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Self-organization mechanism of adaptive colony size sensing in ants

July 17 (Thu) 13:00 - 14:00, 2025

Kazuki Tsuji (Professor, Department of Environmental Sciences and Technology, University of the Ryukyus)

Social insects such as ants and termites are superorganisms, and traits of a colony change in a manner similar to the growth of an individual. The most common pattern is that reproductive castes are produced only when the colony size exceeds a certain threshold, which is well known to be adaptive. This means that social insects can “sense” their own colony size. However, how they achieve this even without visual information in a dark environment was yet largely unknown. We empirically tested the self-organization hypothesis on the proximate mechanism using ant colonies. In Diacamma colonies the monogynous queen is known to increase the effort devoted to queen pheromone–transmission behaviour (patrolling) as the colony grows, as if she perceives colony size. The negative feedback hypothesis assumes that through repeated physical contacts with workers the queen monitors the physiological state (fertility) of workers and increases her patrolling effort when she encounters more fertile workers. Supporting this hypothesis, we found that queens increased patrol effort in response to a higher ratio of fertile workers under the experimental condition of constant colony size. Furthermore, supplementary experiments suggested that cuticular hydrocarbons can mediate the observed queen–worker communication of fertility state. However, when the colony size exceeds a certain value, information transmission fails, resulting in the production of the next generation of reproductive caste. Such a self-organising mechanism of sensing colony size may also operate in other social insects living in small colonies.

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

Event Official Language: English

RIKEN Theory Symposium

July 9 (Wed) - 10 (Thu) 2025

This symposium will bring together leading theorists from the fields of artificial intelligence, quantum information, quantum field theory, quantum gravity, and related areas of mathematics. It aims to stimulate interactions and collaborations across these diverse fields by fostering cross-disciplinary dialogue. It is organized by RIKEN's Pioneering Research Institute (PRI) together with the Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), and the Center for Advanced Intelligence Project (AIP). July, 9th (Wed.) 9:20- 9:30 Opening Remarks Dr. Hirosi Ooguri 9:30 - 10:15　Daniel Jafferis, “Tensor models for 3d gravity” 10:45 - 11:30 Sameer Murthy, “Supersymmetric index of black holes and black strings” Transportation by bus from Wako-campus is available for up to 60 people. Special AIP-PRI-iTHEMS joint seminar Venue: Tokyo Open Space (RIKEN Nihonbashi Campus) 14:30 - 15:15 Sergei Gukov, “Math + AI = AGI” 15:15 - 16:00 Masazumi Honda, “Fracton topological phases and Foliated field theories” 16:30 - 17:15 Richard Kueng, “Learning to predict ground state properties of gapped Hamiltonians” *Due to building access restrictions, this session is open only to participants of the morning session, RIKEN affiliates, or those who have completed the registration form. If you wish to attend, please register via the Related Links section below. July, 10th (Thur.) 9:30 - 10:15 Yifan Wang, “Pinning Defects, Fusion and Factorization” 10:45 - 11:30 Yichul Choi, “Non-Invertible Symmetry and Entanglement Entropy” 11:45 - 12:30 Yuya Kusuki, “Non-invertible Symmetries on Non-orientable Surfaces” 14:00 - 14:45 Heeyeon Kim, “3d TFTs from 4d N=2 BPS particles” 15:15 -16:00 Yuto Moriwaki, “On mathematical formulations of conformal field theory” 16:00 - 16:45 Kantaro Ohmori, “Higher Representation Theory and Excitations of Gauge Theories” 16:45 -16:55 Closing Remarks by Dr. Motoko Kotani Organizer: RIKEN Pioneering Research Institute (PRI) Co-organizers: RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) RIKEN Center for Advanced Intelligence Project (AIP)

Venue: Suzuki Umetaro Hall / Tokyo Open Space (COREDO Nihonbashi)

Event Official Language: English

Boundary Scattering and Non-invertible Symmetries in 1+1 Dimensions

July 4 (Fri) 14:00 - 15:00, 2025

Soichiro Shimamori (Ph.D. Student, Graduate School of Science, Osaka University)

Recent studies by Copetti, Córdova and Komatsu have revealed that when non-invertible symmetries are spontaneously broken, the conventional crossing relation of the S-matrix is modified by the effects of the corresponding topological quantum field theory (TQFT). We extend these considerations to (1+1)-dimensional quantum field theories (QFTs) with boundaries. In the presence of a boundary, one can define not only the bulk S-matrix but also the boundary S-matrix, which is subject to a consistency condition known as the boundary crossing relation. We show that when the boundary is weakly-symmetric under the non-invertible symmetry, the conventional boundary crossing relation also receives a modification due to the TQFT effects. As a concrete example of the boundary scattering, we analyze kink scattering in the gapped theory obtained from the Φ(1,3)-deformation of a minimal model. We explicitly construct the boundary S-matrix that satisfies the Ward-Takahashi identities associated with non-invertible symmetries. This talk is based on the collaboration with Satoshi Yamaguchi.

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

Event Official Language: English

Simulating the spread of infection in networks with quantum computers

June 26 (Thu) 13:00 - 14:00, 2025

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

Many classical stochastic processes can be modeled as Markovian processes, including the spreading of infection in networks. Simulating the Markovian processes using classical computers is generally unscalable for large networks. In this seminar, I will introduce the Hamiltonian evolution on quantum computers and how the Markovian spreading of infection can be efficiently simulated using the Hamiltonian evolution. In particular, we analytically and numerically analyze the evolution of a specifically designed Hamiltonian, and prove that the evolution simulates a classical Markovian process, which describes the well-known epidemiological stochastic susceptible and infectious (SI) model. As an example, we simulate the infection spreading process of the SARS-CoV-2 variant Omicron in a small-world network. The simulation results are qualitative consistent with the infection spreading in the west coast of USA.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

ComSHeL introductions meeting

June 24 (Tue) 14:00 - 15:30, 2025

Following our Launch Meeting on May 1st, in this second meeting of our study group we plan for each member of the ComSHeL Study Group and anyone who joins us that day to introduce their research briefly to get to know one another's focus and expertise. If you are interested in possibly collaborating with ComSHeL members and/or you would like to get to know some of the researchers who joined us as part of iTHEMS new Division of Applied Mathematical Science, please join us. I extended the duration to 90 min (from our usual 60 min) to make sure we have enough time to hear from everyone. Each attendee will have approximately 4 minutes to explain their past, current, or upcoming research and time will be kept strictly. Time might be adjusted on the day of the meeting based on the number of applicants. If you would like to show some slides (max 3 slides), please prepare them in advance and send them to cbeau@riken.jp in PDF format no later than June 20. But no one should feel they must prepare slides: it is fine to speak freely and informally about your work.

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

Event Official Language: English

Spectral flow and applications

June 23 (Mon) 14:00 - 16:00, 2025

Christopher Bourne (Associate Professor, Institute of Liberal Arts and Sciences, Nagoya University)

Given a family of symmetric matrices indexed by a parameter (e.g. time, external field), changing this parameter will cause the eigenvalues to move along the real axis. The spectral flow tracks these eigenvalues and counts how many cross the point 0. This idea turns out to be very useful for both pure mathematics as well as applications to physics and elsewhere. In this talk, I will introduce the spectral flow and how it can be generalised to a variety of settings that are also relevant for applications in quantum physics.

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

Event Official Language: English

Categorification and K-theory

June 20 (Fri) 15:30 - 17:30, 2025

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

In this talk, I will explain and motivate the concept of categorification and present various examples. The Euler characteristic is an invariant of a topological space, that serves as a shadow of a more refined category theoretic invariant—homology—which retains significantly more information. The existence of such a categorical construction underlying a numerical one is a common phenomenon in topology and algebra. I will also discuss Khovanov's question on the existence of categorification of arbitrary rings.

Venue: Seminar Room #359

Event Official Language: English

Programmed chromosome eliminations in flies

June 19 (Thu) 13:00 - 14:00, 2025

Robert Baird (Visiting Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Species that break the traditional rules of genetics and inheritance offer perhaps some of the best opportunities to study fundamental biological questions. Sciarids (fungus gnats) are a species-rich family of flies with highly unorthodox chromosome inheritance. Asymmetric male meiotic divisions result in elimination of the paternal genome every generation, and maternally-controlled eliminations of chromosomes in the developing embryo determine offspring sex. I use a combination of genomics, population genetics, and cytogenetics to understand both the mechanisms and the evolution of this system. I will discuss how these approaches have allowed us to uncover some fascinating biology as well as tackle broader biological questions.

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

Event Official Language: English

Black hole states at finite N

June 18 (Wed) 16:30 - 17:30, 2025

Sunjin Choi (Postdoctoral Fellow, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)

We study new cohomologies for the local BPS operators of the maximal super-Yang-Mills theory to better understand the black hole microstates. We first analyze the index of these black hole operators and explicitly construct their cohomologies to study how they imitate the quantum black holes. We find many towers of states and partial no-hair behaviors where certain gravtions are forbidden to dress these black hole operators. This qualitatively agrees with the behavior of the perturbative hairy BPS black holes or the so-called grey galaxies. Throughout this talk, we mainly focus on a subsector of the field theory corresponding to the BMN matrix theory, which exhibits a black hole-like entropy growth at large N.

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

Event Official Language: English

Charting the landscape of gauge-fermion dynamics

June 16 (Mon) 13:30 - 15:00, 2025

Álvaro Pastor Gutiérrez (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Gauge–fermion quantum field theories are central to our understanding of nature, from QCD to the electroweak sector. Beyond the Standard Model, strongly coupled gauge dynamics offer compelling avenues to address open puzzles. In this talk, I present a cartographic study of gauge–fermion theories across varying numbers of colours and flavours, focusing on the interplay between colour confinement and chiral symmetry breaking. We determine the flavour and colour dependence of the corresponding dynamical scales, providing a unified picture that interpolates between QCD-like regimes—where we recover quantitative agreement with lattice results—and the perturbative conformal limit. The analysis is based on the functional renormalisation group and employs a novel approximation scheme that allows for controlled and flexible access to the non-perturbative dynamics. We further explore the near-conformal regime with walking behaviour and estimate the lower boundary of the Caswell–Banks–Zaks conformal window. This framework enables a self-consistent mapping of the theory space of strongly coupled gauge–fermion systems and yields first-principles results with direct relevance for physics beyond the Standard Model.

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

Event Official Language: English

A New Holographic Entanglement Entropy in the de Sitter space

June 13 (Fri) 16:00 - 17:00, 2025

Yuki Suzuki (Ph.D. Student, Yukawa Institute for Theoretical Physics, Kyoto University)

We propose a new holographic entanglement entropy in the three-dimensional de Sitter space. It is known that the holographic entanglement entropy via Ryu-Takayanagi prescription violates the entropic inequalities that they should satisfy. We propose a kind of extensions of the Ryu-Takayanagi formula so that they satisfy the strong subadditivity. We fix consistent parameter regions of the entropy and finally comment on the implications to the static patch holography.

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

Event Official Language: English

From Galaxies to Cosmological Structures: The Multi-Scale Influence of Cosmic Rays

June 13 (Fri) 14:00 - 15:15, 2025

Ellis Owen (Special Postdoctoral Researcher, Astrophysical Big Bang Laboratory, RIKEN Pioneering Research Institute (PRI))

Cosmic rays interact with astrophysical systems over a broad range of scales. They go hand-in-hand with violent, energetic astrophysical environments, and are an active agent able to regulate the evolution and physical conditions of galactic and circum-galactic ecosystems. Depending on their energy, cosmic rays can also escape from their galactic environments of origin, and propagate into larger-scale cosmological structures. In this talk, I will discuss the impacts of cosmic rays retained in galaxies. I will show they can deposit energy and momentum to alter the initial conditions of star-formation, modify the circulation of baryons around galaxies, and have the potential to regulate long-term galaxy evolution. I will highlight some of the astrophysical consequences of contained hadronic and leptonic cosmic rays in and around galaxies, and how their influence can be probed using signatures including X-rays, gamma-rays and neutrinos. I will also discuss what happens to the cosmic rays that escape from galaxies, including their interactions with the magnetized large-scale structures of our Universe, and the fate of distant high-energy cosmic rays that do not reach us on Earth.

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

Event Official Language: English

Gravitational Lensing in the Schwarzschild Spacetime: Photon Rings in Vacuum and in the Presence of a Plasma

June 12 (Thu) 15:00 - 16:30, 2025

Torben Christian Frost (Postdoctoral Researcher, Kavli Institute for Astronomy and Astrophysics, Peking University, China)

Astrophysical black hole candidates are often surrounded by an accretion disk. In particular the interior region of this accretion disk can consist of a plasma and the trajectories of light rays travelling through this plasma can deviate significantly from the trajectories of light rays travelling through vacuum. While usually these environments are very complex we can already learn a lot about the observable features using simple plasma models. In the context of general relativity for some of these plasma models the equations of motion are fully separable and even analytically solvable. In my talk I will illustrate what we can learn from such models using the Schwarzschild spacetime as background. I will assume that the black hole is surrounded by an inhomogeneous, pressureless, and non-magnetised plasma and solve the equations of motion analytically exact. Then I will assume that we have a luminous disk in the equatorial plane and discuss the impact of the plasma on the so-called photon rings. I will discuss the changes of their geometrical structure, the redshift, and the travel time of the photons compared to photon rings in vacuum and what we can learn about the properties of the plasma. I will also discuss how the presence of the plasma may be able to help us to constrain gravity in the strong field regime. Finally, I will discuss how the obtained results will contribute to designing a multimessenger approach for probing gravity in the strong field regime in the context of the Maxwell-Einstein-Pauli Observatory.

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

Event Official Language: English

Inferring Castration Status and Age-at-Death from Sheepskin Parchments

June 12 (Thu) 13:00 - 14:00, 2025

Ciarán O'Connor (Ph.D. Student, Department of Genetics, Trinity College Dublin, Ireland)

Secondary products such as traction from cattle, wool from sheep, and mobility from horses are invaluable outputs from rearing livestock. The innovative herd management practice of castration enables non-breeding males to be managed safely beyond typical ages of slaughter, greatly improving the productivity of livestock herds. Although osteological methods can identify some morphological differences between castrated and intact males, it is difficult to make clear distinctions between them. However, methylation values are affected by the considerable hormonal changes that occur as a result of castration. For example, castrated male sheep have shown lower biological ages compared to age-matched intact rams (Sugrue et al., 2021). Furthermore, age-at-death has been predicted from reconstructed methylation values in ancient horses, informing on culling practices (Liu et al., 2023). Using an aDNA-specific bisulfite sequencing approach, we have reconstructed CpG methylation values from sheepskin parchments. We have developed machine learning models trained on modern sheep in order to infer traits of interest such as castration and age-at-death. The informative CpG sites have been incorporated into a target capture set to enable cost-effective sequencing of additional samples. This will enable the characterisation of these traits in ancient sheep across time periods, geographical locations, and archaeological contexts.

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

Event Official Language: English

A New Measure of Genuine Multipartite Entanglement

June 6 (Fri) 14:00 - 15:00, 2025

Jaydeep Kumar Basak (Post-doctoral Fellow, Gwangju Institute of Science and Technology (GIST), Republic of Korea)

In this talk, I will introduce ``Latent entropy" (L-entropy) as a novel measure to characterize genuine multipartite entanglement in pure states, applicable to quantum systems with both finite and infinite degrees of freedom. This measure, derived from an upper bound on reflected entropy, attains its maximum for three-party GHZ states and $n=4,5$-party $2$-uniform states. I will also show the generalization of this measure for higher party states. Furthermore, I will discuss an analogue of the Page curve in multiboundary wormholes. If time permits, I will show the behaviour of multipartite entanglement in random states.

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

Event Official Language: English

Exotic Pairing Nature and Charge Ordering in Kagome Superconductor

June 5 (Thu) 15:00 - 16:15, 2025

Wu Xianxin (Associate Professor, CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, China)

Abstract：Recent experimental investigations have identified fascinating electronic orders in kagome metals, such as intriguing superconductivity, charge density wave (CDW) and nematicity. Notably, there is various evidence of spontaneous time-reversal symmetry (TRS) breaking within the CDW phase, pointing to a long-pursued loop current order, though its underlying mechanism remains elusive. In this talk, I will first review the exotic properties of these kagome superconductors. Then, I will discuss the effective model and the unique sublattice texture associated with van Hove singularities in the kagome lattice [1], which turns out to have significant effect on correlated states. Finally, I will present our scenario for realizing a TRS breaking CDW within the kagome lattice and discuss loop-current fluctuation induced unconventional pairing [2-4]. Potential experimental implications will be also discussed.

Venue: via Zoom / #359, Main Research Building

Event Official Language: English

Ecology and Evolution of Mammal-Microbe Interactions

May 29 (Thu) 16:00 - 17:00, 2025

Taichi A Suzuki (Assistant Professor, Biodesign Center for Health Through Microbiomes, Arizona State University, USA)

A critical open question in microbiome research is identifying key host-microbial interactions that influence host fitness. While the disruption of coevolved host-microbial interactions is known to affect host fitness in simpler systems (e.g., insects and their symbionts), understanding the extent and consequences of host-microbial coevolution in more complex systems (e.g., mammals and their gut microbiota) remains a major challenge. My research has identified multiple species of gut microbes in adults and children that share a parallel evolutionary history with humans by analyzing paired human genotypes and bacterial strain genotypes. In another line of work, I applied a selection experiment demonstrating that selection and transmission of the microbiome and its metabolites can alter mouse locomotion behavior within four rounds of microbiome transfer, without any changes to the mouse genome. Finally, I will briefly outline my future plans to study the effects of disrupting evolutionary stable host-microbial associations on the phenotypes of deer mice (Peromyscus spp.) in the Madrean Sky Islands and genetically diverse human populations in Arizona. Biosketch: Assistant Professor at Arizona State University since 2023. MS at University of Arizona, PhD at University of California Berkeley, and Postdoc at Max Planck Institute for Biology. My group integrates evolutionary genomics, microbial ecology, and biomedical research to study host-microbial interactions using wild rodents and humans.

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

Event Official Language: English

SISSI: Supernovae in a Shearing, Stratified Interstellar Medium

May 23 (Fri) 14:00 - 15:15, 2025

Leonard Romano (Ph.D. Student, Ludwig-Maximilians-Universität München, Germany)

Supernovae (SNe) are an important driver of the multiphase structure in the Interstellar Medium (ISM) and play an important role for regulating star formation. SNe inflate large bubbles of hot gas dubbed Supernova Remnants (SNRs) that can remain hot for several 10⁵-10⁶ years, contributing substantially to the volume filling hot phase, galactic outflows and the driving of turbulence in the ISM. In this talk, I am presenting the results of zoom-in simulations of SNRs embedded in a simulated isolated Milky-Way analogue, in order to investigate how environmental effects like shear, vertical stratification and a self-consistently generated ISM can affect various properties of SNRs. I find that initially microscopic SNRs, whose dynamics are dominated by local shock physics, after a few Myr enter a mesoscopic regime, where their dynamics are increasingly dominated by galactic scale processes. Based on these findings, I make predictions about SN-driven large-scale structure, such as galactic outflows and the geometry of large superbubbles in disk galaxies.

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

Event Official Language: English

Moss sporophytes and their consumers: an overlooked interaction

May 22 (Thu) 13:00 - 14:00, 2025

Yume Imada (Assistant Professor, Division of Biological Sciences, Graduate School of Science, Kyoto University)

The evolution of plant-feeding in animals is deeply intertwined with the unintentional transport of diaspores. Zoochory (the dispersal of plant diaspores by animals) has been extensively studied in flowering plants, particularly with regard to seeds and fruits. Bryophytes, in contrast, have poorly been investigated, despite possessing traits favorable for animal-mediated dispersal: they are small, easily transported, and exhibit high totipotent capacity. It has long been believed that bryophytes are rarely consumed by animals. However, our field survey into sporophyte-feeding across diverse forest-dwelling mosses (the largest clade of bryophytes) revealed the ubiquity of spore consumption. This finding prompts a re-evaluation of the ecological function of the sporophyte in the alternation of generations in mosses. Moreover, our data suggest that this interaction may be framed within the mutualism–antagonism continuum. Finally, I aim to clarify key questions surrounding the reproduction and dispersal of spore-producing plants, particularly bryophytes.

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

Event Official Language: English