI to autonomously carry out scientific tasks such as problem analysis, hypothesis generation, and proofs in fields like mathematics and physics. We also examine how proof assistants can address the issue of hallucinations in LLM outputs, and discuss the role of combinatorial creativity in accelerating interdisciplinary research. Finally, we introduce our “AI Mathematician” agent project, demonstrating how integrating large language models with proof assistants can open new horizons in mathematical sciences.

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

Event Official Language: English

Master equations for general non-Markovian processes: the Hawkes process and beyond

February 5 (Wed) at 16:30 - 18:00, 2025

Kiyoshi Kanazawa (Associate Professor, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

The Markovian process is one of the most important classes of stochastic processes. The Markovian process is defined as a stochastic process whose time evolution is independent of the system's entire history and has been extensively studied using the master equation and Fokker-Planck equation approaches. In contrast, non-Markovian processes -- where time evolution depends on the full history of the system -- have not been systematically explored, except for a few special cases, such as semi-Markovian processes. In this talk, we present a recent master-equation approach to general non-Markovian jump processes [1-4]. Beginning with a general non-Markovian jump process, we derive the corresponding master equation through a Markovian-embedding approach. The Markovian embedding is a scheme to add a sufficient number of auxiliary variables to convert a non-Markovian model to a high-dimensional Markovian model. For the case of our model, the one-dimensional non-Markovian model is shown to be equivalent to a Markovian stochastic field theory, and we derive the field master equation correspondingly [4]. As an application, we examine the nonlinear Hawkes process, a history-dependent and self-exciting model frequently used in studying complex systems [1-3]. Additionally, we explore the stochastic thermodynamic framework for general jump processes [5] as another example.

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

Event Official Language: English

Introduction to the stochastic process and its application in physics

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

Kiyoshi Kanazawa (Associate Professor, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

The stochastic process is a popular tool for broad disciplines, such as physics, biophysics, chemistry, neuroscience, economics, and finance. In this lecture course, I will provide an elementary introduction to stochastic processes in physics without assuming rigorous background knowledge of probability theories. Most of the basic topics in stochastic processes will be covered in this lecture course, such as (1) the one-to-one correspondence between stochastic differential equations and master equations, (2) their standard forms, (3) Ito's lemma, and (4) the perturbation theories (the system-size expansion). I will also present its application to statistical physics, such as (5) kinetic theory and (6) a microscopic derivation of the Langevin equation from hard-sphere Hamiltonian dynamics in the dilute gas limit. My goal is to help the audience calculate most of the main calculations by their own hands by providing detailed explanations without abbreviations. This lecture is based on my Japanese notebook, available on my webpage (see the link below). Schedule: (Tue., Feb. 4) 13:00-14:30, 14:45-16:15, 16:30-18:00 (Wed., Feb. 5) 10:30-12:00, 13:00-14:30, 14:45-16:15

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

Event Official Language: English

Can social issues be solved by mathematical science!? - Between Mathematics and Entrepreneurship

February 1 (Sat) at 13:00 - 17:00, 2025

We will be holding the 4th symposium exploring the potential of mathematical science research to address societal challenges. Over the past three years, we have focused on themes such as "Social Implementation of Mathematical Research—Challenges and Overcoming Them," "Connecting Corporate Issues with Mathematical Research," and "Mathematical Research in Companies." In recent years, there has been a global surge in support for startups leveraging cutting-edge scientific and technological innovations. However, there are relatively few cases where mathematical foundation technologies have led to the creation of startups. On the other hand, IT giants of the 21st century, such as Google, have built their success on mathematical technologies, demonstrating the high potential of mathematics as a core technology for startups. This year, we will hear from various organizations that support university-based startups, as well as researchers who have successfully launched their own ventures. Together with the participants, we aim to learn about the intersection of "mathematical foundation technologies" and "startups" and discuss strategies to bridge the gap between the two.

Venue: Hybrid Format (Noyori Conference Hall, Nagoya University and Zoom)

Event Official Language: Japanese

Can AI understand Hamiltonian mechanics?

January 31 (Fri) at 16:00 - 17:00, 2025

Tae-Geun Kim (Ph.D. Student, Department of Physics, Yonsei University, Republic of Korea)

With recent breakthroughs in deep learning, particularly in areas like natural language processing and image recognition, AI has shown remarkable abilities in understanding complex patterns. This raises a fundamental question: Can AI grasp the core concepts of physics that govern the natural world? In this talk, as a first step towards addressing this question, we will discuss the possibility of AI understanding Hamiltonian mechanics. We will first introduce the concept of operator learning, a novel technique that allows AI to learn mappings between infinite-dimensional spaces, and its application to Hamiltonian mechanics by reformulating it within this framework. Then, we will test whether AI can derive trajectories in phase space given an arbitrary potential function, without relying on any equations or numerical solvers. We will then showcase our findings, demonstrating AI's capability to predict phase space trajectories under certain constraints. Finally, we will discuss the limitations, future research directions, and the potential for AI to contribute to scientific discovery.

Venue: via Zoom

Event Official Language: English

D-modules and the Riemann-Hilbert correspondence as a foundation for mixed Hodge modules

January 31 (Fri) at 14:00 - 16:00, 2025

Takahiro Saito (Assistant Professor, Faculty of Science and Engineering, Chuo University)

Algebraic analysis is a field which began with the study of differential equations in an algebraic framework, known as D-modules. The Riemann-Hilbert correspondence lies at the heart of this field, which bridges the worlds of analysis and geometry. Thanks to this, some geometric problems can be studied by using D-module theory, and vice versa. Based on D-module theory, Morihiko Saito introduced the concept of mixed Hodge modules, realizing Hodge theory on constructible sheaves, which brings us a functorial treatment of Hodge theory and various applications. In this talk, we will begin with the linear differential equations on the complex plane and introduce monodromy, regularity and Deligne's Riemann-Hilbert correspondence. Then, as a generalization of it, I will explain the basics of the theory of D-modules and the Riemann-Hilbert correspondence. Finally, I will describe the role they play in the theory of Hodge modules and recent progress in this area. For the audience's background knowledge, I will assume basic complex function theory. I will start with a simple example, so people outside the field are welcome.

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

Event Official Language: English

Effective size and dimension, in biology and beyond

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

Ryosuke Iritani (Senior Research Scientist, iTHEMS)

This talk will be a very short, introductory talk on some fundamental concepts of “effective size” from population-biological, statistical, and mathematical viewpoints.

Venue: via Zoom

Event Official Language: English

Reheating after a cosmological constant relaxation and gravitational waves lensed by a supermassive black hole

January 30 (Thu) at 14:00 - 15:30, 2025

Paul Martens (Postdoctoral Fellow, Department of Physics, The Chinese University of Hong Kong, China)

This presentation will be articulated in two parts. In a first part, I will present the a reheating mechanism that follows a dynamically relaxed cosmological constant. The latter is achieved by the dynamics of a scalar field whose kinetic term is modulated by an inverse power of spacetime curvature. While it is at work against radiative corrections to the dark energy, this process alone would wipe out not only the vacuum energy, but also all other matter contents. A reheating phase is thus introduced, which exploits a null-energy-condition violating sector. In a second part, I shall present a more recent and still ongoing project to describe and characterize the lensing of gravitational waves by an active galactic nuclei (or any supermassive black hole), in the geometric limit. Such systems are simple enough for constraints to be derived with only few assumptions. Yet, they present interesting features that could provide information on e.g. on binary black hole formation mechanisms and quasinormal modes.

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

Event Official Language: English

Quantum Error Mitigation

January 28 (Tue) - 29 (Wed), 2025

Suguru Endo (Ph.D. Researcher, Research Center for Theoretical Quantum Information, NTT Computer and Data Science Laboratories)

Note for registration [2024-12:24]: We are sorry that the number of registration has reached the capacity of the lecture room. Thank you for your understanding. Note for participants [2024-12:18]: For participants, please register from the above form. We may limit the number of participants due to the capacity of the lecture room. For participants in RIKEN who have already answered a questionnaire on this lecture, you do not have to register. Program: Day 1 (Jan. 28th) 10:30-12:00 Lecture 1 12:00-13:30 Lunch time 13:30-15:00 Lecture 2 15:00-15:30 Coffee break 15:30-17:00 Lecture 3 Day 2 (Jan. 29th) 10:30-12:00 Lecture 4 12:00-13:30 Lunch time 13:30-15:00 Lecture 5 15:00-15:30 Coffee break 15:30-17:00 Lecture 6 Abstract: Quantum Error Mitigation (QEM) offers a practical approach to reducing errors in noisy intermediate-scale quantum (NISQ) devices without requiring the encoding of qubits. In this seminar, I will begin by discussing the fundamentals of noise modeling in quantum systems, followed by an overview of QEM techniques, including extrapolation, probabilistic error cancellation (PEC), virtual distillation, quantum subspace expansion, and Clifford data regression. Next, I will present advanced QEM methods, such as the stochastic PEC approach, which mitigates the effects of Lindblad terms in Lindblad master equations and the generalized quantum subspace expansion, which is a unified framework of QEM. I will also explore recent research on the information-theoretic analysis of QEM, shedding light on its fundamental limits and connections to non-Markovian dynamics. Furthermore, I will discuss studies combining QEM with quantum error correction to enhance the reliability of computations in the early fault-tolerant quantum computing era. Lastly, I will highlight the relevance of hybrid tensor networks, particularly their connections to quantum subspace expansion techniques.

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

Event Official Language: English

Architectures and algorithms for early FTQC

January 27 (Mon) at 16:00 - 17:15, 2025

Andreas Thomasen (R&D Engineer, QunaSys Inc.)

The NISQ era of quantum computing is characterized by quantum devices that have low error rates, but no error correction and typically on the order of 100 qubits, whereas the era of FTQC requires devices with full error correction facilitated by hundreds of thousands to millions of qubits for every logical qubit. Due to the distinct requirements and operating characteristics of these devices, algorithms and applications supported by NISQ and FTQC respectively are highly distinct as well. However, this leaves a large gap, both in terms of devices, algorithms and applications which exist in the intermediate regime where partial error correction is possible and the devices support on the order of tens of thousands of qubits. In this seminar we will give a brief introduction to quantum computing for a non-specialist audience. We will then describe device architectures and algorithms that are specifically designed to fill this gap during the so-called early FTQC era. We will present the space-time efficient analogue rotation (STAR) architecture together with some algorithms that are well supported by it, namely quantum selected configuration interaction (QSCI) and statistical phase estimation (SPE). This seminar serves as theoretical background for our QURI SDK hands-on session at a later date. The algorithms introduced are directly available as OSS as described in the link below.

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

Event Official Language: English

Seminar Series for Junior and Senior High School Girls: 'What Should Students Prepare for Their Future in the Age of AI?'

January 25 (Sat) at 14:00 - 18:30, 2025

The RIKEN Center for Advanced Intelligence Project (AIP) and the Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) have jointly planned an event for junior and senior high school students interested in AI, mathematics, and information science. This event introduces the exciting research conducted by scientists in these fields. Join us to explore “The Future Built with AI” and discover what steps students can take now to prepare for the future. We look forward to your participation! For more details, please refer to the related links.

Venue: Nihonbashi AIP Center Open Space & Zoom (Hybrid Format)

Event Official Language: Japanese

Quantitative Characterization of the Cellular Physical Properties to Understand the Organ Regeneration and Cancer Progression

January 23 (Thu) at 16:00 - 17:00, 2025

Takahisa Matsuzaki (Assistant Professor, Department of Applied Physics, Graduate School of Engineering, Osaka University / TechnoArena Associate Professor, Center for Future Innovation, Graduate School of Engineering, Osaka University)

Since the discovery of regulating the differentiation of "single" stem cells by extracellular mechanics, researchers have focused on the mechanobiology of single cells. Our collaborative studies provided the first breakthrough to identify optimal mechanics for multi-cellular, liver organogenesis (Takebe, .., Matsuzaki,.., Yoshikawa et al., Cell Stem Cell 2015, Stem Cell Reports 2018). My motivation is to be a pioneer internationally in understanding the role of heterogenic physical properties in multi-cellular related life-phenomena such as cancer cell adhesion (Matsuzaki et al., Phys Chem Chem Phys 2018, Bioconjugate Chem 2023, PNAS 2024, Osaka University Award 2024.), regeneration of colon/muscle (iScience 2022, Taniguchi,.., Matsuzaki et al., Mucosal Immunology 2023, J. Phys Chem Letter 2014, 2022, 2024.), and bone (Mizuno, .., Matsuzaki et al., Stem Cell Res. Ther. 2022, iScience 2024). In my presentation, I will overview the recent progress in developing fluorescence/interference microscopy combining atomic force microscopy (AFM), and its application to organ regeneration and cancer progression.

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

Event Official Language: English

Probabilistic approach to discrete integrable systems

January 17 (Fri) at 15:30 - 17:30, 2025

Makiko Sasada (Professor, Graduate School of Mathematical Sciences, The University of Tokyo)

The KdV equation and the Toda lattice are two central and widely studied examples of classical integrable systems, and many of their variations have been introduced to the present. In particular, the box-ball system (BBS) is a basic example of a discrete integrable system, which has been revealed to be an ultra-discrete version of the KdV equation and the Toda lattice. The BBS has been studied from various viewpoints such as tropical geometry, combinatorics, and cellular-automaton. As a new perspective, research on probabilistic approaches to this system has been rapidly expanding in recent years, including the application of the Pitman transform, analysis of invariant measures and its generalized hydrodynamics. More recently, we find that the application of the Pitman transform and the study of invariant measures of i.i.d.-type also work in the same manner for the discrete KdV equation and the discrete Toda lattice. Further research has begun on the relationship between the Yang-baxter maps and the existence of i.i.d.-type invariant measures for the discrete integrable systems. In this talk, I will introduce these new research topics that have been spreading over the past several years from the basics. This talk is based on several joint works with David Croydon, Tsuyoshi Kato, Satoshi Tsujimoto, Ryosuke Uozumi, Matteo Mucciconi, Tomohiro Sasamoto, Hayate Suda and Stefano Olla.

Venue: Seminar Room #359

Event Official Language: English

Principles of the evolution of human social structures: kinship and gift-giving

January 16 (Thu) at 16:00 - 17:15, 2025

Kenji Itao (Special Postdoctoral Researcher, Computational Group Dynamics Collaboration Unit, RIKEN Center for Brain Science (CBS))

Anthropologists have long noted structural similarities among geographically distant societies. To investigate the origins of these patterns, I develop simple models of human interactions based on field observations, simulating the emergence of social structures. This talk focuses on two key topics. The first examines the evolution of kinship structures in clan societies [1, 2, 3]. By modeling kin and in-law cooperation alongside mating competition, I show how cultural groups with specific marriage rules spontaneously emerge. The second explores the transition of social organizations through competitive gift-giving [4, 5]. By modeling how gifts deliver material goods to recipients and confer social reputation upon donors, I demonstrate transitions across four phases—band, tribe, chiefdom, and kingdom—each characterized by distinct social networks and distributions of wealth and reputation. In both cases, I highlight the alignment between theoretical predictions and empirical observations, offering quantitative criteria and empirically measurable explanatory parameters for classifying social structures.

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

Event Official Language: English

Visit by ASCENT-6E high school students

January 13 (Mon) at 10:40 - 16:00, 2025

PROGRAMME Visit of students enrolled in the ASCENT Program at Chiba University Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS): RIKEN Wako Campus (Wako City, Saitama) Event date: Monday, January 13th, 2025 ASCENT-6E Program: iTHEMS members: Schedule 10:30-10:40 (10 min): Arriving procedure 10:40-11:00 (20 min) at meeting room on the 4th floor, Main Research Building Introduction of students (to hear their names and scientific fields of interest). We will provide colour-coded badges to write their names and the colour would represent their field of interest (e.g., blue for biology, green for math, red for physics). 11:00-11:10 (10 min) Bathroom break 11:10-12:00 (50 min) at meeting room on the 4th floor, Main Research Building First set of talks by iTHEMS members (10 min each) Tetsuo Hatsuda (Physics, mathematics) Catherine Beauchemin (Physics, biology) Tsukasa Tada (Physics, mathematics) Gen Kurosawa (Biology) Misako Tatsuuma (Physics) 12:00-12:50 (50 min) at Common Space in the 4th floor of Main Research Building (tentative) Discussion Lunch with students 12:50-13:40 (50 min) at meeting room on the 4th floor, Main Research Building Second set of talks by iTHEMS members (10 min each) Akihisa Yamamoto (Physics, biology) Ryo Namba (Physics) Christy Kelly (Mathematics, physics) Rumi Hasegawa (Physics) Jose Gutierrez (Biology) 13:40-13:50 (10 min) at meeting room on the 4th floor, Main Research Building Brief overview of iTHEMS and RIKEN programmes (T.Hatsuda, C.Beauchemin, or T. Tada) (e.g., JRA, IPA, SPDR, RS/SRS) 13:50-14:00 (10 min) Bathroom break 14:00-14:15 (15 min) at meeting room on the 4th floor, Main Research Building (tentative) Short statements by Prof. Jun Nomura and ASCENT program coordinators Qian Wang and Hina Morishige 14:15-16:00 (105 min) at Common Space in the 4th floor of Main Research Building (tentative) Informal discussions among ASCENT program students and iTHEMS members over some snacks and coffee. iTHEMS members will spread at different areas in the common space of 3rd floor and will display posters or conduct activities that can facilitate discussion. If posters are used, they may be the ones used in the Now & Next or new ones.

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

Event Official Language: English

Search for BSM particles from high energy supernova neutrinos

January 10 (Fri) at 14:00 - 15:15, 2025

Kensuke Akita (JSPS Research Fellow, Graduate School of Science, The University of Tokyo)

Light hypothetical particles with masses up to O(100) MeV can be produced in the core of supernovae. Their subsequent decays to neutrinos can produce a flux component with higher energies than the standard flux. We study the impact of heavy neutral leptons, Z′ bosons, in particular U(1)Lμ−Lτ and U(1)B−L gauge bosons, and majorons coupled to neutrinos flavor-dependently. We obtain new strong limits on these particles from no events of high-energy SN 1987A neutrinos and their future sensitivities from observations of galactic supernova neutrinos.

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

Event Official Language: English