Dynamics of Phase Transitions: Between First and Second Order

October 8 (Tue) at 16:00 - 17:30, 2024

Fumika Suzuki (CNLS Postdoctoral Research Associate, T4 / Center for Nonlinear Studies, Los Alamos National Laboratory, USA)

Phase transitions are typically classified as either first-order or second-order. The formation of topological defects in second-order phase transitions is well described by the Kibble-Zurek mechanism, while nucleation theory addresses first-order phase transitions. However, certain systems, such as superconductors and liquid crystals, can exhibit “weakly first-order” phase transitions that do not fit into these established frameworks. In this presentation, I introduce a new theoretical approach that combines the Kibble-Zurek mechanism with nucleation theory to explain topological defect formation in weakly first-order phase transitions. Additionally, I will discuss nonlinear quantum phase transitions that exhibit behaviors similar to weakly first-order transitions, which can be related to experiments with ultra-cold Rydberg atoms.

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

Event Official Language: English

Understanding Diffusion Models by Feynman's Path Integral

October 9 (Wed) at 15:00 - 16:30, 2024

Yuji Hirono (Assistant Professor, Department of Physics, Graduate School of Science, Osaka University)

Diffusion models have emerged as powerful tools in generative modeling, especially in image generation tasks. In this talk, we introduce a novel perspective by formulating diffusion models using the path integral method introduced by Feynman for describing quantum mechanics. We find this formulation providing comprehensive descriptions of score-based diffusion generative models, such as the derivation of backward stochastic differential equations and loss functions for optimization. The formulation accommodates an interpolating parameter connecting stochastic and deterministic sampling schemes, and this parameter can be identified as a counterpart of Planck's constant in quantum physics. This analogy enables us to apply the Wentzel-Kramers-Brillouin (WKB) expansion, a well-established technique in quantum physics, for evaluating the negative log-likelihood to assess the performance disparity between stochastic and deterministic sampling schemes.

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

Event Official Language: English

Joint Seminar on cosmology and related topics

October 10 (Thu) at 14:00 - 18:00, 2024

Koki Tokeshi (Postdoctoral Researcher, Institute for Cosmic Ray Research (ICRR), The University of Tokyo)
Misako Tatsuuma (Research Scientist, iTHEMS)
Puttarak Jai-akson (Postdoctoral Researcher, iTHEMS)

Joint Seminar is a seminar series that is held regularly in Tokyo and its vicinity. The topics are on cosmology and related areas. The seminar venue alternates among the universities and research institutes in the Kanto area, and this time it is held at RIKEN. Among the 3 speakers in the event, Dr. Misako Tatsuuma and Dr. Puttarak Jai-akson from iTHEMS will give talks, together with an external speaker Dr. Koki Tokeshi (ICRR, U. Tokyo). The time table of the event is as follows: Date: October 10th (Thu), 14:30. (room will open at 14:00) Place: RIKEN iTHEMS Wako Campus, Okochi Hall Program: 14:00 Room open 14:30 Koki Tokeshi’s talk（ICRR, 45 min） 15:15 Break & free discussion（15 min） 15:30 Misako Tatsuuma’s talk（RIKEN iTHEMS, 45 min） 16:15 Break & free discussion（15 min） 16:30 Puttarak Jai-akson’s talk（RIKEN iTHEMS, 45 min） 17:15 Free Discussion（15 min） 17:30 Close (go to dinner) Titles and abstracts: 1st Speaker: Koki Tokeshi (ICRR) Title: Exact solutions in stochastic inflation Abstract: The stochastic formalism of inflation, or stochastic inflation for short, enables us to study the dynamics of large-scale primordial fluctuations in a non-perturbative way. I will present a class of all the possible exact expressions for statistical quantities such as distribution and correlation functions of a test field in the expanding universe, given that the significance of exact solutions in cosmology cannot be overemphasised. To this aim, a sequence of isospectral Hamiltonians and an underlying symmetry called shape invariance are exploited. 2nd Speaker: Misako Tatsuuma (RIKEN iTHEMS) Title: Numerical Simulations of the Strengths of Dust Aggregates in Planet Formation Abstract: Planet formation is the growth process from sub-micrometer-sized dust grains to planets larger than 10,000 km. This growth process can be broadly divided into two phases: the initial growth to kilometer-sized planetesimals, which involves the adhesion of dust grains through intermolecular forces such as van der Waals forces and hydrogen bonds, and the subsequent growth to planets, driven by gravitational forces. Currently, no unified planetesimal formation theory can fully explain both observations of protoplanetary disks, where planet formation takes place, and the exploration results of small bodies in the solar system, such as asteroids and comets, which are considered remnants of planetesimals. Constructing such a theory is the ultimate goal of planet formation studies. To investigate planetesimal formation based on the exploration results of small solar system bodies, we have used the discrete element method (DEM) to calculate the tensile and compressive strengths of dust aggregates, constructing their physically-based models that we have compared to the properties of small solar system bodies. This talk will focus on the methodologies used in these studies. 3rd Speaker: Puttarak Jai-akson (RIKEN iTHEMS) Title: Null Surfaces Through The Looking-Glass Abstract: Carrollian physics has recently become a prominent topic in theoretical physics, especially in gravitational studies and flat-space holography. Understanding Carrollian geometries and symmetries is essential to the modern interpretation of null surfaces, whether at finite distances or asymptotic infinities. In this talk, I will introduce Carrollian geometries as intrinsic to any generic null surface, and highlight the profound analogy between gravitational dynamics on null surfaces and Carrollian hydrodynamics. Additionally, I will discuss the phase space structure and symmetries associated with these geometries, shedding light on their implications for gravitational theories and potentially for holographic dualities.

Venue: Okochi Hall

Event Official Language: English

The laser light shed on Darwin’s ‘Abominable mystery’

October 10 (Thu) at 16:00 - 17:00, 2024

Chiharu Kato (Ph.D. Student, Department of Biological Sciences, Graduate School of Science, The University of Tokyo)

Reproductive isolation is the inability of a species to breed with related species and thus is a key to evolution of new species in flowering plants. In interspecific crosses between closely related species, a stage of pollen tube reception by female tissues of the pistil act as a pivotal hybridization barrier. Within the genus Arabidopsis, pistils of Arabidopsis thaliana can be fertilized by pollen from its relative species, but about half of the ovules reject the release of sperm from heterospecific pollen tubes and these rejected pollen tubes continue growing inside the embryo sacs (referred to as pollen tube overgrowth). A loss-of function mutant line of ARTUMES gene, encoding a subunit of the oligosaccharyltransferase complex, pollinated with heterospecific pollen shows a higher overgrowth rate than the wild type, suggesting that ARTUMES is involved in interspecific pollen tube reception. However, its molecular mechanism is largely unknown. Here, we report that some knockout lines of receptor kinases show ARTUMES mutant-like impairment in interspecific pollen tube reception, indicating that these receptor kinases might be potentially the target proteins of ARTUMES. We anticipate these receptors recognize the ligands from conspecific (self) pollen and heterospecific pollen either in the presence of ARTUMES, thus they can lead successful interspecific fertilization. We also identified ARTUMES mutant shows abnormal calcium dynamics in their female tissue during pollen tube reception. In this talk, I would like to briefly mention about how mathematical modeling can be promoting to pursue the questions regarding calcium dynamics reflecting male-female communication during fertilization. We anticipate these mechanisms that enable interspecific fertilization contribute to rapid development and diversification of flowering plants in recent geological time.

Venue: via Zoom

Event Official Language: English

RIKEN Quantum Workshop on “Quantum-Like Modeling” in Cognitive & Social Sciences

October 11 (Fri) at 14:00 - 19:00, 2024

Recently, there has been a growing trend to consider cognitive, and social phenomena as Open Quantum Systems, and to mathematically define the fundamental principles behind them through so-called “Quantum-Like Modeling”. It has been extremely difficult to systematically explain complexities of such phenomena within humans’ cognitive traits based on classical “rational” reasoning. Quantum-Like Modeling suggests that using quantum probability calculus and its applications could be useful to rationalize such phenomena and expand previous understandings, obtained through simple linear algebra, by applying quantum formalizations. Just as physicists explored a new branch of mathematics, the theory of operators in complex Hilbert space, to describe the quantum phenomena in an effective way, considerations here will be built on the methodology and mathematical apparatus of quantum theory and directed to applications outside of physics, namely to, cognition, psychology, decision-making, economics, finances, as well as the social and political sciences. Programme 14:00~14:10 Atsushi Iriki: Introduction. Potential of quantum computing for humanities 14:10~15:10 Andrei Khrennikov: Tutorial. Ubiquitous Quantum: from genetics and biological evolution to cognition, psychology, decision making, and social science 15:10~15:40 Masanao Ozawa: Quantum Instrument -- Measurement to cognition with QC-simulation Break 16:00~16:30 Haruki Emori: Applications of quantum computers to cognitive sciences based on Quantum Instrument 16:30~17:00 Miho Fuyama: Subjective Experiences and Superposition State in Narrative Reading 17:00~17:30 General Discussion 18:00~19:00 Networking Mixer (RIKEN canteen #1) Registration Deadline September 26 (Thur), 2024 (for those attending both the workshop and networking mixer (banquet, free of charge)) October 4 (Fri), 2024 (for those attending only the workshop)

Venue: Seminar Room #359

Event Official Language: English

Foliation Matter Phase and Godbillon-Vey Invariant

October 16 (Wed) at 15:00 - 17:00, 2024

Taiichi Nakanishi (Ph.D. Student, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

It has been a main topic in today's physics to classify matter phases. Especially, topologically ordered phases are attracting much attension from broad perspective. However, most of mathematical structures other than the topology are not investigated yet in physics. In this talk, we present a physical model which is strongly connected to the foliation structure of the space manifold, and its field theoretical description. In such a foliation field theory, we can see the structure is highly connected to the mathematical invariant of foliation structures called Godbillon-Vey invariant. This work would be a fiest step toward shining a light on mathematical structures used in physics. This work is based on arXiv:2408.05048 with Hiromi Ebisu, Masazumi Honda, and Soichiro Shimamori.

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

Event Official Language: English

Digital Twinning of Plant Internal Clocks for Robotics and Virtual Reality Enhancements in Agriculture

October 17 (Thu) at 16:00 - 17:00, 2024

Hirokazu Fukuda (Professor, Graduate School of Engineering, Osaka Metropolitan University)

Digital twinning, widely used in fields like industrial and agricultural engineering, creates digital replicas of physical systems. When applied to plant circadian clocks, these digital twins simulate physiological processes governed by circadian rhythms. This technology aids in predicting and optimizing plant growth and productivity in controlled environments, such as greenhouses and plant factories (vertical farms). By understanding key processes like photosynthesis and nutrient uptake, researchers can more effectively manage environmental factors, boosting crop yields and reducing waste. The integration of robotics and virtual reality further enhances these systems, enabling precise automation and real-time optimization. This presentation will explore these advancements, with a focus on mathematical models for controlling circadian clocks.

Venue: via Zoom

Event Official Language: English

Open Effective Field Theories for primordial cosmology

October 18 (Fri) at 14:00 - 15:30, 2024

Thomas Colas (Postdoc, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK)

Imprints of new physics on observable cosmology may require the modelling of dissipation and noise. In this talk, I will present an open effective field theory for primordial cosmology where the inflaton sector interacts with an unknown environment. The approach recovers the usual effective field theory of inflation in a certain limit and extends it to account for local dissipation and noise. Non-Gaussianities are generated that peak in the equilateral configuration for large dissipation and in the folded configurations for small dissipation. The construction provides an embedding for local dissipative models of inflation and a framework to study dissipative and stochastic effects in cosmology.

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

Event Official Language: English

Young's convolution inequality on locally compact groups

October 18 (Fri) at 15:00 - 17:00, 2024

Takashi Satomi (Special Postdoctoral Researcher, iTHEMS)

Young's convolution inequality is one of the elementary inequalities in functional and harmonic analysis, and this inequality is related to various theories in mathematics, physics, and computer theory. In addition, it is known that Young's inequality can be generalized to any locally compact group. In this talk, we introduce the definition of locally compact groups and the statement of Young's inequality with several examples. Finally, we see the speaker's recent results about refining Young's inequality for several locally compact groups, including the special linear groups.

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

Event Official Language: English

iTHEMS Science Outreach Workshop 2024

November 15 (Fri) - 17 (Sun), 2024

This year's meeting on "Outreach of RIKEN iTHEMS 2024@Sendai&Zoom" will be held from FRI November 15 to SUN November 17, as a face-to-face meeting at TOKYO ELECTRON House of Creativity of Tohoku Forum for Creativity in cooperation with iTHEMS SUURI-COOL (Sendai) using ZOOM for the necessary part as well.

Venue: TOKYO ELECTRON House of Creativity, Katahira Campus, Tohoku University (Main Venue) / via Zoom

Event Official Language: Japanese

Solving inverse problem via latent variable optimization of diffusion models: An application to CT reconstruction

November 25 (Mon) at 14:00 - 15:00, 2024

Sho Ozaki (Assistant Professor, Graduate School of Science and Technology, Hirosaki University)

Inverse problems are widely studied in various scientific fields, including mathematics, physics, and medical imaging (such as CT and MRI reconstructions). In this talk, I will present a novel method for solving inverse problems using the diffusion model, with an application to CT reconstruction. The diffusion model, which is a core component of recent image-generative AI, such as Stable Diffusion and DALL-E3, is capable of producing high-quality images with rich diversity. The imaging process in CT (i.e., CT reconstruction) is mathematically an inverse problem. When the radiation dose is reduced to minimize a patient's exposure, image quality deteriorates due to information loss, making the CT reconstruction problem highly ill-posed. In the proposed method, the diffusion model, trained with a large dataset of high-quality images, serves as a regularization technique to address the ill-posedness. Consequently, the proposed method reconstructs high-quality images from sparse (low-dose) CT data while preserving the patient's anatomical structures. We also compare the performance of the proposed method with those of other existing methods, and find that the proposed method outperforms the existing methods in terms of quantitative indices.

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

Event Official Language: English

The 27th MACS Colloquium

November 25 (Mon) at 14:45 - 18:00, 2024

Ryusuke Hamazaki (RIKEN Hakubi Team Leader, Nonequilibrium Quantum Statistical Mechanics RIKEN Hakubi Research Team, RIKEN Cluster for Pioneering Research (CPR))
Teruaki Enoto (Associate Professor, Department of Physics, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

14:45-15:00 Teatime discussion 15:00-16:00 Talk by Dr. Ryusuke Hamazaki (RIKEN Hakubi Team Leader, Nonequilibrium Quantum Statistical Mechanics RIKEN Hakubi Research Team) 16:15-17:15 Talk by Dr. Teruaki Enoto (Associate Professor, Department of Physics, Division of Physics and Astronomy, Graduate School of Science, Kyoto University) 17:15-18:00 Discussion

Venue: Maskawa Hall, 1F, Maskawa Building for Education and Research

Event Official Language: Japanese

Third Workshop on Density Functional Theory: Fundamentals, Developments, and Applications (DFT2025)

March 25 (Tue) - 27 (Thu), 2025

The density functional theory (DFT) is one of the powerful methods to solve quantum many-body problems, which, in principle, gives the exact energy and density of the ground state. The accuracy of DFT is, in practice, determined by the accuracy of an energy density functional (EDF) since the exact EDF is still unknown. Currently, DFT has been used in many communities, including nuclear physics, quantum chemistry, and condensed matter physics, while the fundamental study of DFT, such as the first principle derivations of an accurate EDF and methods to calculate many observables from obtained densities and excited states. However, there has been little opportunity to have interdisciplinary communication. On December 2022, we had the first workshop on this series (DFT2022) at Yukawa Institute for Theoretical Physics, Kyoto University, and several interdisciplinary discussions and collaborations were started. On February 2024, we had the second workshop on this series (DFT2024) at RIKEN Kobe Campus, and more stimulated discussion occured. To keep and extend collaborations, we organize the third workshop. Since the third workshop, we extend the scope of the workshop to the development and application of DFT as well. In this workshop, the current status and issues of each discipline will be shared towards solving these problems by meeting together among researchers in mathematics, nuclear physics, quantum chemistry, and condensed matter physics. This workshop mainly comprises lectures/seminars on cutting-edge topics and discussion, while sessions composed of contributed talks is also planned.

Venue: 8F, Integrated Innovation Building (IIB)

Event Official Language: English