セミナー

Ensemble transform Kalman filter (ETKF)

2025年9月3日(水) 13:00 - 14:00

岩中 達郎 (理化学研究所 計算科学研究センター (R-CCS) データ同化研究チーム リサーチアソシエイト)

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

A Fresh Look at Late-Time Hawking Radiation

2025年9月2日(火) 14:00 - 15:30

ウェイシャン・シャオ (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 基礎科学特別研究員)

There is now a common belief that non-perturbative quantum gravity effects are relevant for resolving the black hole information puzzle. But could such effects also largely alter Hawking radiation itself, the main culprit that led to the puzzle in the first place? There are two main lessons that I would like to convey from this presentation: 1. For large black holes formed by dynamical collapse, the usual description of Hawking radiation in the low-energy effective theory breaks down at an early stage, signaling the need for a UV theory to describe the origin of late-time radiation. 2. In UV models of the radiation field that incorporate a form of nonlocality motivated by string theory, Hawking radiation becomes a transient phenomenon that occurs only for a brief period of time. This behavior suggests a major deviation from the conventional picture of black hole evaporation based on local quantum field theory.

会場: via Zoom / 理化学研究所 和光キャンパス 3階 359号室

イベント公式言語: 英語

Dust formation in the universe: reconstructing of theoretical models

2025年8月29日(金) 14:00 - 15:15

田中 今日子 (東京女子大学 現代教養学部 情報数理科学科 特任准教授)

The formation process of cosmic dust is the starting point of solid matter and is important for understanding the evolution of cosmic material and planet formation processes. The nucleation process at the initial stage of the phase transition is a key to how cosmic dust is formed and evolves. Recent studies of the nucleation have shown possibilities that are very different from the theoretical models that have been considered so far. We have investigated the nucleation process using molecular dynamics simulations, which allow us to observe the nucleation process at the molecular level and obtain new information. We also present our attempt to develop and reconstruct a new theoretical model to elucidate a comprehensive picture of cosmic dust formation in collaboration with experiments.

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

Shadow formation in gravitational collapse: redshift and blueshift by spacetime dynamics

2025年8月28日(木) 16:00 - 17:30

古賀 泰敬 (大阪工業大学 情報科学部 情報知能学科 助教)

A black hole illuminated by a background light source is observed as a black hole shadow. For a black hole formed by the gravitational collapse of a transmissive object, redshift of light due to the spacetime dynamics is expected to play a crucial role in the shadow formation. In this talk, we investigate the redshift of light caused by the spacetime dynamics. First, we consider a spherical shell model. We see that the collapse of a shell typically leads to the redshift of light, while blueshift can be also observed in some cases. This result suggests that a shadow image is generally formed in the late stage of the gravitational collapse of a transmissive object. Second, we consider a general, dynamical, spherically symmetric spacetime and propose a new covariant formula for the redshift of light. This formula relates the dynamical redshift to the energy-momentum tensor of the background spacetime and provides its intuitive interpretation with Newtonian analogy.

会場: via Zoom / 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

The link between ecology and evolution in the speciation process

2025年8月28日(木) 13:00 - 14:00

ホセ サイード・グティエレス オルテガ (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)

Both ecological and evolutionary processes shape biodiversity, but these are usually studied separately. Ecologists focus on current dynamics, while evolutionary biologists examine long-term changes. The intersection between the two perspectives lies in understanding speciation: the process of how new species arise. Understanding speciation can clarify how ecological processes build up into the global patterns we see in evolution, and in turn, how evolutionary trends promote ecological processes. Using observational data compiled from macroecological and phylogenetic methods on multiple plant and animal groups, I suggest that the ecological patterns left by the factors promoting speciation in a community correspond to the speciation/extinction dynamics within that community. This ecological-phylogenetic correspondence represents a connection between the ongoing and the long-term dynamics, an idea that may unify the disciplines of ecology and evolution. I expect this talk can promote discussion on the topics of eco-evolutionary dynamics, so that I can get some feedback from you, and that we can create chances for collaboration.

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

磁気回転効果による中性子星の自転と中性子スピンの間の角運動量変換

2025年8月28日(木) 10:00 - 12:00

舟木 博志 (慶応義塾大学 理工学部 特任助教)

[NOTE] 本インフォーマルセミナーは長瀧天体ビッグバン研究室により主に企画されており、日本語で行われます。また、GWX-EOS Working Group および iTHEMS-ABBL Joint Astro Study Groupとのジョイントイベントです。 概要: 本講演では、中性子星のクラストとコアの間で角運動量が交換される新たなメカニズムを、磁気回転効果を介して提案する。拡張された流体力学を用いることで、中性子星の自転に相当するマクロな角運動量と、中性子の軌道およびスピンから生じるミクロな角運動量の相互作用を取り込む。クラストにおけるマクロスケールな回転がコア内のミクロスケール角運動量に影響を与え、中性子スピン偏極を引き起こすことを明らかにし、(反)グリッチの代替シナリオを提案する。本研究は、中性子星物理学でこれまで見逃されていたマルチスケール角運動量相互変換を浮き彫りにし、磁気回転天文学の新たな道が拓かれると期待される。

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: 日本語

Analysis of inflationary models in higher-dimensional uniform inflation

2025年8月27日(水) 16:00 - 18:00

廣瀬 拓哉 (九州産業大学 教育研究施設 基礎教育サポートセンター 特任助教)

In this talk, we consider higher-dimensional uniform inflation, in which the extra dimensions expand at the same rate as three-dimensional non- compact space during inflation. We compute the cosmological perturbation in $D+4$ dimensions and derive the spectral index $n_s$ and the tensor- scalar ratio $r$. We analyze five inflationary models: chaotic inflation, natural inflation, quartic hilltop inflation, inflation with spontaneously broken SUSY, and $R^2$ inflation. By combining the results from these models with the Planck 2018 constraints, we discuss that it is not desirable for the extra-dimensional space to expand at the same rate as the three-dimensional non-compact space, except for the case of one extra dimension. This talk is based on arXiv:2501.13581[hep-ph].

会場: セミナー室 (359号室)

イベント公式言語: 英語

Observational constraint of non-scalar phantom dark energies

2025年8月26日(火) 16:00 - 17:30

Hsu-Wen Chiang (Postdoc, Department of Physics, Southern University of Science and Technology, China)

Recent observation of DESI strongly disfavors cosmological constant. Given the lack of constraint regarding the fundamental field that constitutes a dynamical dark energy, people traditionally resort on a hypothetical scalar field. We instead consider minimally coupled non-spinless field as alternative, specifically the extended Proca-Nuevo theory (spin-1) and 3-form field (spin-3). Both theories at the background level permit pure phantom (w < -1) and phantom crossing (w < -1 to w > -1) scenarios. Furthermore, with reasonable choice of EFT parameters we can decouple the scalar perturbation of the dark energy from the matter sector. However, the Lorentz constraint within the higher-spin field inevitably modifies the response of the scalar potential to the matter perturbation. This leads to an enhancement of the matter power spectrum most obvious in BAO fullshape analysis. We then perform MCMC analysis and show that the Hubble tension is alleviated, and the non-spin-0 models are preferred marginally over a cosmological constant.

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 Discussion on Quantum Machine Learning for Medical Data

2025年8月26日(火) 14:00 - 15:00

杉本 聡 (理化学研究所 数理創造研究センター (iTHEMS) 数理展開部門 医科学データ駆動数理チーム 上級研究員)

Our team is investigating the applicability of machine learning using quantum computers to medical data. In this talk, we will provide a brief overview of supervised machine learning for medical data as a topic for discussion.

会場: via Zoom

イベント公式言語: 英語

Tamely Ramified Geometric Langlands Correspondence

2025年8月22日(金) 15:00 - 19:00

Yuki Matsubara (Ph.D. Student, Centre for Quantum Mathematics, University of Southern Denmark, Denmark)

The geometric Langlands correspondence (GLC) is a geometric analogue of the Langlands conjecture in number theory, relating algebraic geometry, representation theory, and many other areas. Since A. Kapustin and E. Witten pointed out the relation between GLC and mirror symmetry, there have been various studies on GLC from a physics perspective as well as a mathematical perspective. First talk: An introduction to Langlands conjecture for everyone This is an entirely accessible overview of the Langlands conjecture. Starting from famous topics, such as the Pythagorean theorem and Fermat’s Last Theorem, I will introduce the statement and motivations behind the Langlands conjecture. No prior background will be assumed, and technical details will often be sketched rather than fully developed, so that anyone with a general mathematical curiosity can follow along. Second talk: On a certain tamely ramified geometric Langlands correspondence In this talk, I will present my research. Arinkin’s 2001 result established the geometric Langlands correspondence for the case G = SL2 on the complex projective line P1 with four fixed regular singularities. When one attempts to extend this to five or more singularities, it turns out to be more natural to decompose the correspondence into a Radon transform-type correspondence and a “GLC‑like” correspondence. I will report on the calculations of cohomology that support the proof of this GLC‑like correspondence in the P1 with five fixed regular singularities case.

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

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