Seminar
710 events
-
SeminarHow to define a Majorana fermion?
February 20 (Thu) at 13:00 - 14:30, 2025
Kazuo Fujikawa (Professor Emeritus, The University of Tokyo)
It is fundamental in particle physics if the neutrino is a Dirac fermion or a Majorana fermion, and the seesaw model gives naturally a Majorana neutrino in an extension of the Standard Model. However, the commonly used chirality changing \(pseudo-C symmetry \) \(\nu^{\tilde C}_L=C\overline{\nu_L}^T\) of a chiral fermion is not defined in Lagrangian field theory. Precisely speaking, the neutrinoless double beta decay is not described by the pseudo-C symmetry. The Majorana neutrino obtained after a Bogoliubov-type canonical transformation, which is the one originally defined by Majorana using a Dirac-type fermion, describes consistently all the properties expected for the Majorana neutrino. Physical implication of this fact is briefly discussed.
Venue: #359, 3F, Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
-
Seminar
Investigating the Crust Urca Process in Accretion Neutron Stars: Implications for Superburst Ignition and Hot Cooling Curve of MAXI J0556-332
February 7 (Fri) at 16:00 - 17:15, 2025
Hao Huang (Ph.D. Student, Institute of Modern Physics, China)
This seminar investigates the Urca cooling strength of the 63Fe-63Mn pair, which varies due to uncertainties in the spin-parity of 63Fe, relevant to the Island of Inversion at N = 40. We present simulations that analyze the impact of this cooling mechanism on the thermal evolution of neutron star crusts, focusing on superburst ignition and anomalous hot quiescent phase cooling of MAXI J0556-332. Additionally, we explore the potential crust Urca process through the anomalous cooling curve of MAXI J0556-332, fitting observational data to determine neutron star mass and radius preferences. Preliminary results suggest that neutron stars with a crust Urca process tend to have smaller masses and larger radii, highlighting the need for precise β-decay measurements to further understand these phenomena.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English
-
Seminar
Fireworks in the cosmos: The Hidden Power of Nuclear Reactions
February 7 (Fri) at 14:00 - 15:15, 2025
Irin Sultana (Ph.D. Student, Department of Physics, Central Michigan University, USA)
Neutron stars in low-mass X-ray binaries, accreting hydrogen- or helium-rich material from a companion star, frequently exhibit thermonuclear runaways on their surfaces known as Type-I X-ray bursts (XRBs). These bursts are powered by nuclear processes, such as the triple-$\alpha$ process, the $\alpha p$ process, and the rapid proton capture process, which play a critical role in model-observation comparisons. In this study, we investigate the impact of nuclear reaction uncertainties on XRBs using the ONEZONE model (Cyburt et al., 2016), considering different accreted compositions and accretion rates for the binary systems that are within the range of observed burst sources. The study is carried out in two stages. First, we determine the burst ignition conditions by simulating the settling of the accreted material with a full reaction network and a semi-analytical model. Second, we perform a sensitivity analysis by varying proton- and alpha-induced reaction rates in JINA REACLIBV2.2 within their estimated uncertainties. We explore the influence of these reactions on the XRBs light curve and the final abundances. The findings highlight key nuclear reactions that significantly affect XRB observables and the final abundances produced, offering guidance for future experimental efforts to improve our understanding of the uncertainties in the reaction rates involved in XRBs.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
-
Seminar
A coarse-grained model of disordered RNA for simulations of biomolecular condensates
February 6 (Thu) at 16:00 - 17:00, 2025
Ikki Yasuda (Ph.D. Student, Graduate School of Science and Technology, Keio University)
Protein-RNA condensates are involved in a range of cellular activities. Coarse-grained molecular models of intrinsically disordered proteins have been developed to shed light on and predict single-chain properties and phase separation. An RNA model compatible with such models for disordered proteins would enable the study of complex biomolecular mixtures involving RNA. Here, we present a sequence-independent coarse-grained, two-bead-per-nucleotide model of disordered, flexible RNA based on a hydropathy scale. We parameterize the model, which we term CALVADOS-RNA, using a combination of bottom-up and top-down approaches to reproduce local RNA geometry and intramolecular interactions based on atomistic simulations and in vitro experiments. The model semi-quantitatively captures several aspects of RNA-RNA and RNA-protein interactions. We examined RNA-RNA interactions by comparing calculated and experimental virial coefficients, and non-specific RNA-protein interaction by studying reentrant phase behavior of protein-RNA mixtures. We demonstrate the utility of the model by simulating the formation of mixed condensates consisting of the disordered region of MED1 and RNA chains, and the selective partitioning of disordered regions from transcription factors into these, and compare the results to experiments. Despite the simplicity of our model we show that it captures several key aspects of protein-RNA interactions and may therefore be used as a baseline model to study several aspects of the biophysics and biology of protein-RNA condensates.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
-
Seminar
Master equations for general non-Markovian processes: the Hawkes process and beyond
February 5 (Wed) at 16:30 - 18:00, 2025
Kiyoshi Kanazawa (Associate Professor, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)
The Markovian process is one of the most important classes of stochastic processes. The Markovian process is defined as a stochastic process whose time evolution is independent of the system's entire history and has been extensively studied using the master equation and Fokker-Planck equation approaches. In contrast, non-Markovian processes -- where time evolution depends on the full history of the system -- have not been systematically explored, except for a few special cases, such as semi-Markovian processes. In this talk, we present a recent master-equation approach to general non-Markovian jump processes [1-4]. Beginning with a general non-Markovian jump process, we derive the corresponding master equation through a Markovian-embedding approach. The Markovian embedding is a scheme to add a sufficient number of auxiliary variables to convert a non-Markovian model to a high-dimensional Markovian model. For the case of our model, the one-dimensional non-Markovian model is shown to be equivalent to a Markovian stochastic field theory, and we derive the field master equation correspondingly [4]. As an application, we examine the nonlinear Hawkes process, a history-dependent and self-exciting model frequently used in studying complex systems [1-3]. Additionally, we explore the stochastic thermodynamic framework for general jump processes [5] as another example.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
-
Seminar
Introduction to the stochastic process and its application in physics
February 4 (Tue) - 5 (Wed), 2025
Kiyoshi Kanazawa (Associate Professor, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)
The stochastic process is a popular tool for broad disciplines, such as physics, biophysics, chemistry, neuroscience, economics, and finance. In this lecture course, I will provide an elementary introduction to stochastic processes in physics without assuming rigorous background knowledge of probability theories. Most of the basic topics in stochastic processes will be covered in this lecture course, such as (1) the one-to-one correspondence between stochastic differential equations and master equations, (2) their standard forms, (3) Ito's lemma, and (4) the perturbation theories (the system-size expansion). I will also present its application to statistical physics, such as (5) kinetic theory and (6) a microscopic derivation of the Langevin equation from hard-sphere Hamiltonian dynamics in the dilute gas limit. My goal is to help the audience calculate most of the main calculations by their own hands by providing detailed explanations without abbreviations. This lecture is based on my Japanese notebook, available on my webpage (see the link below). Schedule: (Tue., Feb. 4) 13:00-14:30, 14:45-16:15, 16:30-18:00 (Wed., Feb. 5) 10:30-12:00, 13:00-14:30, 14:45-16:15
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
-
Seminar
D-modules and the Riemann-Hilbert correspondence as a foundation for mixed Hodge modules
January 31 (Fri) at 14:00 - 16:00, 2025
Takahiro Saito (Assistant Professor, Faculty of Science and Engineering, Chuo University)
Algebraic analysis is a field which began with the study of differential equations in an algebraic framework, known as D-modules. The Riemann-Hilbert correspondence lies at the heart of this field, which bridges the worlds of analysis and geometry. Thanks to this, some geometric problems can be studied by using D-module theory, and vice versa. Based on D-module theory, Morihiko Saito introduced the concept of mixed Hodge modules, realizing Hodge theory on constructible sheaves, which brings us a functorial treatment of Hodge theory and various applications. In this talk, we will begin with the linear differential equations on the complex plane and introduce monodromy, regularity and Deligne's Riemann-Hilbert correspondence. Then, as a generalization of it, I will explain the basics of the theory of D-modules and the Riemann-Hilbert correspondence. Finally, I will describe the role they play in the theory of Hodge modules and recent progress in this area. For the audience's background knowledge, I will assume basic complex function theory. I will start with a simple example, so people outside the field are welcome.
Venue: #359 3F, Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
-
SeminarQuantum Error Mitigation
January 28 (Tue) - 29 (Wed), 2025
Suguru Endo (Ph.D. Researcher, Research Center for Theoretical Quantum Information, NTT Computer and Data Science Laboratories)
Note for registration [2024-12:24]: We are sorry that the number of registration has reached the capacity of the lecture room. Thank you for your understanding. Note for participants [2024-12:18]: For participants, please register from the above form. We may limit the number of participants due to the capacity of the lecture room. For participants in RIKEN who have already answered a questionnaire on this lecture, you do not have to register. Program: Day 1 (Jan. 28th) 10:30-12:00 Lecture 1 12:00-13:30 Lunch time 13:30-15:00 Lecture 2 15:00-15:30 Coffee break 15:30-17:00 Lecture 3 Day 2 (Jan. 29th) 10:30-12:00 Lecture 4 12:00-13:30 Lunch time 13:30-15:00 Lecture 5 15:00-15:30 Coffee break 15:30-17:00 Lecture 6 Abstract: Quantum Error Mitigation (QEM) offers a practical approach to reducing errors in noisy intermediate-scale quantum (NISQ) devices without requiring the encoding of qubits. In this seminar, I will begin by discussing the fundamentals of noise modeling in quantum systems, followed by an overview of QEM techniques, including extrapolation, probabilistic error cancellation (PEC), virtual distillation, quantum subspace expansion, and Clifford data regression. Next, I will present advanced QEM methods, such as the stochastic PEC approach, which mitigates the effects of Lindblad terms in Lindblad master equations and the generalized quantum subspace expansion, which is a unified framework of QEM. I will also explore recent research on the information-theoretic analysis of QEM, shedding light on its fundamental limits and connections to non-Markovian dynamics. Furthermore, I will discuss studies combining QEM with quantum error correction to enhance the reliability of computations in the early fault-tolerant quantum computing era. Lastly, I will highlight the relevance of hybrid tensor networks, particularly their connections to quantum subspace expansion techniques.
Venue: #435-437, 4F, Main Research Building
Event Official Language: English
-
Seminar Tomorrow
Architectures and algorithms for early FTQC
January 27 (Mon) at 16:00 - 17:15, 2025
Andreas Thomasen (R&D Engineer, QunaSys Inc.)
The NISQ era of quantum computing is characterized by quantum devices that have low error rates, but no error correction and typically on the order of 100 qubits, whereas the era of FTQC requires devices with full error correction facilitated by hundreds of thousands to millions of qubits for every logical qubit. Due to the distinct requirements and operating characteristics of these devices, algorithms and applications supported by NISQ and FTQC respectively are highly distinct as well. However, this leaves a large gap, both in terms of devices, algorithms and applications which exist in the intermediate regime where partial error correction is possible and the devices support on the order of tens of thousands of qubits. In this seminar we will give a brief introduction to quantum computing for a non-specialist audience. We will then describe device architectures and algorithms that are specifically designed to fill this gap during the so-called early FTQC era. We will present the space-time efficient analogue rotation (STAR) architecture together with some algorithms that are well supported by it, namely quantum selected configuration interaction (QSCI) and statistical phase estimation (SPE). This seminar serves as theoretical background for our QURI SDK hands-on session at a later date. The algorithms introduced are directly available as OSS as described in the link below.
Venue: #359, 3F, Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
-
Seminar
Seminar Series for Junior and Senior High School Girls: 'What Should Students Prepare for Their Future in the Age of AI?'
January 25 (Sat) at 14:00 - 18:30, 2025
The RIKEN Center for Advanced Intelligence Project (AIP) and the Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) have jointly planned an event for junior and senior high school students interested in AI, mathematics, and information science. This event introduces the exciting research conducted by scientists in these fields. Join us to explore “The Future Built with AI” and discover what steps students can take now to prepare for the future. We look forward to your participation! For more details, please refer to the related links.
Venue: Nihonbashi AIP Center Open Space & Zoom (Hybrid Format)
Event Official Language: Japanese
-
Seminar
Quantitative Characterization of the Cellular Physical Properties to Understand the Organ Regeneration and Cancer Progression
January 23 (Thu) at 16:00 - 17:00, 2025
Takahisa Matsuzaki (Assistant Professor, Department of Applied Physics, Graduate School of Engineering, Osaka University / TechnoArena Associate Professor, Center for Future Innovation, Graduate School of Engineering, Osaka University)
Since the discovery of regulating the differentiation of "single" stem cells by extracellular mechanics, researchers have focused on the mechanobiology of single cells. Our collaborative studies provided the first breakthrough to identify optimal mechanics for multi-cellular, liver organogenesis (Takebe, .., Matsuzaki,.., Yoshikawa et al., Cell Stem Cell 2015, Stem Cell Reports 2018). My motivation is to be a pioneer internationally in understanding the role of heterogenic physical properties in multi-cellular related life-phenomena such as cancer cell adhesion (Matsuzaki et al., Phys Chem Chem Phys 2018, Bioconjugate Chem 2023, PNAS 2024, Osaka University Award 2024.), regeneration of colon/muscle (iScience 2022, Taniguchi,.., Matsuzaki et al., Mucosal Immunology 2023, J. Phys Chem Letter 2014, 2022, 2024.), and bone (Mizuno, .., Matsuzaki et al., Stem Cell Res. Ther. 2022, iScience 2024). In my presentation, I will overview the recent progress in developing fluorescence/interference microscopy combining atomic force microscopy (AFM), and its application to organ regeneration and cancer progression.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
-
Seminar
Probabilistic approach to discrete integrable systems
January 17 (Fri) at 15:30 - 17:30, 2025
Makiko Sasada (Professor, Graduate School of Mathematical Sciences, The University of Tokyo)
The KdV equation and the Toda lattice are two central and widely studied examples of classical integrable systems, and many of their variations have been introduced to the present. In particular, the box-ball system (BBS) is a basic example of a discrete integrable system, which has been revealed to be an ultra-discrete version of the KdV equation and the Toda lattice. The BBS has been studied from various viewpoints such as tropical geometry, combinatorics, and cellular-automaton. As a new perspective, research on probabilistic approaches to this system has been rapidly expanding in recent years, including the application of the Pitman transform, analysis of invariant measures and its generalized hydrodynamics. More recently, we find that the application of the Pitman transform and the study of invariant measures of i.i.d.-type also work in the same manner for the discrete KdV equation and the discrete Toda lattice. Further research has begun on the relationship between the Yang-baxter maps and the existence of i.i.d.-type invariant measures for the discrete integrable systems. In this talk, I will introduce these new research topics that have been spreading over the past several years from the basics. This talk is based on several joint works with David Croydon, Tsuyoshi Kato, Satoshi Tsujimoto, Ryosuke Uozumi, Matteo Mucciconi, Tomohiro Sasamoto, Hayate Suda and Stefano Olla.
Venue: Seminar Room #359
Event Official Language: English
-
Seminar
Principles of the evolution of human social structures: kinship and gift-giving
January 16 (Thu) at 16:00 - 17:15, 2025
Kenji Itao (Special Postdoctoral Researcher, Computational Group Dynamics Collaboration Unit, RIKEN Center for Brain Science (CBS))
Anthropologists have long noted structural similarities among geographically distant societies. To investigate the origins of these patterns, I develop simple models of human interactions based on field observations, simulating the emergence of social structures. This talk focuses on two key topics. The first examines the evolution of kinship structures in clan societies [1, 2, 3]. By modeling kin and in-law cooperation alongside mating competition, I show how cultural groups with specific marriage rules spontaneously emerge. The second explores the transition of social organizations through competitive gift-giving [4, 5]. By modeling how gifts deliver material goods to recipients and confer social reputation upon donors, I demonstrate transitions across four phases—band, tribe, chiefdom, and kingdom—each characterized by distinct social networks and distributions of wealth and reputation. In both cases, I highlight the alignment between theoretical predictions and empirical observations, offering quantitative criteria and empirically measurable explanatory parameters for classifying social structures.
Venue: via Zoom / Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English
-
Seminar
Search for BSM particles from high energy supernova neutrinos
January 10 (Fri) at 14:00 - 15:15, 2025
Kensuke Akita (JSPS Research Fellow, Graduate School of Science, The University of Tokyo)
Light hypothetical particles with masses up to O(100) MeV can be produced in the core of supernovae. Their subsequent decays to neutrinos can produce a flux component with higher energies than the standard flux. We study the impact of heavy neutral leptons, Z′ bosons, in particular U(1)Lμ−Lτ and U(1)B−L gauge bosons, and majorons coupled to neutrinos flavor-dependently. We obtain new strong limits on these particles from no events of high-energy SN 1987A neutrinos and their future sensitivities from observations of galactic supernova neutrinos.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
-
Seminar
Krylov subspace method for quantum dynamics
December 23 (Mon) at 14:00 - 15:00, 2024
Kazutaka Takahashi (Postdoctoral Researcher, Department of Physics and Materials Science, University of Luxembourg, Luxembourg)
For a given system, the structure of the minimal subspace where the state unfolds determines the static and dynamical properties of the state. The Krylov subspace method is a mathematical framework for constructing the space systematically and has been applied to a wide variety of problems. The method was applicable only for systems with time-indepedent generators. As applications to quantum dynamics with time-dependent Hamiltonians, we discuss the constrution of the adiabatic gauge potential and the generalization of the Krylov algorithm to time-dependent generators.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
-
Seminar
EOS Dependence on Cooling of Isolated Neutron Stars
December 20 (Fri) at 14:00 - 15:15, 2024
Stavros Fakiolas (Ph.D. Student, University of Oxford, UK)
Neutron stars - the densest stars in the Universe - cool down mainly by loss of neutrinos, emitted from the stars' interior due to particle reactions. By comparing cooling models with observed surface temperature or luminosity, one can probe the properties of high-density matter, such as what kind of particles and states exist inside neutron stars. In this presentation, I will first review cooling theory, focusing on the neutrino cooling processes. In particular, we focus on the equation of state (EOS) uncertainties, which significantly affect cooling curves. We discuss aspects such as the effect of including hyperons in our EOS. Using the updated cooling code, C-HERES, we calculate cooling curves with different EOS. Finally, we present the future prospects for this study.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
-
Seminar
Applied plant genomics for evolutionary history, agriculture, and conservation
December 19 (Thu) at 16:00 - 17:00, 2024
Antonio Hernández-López (Professor, National Autonomous University of Mexico, Mexico)
I will explore the transformative role of genomic tools in understanding biological diversity across a range of organisms. By delving into the genetic blueprints of various species, we can unravel evolutionary histories, identify key traits for conservation, and develop strategies to preserve endangered ecosystems. Additionally, I will discuss practical applications of genomic data, such as enhancing agricultural biodiversity, improve traditional uses, and fostering sustainable development. Through case studies and recent advancements, this presentation highlights the critical intersection of genomics, biodiversity preservation, and its multifaceted uses in addressing global challenges.
Venue: via Zoom
Event Official Language: English
-
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 state-of-the-art problems. A promising approach to overcoming these scaling limitations involves combining NFs with non-equilibrium 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 non-equilibrium 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
Dark Matter and Neutron Stars: A Gravitational Laboratory for the Unknown
December 18 (Wed) at 10:00 - 11:30, 2024
Ankit Kumar (Postdoctoral Fellow, Faculty of Science and Technology, Kochi University)
Dark matter (DM), a mysterious non-luminous component of the universe, dominates the mass distribution in galaxies and clusters yet remains elusive in its interactions beyond gravity. Neutron stars (NSs), among the most compact objects in the universe, provide unique astrophysical laboratories to investigate the interplay between DM and extreme matter due to their immense densities and gravitational fields. In this talk, I will briefly outline the mechanisms through which DM could be gravitationally captured by NSs, including during their formation and evolution. The primary focus will then shift to the structural and observable implications of DM admixed NSs. I will discuss the theoretical frameworks used to model DM admixed NSs and how DM parameters, such as particle mass and density profiles, modify the equation of state and structural stability of these stars. Observational constraints from pulsars like PSR J0740+6620 and gravitational wave events such as GW170817 will be highlighted as critical tools for deducing DM characteristics and testing theoretical model predictions. By presenting insights from recent studies, including our own work, this talk aims to demonstrate how astrophysical observations can constrain DM parameters and provide a deeper understanding of DM’s role in dense astrophysical environments. I will conclude with a discussion of future prospects for advancing both theoretical models and observational strategies in this interdisciplinary field.
Venue: via Zoom
Event Official Language: English
-
Seminar
7th QGG Intensive Lectures: Emergence of space-time in matrix models
December 17 (Tue) - 19 (Thu), 2024
Asato Tsuchiya (Professor, Shizuoka University)
Emergence of space-time 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 space-time in matrix models. The topics I discuss include dynamical triangulation, double scaling limit, eigenvalue instanton, large-N reduction, T-duality for D-brane 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: #435-437, 4F, Main Research Building
Event Official Language: English
710 events