Mathematical Application Research Team Meeting #19

September 28 (Mon) 14:00 - 15:15, 2026

Antoine Diez (Research Scientist, Mathematical Application Research Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

In this meeting, Antoine Diez will give a talk on his work in progress regarding "Scaling limits for active Laguerre tessellations."

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

Event Official Language: English

121st Data Assimilation and Prediction Science Seminar

September 28 (Mon) 14:00 - 16:00, 2026

Shunji Kotsuki

Title: "Exploring Live Cameras for Actionable Weather Prediction: Recent Studies with Chiba University’s BAECAST Network" Abstract: Numerical weather prediction has advanced substantially through improvements in observing technologies, data assimilation methods, and numerical weather prediction (NWP) models. More recently, artificial intelligence (AI) has increasingly been used to develop surrogates for NWP models and to advance nonlinear and non-Gaussian data assimilation. These developments are expected to enable more effective use of large volumes of observational data, including satellite observations. To further improve weather forecast accuracy, it is important not only to refine data assimilation methods and NWP models but also to explore new sources of observations. Our research focuses on the vast amounts of data generated by live-streaming cameras already deployed in everyday settings. Many of these cameras capture aspects of weather conditions, and harnessing this information could contribute to further improvements in weather prediction. This talk will present several studies on weather forecasting and diagnostics using live-streaming cameras installed at Chiba University. I will introduce BAECAST, an approach to visual weather forecasting, and discuss which meteorological variables can be retrieved from live-camera imagery. I will also present our efforts to transform the nature of weather forecasts using live-camera data using a conditional diffusion model.

Venue: Hybrid Format (RIKEN R-CCS room C107 and Zoom) / via Zoom

Event Official Language: English

7-Branes in Non-SUSY String Theory

September 24 (Thu) 15:00 - 17:00, 2026

Masashi Kawahira (Program-Specific Researcher, Yukawa Institute for Theoretical Physics, Kyoto University)

7-branes play an important role in probing the strongly coupled regime of type IIB superstring theory. In this talk, we discuss whether analogous objects exist in type 0B string theory, which can be regarded as a non-supersymmetric counterpart of type IIB superstring theory. Specifically, we investigate their existence based on the self-duality group of type 0B string theory recently proposed by Baykara, Dudas, and Vafa. This talk is based on joint work with Hiroki Wada (Tohoku University) and Naoto Kan (The University of Osaka), arXiv:2608.16522 [hep-th].

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

Event Official Language: English

Quantum Information: Entanglement of Mathematics & Physics

September 21 (Mon) - 23 (Wed) 2026

This workshop brings together mathematicians and physicists to explore the deep connections among quantum information, mathematics, and physics. Topics span quantum gravity, condensed matter physics, quantum computing, and quantum error correction, with an emphasis on the mathematical structures that underlie entanglement and quantum information across these fields. The program is designed to foster genuine cross-disciplinary dialogue, allowing ample time for discussion alongside formal talks. [Invited speakers] Akira Furusaki (RIKEN CEMS/iTHEMS) Marcel Franz (UBC / SBQMI) Ching-Kai Chiu (iTHEMS) Jasmin Bedow (UBC) Max McGinley (UBC) Yosuke Kubota (Kyoto University) Shunji Matsuura (RIKEN iTHEMS) Bartosz Regula (RIKEN RQC) Ryuji Takagi (University of Tokyo) Sisi Zhou (Perimeter Institute) Olivia Di Matteo (UBC / SBQMI) Daochen Wang (UBC Computer Science) Polina Feldmann (UBC) Masazumi Honda (RIKEN iTHEMS) Yasuyuki Kawahigashi (RIKEN iTHEMS) Carolyn Zhang (UBC) Masahito Yamazaki (Kavli IPMU, University of Tokyo) Aswin Parayil Mana (University of Tokyo) Alex May (Perimeter Institute) Masamichi Miyaji (RIKEN iTHEMS) Mark Van Raamsdonk (UBC Physics & Astronomy)

Venue: University of British Colombia / via Zoom

Event Official Language: English

Tannaka duality for spectral sheaves on compact Hausdorff spaces

September 17 (Thu) 15:00 - 16:30, 2026

Ko Aoki (Postdoc, University of Copenhagen, Denmark)

Tannaka duality asks to what extent a geometric object can be recovered from a category naturally associated with it. In this talk, the geometric objects are topological spaces, and the associated categories are their categories of sheaves of spectra. I showed that, for compact Hausdorff spaces X and Y, every colimit-preserving symmetric monoidal functor from Shv(X; Sp) to Shv(Y; Sp) arises uniquely from a continuous map from Y to X, where Shv(X; Sp) denotes the (∞, 1)-category of sheaves of spectra on X. The main ingredient is an adjunction between the construction of sheaves and a new variant of the smashing spectrum. I will also discuss variants of this machinery to broader classes of spaces, including ongoing work on toposes.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

Primtive form of singularity and mirror symmetry

September 11 (Fri) 15:30 - 17:30, 2026

Zhe Wang (Research Scientist, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

In 1980s, K. Saito introduced the primitive forms in his study of periods as to generalize the elliptic period integral theory to higher dimensions. An important consequence was that there exists a flat structure on the space of universal unfolding of a singularity. Later after Witten proposed his famous conjecture relating the intersection theory on moduli space to the integrable hierarchy, this flat structure was re-discovered by Dubrovin, and nowadays it is referred as a Frobenius mafniold structure. Frobenius mafniolds provide a convenient tool for formulating the mirror symmetry, which was a special type of duality among string theories orginally studied by physicits. In this talk, I will explain the related constructions, and show by examples how the study of primitive forms gives prediction of geometric quantities such as Gromov-Witten invariants.

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

Event Official Language: English

Making robust reionisation 21 cm signal predictions with C21LRT

September 11 (Fri) 14:00 - 15:15, 2026

Qin Han (JSPS International Research Fellow, Shibaura Institute of Technology)

The redshifted 21 cm line signal is a unique probe for the Epoch of Reionisation by tracking the evolution of the averaged intergalactic medium properties as well as their fluctuations, enabling tomographic studies. Accurate modelling of the 21 cm global and power spectrum signals is crucial for interpreting measurements from current and forthcoming 21 cm experiments. Theoretical predictions usually post-process reionisation simulations with optical depth approximation, which treats local line broadening and peculiar velocities approximately and often leads to divergences due to its velocity gradient term. I will present our cosmological 21 cm line radiative transfer (C21LRT) formulation which resolve these issues naturally. I will compare the 21-cm signals calculated with C21LRT and the conventional optical depth method, and highlight the need to fully quantify the uncertainties of using the optical depth method for exploring the 21-cm signals associated from various possible reionisation scenarios.

Venue: Hybrid Format (2F #220 and Zoom), Main Research Building

Event Official Language: English

Magic state distillation and cultivation #2

September 10 (Thu) 13:30 - 17:00, 2026

Yutaka Hirano (Research Scientist, Nanofiber Quantum Technologies)

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

Event Official Language: Japanese

Magic state distillation and cultivation #1

September 10 (Thu) 10:30 - 12:00, 2026

Yutaka Hirano (Research Scientist, Nanofiber Quantum Technologies)

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

Event Official Language: Japanese

How fungi generate one of the highest pressures in biology: the cell wall as a living nanoporous material

September 7 (Mon) 14:00 - 15:00, 2026

Naoyoshi Kumakura (Senior Research Scientist, RIKEN Center for Sustainable Resource Science (CSRS))

Many devastating crop diseases, including anthracnose and rice blast, begin when a fungal pathogen builds a single infection cell called an appressorium. This single cell generates up to ~8 megapascals of turgor pressure (roughly 40 times a car tire’s air pressure), among the highest documented in any living organism, to physically rupture the plant's tough surface. This pressure arises because the cell wall acts as a semipermeable membrane, retaining internal osmolytes such as glycerol while allowing water to pass. What confers this selective permeability had remained unknown for decades: melanin was long assumed responsible, but turgor still forms in melanin-deficient mutants. Using genome editing and direct biochemical analysis of these fungi, we identified two enzymes, PKS2 and PBG13, that synthesize a novel polymer from dihydroxyhexanoic acid (DHHA), which narrows cell-wall pore size at the nanometer scale and is required for turgor generation (Kumakura* et al., Science, 2026). I will frame this system as a living adaptive porous material and discuss questions open to mathematical and physical modeling, including how pore geometry sets the limits of selective permeability.

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

Event Official Language: English

SNP School 2026

September 7 (Mon) - 11 (Fri) 2026

We are pleased to announce that the SNP School 2026 will be held at Aobayama Campus, Tohoku University, from 7th to 11th, September, 2026. This is the 15th of the series which has been held every year since 2012. The school provides lectures that cover subjects from basics to the frontiers of strangeness nuclear physics as well as other related fields such as astrophysics, atomic physics, etc. Lecturers are invited both from theoretical or experimental physics, and their materials are prepared to be useful to students and also to researchers who would have wider interests. For more details, please see the related link.

Venue: via Zoom

Event Official Language: English

The 11th Intensive Lectures on Quantum Gravity

September 7 (Mon) - 9 (Wed) 2026

Yasuyuki Hatsuda (Associate Professor, Department of Physics, Faculty of Science, Rikkyo University)

In the 11th event of the Intensive Lecture Series, organized by the Quantum Gravity Gatherings (QGG) study group at RIKEN iTHEMS, we will have Prof. Yasuyuki Hatsuda from Rikkyo University, who will deliver a three-day lecture series on the analytic methods in black hole perturbation theory. Black hole perturbation theory plays a very important role in the developments of modern physics. For instance, in gravitational wave astronomy, it can describe the ringdown phase during the merger events of binary black holes. As the frequency and decay rate of each quasinormal mode are unique to the remnant black hole, one can test extreme-gravity physics by extracting those modes from the ringdown signal. In addition, the computation of black hole quasinormal modes based on black hole perturbation theory has relations connecting to conformal field theories and even to the computations of tidal Love numbers. With the broad applications, we expect this lecture series to provide fresh perspectives to researchers across a wide range of fields and to inspire new directions in their own research. The lectures will be delivered in a blackboard-style format (in English), designed to foster interaction, active participation, and in-depth Q&A discussions. In addition, short talk sessions will be held, giving participants the opportunity to present briefly on topics of their choice. Through this informal and dynamic setting, we hope to spark active interactions among participants and create an environment where ideas can be shared openly and enthusiastically. This event will take place in person only. Target audience: Senior scholars, early-career researchers, and students are all warmly welcome. Registration deadline: July 31, 2026

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

Event Official Language: English

Efficient iBF: Balanced Integration of Fragmented Matching Markets for Welfare Improvement

September 4 (Fri) 15:30 - 17:00, 2026

Fuhito Kojima (Professor, Department of Economics, The University of Tokyo)

Matching markets often suffer from fragmentation, which leads to inefficiency. We model a fragmented market in a school-choice context and offer a practically relevant method for integration. Specifically, each student and school belong to a region, and we allow for inter-regional transfer of students with "balancedness" constraint: a matching is said to be balanced if, for each region, the outflow of students from that region to other regions is equal to the inflow of students from the latter to the former. Using a directed bipartite graph defined on students and schools, we characterize the set of Pareto efficient matchings among those that are individually rational, balanced and fair (efficient iBF). We also provide a class of polynomial-time algorithms to compute such matchings. When each region favors local students in their priority, the outcome of an algorithm from this class weakly improves student welfare upon the outcome where each region independently uses the deferred acceptance mechanism. Various real-life examples of fragmentation are discussed, and we illustrate how our method would address the issue.

Venue: Okochi Hall (Main Venue) / via Zoom

Event Official Language: English

Dualizable Additive Categories

September 4 (Fri) 14:00 - 15:30, 2026

Vladimir Sosnilo (Research Scientist, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

We will discuss the notion of a dualizable additive category. Examples include the category of connective modules over an almost ring in the sense of Gabber--Ramero and the category of nuclear modules in the sense of Clausen and Scholze. Most of the theory parallels the theory of dualizable stable categories, and, in particular, any dualizable additive category can be represented as the category of connective modules over a connective almost ring. The theory is also equivalent to the theory of compactly assembled additive categories of Efimov. As the main application of the theory, we prove a universal property of the category of nuclear modules over uniform Tate rings, that doesn't involve condensed mathematics. This talk is based on a joint work with Ishan Levy and Jiancheng Liang.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

Cancellation of loop corrections to soft power spectrum of inflation

September 3 (Thu) 16:30 - 18:00, 2026

Muzi Hong (Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Inflation theory provides an explanation for the seeds of structure formation and inhomogeneities in the cosmic microwave background (CMB) through quantum fluctuations stretched to cosmological scales during inflation. Mechanisms that enhance small-scale curvature perturbations during inflation can lead to the formation of primordial black holes after horizon re-entry. Recently, some arguments have claimed that loop corrections from such enhanced small-scale fluctuations can give a scale-invariant contribution to the large-scale power spectrum and thereby spoil the inflationary prediction for the CMB. This appears to challenge the standard tree-level expectation that large-scale curvature perturbations are conserved on superhorizon scales in single-clock inflation, and has ignited discussion. In this talk, I will show that the scale-invariant contribution from the enhanced small-scale fluctuations indeed cancels, both in an explicit one-loop calculation and as a consequence of the diffeomorphism symmetry of General Relativity. This seminar is jointly organized by the iTHEMS–ABBL Joint Astro Study Group and the Cosmology Study Group.

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

Event Official Language: English

Can Electric Sheep Evolve? Engineering Evolution in Populations of Language-Model Agents

September 3 (Thu) 15:00 - 16:00, 2026

Ivan Romić (Research Scientist, Mathematical Social Science Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

The idea of artificial intelligence that evolves has long been a theme in science fiction. It also has roots in early research on complex adaptive systems and artificial societies, including Holland’s Echo framework and Epstein and Axtell’s Sugarscape, which modeled adaptation, resource competition, reproduction, and cultural transmission among artificial agents. Contemporary LLM development, however, has largely centered on pretrained models and gradient-based post-training, while explicitly Darwinian population processes have remained comparatively peripheral. This seminar reviews an emerging literature on evolutionary optimization, cultural transmission, and population dynamics in LLM-based agents. I distinguish systems that merely borrow evolutionary terminology from those implementing meaningful variation, heredity, and reproduction. I then assess the strengths and limitations of current studies and ask whether such processes can support cumulative adaptation, collective intelligence, and potentially new levels of organization among artificial agents.

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

Event Official Language: English

Computational demands shape seizure susceptibility in recurrent neural networks

September 3 (Thu) 13:00 - 14:00, 2026

Sebastian Eydam (Research Scientist, Neural Circuits and Computations Unit, RIKEN Center for Brain Science (CBS))

Why do some brain areas slip into seizures more readily than others? Anatomy and physiology are part of the story, but in this talk we argue that the computation a network performs is itself a determinant of its vulnerability. Working in the language of recurrent neural networks and attractor dynamics, we contrast two computational regimes: networks that represent continuous variables (e.g. tracking a continuous position in space) establish barrier-free state manifolds, whereas networks that store discrete memories have to separate different states by establishing deep wells. A simple energy-landscape picture suggests that continuous networks can amplify perturbations into runaway activity more easily while discrete networks contain them. We test this idea across three systems: handcrafted spiking attractor networks, recurrent networks trained on continuous or discrete computational tasks, and in vivo Neuropixels recordings comparing medial entorhinal cortex (continuous, grid-cell dynamics) with hippocampal CA3 (discrete memory). Under a shared disinhibitory "seizure perturbation," the continuous systems destabilize sooner and drive stronger epileptiform activity, and causal silencing shows this depends on intact entorhinal output. Together, these results establish a direct link between the computation a network is built to perform and its susceptibility to seizures, showing that the very features that enable a network to process information also shape its vulnerability to pathological transitions.

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

Event Official Language: English

Finite cut-off holography and Matrix models

September 3 (Thu) 10:30 - 11:45, 2026

Sounak Pal (Student, Indian Institute of Technology Gandhinagar, India)

In this talk, I will discuss finite-cutoff models of two-dimensional topological gravity and their relation to random matrix theories. Random matrix models have emerged as a useful tool for understanding and refining semiclassical holographic dualities, particularly in low-dimensional quantum gravity. I will begin with a brief introduction to large-(N) matrix models and then describe their connection to low-dimensional topological quantum field theories. Along the way, I will highlight how introducing a finite cutoff can lead to significant modifications in the growth of the black-hole interior compared with the matrix-model description of pure JT gravity. Finally, I will discuss the relation between (TT-bar)-deformed Schwarzian theories and their gravitational bulk duals, emphasizing how these deformations provide an avenue for exploring finite-cutoff holography and possible departures from the standard JT-gravity picture.

Venue: #359, 3F, Main Research Building / via Zoom

Event Official Language: English

1st MSS–COGNAC Joint Workshop

September 2 (Wed) 13:00 - 18:00, 2026

First joint workshop between Mathematical Social Science Team from iTHEMS and Computational Group Dynamics Collaboration Unit from CBS. We will introduce ourselves, discuss our research interests and ongoing projects, and explore potential collaborations between the two teams. Schedule 13:00–13:10 Welcome & brief introductions 13:10–13:30 Wataru Toyokawa (COGNAC) 13:30–13:50 Nikoleta Glynatsi (MSS) 13:50–14:10 Ryutaro Mori (COGNAC) 14:10–14:30 Yohsuke Murase (MSS) 14:30–14:50 Alex Witt (COGNAC) 14:50–15:00 Buffer / informal discussion 15:00–16:00 BTCC coffee break 16:00–16:20 Ivan Romic (MSS) 16:20–16:40 Katja Sangati (COGNAC / Kyoto University) 16:40–17:00 Brian Mintz (MSS) 17:00–17:20 Kazuya Horibe (COGNAC) 17:20–17:40 Shinobu Utsumi (MSS) 17:40–18:00 Natsuki Ogusu (COGNAC) 18:30– Banquet in Wako (venue TBA)

Venue: S305 Seminar Room, Brain Science Central Building, RIKEN Wako Campus

Event Official Language: English