Seminar

Development of a real-time object tracking and response system

January 29 (Thu) 13:00 - 14:00, 2026

Isaac Planas Sitja (Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

I will introduce the real-time tracking software and automatic response system that we are developing: TracktorLive. We created a modular system to overcome several issues in close-loop experiments, with the aim to automatise mechanical stimulus delivery or time-consuming actions, and provide tools for VR experiments in animals. This tracker, coded as a Python package, separates the processes into server and client functions to run several processes in parallel, which minimises the frame processing time, and allows running on low-end computers. We hope to implement LLM or AI functions as server processes in the future.

Venue: Seminar Room #359

Event Official Language: English

iTHEMS Cosmology Forum n°5 - Effective Field Theory approaches across the Universe

January 29 (Thu) 10:00 - 17:00, 2026

Katsuki Aoki (Research Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
Toshifumi Noumi (Associate Professor, Graduate School of Arts and Sciences, The University of Tokyo)
Lucas Pinol (CNRS Researcher, Laboratoire de Physique de l’École Normale Supérieure (LPENS), CNRS/École Normale Supérieure, France)

This fifth workshop will bring together researchers exploring the effective field theory (EFT) framework in diverse cosmological contexts (https://indico2.riken.jp/event/5435/overview). Topics will include EFT formulations of interacting dark matter and dark energy, open EFTs for gravity, and multi-field inflationary dynamics. By highlighting recent progress and open questions, the workshop seeks to bridge insights from the early and late universe through the unifying language of EFT. In addition to the invited talks, the workshop will feature a panel discussion designed to promote interaction between the speakers and participants. One of the key goals of this event is to foster collaboration among researchers working in neighboring fields, and to encourage participation from young and early-career researchers who are interested in, but may not yet have worked on, these themes. The workshop welcomes a broad audience with an interest in theoretical cosmology, gravitation, and quantum field theory. The workshops are organised by the Cosmology Study Group at RIKEN iTHEMS.

Venue: Okochi Hall

Event Official Language: English

DEEP-IN-iPI Joint Meeting

January 26 (Mon) - 30 (Fri) 2026

Xingyu Guo (Lecturer, Institute of Quantum Matter, South China Normal University, China)
Gert Aarts (Professor, Department of Physics, Swansea University, UK)
Shuzhe Shi (Assistant Professor, Physics Department, Tsinghua University, Beijing, China)
Sung Hak Lim (Senior Researcher, Center for Theoretical Physics of the Universe (CTPU-PTC), Institute for Basic Science (IBS), Republic of Korea)
Jinyang Li (Ph.D. Student, Program of Particle and Nuclear Physics, The Graduate University for Advanced Studies (SOKENDAI))
Yingying Xu (Research fellow, Department of Mathematics and Statistics, University of Helsinki, Finland)

The series of DEEP-IN meetings (Jan 26–30, 2026) are joint with UTokyo Institute for Physics of Intelligence (iπ), which is a multi-day scientific program bringing together researchers to explore quantum simulations, machine learning physics, and applications in particle and nuclear physics. The tentative schedule is, UTokyo-iπ Session (Venue: #512, Faculty of Science Bldg.1, School of Science, UTokyo) Day 1: Jan 26 (Mon) 14:30–16:00 Onset of Bjorken flow in a quantum many-body simulation of the massive Schwinger model, Shuzhe Shi Day 2: Jan 27 (Tue) 14:30–16:00 Physics of Diffusion Models, Gert Aarts 16:00–17:30 Discovering Symmetry from Energy-Based Diffusion Models, Jinyang Li RIKEN-iTHEMS Session (Venue: Seminar Room #359, Main Research Building) Day 3: Jan 28 (Wed) 14:30–16:00 Understanding Galactic Dark Matter with Generative Models, Sung Hak Lim 16:00–18:00 Free Discussion ML Physics-1 Day 4: Jan 29 (Thu) 10:00–11:30 Quantum Simulations of HEP and Beyond, Xingyu Guo 14:30–16:00 Physics of Machine Learning, Gert Aarts 16:00–17:30 Storage capacity of perceptron with variable selection, Yingying Xu Day 5: Jan 30 (Fri) 11:00–14:00: Free Discussion ML Physics-2

Venue: via Zoom / Seminar Room #359 / Faculty of Science Bldg.1, School of Science, The University of Tokyo, Hongo Campus

Event Official Language: English

Evolution of sterile soldier castes in aphids

January 21 (Wed) 13:00 - 14:00, 2026

Keigo Uematsu (Assistant Professor, Keio University)

This seminar is jointly organized with the RIKEN Center for Sustainable Resource Science (CSRS). Social evolution in aphids is tightly linked to the formation of galls on their host plants. Galls provide efficient colony defense and nutritionally rich feeding sites such that colony members need not forage outside, leading to high intra-group relatedness. Typically, social aphids form a gall on their primary host plant, after which winged morphs disperse to secondary host plants and establish a free-living, open colony. Remarkably, sterile soldier castes have independently evolved twice in these open colonies, where individuals live on plant surfaces without modifying their structure. These aphids raise intriguing questions about the prerequisites for eusocial evolution and the mechanisms by which two distinct social systems are maintained within a single genome. In this talk, I will first provide an overview of the life cycle and the diversity of altruistic behaviors in gall-forming aphids, and then present our studies of the evolution of a sterile soldier caste in aphids inhabiting open colonies. From a developmental perspective, we tested the hypothesis that the sterile soldiers evolved through the co-option of pre-existing soldier phenotypes in a gall, based on similarity in morphology, transcriptome and behavior. From an ecological perspective, we investigated the kin structure and altruistic behavior of young nymphs in the open colonies of pre-eusocial species, and demonstrate that young aphids exhibit altruism by yielding feeding sites to older kin. Together, we propose that the open colonies of social aphids provide an ideal model system for studying the evolution of altruism.

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

Event Official Language: English

Analog variational quantum eigensolver for neutral atomic quantum simulators

January 20 (Tue) 10:00 - 12:00, 2026

Kazuma Nagao (Postdoctoral Researcher, Computational Materials Science Research Team, RIKEN Center for Computational Science (R-CCS))

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

Event Official Language: English

Introduction to the gravitational wave background from the primordial universe

January 16 (Fri) 16:00 - 17:15, 2026

Ryo Namba (Senior Research Scientist, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Being genuine propagating degrees of freedom of the spacetime metric, gravitational waves (GWs) serve as an independent "eye" through which we can probe the evolution history of our universe. They are complementary to electromagnetic observables such as cosmic microwave background (CMB) and can act as direct messengers from the earliest stage of the universe, where conventional probes lose access. In particular, a stochastic background of GWs is widely regarded as a smoking gun of cosmic inflation. In this talk, I introduce the basic theoretical framework for GWs produced in the primordial universe and discuss how they arise from vacuum fluctuations of the metric. I also outline additional production mechanisms sourced by matter fields in the early universe and contrast their characteristic observational signatures with those of vacuum tensor modes. The emphasis of my talk will be on physical intuition and analytic derivations, with the aim of making the subject accessible to non-specialists in the astrophysics community.

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

Event Official Language: English

A one-world interpretation of quantum mechanics

January 16 (Fri) 14:00 - 16:00, 2026

Isaac Layton (Postdoctoral Researcher, Department of Physics, Graduate School of Science, The University of Tokyo)

The measurement problem arises in trying to explain how the objective classical world emerges from a quantum one. In this talk I’ll advocate for an alternative approach, in which the existence of a classical system is assumed a priori. By asking that the standard rules of probability theory apply to it when it interacts with a system linearly evolving in Hilbert space, I’ll show that with a few additional assumptions one can recover the unitary dynamics, collapse and Born rule postulates from quantum theory. This gives an interpretation of quantum mechanics in which classically definite outcomes are always assigned probabilities, rather than superpositions, giving one-world instead of many. The main technical tool used is a change of measure on the space of classical paths, the functional form of which characterises the quantum dynamics and Born rules of a class of quantum-like theories. Time allowing, I will also discuss how these results clarify which additional assumptions must be accepted if one wishes to seriously consider classical alternatives to quantum gravity.

Venue: #445-447, 4F, Main Research Building / via Zoom

Event Official Language: English

Classical Spinning Black Hole Scattering from Quantum Amplitudes

January 15 (Thu) 14:00 - 15:30, 2026

Dogan Akpinar (Ph.D. Student, Higgs Centre for Theoretical Physics, School of Physics and Astronomy, University of Edinburgh, UK)

Scattering amplitudes have recently become a powerful tool for extracting classical observables in two-body gravitational dynamics, with direct relevance for current and future gravitational-wave experiments. In this talk, I will review how quantum scattering amplitudes can be used to obtain classical black hole scattering observables. A key focus will be the inclusion of spin effects, modelled by treating black holes as point particles in fixed-spin representations. This approach introduces a subtle ambiguity in the separation between classical and quantum information, which we resolve using our spin interpolation method. Leveraging this, we obtain, for the first time, the classical two-loop amplitude accurate to quartic order in spin, from which we extract physical observables such as linear and angular impulses using covariant Dirac brackets. Remarkably, the resulting amplitude obeys a spin-shift symmetry, remaining invariant under a shift of the black hole spin by the momentum transfer in the scattering process. Motivated by this structure, we examine the conserved quantities governing scattering and show that—at least asymptotically—the probe dynamics remain integrable through quartic order in spin. Under this asymptotic integrability, together with the spin-shift symmetry, we demonstrate that the quartic-in-spin radial action is fully determined by the aligned-spin sector. Taken together, these results advance our understanding of spinning black hole scattering and illuminate new structural features of Kerr dynamics.

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

Event Official Language: English

Enhancing the methodological framework for inferring selection with ancient DNA: theoretical insights, improvements and comparison

January 15 (Thu) 13:00 - 14:00, 2026

Lucas Sort (Postdoctoral Researcher, Mathematical Genomics RIKEN ECL Research Unit, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Over the past decade, the emergence of ancient DNA has opened new opportunities for studying evolutionary processes. However, inferring signals of selection from such data remains a methodological challenge since controlling for population stratification, admixture, and dynamically changing demographic histories, among other confounding evolutionary processes, is difficult. In this context, ancient DNA time series data, which have proliferated, have led to the development of methods based on two main frameworks: Hidden Markov Models and Generalized Linear Mixed Models. In this work, we aim to clarify how these frameworks relate to the classical Wright–Fisher model, enabling targeted modeling improvements and producing more relevant comparisons across methods.

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

Event Official Language: English

LEVERAGING EARTH OBSERVATIONS WITH MACHINE-LEARNING APPROACHES FOR WATER CYCLE MONITORING

January 13 (Tue) 10:30 - 12:00, 2026

Victor Pellet (Professor, Laboratoire de Météorologie dynamique (LMD-X), Ecole Polytechnique, France)

Earth observation satellites provide unprecedented information to monitor the different components of the water cycle, from soil moisture to river dynamics. However, fully exploiting these observations remains challenging due to sensor limitations, data heterogeneity, complex physical processes, and spatio-temporal resolution constraints. This seminar provides an overview of machine-learning approaches that accompany and enhance remote sensing for water cycle analysis. It illustrates how statistical and machine-learning techniques can improve the exploitation of Earth observation (EO) data at different processing levels, from Level 1 to Level 4. Four examples are presented: (i) compressing hyperspectral information to reduce observation dimensionality, (ii) improving the retrieval of soil moisture from space by exploiting spatial patterns and handling missing data, (iii) harmonizing multi-source EO at the global scale for consistent water cycle monitoring, and (iv) modeling river dynamics using data-driven approaches. Together, these examples highlight the potential of machine-learning techniques to better integrate observations and improve our understanding of hydrological processes.

Venue: R107, Computational Science Research Building

Event Official Language: English

Median-based estimators for randomized quasi-Monte Carlo integration

January 9 (Fri) 15:00 - 17:00, 2026

Kosuke Suzuki (Associate Professor, Yamagata University)

High-dimensional numerical integration is a ubiquitous challenge across various fields, from mathematical finance to computational physics and Bayesian statistics. While standard Monte Carlo (MC) methods are robust, their probabilistic error convergence rate of $O(N^{-1/2})$ is often insufficient for demanding applications. In this talk, I will introduce Quasi-Monte Carlo (QMC) and Randomized QMC (RQMC) methods, which offer a powerful framework for accelerating integration using low-discrepancy point sets. A key advantage of this deterministic approach is its ability to achieve a convergence rate of $O(N^{-1+\epsilon})$, significantly outperforming the standard MC rate. The second part of the talk will focus on the construction of point sets, specifically lattice rules and digital nets. I will explain how these methods achieve higher-order convergence rates, faster than $O(N^{-1})$, for sufficiently smooth integrands. I will also discuss their randomized variants and demonstrate how RQMC with mean-based estimators provides practical error estimation while maintaining high-order convergence. Finally, I will discuss recent progress in RQMC involving median-based estimators. I will highlight how these estimators achieve almost optimal convergence rates for various function spaces without requiring prior knowledge of the integrand.

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

Event Official Language: English

Higher Gauge Structures and Invariant Action Principles

January 6 (Tue) 15:15 - 16:15, 2026

Sebastián Salgado (External Researcher, Instituto de Alta Investigacion, Universidad de Tarapaca, Chile)

I present the systematic construction of gauge theories based on free differential and L-infinity algebras. This provides a consistent algebraic framework for constructing gauge-invariant theories whose field content is extended by higher-degree differential forms as gauge potentials. I derive explicit expressions for the corresponding extended Chern-Simons actions and the generalized anomaly terms that emerge from them. Possible applications to gravity and supergravity will also be discussed.

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

Event Official Language: English

Invitation to Random Tensor Models: from random geometry, enumeration of tensor invariants, to characteristic polynomials

January 6 (Tue) 13:30 - 14:30, 2026

Reiko Toriumi (Associate Professor, Okinawa Institute of Science and Technology Graduate University (OIST))

I will introduce random tensor models by first reviewing their motivation coming from random geometric approach to quantum gravity. Then, I will selectively present some of the interesting research results, by highlighting recent results on enumeration of graphs representing tensor invariants, and reporting our recent work on a new notion of characteristic polynomials for tensors via Grassmann integrals and distributions of roots of random tensors. The latter two are based on arXiv:2404.16404[hep-th] and arXiv:2510.04068[math-ph]

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

Event Official Language: English

Topological Image Analysis

December 25 (Thu) 12:00 - 13:00, 2025

Shizuo Kaji (Professor, Institute of Mathematics for Industry, Kyushu University / Professor, Center for Science Adventure and Collaborative Research Advancement (SACRA), Graduate School of Science, Kyoto University)

Topological Data Analysis (TDA) applies algebraic topology to the study of data such as point clouds. When applied to image and volumetric data, TDA provides a way to capture the topological features that characterise shapes and spatial structures. In this talk, I will outline the strengths and limitations of TDA for image analysis, and compare its capabilities with those of deep neural networks. I will also present hands-on examples using our open-source software Cubical Ripser. Finally, I will highlight a new direction in the use of TDA for image processing.

Venue: Room C501, West Zone 1 Building D, Ito Campus, Kyushu University, SUURI-COOL (Kyushu) (Main Venue) / via Zoom

Event Official Language: English

Cosmological correlators beyond the de-Sitter invariance

December 24 (Wed) 15:00 - 17:00, 2025

Zhu Yuhang (Postdoctoral Researcher, Particle Theory and Cosmology Group, Center for Theoretical Physics of the Universe (CTPU), Institute for Basic Science (IBS), Republic of Korea)

Cosmological correlators serve as powerful probes of the physics that governed the Universe in its earliest moments. Yet analytic calculations of correlators involving massive spinning fields are highly challenging. Recent progress in the cosmological bootstrap program has greatly deepened our understanding of these correlators. In this talk, we will show how to extend the bootstrap program beyond exact de Sitter invariance by studying two types of symmetry breaking: explicit scale-invariance breaking and boost breaking. We will present the boundary differential equations that characterise correlators in these settings and highlight the rich phenomenology that emerges. Finally, we will also show recent developments in approximation methods, based on the combination of exact WKB and saddle-point method, which provide a precise, efficient, and physically transparent way to capture and classify the non-analytic features of correlators.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

Neural Network Quantum States for Quarkonium in Medium: Real-Time Open Quantum-System Dynamics

December 19 (Fri) 16:00 - 17:00, 2025

Tom Magorsch (Ph.D. Student, Department of Physics, Technical University of Munich, Germany)

Many phenomena in high energy physics can not be described by Euclidean-time Monte Carlo estimates alone, but require genuine real-time evolution and a treatment of non-equilibrium effects. However, such simulations are computationally challenging. One such example is the evolution of heavy quarkonium in the quark gluon plasma produced in heavy-ion collisions. In this talk, I will introduce the open quantum system treatment of in-medium quarkonium. I will then give an overview on neural network quantum states as a variational approach to the real-time simulation of open quantum systems. As a controlled benchmark system, I will study the application to the Caldeira-Leggett model and conclude with an outlook on future applications of neural network based simulation of quarkonia in medium.

Venue: via Zoom

Event Official Language: English

Two-component dark matter scenario in a pseudo-Nambu-Goldstone dark matter model - Tomohiro Abe

December 18 (Thu) 14:00 - 15:30, 2025

Tomohiro Abe (Assistant Professor, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University)

The WIMP dark matter (or thermal dark matter) is one of the leading candidates for dark matter and is widely studied. On the other hand, recent progress in direct detection experiments places severe constraints on WIMP dark matter models. Pseudo-Nambu-Goldstone boson dark matter models (pNG DM models) can explain the measured value of the dark matter energy density via the freeze-out mechanism and also naturally suppress the dark matter-nucleon scattering. The amplitudes for the processes are proportional to the momentum transfer squared from the dark sector to the visible sector; It is suppressed by t ~ 0 for the dark matter-nucleon scattering process, while it is proportional to s ~ 4 m_DM^2 for annihilation processes. The simplest realization faces the domain wall problem and needs to be extended. Several models have been proposed, but each model brings other issues, a large hierarchy in new energy scales, parameter tunings, and a Landau pole of a new gauge coupling. In this talk, I would like to propose a new pNG DM model based on SU(2)_gauge times SU(2)_global symmetry that overcomes those issues. The model predicts a two-component DM scenario, where one is pNG, and the other is an ordinary WIMP. I will show that the effective spin-independent cross section in the direct detection experiments is smaller than the current upper bound and larger than the prospect of the Darwin project in a wide range of parameter space in the two-component DM scenario.

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

Event Official Language: English

Origin and evolutionary history of an urban underground mosquito

December 18 (Thu) 13:00 - 14:00, 2025

Yuki Haba (Postdoc, Zuckerman Institute, Columbia University, USA)

Urbanization is rapidly reshaping landscapes around the world, which poses questions about whether and how quickly animals and plants can adapt. Culex pipiens form molestus, more commonly known as the "London Underground mosquito," has been held up as a benchmark for the potential speed and complexity of urban adaptation. This intraspecific lineage within Cx. pipiens, a major West Nile virus vector, is purported to have evolved human biting and a suite of other human-adaptive behaviors in the subways and cellars of northern Europe within the past 200 years. Form molestus features prominently in textbooks as well as scholarly reviews of urban adaptation. Yet, the hypothesis of in situ urban evolution has never been rigorously tested. I will talk our recent efforts to understand the contentious origin and evolutionary history of the urban, human-biting mosquito. Our synthesis and meta-analysis of rich yet confusing literature show that its London Underground origin is unlikely (Haba and McBride 2022 Current Biology). Whole genome resequencing and population genomics of 800+ mosquitoes across ~50 countries again debunk the in situ evolution hypothesis and instead support that molestus first adapted to human environments >1000 years ago in the Mediterranean or Middle East, most likely in ancient Egypt or another early agricultural society (Haba et al. 2025 Science). I will outline implications of our results in urban evolutionary biology as well as in public health. Speaker Bio Yuki Haba, Ph.D., is an evolutionary biologist passionate about understanding how and why diverse behaviors evolve in nature. He is currently a Leon Levy Scholar in Neuroscience at Columbia University's Zuckerman Mind Brain Behavior Institute. He aims to take multi-desciplinary approaches, combining genomics, neuroscience, and field-based behavioral ecology to comprehensively understand the evolution of behavior. Yuki completed his PhD at Princeton, MA at Columbia, and undergraduate degree at the University of Tokyo. Personal webpage: https://yukihaba.github.io/

Venue: Seminar Room #359

Event Official Language: English

A bi-fidelity Asymptotic-Preserving Neural Network approach for multiscale kinetic problems

December 17 (Wed) 11:00 - 12:00, 2025

Liu Liu (Assistant Professor, Department of Mathematics, The Institute of Mathematical Sciences, The Chinese University of Hong Kong, Hong Kong)

In this talk, we will introduce a bi-fidelity Asymptotic-Preserving Neural Network (BI-APNNs) framework, designed to efficiently solve forward and inverse problems for the linear Boltzmann equation. Our approach builds upon the previously studied Asymptotic-Preserving Neural Network (APNNs), which employs a micro-macro decomposition to handle the model’s multiscale nature. We specifically address a bottleneck in the original APNNs: the slow convergence of the macroscopic density in the near fluid-dynamic regime. This strategy significantly accelerates the training convergence as well as improves the accuracy of the forward problem solution, particularly in the fluid-dynamic limit. We show several numerical experiments on both linear Boltzmann and the Boltzmann-Poisson system that this new BI-APNN method produces more accurate and robust results for forward and inverse problems compared to the standard APNNs. This is a joint work with Zhenyi Zhu and Xueyu Zhu.

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

Event Official Language: English

Phase transition in parametrized quantum circuits

December 16 (Tue) 10:00 - 12:00, 2025

Xiaoyang Wang (Postdoctoral Researcher, Quantum Mathematical Science Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

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

Event Official Language: English