Categorification and K-theory

June 20 (Fri) at 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

5th Mathematical Application Research Team Meeting

June 20 (Fri) at 14:00 - 15:30, 2025

Taketo Sano (Research Scientist, Mathematical Application Research 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

Programmed chromosome eliminations in flies

June 19 (Thu) at 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

Gauge-equivariant multigrid neural networks

June 19 (Thu) at 10:30 - 12:00, 2025

Tilo Wettig (Professor, Universität Regensburg, Germany)

In lattice QCD simulations, the most time-consuming element is typically the solution of the Dirac equation in the presence of a given gauge field. The current state of the art is to use a multigrid preconditioner to reduce the condition number of the Dirac operator matrix. We show how such preconditioners can be constructed using gauge-equivariant neural networks. For the multigrid solve we employ parallel-transport convolution layers. For the multigrid setup we consider two versions: the standard construction based on the near-null space of the operator, and a gauge-equivariant construction using pooling and subsampling layers. We show that both versions eliminate critical slowing down.

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

Event Official Language: English

Black hole states at finite N

June 18 (Wed) at 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

Identifying Lightning Structures and Predicting Cloud Properties

June 18 (Wed) at 15:00 - 16:00, 2025

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

This third talk in the DEEP-IN series focuses on using unsupervised machine learning to identify and predict patterns in atmospheric phenomena. We begin by demonstrating how clustering and dimensionality reduction techniques can uncover coherent lightning patterns from high-dimensional LOFAR (LOw Frequency ARray) data, offering insight into large-scale organization. We then show how generative diffusion models enable super-resolution retrieval of cloud properties for all day from satellite observations. This is an informal seminar, we will start with the methodology and some practical examples, and finally reserve time for everyone interested to discuss it together.

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

Event Official Language: English

Charting the landscape of gauge-fermion dynamics

June 16 (Mon) at 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) at 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) at 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) at 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) at 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

Collective Behaviors and Deep Learning Applications

June 11 (Wed) at 15:00 - 16:00, 2025

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

Understanding and modeling collective pedestrian behavior, particularly under extreme conditions, is a challenging problem that combines cognition, physics, and data analysis. In the second talk of DEEP-IN series, I will explore how deep learning can reveal the underlying principles of crowd dynamics from data. Starting with a bounded rationality framework, we demonstrate how deep learning can quantify evacuation dynamics and reveal hidden patterns in collective motion. Specifically, we demonstrate how macroscopic observables, such as entropy and kinetic energy, can be extracted from microscopic trajectories in simulations and real-world data. This is an informal seminar, we will start with the methodology and some practical examples, and finally reserve time for everyone interested to discuss it together.

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

Event Official Language: English

Quantum Decryption from technological perspective to business opportunities

June 6 (Fri) at 16:00 - 17:30, 2025

Sho Sugiura (CEO, BlocQ, Inc.)

Quantum decryption is a foundational application of fault-tolerant quantum computing (FTQC), essential for future cryptographic security. While quantum simulations, especially quantum chemistry, dominate current quantum computing research, quantum decryption remains less explored despite its significance. In this talk, we give a business style talk that overviews the current status of quantum decryption and our company's pioneering efforts to advance practical FTQC-based solutions. We discuss recent technological advancements and outline our strategic initiatives aimed at leading the field toward secure communications.

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

Event Official Language: English

A New Measure of Genuine Multipartite Entanglement

June 6 (Fri) at 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

4th Mathematical Application Research Team Meeting

June 6 (Fri) at 14:00 - 15:30, 2025

Sinya Aoki (Deputy Director, Fundamental Quantum Science Program, TRIP Headquarters, RIKEN)

An alternative view on AdS/CFT correspondence

Venue: #345-347, Main Research Building, RIKEN Wako Campus (Main Venue) / via Zoom

Event Official Language: English

Exotic Pairing Nature and Charge Ordering in Kagome Superconductor

June 5 (Thu) at 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

Solving Inverse Problems with Physics-Driven Deep Learning

June 4 (Wed) at 15:00 - 16:00, 2025

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

This talk kicks off a four-part seminar series on the DEEP-IN WG, an interdisciplinary working group exploring how modern deep learning — including deep generative models — can tackle inverse problems across scientific domains. In addition to DEEP-IN activities, I will present a new framework and vision, motivated by the growing synergy between physics-driven designs for deep learning and scientific discovery, as discussed in our recent review article. Future talks will demonstrate machine learning applications in collective behaviors, weather systems, and lattice field simulations. This is an informal seminar, we will start with the methodology, give some practical examples, and finally reserve time for everyone interested to discuss it together.

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

Event Official Language: English

Extracting particle mass on quantum computers: state preparation and measurement

June 3 (Tue) at 11:00 - 12:30, 2025

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

In this seminar, I will introduce the procedure of extracting particle mass from the ab initio calculation using quantum computers, including two essential steps: state preparation and measurement. For the measurement process, in our recent work "Computing n-time correlation functions without ancilla qubits" [arXiv:2504.12975], we developed a measurement method for correlation functions without ancilla qubits, circumventing longstanding hardware constraints of limited qubit connectivity and short-range control operations. We demonstrate our method using IBM quantum hardware and successfully reproduce the noiseless results of the Schwinger model hadron mass within a relative error of 0.18%, even in the presence of realistic hardware limitations and noise. For the state preparation process, another work "Performance guarantees of light-cone variational quantum algorithms for the maximum cut problem" [arXiv:2504.12896] focused on the accuracy of the state preparation using variational quantum algorithms (VQAs). We propose a light-cone VQA with provable performance guarantees, whose single round has higher accuracy than the 3-round standard VQA for the maximum cut problem. We experimentally validated the single-round light-cone VQA using IBM quantum hardware with solution accuracy that exceeds the known classical hardness threshold in both a 72-qubit demonstration and a 148-qubit demonstration.

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

Event Official Language: English