This session features two speakers: Hector Banos, Assistant Professor of Mathematics at California State University, whose research focuses on phylogenetic inference and network models, and Benjamin Teo, a Postdoctoral Researcher at the University of Melbourne, working on probabilistic and computational methods for continuous trait evolution on phylogenetic networks. See below for details.

【Talk 1】
Speaker: Hector Banos
Title: Bringing a Knife to a Gunfight: Pitfalls of Phylogenetic Inference under Model Misspecification
Abstract:
Phylogenetic networks provide a flexible framework for representing evolutionary histories that include hybridization, introgression, and other reticulate processes. However, inferring such networks remains computationally and statistically difficult. Many current methods often scale only to restricted classes of networks. Consequently, researchers frequently analyze their data using simpler models (most commonly phylogenetic trees) even when there is strong evidence that the underlying evolutionary history is more complex.

In this talk, we examine the impact of model misspecification on phylogenetic inference, focusing on situations in which data are generated by a complex network but are analyzed using simpler tree or network models. I then show how this mismatch can influence the topology of inferred trees, as well as the structure of inferred networks. These results highlight the limitations and the practical consequences of using simplified models for phylogenetic inference.

【Talk2】
Speaker: Benjamin Teo
Title: Adapting cluster graphs for inference of continuous trait evolution on phylogenetic networks
Abstract:
I consider a new approach ("loopy belief propagation") for fitting Gaussian models on a phylogenetic network to explain the data observed across present-day species for a continuous univariate or multivariate trait. We previously showed [1] that a trait evolution model coupled to a network can be readily cast as a probabilistic graphical model, so that the likelihood can be efficiently computed using a dynamic programming framework ("belief propagation") defined on an auxiliary graph ("cluster graph") that is tree-structured. Even so, maximum likelihood estimation can grow computationally prohibitive for large complex networks.

Belief propagation can be applied more generally to non-tree ("loopy") cluster graphs to compute a factored energy approximation to the log-likelihood. "Loopy" belief propagation may provide a more practical trade-off between estimation accuracy and runtime. However, the influence of cluster graph structure on this trade-off is not precisely understood.

We conduct a simulation study using our Julia package PhyloGaussianBeliefProp [2] to investigate how varying the maximum cluster size of a cluster graph affects this trade-off. We discuss recommended choices for maximum cluster size, and prove the equivalence of likelihood-based and factored-energy based estimates for the homogeneous Brownian motion trait model.

The talk is based on our preprint [3]. I will introduce the key concepts from the ground up.

The recent discovery of noninvertible symmetries—a radical extension of conventional symmetry—has challenged long-standing paradigms in condensed matter physics and quantum information and opened new territory in both theory and technology. Unlike ordinary symmetries, which can be inverted, these symmetries behave like projections (one-way operations) yet still strongly constrain quantum dynamics and enable new classes of phases and phase transitions. However, their role in organizing and stabilizing novel quantum phases remains poorly understood. One important example is a symmetry protected topological (SPT) phase, characterized by nontrivial edge modes and potential applications in quantum information. In this talk, I will discuss the classification of noninvertible symmetry-protected topological (NISPT) phases in both closed and open quantum systems using a duality-based method, and present concrete lattice realizations. These lattice models provide controlled playgrounds in which the physics of noninvertible symmetry can be explored numerically and, potentially, experimentally.

Quantum gravity remains one of the major challenges in modern physics. Even at the most fundamental level, there is no experimental confirmation of whether a mass placed in a spatial superposition generates a corresponding superposition of gravitational fields. In recent years, experiments aiming to create gravity-induced quantum entanglement have attracted significant attention as a way to probe the quantum nature of non-relativistic gravity. In particular, optomechanical systems, which exploit the interaction between light and mechanical oscillators, provide a promising platform for such studies. We are pursuing experiments at the milligram scale, which lies between the smallest mass scale at which classical gravity has been tested and the largest mass scale at which quantum states of mechanical oscillators have been realized [1]. In this seminar, I will discuss experimental approaches to testing the quantum nature of gravity using suspended and levitated mirrors. I will also discuss our recent proposal to use inverted oscillators to enhance gravity-induced entanglement exponentially [2].

The analytic structure of scattering amplitudes provides a framework for mapping the fundamental properties of a high-energy (UV) theory onto non-perturbative constraints for low-energy (IR) effective field theories. While this structure is well understood in flat space, its extension to de Sitter space is hindered by the expanding background, which complicates the definition of asymptotic states and breaks time-translation symmetry. In this talk, I will outline a foundational approach to bridging this gap. I will demonstrate how the analytic properties of flat-space amplitudes are imprinted on their de Sitter counterparts. The ultimate goal of this program is to derive Swampland-type constraints for cosmological EFTs, ensuring they admit a consistent UV completion.

While my career began in a linear way, it gradually opened into a non-traditional path through unexpected mergings, where theoretical nuclear physics, filmmaking, and creative public and academic engagement intertwined. I will share how scientific inquiry, artistic practice, and storytelling began shaping one another, opening new ways to explore complexity, emotion, and connection. Drawing on work from my physics research to cinema projects like Rare Connections, I will reflect on how curiosity and creative thinking move freely across science and art, deepening each and expanding how we understand the human experience. My aim is to offer a perspective on the possibilities that emerge when we allow our multitudes to meet and transform one another.

This joint workshop will bring together physicists and mathematicians who work with asymptotics and perturbation theory techniques. This includes theorists in cosmology, high energy physics, quantum gravity, solar physics, astrophysics.

Workshop overview
Over three days, there will be approximately 15 invited (1 hour slot) or contributed (20-30 min slot) talks about:
Fundamental asymptotics and perturbation theory techniques used in theoretical physics. Various applications of asymptotics and perturbation theory techniques in (wave transport or oscillation related) astrophysics and cosmology eigenvalue problems.

The workshop will also feature hands-on Mathematica and Python tutorials introducing:
Practical use of WKB methods in applied mathematics for any “Schrodinger-like” wave equations, Resummation methods in high energy theory, Deriving normal modes in stars, and their application to tidal evolution in binary star or planet systems, Eigenvalue problems in core collapse supernova theory.

The RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) and the Faculty of Science at Nara Women's University are promoting a project to foster female researchers under the auspices of the RIKEN Diversity Promotion Office. As part of the program, 21 undergraduate and graduate students from Nara Women's University will visit several laboratories on the RIKEN Wako campus to ask questions about their research and hold workshops with iTHEMS researchers.

Organizers:
RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)
Faculty of Science, Nara Women's University

March 2 (Mon)
13:15-14:15
Center for Brain Science (CBS) (C56 Ikenohata Building)
Laboratory for Multi-scale Biological Psychiatry (Team Director: Akiko Hayashi-Takagi)

14:30-15:45
Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) (C01 Main Research Building, 4th Floor Rooms 435-437)
Introduction to iTHEMS: Tetsuo Hatsuda (iTHEMS Division Director of Applied Mathematical Science)
Lecture and Q&A: Megumi Oya (iTHEMS Medical Science Data-driven Mathematics Team Postdoctoral Researcher)

16:00-17:30
Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) (C01 Main Research Building, 4th Floor Rooms 435-437)
Lecture and Q&A: Leo Spiedel (iTHEMS ECL Research Unit Leader)

18:00-20:30 Networking Session (C01, Research Main Building 3F East Side (Okochi Hall Side))

March 3 (Tue)
9:00-10:30
RIBF Facility, RIKEN Nishina Center (RNC)

11:15-12:00
Center for Quantum Computing (RQC)
Optical Quantum Control Research Team (Team Director: Hidehiro Yonezawa)

The interplay between black hole interior dynamics and quantum chaos provides a crucial framework for probing quantum effects in quantum gravity. According to the holographic "Complexity=Volume" proposal, we investigated non-perturbative generating function of geodesic length in Jackiw-Teitelboim (JT) gravity to uncover universal signatures of quantum chaos and quantum complexity. We observed that the generating function interpolates between two major probes of quantum chaos - spectral form factor and complexity - highlighting its utility as a probe of chaotic spectrum in quantum gravity. Generalizing the result to general chaotic systems, we demonstrated that time evolution of the complexity is universally governed by a certain pole structure of observables, suggesting a validity of wide class of observables as a probe of quantum chaos in quantum gravity.

The world is filled with numerous odors that are impossible to experience all in our lifetime. Perhaps to cope with this situation, the brain is equipped with an ability to recognize whether an odor is attractive or aversive even from the first encounter and guide adaptive behavior. However, how information about the innate value of odors (attractiveness/aversiveness) is computed and transformed into appropriate behavioral outputs in the brain remains poorly understood. We are addressing this question in the olfactory circuit of fruit flies by combining behavioral analysis in virtual reality, comprehensive neuronal activity imaging, neuronal connectivity analysis, and computational modeling. In this talk, I will present our latest efforts to decipher how odor value is computed and how this information is transformed into motor-related signals in a tiny brain.

The Mathematical Application Research Team is pleased to welcome Chiyaha Jibiki, who will join the team as an SPDR in April. He will give a talk at this meeting prior to his official start date. Everyone is welcome to join the meeting.

Title: Left-Orders and Dynamics: Applications to Hyperbolic Geometry and Low-Dimensional Topology

Abstract: A left-order on a group is a total order that is invariant under left-multiplication. The concept dates back to the early 20th century, when Dedekind and Hölder characterized the natural order on the real line purely in terms of group actions.
In the 21st century, this theory has evolved significantly through connections with discrete dynamical systems. Currently, there is active research linking geometric structures to left-orders on geometrically significant groups, such as fundamental groups and mapping class groups.
In this talk, I will introduce the framework of left-order theory, starting from the simple perspective of binary operations on infinite sets. I will then provide an overview of the field by presenting, as much as possible, the diverse applications arising from its high versatility. In particular, I will discuss the speaker's recent results concerning the structure of the space of left-orders (comparisons between left-orders) and methods for constructing specific left-orders.
This talk includes joint work with Shuhei Maruyama (Kanazawa University).

The two fundamental questions—“What is quantum?” and “What is spacetime?”—are deeply intertwined. On one hand, the formulation and interpretation of quantum theory depend both implicitly and explicitly on our conceptions of time and space. On the other hand, we believe that fully taking into account the quantum character of nature will force us to revise our understanding of spacetime. These two conceptual problems lie at the heart of the unsolved challenge of how to quantize classical spacetime, and conversely, how (semi-) classical descriptions of spacetime emerge from quantum theory. Furthermore, if the entire matter-spacetime system is a kind of quantum many-body system, thermodynamics—which governs its statistical behaviors—should play a key role in elucidating these problems.

This workshop will discuss the question “How can quantum theory and spacetime be understood in a consistent manner?” from a fundamental and broad perspective. To tackle this challenge, we gather researchers in foundations of quantum theory, quantum gravity, and related fields from around the world, providing a "space and time" to share various ideas with open minds and engage in lively discussions. By exploring new concepts and principles, we hope to uncover directions to guide quantum theory over the next 100 years.

This workshop covers…

Foundations of quantum theory
Quantum gravity and emergence of spacetime
Formulation of semi-classical gravity
Experimental aspects of fundamental properties in nature and quantum gravity
Foundations of quantum many-body systems and thermodynamics
Other related topics are welcome.

We welcome short talk presentations and poster presentations.

This event is a workshop jointly organized by KEK Theory Center and RIKEN iTHEMS.

Living systems operate far from equilibrium under continuous time-varying forcing across multiple temporal and spatial scales. From neural and cardiovascular rhythms to microcirculatory dynamics and circadian cycles, physiological processes are inherently nonautonomous. Classical stability concepts based on autonomous attractors and stationary limit cycles are therefore insufficient to explain how such systems remain robust yet adaptable.
In this talk, I will introduce chronotaxicity as a framework for nonautonomous oscillatory systems possessing time-dependent point attractors and contraction regions. Chronotaxic systems maintain stability under continuous forcing, providing a rigorous theoretical description of dynamic robustness.
To illustrate the generality of this concept, I will show how chronotaxicity can be observed in a controlled physical experiment. I will then present a new order parameter based on angular velocity for quantifying phase dynamics in numerical simulations of coupled nonautonomous oscillators, along with the methods collected in the Multiscale Oscillatory Dynamics Analysis (MODA) toolbox for analysing time-dependent oscillatory behaviour.
This approach provides a unified perspective on dynamic stability in complex systems, highlighting how living systems remain robust yet adaptable and suggesting quantitative signatures of dysfunction in health and disease. While the focus is on physiological and numerical models, it is broadly applicable to complex nonautonomous systems, underscoring its generality as a dynamical principle.

Quantum invariants are invariants of knots and 3-manifolds which relate deeply to mathematical physics and representation theory.
In recent years, it has become increasingly clear that it is also deeply related to number theory, that is, quantum modularity for quantum invariants.
This topic is interesting from a topological viewpoint since this is a refinement of establishing asymptotic expansions of quantum invariants, which is an important problem in quantum topology,
and is interesting from a number-theores[tic viewpoint since this gives examples of quantum modular forms, which are mysterious objects in number theory.

I obtained two linked results on topology and number theory:
Establishing explicit asymptotic expansions of quantum invariants for negative definite plumbed 3-manifolds and establishing quantum modularity of false theta functions in full generality.

In this talk, I will outline previous progress on quantum modularity for quantum invariants and my results.

We investigate the critical behavior of a family of Z2-symmetric scalar field theories on the Bethe lattice (the tree limit of regular hyperbolic tessellations) using both the non-perturbative Functional Renormalization Group and perturbation theory. Due to the hyperbolic nature of Bethe lattices, the Laplacian lacks a zero mode and exhibits a spectral gap. We demonstrate that closing the spectral gap via a modified Laplacian leads to novel critical behavior governed by interacting fixed points. This stands in contrast to the nearest-neighbor Ising model, which exhibits a phase transition with mean-field critical exponents. We further comment on the possible reasons for such a deviation.

PROGRAM:

9h45 - 10h15 Registration & Coffee

10h15 - 10h20 Opening Remarks - Satoshi Iso (RIKEN), Director of iTHEMS

10h20 - 11h20 SESSION 1 - Chair: Tetsuo Hatsuda (RIKEN)

Yoshihiko Susuki (Kyoto University): Koopman resolvents in dynamical systems and control

11h20 -11h40 Free Discussions

11h40 - 13h00 Lunch Break & Discussions

13h00-14h00 SESSION 2 - Chair: Narumi Fujii (Institute of Science Tokyo)

Alexandre Mauroy (University of Namur, Belgium): Analytic EDMD method for spectral analysis of fixed point dynamics

14h00 - 14h30 Coffee Break & Discussions

14h30 - 15h30 SESSION 3 - Chair: Tetsuo Hatsuda (RIKEN)

Hiroya Nakao (Institute of Science Tokyo): Koopman operator analysis of coupled oscillator systems

15h30 - 16h00 Coffee Break & Discussions

16h00 - 17h00 SESSION 4 - Chair: Riccardo Muolo (RIKEN)

Yuzuru Kato (Future University Hakodate): Analysis of quantum nonlinear oscillators on the basis of Koopman operator theory

17h00 - 17h05 Closing Remarks - Tetsuo Hatsuda, Chair of the Workshop

17h05 - 18h00 Free Discussions

Understanding how complex organs reliably form during development remains a key question in biology. In this talk, I discuss how gene regulatory networks may generate skeletal patterns in the vertebrate limb, using Sox9 expression as a proxy, as it marks the earliest stages of cartilage formation. To address this, I developed new computational tools for reconstructing spatiotemporal gene expression and built models ranging from machine learning approaches to mechanistic frameworks. These analyses reveal that limb patterning cannot be explained by a single universal mechanism. Instead, different regions of the limb appear to use distinct regulatory strategies, uncovering an unexpected qualitative modularity in skeletal development. Together, these findings lead to a new hypothesis in which other systems, such as the vasculature may actively shape skeletal spacing in specific limb regions.

Correlation functions of local operators in Quantum Field Theory (QFT) on hyperbolic space can be fully characterized by the set of QFT data. These are the scaling dimensions of boundary operators, the boundary Operator Product Expansion (OPE) coefficients and the Boundary Operator Expansion (BOE) coefficients that characterize how each bulk operator can be expanded in terms of boundary operators. For simplicity, we focus on two dimensional QFTs and derive a universal set of first order Ordinary Differential Equations (ODEs) that encode the variation of the QFT data under an infinitesimal change of a bulk relevant coupling. In principle, our ODEs can be used to follow a renormalization group flow starting from a solvable QFT into a strongly coupled phase and to the flat space limit.

Recent advances in X-ray spectroscopic observation have enabled researchers to reveal distinct clumpy structures in the super-Eddington outflows from the supermassive black hole in PDS 456 (XRISM Collaboration 2025), initiating detailed investigation of fine-scale structures in accretion-driven outflows. In this talk, I will introduce our high-resolution, two-dimensional radiation-hydrodynamics simulations with time-varying and anisotropic initial and boundary conditions that reproduce clumpy outflows from super-Eddington accretion flows. The resulting clumpy outflows extend across a wide range of radial distances and polar angles, exhibiting typical properties such as a size of ~10 rg (where rg is the gravitational radius), a velocity of ~0.05–0.2 c (where c is the speed of light), and about five clumps along the line of sight. Although the velocities are slightly smaller, these characteristics reasonably resemble those obtained from the XRISM observation. The gas density of the clumps is on the order of 10^-13–10^-12 g cm^-3, and their optical depth for electron scattering is approximately 1–10. The clumpy winds accelerated by radiation force are considered to originate from the region within <300 rg.