Seminar
670 events

Seminar
Stochastic Normalizing Flows for Lattice Field Theory
December 18 (Wed) at 15:30  16:30, 2024
Elia Cellini (PhD, Department of Physics, University of Turin, Italy)
Normalizing Flows (NFs) are a class of deep generative models that have recently been proposed as efficient samplers for Lattice Field Theory. Although NFs have demonstrated impressive performance in toy models, their scalability to larger lattice volumes remains a significant challenge, limiting their application to stateoftheart problems. A promising approach to overcoming these scaling limitations involves combining NFs with nonequilibrium Markov Chain Monte Carlo (NEMCMC) algorithms, resulting in Stochastic Normalizing Flows (SNFs). SNFs harness the scalability of MCMC samplers while preserving the expressiveness of NFs. In this seminar, I will introduce the concepts of NEMCMC and NFs, demonstrate their combination into SNFs, and outline their connections with nonequilibrium thermodynamics. I will conclude by discussing key aspects of SNFs through their application to Effective String Theory, SU(3) gauge theory, and conformal field theory.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Seminar
7th QGG Intensive Lectures: Emergence of spacetime in matrix models
December 17 (Tue)  19 (Thu), 2024
Asato Tsuchiya (Professor, Shizuoka University)
Emergence of spacetime is a key concept in matrix models as a nonperturbative formulation of string theory. In this lecture, starting with a brief introduction to nonperturbative effects in string theory, I will review various aspects of emergence of spacetime in matrix models. The topics I discuss include dynamical triangulation, double scaling limit, eigenvalue instanton, largeN reduction, Tduality for Dbrane effective theories (orbifolding), noncommutative geometry and covariant derivative interpretation. Finally, I will introduce the type IIB matrix model. (This is the 7th Intensive Lectures by Quantum Gravity Gatherings in iTHEMS. ) Program December 17 10.15~10.30 Registration and Coffee 10.30~12.00 Lecture 1 12.00~13.30 Lunch 13.30~15.00 Lecture 2 15.00~16.00 Coffee break 16.00~17.00 Lecture 3 17.30~19.30 Banquet December 18 10.15~11.45 Lecture 4 11.45~13.30 Lunch 13.30~15.00 Lecture 5 15.00~16.00 Coffee break 16.00~17.00 Lecture 6 December 19 10.15~11.45 Lecture 7 11.45~13.30 Lunch 13.30~15.00 Lecture 8 15.00~16.00 Coffee break 16.00~17.00 Lecture 9
Venue: #435437, 4F, Main Research Building
Event Official Language: English

Seminar
Detecting single gravitons with quantum sensing
December 16 (Mon) at 14:00  15:30, 2024
Germain Tobar (PhD Fellow, Stockholm University, Norway)
Venue: #359, 3F, Seminar Room #359
Event Official Language: English

Seminar
How Neural Networks reduce the Fermionic Sign Problem and what we can learn from them
December 11 (Wed) at 15:30  16:30, 2024
Johann Ostmeyer (Postdoctoral Fellow, HelmholtzInstitut für Strahlen und Kernphysik, University of Bonn, Germany)
When simulating fermionic quantum systems, nonperturbative Monte Carlo techniques are often the most efficient approach known to date. However, beyond half filling they suffer from the socalled sign problem, i.e. negative "probabilities", so that stochastic sampling becomes infeasible. Recently, considerable progress has been made in alleviating the sign problem by deforming the integration contour of the path integral into the complex plane and applying machine learning to find nearoptimal alternative contours. In this talk, I am going to present a particularly successful architecture, based on complexvalued affine coupling layers. Furthermore, I will demonstrate how insight gained from the trained network can be used for simpler analytic approaches.
Venue: via Zoom / Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Seminar
The Long Road towards Quantum Simulations of the Standard Model
December 6 (Fri) at 11:00  12:00, 2024
Dorota Grabowska (Research Assistant Professor, InQubator for Quantum Simulations (IQuS), University of Washington, USA)
The Standard Model of Particle Physics, encapsulating the vast majority of our understanding of the fundamental nature of our Universe, is at its core a gauge theory. Much of the richness of its phenomenology can be traced back to the complicated interplay of its various gauged interactions. While massive theoretical and algorithmic developments in classical computing have allowed us to probe many of these aspects, there remain a plethora of open questions that do not seem amenable to these methods. With a fundamentally different computational strategy, quantum computers hold the potential to address these open questions. However, a long road lies ahead of us before this potential may be realized. In this talk, I discuss a key step on this journey: constructing lattice gauge Hamiltonians that can be efficiently simulated on digital quantum devices. In particular, I focus on recent work that develops a fully gauge fixed Hamiltonian for SU(2) without fermions. Not only is this formulation wellsuited for "close to continuum" simulations, it is also significantly less nonlocal than might be initially expected.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Seminar
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 imagegenerative AI, such as Stable Diffusion and DALLE3, is capable of producing highquality 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 illposed. In the proposed method, the diffusion model, trained with a large dataset of highquality images, serves as a regularization technique to address the illposedness. Consequently, the proposed method reconstructs highquality images from sparse (lowdose) 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

Seminar
Machine learning applications in neutron star physics
November 19 (Tue) at 15:00  16:30, 2024
Márcio Ferreira (Researcher, Physics Department, University of Coimbra, Portugal)
The equation of state and the internal composition of a neutron star are still unanswered questions in astrophysics. To constrain the different composition scenarios inside neutron stars, we rely on pulsars observations and gravitational waves detections. This seminar shows different applications of supervised/unsupervised machine learning models in neutron stars physics, such as: i) extract the equation of state; ii) infer the proton fraction; iii) detect the possible existence of a second branch in the massradius diagram; and iv) detect the presence of hyperons. Márcio Ferreira is a researcher at the Center for Physics at the University of Coimbra, Portugal, focusing on the application of machine learning to astrophysics and materials science. His work utilizes generative and descriptive models to address key questions in these fields. With a PhD in high energy physics and a Master’s in quantitative methods for finance, Márcio also merges his expertise in physics with an interest in financial market dynamics.
Venue: #359, 3F, Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Heterostyly and the evolution of mating system in plants
October 31 (Thu) at 16:00  17:00, 2024
Jeffrey Fawcett (Senior Research Scientist, iTHEMS)
Many organisms exhibit various strategies to avoid selffertilization and promote outcrossing (mating with different individuals). Such strategies have repeatedly evolved and been disrupted throughout evolution, resulting in a remarkable diversity of mating systems. The most wellknown strategy is sexual dimorphism, in which mating is only successful between opposite sexes (e.g. male and female) which exhibit different morphology (e.g. males and females look different). However, some plants, including buckwheat that I have been studying, have evolved a strategy where all individuals either have flowers with long or short styles (female organ), referred to as heterostyly or distyly, and mating is typically only successful between individuals with longstyled flowers and those with shortstyled flowers, i.e., outcrossing is promoted by floral dimorphism that is not associated with sexes. While how such a system evolves and its genetic basis are still largely unknown, the genomic region responsible for heterostyly has been identified in many different species within the past year or two, revealing some interesting parallels between independently evolved systems. In this seminar, I will introduce these recent findings and discuss how heterostyly may be linked to the diverse mating systems observed in plants. I will also introduce what we have been doing and are planning/hoping to do in buckwheat and its related species.
Venue: via Zoom / Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Seminar
Quantum signature kernels
October 30 (Wed) at 14:00  15:00, 2024
Samuel Crew (Postdoctoral Fellow, Imperial College London, UK)
Arising from rough path theory, the signature transform captures features of timeseries data by constructing a socalled path signature. This feature has proven valuable for various machine learning tasks. However, computing the associated signature kernel classically remains computationally intensive. In this talk, I will present recent developments in generalising the signature kernel to randomised Lie group path developments. I will discuss a quantum approach via matrix models with an associated unitary quantum signature kernel to propose a quantum algorithm for its computation.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Seminar
Holographic Gubser flow
October 29 (Tue) at 13:30  14:30, 2024
Sukrut Mondkar (Postdoctoral Researcher, HarishChandra Research Institute, India)
Gubser flow is an evolution with cylindrical and boost symmetries, which can be best studied by mapping the future wedge of Minkowski space ℝ^{(3,1)} to dS_3 × ℝ in a conformal relativistic theory. Here, we sharpen the analytic results of Banerjee, Mitra, Mukhopadhyay Soloviev, EPJC (2024) and validate them via the first numerical exploration of the Gubser flow in a holographic conformal field theory. Remarkably, the leading generic behavior at large de Sitter time is freestreaming in transverse directions and the subleading behavior is that of a color glass condensate. We also show that Gubser flow can be smoothly glued to the vacuum outside the future Minkowski wedge generically given that the energy density vanishes faster than any power when extrapolated to early proper time or to large distances from the central axis. We find that at intermediate times the ratio of both the transverse and longitudinal pressures to the energy density converge approximately to a fixed point which is hydrodynamic only for large initial energy densities. We argue that our results suggest that the Gubser flow is better applied to collective behavior in jets rather than the full medium in the phenomenology of heavy ion collisions and can reveal new clues to the mechanism of confinement. The talk will be based on Mitra, Mondkar, Mukhopadhyay, Soloviev, arxiv:2408.04001/hepth (accepted for publication in JHEP).
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Asymmetries in Stripped Envelope Supernovae
October 25 (Fri) at 14:00  15:15, 2024
Thomas Maunder (Ph.D. Student, Department of Astronomy, Monash University, Australia)
The explosion mechanism of supernovae is not yet fully understood. In order to better understand the innerworkings of the explosion we need to be able to test our models with observations. Current hydrodynamic simulations of stellar explosions often do not provide photometry or spectroscopy as this requires a treatment of the radiation transport of the ejecta. This project takes hydrodynamic simulations of Type Ib/c (strippedenvelope) supernovae and then performs Monte Carlo Radiative Transport simulations on the ejecta to obtain results we can compare with observations. We choose strippedenvelope supernovae because the lack of Hydrogen shell provides a more direct view into the core and the asymmetries of the explosion mechanism. Through these comparisons between models and observations we can improve our understanding of the explosion mechanism in corecollapse supernovae.
Venue: via Zoom
Event Official Language: English

Seminar
The hidden language of light: Polarization signals in cuttlefish courtship
October 24 (Thu) at 16:00  17:00, 2024
Arata Nakayama (Postdoctoral Fellow, Atmosphere and Ocean Research Institute, The University of Tokyo)
The most conspicuous signals are generally the most attractive; this principle underlies the evolution of sexual signal. While the sexual signal design and its exceptional diversity have primarily explored on the color (wavelength) of light, various animals utilize a different property of light for signaling: polarization. In short, polarization is a third physical property of light, alongside color and intensity, and refers to the orientation of light waves' vibrations. While most vertebrate species, including humans, cannot perceive polarized light, some invertebrate species, such as crustaceans and cephalopods (e.g., octopus, squid, and cuttlefish), can detect the polarization of light and reflect polarized light from their body surfaces, suggesting that the polarization of light might function as a communication signal. In our study, by focusing on the sexually ornamented trait and the courtship behavior of specific cephalopod species, we found an polarization courtship signal, which is extremely conspicuous from the perspective of cephalopod polarization vision. Additionally, we conducted morphological observations and optical analyses of their polarizationreflective body surfaces, uncovering a novel mechanism for generating complex polarization patterns. In this gethering, I will provide a general introduction to the role of polarization as a visual cue and signal, followed by an overview of our study on the unique courtship behavior involving polarization signaling in the cuttlefish Sepia andreana.
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

Seminar
Open Effective Field Theories for primordial cosmology
October 18 (Fri) at 13:30  15:00, 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. NonGaussianities 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

Seminar
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 realtime optimization. This presentation will explore these advancements, with a focus on mathematical models for controlling circadian clocks.
Venue: via Zoom
Event Official Language: English

Seminar
Foliation Matter Phase and GodbillonVey 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 GodbillonVey 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

Seminar
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 lossof 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 mutantlike 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 malefemale 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

Seminar
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 Jaiakson (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 Jaiakson 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 Jaiakson’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 largescale primordial fluctuations in a nonperturbative 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 submicrometersized dust grains to planets larger than 10,000 km. This growth process can be broadly divided into two phases: the initial growth to kilometersized 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 physicallybased 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 Jaiakson (RIKEN iTHEMS) Title: Null Surfaces Through The LookingGlass Abstract: Carrollian physics has recently become a prominent topic in theoretical physics, especially in gravitational studies and flatspace 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

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 scorebased 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 WentzelKramersBrillouin (WKB) expansion, a wellestablished technique in quantum physics, for evaluating the negative loglikelihood to assess the performance disparity between stochastic and deterministic sampling schemes.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
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 firstorder or secondorder. The formation of topological defects in secondorder phase transitions is well described by the KibbleZurek mechanism, while nucleation theory addresses firstorder phase transitions. However, certain systems, such as superconductors and liquid crystals, can exhibit “weakly firstorder” phase transitions that do not fit into these established frameworks. In this presentation, I introduce a new theoretical approach that combines the KibbleZurek mechanism with nucleation theory to explain topological defect formation in weakly firstorder phase transitions. Additionally, I will discuss nonlinear quantum phase transitions that exhibit behaviors similar to weakly firstorder transitions, which can be related to experiments with ultracold Rydberg atoms.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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