セミナー

Femtoscopy: Probing Fundamental Matter Properties at the Fermi Scale

2025年8月22日(金) 13:30 - 15:00

Yijie Wang (Postdoctoral Researcher, Tsinghua University, Beijin, China / 理化学研究所 仁科加速器科学研究センター (RNC) RI物理研究室 客員研究員)

Femtoscopy, a cutting-edge technique grounded in intensity interferometry (correlation function analysis), enables in-depth exploration of fundamental properties of matter, including space, time, and interactions, at the Fermi scale. Originating from the Hanbury Brown and Twiss (HBT) correlation function, which was utilized in 1956 to measure the angular radius of Sirius, this method has been extended to the subatomic realm, emerging as a pivotal tool for deciphering space-time structures and particle interactions. This talk focuses on three representative femtoscopy studies: First, by combining femtoscopic interferometry with optical deblurring algorithms, it reveals the non-Gaussian freeze-out spatial distribution of protons and antiprotons in Au+Au relativistic heavy-ion collisions, challenging conventional wisdom [Chinese Physics Letters 42, 031401 (2025)]. Second, in the 30 MeV/u ⁴⁰Ar + ¹⁹⁷Au reaction, femtoscopy is employed to determine the proton emission timescale at approximately 100 fm/c and uncover the kinetic law of preferential emission of neutron-rich particles, making an “ultra-fast” video for heavy-ion collisions [Physics Letters B, 825, 136856 (2022)]. Third, using a high-resolution neutron array, femtoscopy accurately measures the neutron-neutron scattering length and effective range, as well as the space-time size of the neutron emission source, providing crucial data for the study of charge symmetry breaking in nuclear forces and nuclear symmetry energy [Physical Review Letter, 134, 222301 (2025)]. These achievements fully demonstrate the significant value of femtoscopy in advancing the frontiers of nuclear and particle physics, spanning from experimental observations to theoretical modeling. Dr. Yijie Wang is the Post Doc of Tsinghua University and Visiting Scientist of RIKEN. He studied physics at Jilin University, China, and obtained his Ph. D. degree at Tsinghua University in 2021. Then, he continued researches in Tsinghua University as Post Doc up to now. His interests focus on heavy ion collision experiment, nuclear equation of state, advanced detection system development and femtoscopy.

会場: セミナー室 (359号室) 3階 359号室 (メイン会場) / via Zoom

イベント公式言語: 英語

Positive neutrino masses with DESI DR2 via matter conversion to dark energy

2025年8月21日(木) 14:30 - 16:00

Kevin Croker (Assistant Research Scientist, Arizona State University, USA)

The Dark Energy Spectroscopic Instrument (DESI) is a massively parallel spectroscopic survey on the Mayall telescope at Kitt Peak, which has released measurements of baryon acoustic oscillations determined from over 14 million extragalactic targets. We combine DESI Data Release 2 with CMB datasets to search for evidence of matter conversion to dark energy (DE), focusing on a scenario mediated by stellar collapse to cosmologically-coupled black holes (CCBH). In this physical model, which has the same number of free parameters as LambdaCDM, DE production is determined by the cosmic star formation rate density (SFRD), allowing for distinct early- and late-time cosmologies. Using two SFRDs to bracket current observations, we find that the CCBH model: accurately recovers the cosmological expansion history, agrees with early-time baryon abundance measured by BBN, reduces tension with the local distance ladder, and relaxes constraints on the summed neutrino mass. For these SFRDs, we find a peaked positive summed mass < 0.149 eV (95% confidence) and summed mass equal to 0.106 +0.050 -0.069 eV respectively, in good agreement with lower limits from neutrino oscillation experiments. A peak in positive summed neutrino mass results from late-time baryon consumption in the CCBH scenario and is expected to be a general feature of any model that converts sufficient matter to dark energy during and after reionization.

会場: セミナー室 (359号室) 3階 359号室

イベント公式言語: 英語

Detecting ghost ancestors in the human lineage

2025年8月21日(木) 13:00 - 14:00

シュパイデル 玲雄 (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 数理遺伝学理研ECL研究ユニット 理研ECL研究ユニットリーダー)

イベント公式言語: 英語

Perturbed Observation

2025年8月20日(水) 13:00 - 14:00

会場: 計算科学研究棟 R511 (メイン会場) / via Zoom

イベント公式言語: 英語

Dynamic Scaling Analysis for Enzymatic Degradation and Network Growth of DNA Liquid Droplets

2025年8月14日(木) 13:00 - 14:00

舘野 道雄 (JSPS Overseas Research Fellow, Material Research Laboratory, University of California Santa Barbara, USA)

In this talk, I will introduce two novel pattern formation dynamics exhibited by phase-separated liquid droplets composed of DNA nanoparticles: 1) By enzymatically inactivating the phase-separation ability of the nanoparticles, we observed the process by which droplets gradually disappeared. Notably, the droplet-size distribution density remained unchanged, while only the total number of droplets decreased over time. 2) We also observed the formation of a novel two-dimensional wire-like network pattern, in which two types of droplets are arranged in a one-dimensional, alternating manner. We confirmed that the characteristic size of the network follows power-law growth over nearly two decades, with a universal growth exponent that is independent of droplet viscosity and inter-droplet wetting affinity. We analyze these results within the framework of the dynamic scaling hypothesis and discuss the physical mechanisms underlying these behaviors.

イベント公式言語: 英語

Extended Kalman filter: Lecture 2

2025年8月13日(水) 13:00 - 14:00

会場: 計算科学研究棟 (メイン会場) / via Zoom

イベント公式言語: 英語

Cosmological Collider with Boundary Interactions

2025年8月7日(木) 16:00 - 17:30

Yi Wang (Professor, Department of Physics, Hong Kong University of Science and Technology, Hong Kong)

We first review cosmological collider physics. Namely, how the mass, spin, width and parity of the primordial particles during inflation may be read off from the density correlations in the CMB and the Large Scale Structure of the universe, and how this can be related to particle physics such as the Standard Model. After that, we will introduce relations between bulk and boundary terms in cosmological collider physics, and highlight a class of interactions which were overlooked in the literature.

会場: via Zoom

イベント公式言語: 英語

iTHEMS Biology welcomes another new member!

2025年8月7日(木) 13:00 - 14:15

孔 星植 (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 研究員)

This meeting will be used to welcome another new members to the iTHEMS Biology Study Group: Dr. Sungsik Kong, who is joining iTHEMS Fundamental Division as a Research Scientist. He will give us a 15-20 min talk to introduce his research. If time permits, let's also use this time to catch up on each other's current research. I hope that many people will join us to welcome this new member and come meet him and hear about his research.

会場: Zoomのみに変更

イベント公式言語: 英語

DA Seminar: Prof. Dai Yamazaki and Hannah Cloke

2025年8月6日(水) 15:00 - 16:30

ダイ・ヤマザキ (東京大学 生産技術研究所)
Hannah Cloke (Professor, Department of Meteorology, University of Reading, UK)

The seminar will be jointly given by Associate Professor Dai Yamazaki (The university of Tokyo) and Professor Hannah Cloke (University of Reading). Speaker 1: Associate Professor Dai Yamazaki (Institute of Industrial Science, The University of Tokyo) Title: How can we achieve fast and realistic simulation of river and flood dynamics on the global scale? Abstract: Modeling river hydrodynamics across continental-scale basins is challenging due to their inherently multiscale nature. On one hand, we must account for the water budget along river systems that extend over 1,000 km. On the other hand, water movement within channels and floodplains is governed by topographic features smaller than 100 meters. The global river model CaMa-Flood addresses this complexity by employing the Catchment-based Macro-scale Floodplain modeling approach (CMF approach). This method approximates the relationship between water volume, flood extent, and water depth through sub-grid scale parameterizations. These parameters, derived from high-resolution satellite-based digital elevation models (DEMs) and hydrography datasets, enable realistic simulation of river discharge and flood stages—without explicitly resolving small-scale floodplain dynamics. To further accelerate simulations, recent developments in CaMa-Flood have introduced several performance optimizations, including MPI/OpenMP parallelization, SIMD vectorization, sparse matrix implementation, and a GPU-enabled Python version. These enhancements make the model more suitable for large-scale and near-real-time applications such as global flood monitoring and climate impact assessment. Speaker 2: Professor Hannah Cloke (Department of Meteorology, University of Reading) Title: Preparing for floods in an uncertain future

会場: Hybrid Format (RIKEN R-CCS room 107 and Zoom) (メイン会場) / via Zoom

イベント公式言語: 英語

Coupling AI and SMC-based algorithms: Inference of population structure from single genome sequencing analysis

2025年8月6日(水) 14:00 - 15:00

アルバ・ニエト エレディア (Ph.D. Student, L'Institut de Systématique, Évolution, Biodiversité, France)

The unprecedented availability of whole genome sequences has transformed population genetics, allowing researchers to reconstruct past demographic histories with greater resolution. Among the most widely used approaches for this purpose are methods grounded in the Sequentially Markovian Coalescent (SMC) framework, which leverage patterns of coalescence with recombination to infer fluctuations in effective population size over time. These fluctuations inform about past population trends, especially for endangered populations and extinct species. However, despite their success, these methods often rest on simplifying assumptions. Most notably, random mating among all the individuals in a population (panmixia) assumption can lead to biased or misleading inferences when applied to populations with underlying genetic and/or geographical structure. For instance, changes in ancestral population size and population structure can lead to confounding signals in the historical coalescent rate, which presents an non identifiability problem, resulting in misleading interpretations that primarily affect the analysis in species of conservation interest. After revising and detecting as systematic bias in SMC-based algorithms associated to population structure, we investigate the power of emerging summary statistics derived from whole genome data, proposing a novel deep learning framework that integrates the latent information contained in SMC transition matrices to distinguish between signals of population structure and true demographic change. By transforming these matrices into image-like representations, we develop a method based on deep convolutional neural networks (CNNs) in combination with perceptrons to classify demographic histories and predict key parameters of structured models, applying strategies of transfer learning. This approach enables discrimination between structured and panmictic populations and further infers specific features of the underlying demographic model. By blending the strengths of the modelling of coalescence with recombination of SMC-based approaches, deep learning, and coalescent simulations, this methodology offers a new avenue for scalable demographic inference considering structured populations.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

LeanConjecturer: Automatic Generation of Mathematical Conjectures for Theorem Proving

2025年8月1日(金) 16:00 - 18:00

恩田 直登 (Project Research Engineer, Research Administrative Division, Omron Sinic X Corporation)

We introduce LeanConjecturer, a pipeline for automatically generating university-level mathematical conjectures in Lean 4 using Large Language Models (LLMs). Our hybrid approach combines rule-based context extraction with LLM-based theorem statement generation, addressing the data scarcity challenge in formal theorem proving. Through iterative generation and evaluation, LeanConjecturer produced 12,289 conjectures from 40 Mathlib seed files, with 3,776 identified as syntactically valid and non-trivial, that is, cannot be proven by aesop tactic. We demonstrate the utility of these generated conjectures for reinforcement learning through Group Relative Policy Optimization (GRPO), showing that targeted training on domain-specific conjectures can enhance theorem proving capabilities. Our approach generates 103.25 novel conjectures per seed file on average, providing a scalable solution for creating training data for theorem proving systems. Our system successfully verified several non-trivial theorems in topology, including properties of semi-open, alpha-open, and pre-open sets, demonstrating its potential for mathematical discovery beyond simple variations of existing results.

会場: via Zoom / セミナー室 (359号室) 3階 359号室

イベント公式言語: 英語

Targeting SARS-CoV-2 RNA: Insights for RNA-Directed Drug Discovery

2025年7月31日(木) 13:00 - 14:30

マリア・イヴォニナ (九州大学 エネルギー研究教育機構 学術研究員)

Traditional pharmacology fights virus infections by targeting proteins including enzymes, receptors, and structural proteins to break up the viral machinery. Nucleic acid-targeting therapies, on the other hand, can act directly on the genetic code of viruses, blocking their replication or translation in host cells. Coronaviruses and HIV are examples of RNA viruses that use a process called -1 programmed ribosomal frameshifting (-1 PRF) to produce their viral proteins. In this process, the translating ribosome is forced to shift into the alternative reading frame, replicating mRNA in the wrong order. Using small-molecule compounds to block this mechanism could be a promising way to neutralize such viruses. It is difficult to experimentally study the interactions between RNA and a drug candidate to understand where the drug binds and how it changes the shape of the viral RNA. I will discuss how Molecular Dynamics simulations are used to explore the conformational dynamics of mRNA structural elements and to investigate what happens when an antiviral agent binds to it. Additionally, I will show how the quantum-chemical orbital interaction analysis we developed, called Through-Space/Through-Bond Energy Decomposition Analysis (TS/TB-EDA), reveals which RNA nucleotides, at the atomic level, are critical for binding. This molecular modelling approach reveals strategies for targeting structured RNA elements — a crucial step toward expanding the arsenal of RNA-targeting therapeutics for future pandemics.

会場: 研究本館 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Bridging applied math and quantum many-body physics and beyond via tensor methods

2025年7月23日(水) 16:00 - 17:00

品岡 寛 (埼玉大学)

In modern physics, high-dimensional functions and operators naturally arise in a wide range of contexts, including turbulence simulations, parameter-dependent partial differential equations (PDEs), and quantum field theory. Efficient representations and computations with such high-dimensional objects pose major challenges across disciplines. Dimensionality reduction techniques such as the Quantics Tensor Train (QTT) [1] and Tensor Cross Interpolation (TCI) [2] were originally developed in applied mathematics. In our work, we have extended these methods to quantum many-body problems, demonstrating their effectiveness in handling complex high-dimensional structures in theoretical physics [3–10]. Given their generality, QTT and TCI are expected to find applications beyond quantum theory itself, in fields such as statistical field theory, model reduction, and control of complex systems, where similar high-dimensional structures emerge. This presentation will first review the computational bottlenecks that arise in quantum many-body simulations and other high-dimensional problems. Then, we will introduce QTT and TCI from a broader, method-oriented perspective, aiming to bridge applied mathematics and quantum theoretical physics.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Supersymmetric field theories and homotopy theory

2025年7月23日(水) 13:00 - 14:30

山下 真由子 (Junior Research Faculty member, Perimeter Institute for Theoretical Physics, Canada)

I will give a general introduction and overview on the Segal-Stolz-Teichner program, which tries to relate supersymmetric field theories in physics with homotopy theory in mathematics.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Mesoscopic transport via one-dimensional chain with Localized two-body loss

2025年7月23日(水) 10:00 - 11:30

柿元 健佑 (早稲田大学 理工学術院 基幹理工学部 博士課程)

Mesoscopic transport has long served as a powerful probe into the quantum behavior of matter; however, the role of dissipation in such systems remains unresolved. In recent years, quantum simulations of mesoscopic systems with ultracold atomic gases have made significant progress, particularly through the use of optical tweezers to induce local dissipation via atom loss. In this talk, we discuss a two-terminal mesoscopic system in which two-body loss occurs locally at the center of a one-dimensional chain, modeling a dissipative quantum point contact. To analyze this setup, we employ the Keldysh Green’s function formalism in combination with a noise-field representation of Lindblad dynamics. Our analysis reveals that the dissipation strength depends on the occupation number of the central dissipative site, leading to a weaker suppression of particle current in the weakly dissipative regime compared to the case of one-body loss.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

A free probability approach to quantum chaos in random matrix ensembles

2025年7月22日(火) 16:00 - 17:00

プラティック・ナンディ (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 特別研究員)

In free probability theory, quantum chaos is marked by “free independence” between observables at early and late times, causing certain statistical measures (cumulants) to vanish. Motivated by this, we study the statistics of a time-evolved operator in the Rosenzweig-Porter (RP) random matrix ensembles. Analyzing operator statistics for different spin operators across these regimes reveals close alignment with free probability predictions in the ergodic phase, contrasted by persistent deviations in the fractal and localized phases even at late times. Using the distance measures and statistical methods, we define and characterize the onset of the free time in the ergodic phase. The talk is based on arXiv: 2506.04520.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Detectability of post-Newtonian classical and quantum gravity via quantum clock interferometry

2025年7月22日(火) 14:00 - 15:00

若桑 江友里 (名古屋大学 大学院情報学研究科数理情報学専攻 特任准教授)

Understanding physical phenomena at the intersection of quantum mechanics and general relativity remains a major challenge in modern physics. While various experimental approaches have been proposed to probe quantum systems in curved spacetime, most focus on the Newtonian regime, leaving post-Newtonian effects such as frame dragging largely unexplored. In this study, we propose and theoretically analyze an experimental scheme to investigate how post-Newtonian gravity affects quantum systems. We consider two setups: (i) a quantum clock interferometry configuration designed to detect the gravitational field of a rotating mass, and (ii) a scheme exploring whether such effects could mediate entanglement between quantum systems. Due to the symmetry of the configuration, the proposed setup is insensitive to Newtonian gravitational contributions but remains sensitive to the frame-dragging effect. Assuming the validity of the quantum equivalence principle, this approach may provide insights not only into the quantum nature of gravity but also into whether spacetime itself exhibits quantum properties. However, our analysis reveals that, within realistic experimental parameters, the expected effects are too small to be detected. We discuss possible interpretations of this undetectability, and its implications for tests of quantum gravity.

会場: 研究本館 (メイン会場) / via Zoom

イベント公式言語: 英語

ComSHeL collaboration planning

2025年7月22日(火) 14:00 - 15:00

The objective of this 3rd monthly meeting of the ComSHeL Study Group is to discuss specific collaborations we could undertake across our own Teams/Divisions on projects of common interest to take advantage of our complementary skills and expertise. We also want to consider how ComSHeL could help respond to specific calls for focus in certain research areas within RIKEN and the broader funding landscape.

会場: 研究本館 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Peaks sphericity of non-Gaussian random fields

2025年7月22日(火) 10:30 - 12:00

上保 みちる (お茶の水女子大学 理学部 博士課程／日本学術振興会 特別研究員 DC)

We formulate the statistics of peaks of non-Gaussian random fields and implement it to study the sphericity of peaks. For non-Gaussianity of the local type, we present a general formalism valid regardless of how large the deviation from Gaussian statistics is. For general types of non-Gaussianity, we provide a framework that applies to any system with a given power spectrum and the corresponding bispectrum in the regime in which contributions from higher-order correlators can be neglected. We present an explicit expression for the most probable values of the sphericity parameters, including the effect of non-Gaussianity on the profile. We show that the effects of small perturbative non-Gaussianity on the sphericity parameters are negligible, as they are even smaller than the subleading Gaussian corrections. In contrast, we find that large non-Gaussianity can significantly distort the peak configurations, making them much less spherical.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Thermal evolution of accreting neutron stars

2025年7月20日(日) 16:00 - 17:30

Martin Javier Nava-Callejas (Postdoc, Université Libre de Bruxelles, Belgium)

Neutron stars undergoing mass accretion at low-mass X-ray binary systems (LMXBs) represent an outstanding opportunity to test our current models for nuclear matter and its properties, in particular those related to thermonuclear reactions at the surface, as well as the evolution of their ashes via weak reactions. While some aspects are relatively well understood, there are others which call out for further attention or a re-examination of what we so far know. In this talk I will discuss the current state-of-art regarding the modelling of thermal evolution of these objects and will introduce a new method aimed to simplify the calculation of thermal evolution during accreting episodes.

会場: via Zoom

イベント公式言語: 英語