セミナー
1011 イベント
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セミナー
Relativistic Jet Simulations and Modeling on Horizon Scale
2024年2月8日(木) 13:00 - 14:30
水野 陽介 (T.D. Lee Fellow / Associate Professor, Tsung-Dao Lee Institute, Shanghai Jiao Tong University, China)
Relativistic jets are launched in the vicinity of the central black holes and emit powerful radiation across the electromagnetic spectrum. According to our current understanding, relativistic jets are launched by directly tapping the rotational energy of spinning black holes via the so-called Blandford-Znajek process. In addition to the spin of the black hole, numerical simulations showed the amount of accreted magnetized flux has a major impact on the formation of relativistic jets. We have investigated the radiative signatures of self-consistently launched relativistic jets using 3D general relativistic magneto-hydrodynamical simulations and general relativistic radiative transfer calculations in horizon scale to the connection with large-scale structure. We discuss our findings and comparison with observations.
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
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セミナー
Recent advances in nuclear Density Functional Theory and applications to the nuclear response
2024年2月6日(火) 13:30 - 15:00
ジャンルカ・コロ (Professor, Department of Physics, University of Milan, Italy / Professor, Sezione di Milano, INFN, Italy)
In this contribution, I will give an overall (and, of course, biased) view of the general status of DFT. I will stress that, in contrast to ab initio methods, DFT is the only framework that allows the study of excited states, including those lying at relatively high energy. Accordingly, I will focus on the nuclear response. After a reminder on the nuclear Giant Resonances and the link with the nuclear equation of state, I will discuss the projection methods to restore symmetries in the calculations of deformed systems. While symmetry-restored calculations are nowadays of common use in the study of ground-state properties and low-lying excitations, similar realistic investigations for the nuclear response are essentially missing in the literature. Recently, we have implemented an exact Angular Momentum Projection (AMP) on top of Skyrme-Random Phase Approximation (RPA) calculations in a projection after variation (PAV) scheme, for the first time. The results will be critically analysed in the case of the monopole response, also taking into account the experimental investigations that can be envisioned for well-deformed systems. If time allows, the nuclear response will be also discussed as a way to improve the current density functionals and ground them on ab initio nuclear theory. This seminar is co-hosted by Nuclear Many-body Theory Laboratory and Few-body Systems in Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science.
会場: 理化学研究所 和光キャンパス RIBF棟 2階 大会議室 (メイン会場) / via Zoom
イベント公式言語: 英語
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Nuclear Energy-Density Functional Approach to Bridging Neutron-Rich Nuclei and Neutron Stars
2024年2月5日(月) 13:30 - 15:00
吉田 賢市 (大阪大学 核物理研究センター 准教授)
Understanding the properties of neutron-rich nuclei has been a central subject in low-energy nuclear physics. The great interest lies not only in the pursuit of a variety of structures and the elucidation of the mechanisms of their occurrence but also in obtaining insights into the structure of the inner crust of neutron stars. With advances in neutron-star observation techniques, the structure of neutron stars has been becoming better understood. The data accumulated from these observations unveil properties of neutron-rich matter that are otherwise inaccessible through terrestrial experiments. In this talk, I will introduce an attempt to construct a nuclear energy-density functional (EDF) inspired by the observations and then demonstrate its applicability to nuclear structure problems, including mass and deformation. One intriguing aspect of neutron stars is the emergence of superfluidity, especially the occurrence of spin-triplet pairing. I will discuss the unconventional pairing in nuclei within the nuclear EDF framework and give perspectives on the study of the phase diagram of the superfluidity in neutron stars. This seminar is co-hosted by UKAKUREN.
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
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セミナー
Competition across scales in biology
2024年1月31日(水) 11:00 - 12:00
シダルタ・ゴヤル (Associate Professor, Department of Physics, University of Toronto, Canada)
Many biological phenomena emerge from interaction and competition between its parts. I will share some examples across biological scales where data-driven theory can reveal new rules of biological competition. At the molecular scale competition between mitochondrial genomes within budding yeast depends on genome architecture; dynamics of adaptive immunity in microbes reveal different modalities of competition and coexistence of bacteria and its phages; in mammals cellular reprogramming may be driven by elite clones, and tumor response to drugs is driven by "epigenetic" switching. Going beyond, I will present some ideas on understanding dynamical systems that govern cell fate dynamics and if competition may play a role in it. Short bio: Sidhartha Goyal got his PhD in Physics at Princeton in 2009 and then moved to Kavli Institute for Theoretical Physics, Santa Barbara for a postdoc. He got his first degree in Electrical Engineering from IIT Bombay. He is now an Associate Professor in the Physics Department at University of Toronto interested in collective phenomena in biology across scales.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Quantum Enhancement in Dark Matter Detection with Quantum Computation
2024年1月22日(月) 16:00 - 18:00
Thanaporn Sichanugrist (東京大学 大学院数理科学研究科 博士課程)
陳 詩遠 (東京大学 素粒子物理国際研究センター (ICEPP) 特任助教)Title: Wave-like Dark Matter Search Using Qubits Abstract: The rapid controllability required for quantum computers makes the currently proposed quantum bit modalities also attractive as electromagnetic field sensors. One of the promising applications is wave-like dark matter searches, where the electric field converted from the coherent dark matter excites the qubits, leading to detectable signals [Phys. Rev. Lett. 131, 211001]. The quantum coherence between the qubits can be utilized to enhance the signal rate in a multi-qubit system. By designing an appropriate quantum circuit to entangle the qubits, it was found that the signal rate can scale proportionally to $n_q^2$, with $n_q$ being the number of sensor qubits, rather than linearly with $n_q$ [arXiv: 2311.10413]. In the seminar, we overview the theoretical framework of the search, elaborate on the signal-enhancing mechanism driven by quantum entanglement with specific examples of the quantum circuits, and discuss how the scheme can be implemented in the platform of future fault-tolerant quantum computers. We also provide the introduction of the experimental realization, and report the status of the experimental works carried out in UTokyo/ICEPP.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Knot Theory in Doubly Periodic Tangles and Applications
2024年1月19日(金) 15:00 - 16:30
ソニア・マムーディ (東北大学 材料科学高等研究所 (AIMR) 数学連携グループ 助教)
Doubly periodic entangled structures offer an interesting framework for modeling and investigating diverse materials and physical phenomena, from micro to large scales. Specifically, a doubly periodic tangle (DP tangle) is characterized as an embedding of an infinite number of curves in the thickened plane, derived as the lift of a link in the thickened torus to the universal cover. DP tangles play a crucial role in scientific research, particularly in fields such as materials science, molecular chemistry, and biology. Despite their widespread applications, a universally accepted mathematical description of DP tangles is currently lacking. One of the key challenges arises from the infinite possibilities in choosing a periodic cell (referred to as a motif) for a DP tangle, taking into account various periodic boundary conditions. In this presentation, we conduct a comprehensive examination of the concept of topological equivalence of DP tangles, offering insights into potential classifications and applications in the process.
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Quantum features in cosmological perturbations?
2024年1月18日(木) 14:15 - 15:00
アモリ・ミケリ (理化学研究所 数理創造プログラム (iTHEMS) 特別研究員)
The statistical properties of the CMB anisotropies, reflecting the curvature inhomogeneities in the very early Universe, are very well accounted for by assuming that the inhomogeneities come from amplified vacuum fluctuations. This scenario makes the cosmological perturbations a possible observational window on the interplay between quantum degrees of freedom and gravity. I will review the discussions on the current presence or absence of quantum features in the perturbations, emphasising the quantum information approaches to this question, and comment on the observability of these features.
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Gravitational lensing on superposed curved spacetime
2024年1月18日(木) 13:30 - 14:15
郭 優佳 (名古屋大学 大学院理学研究科 博士課程)
In 2017, Bose et al. proposed a tabletop experiment to observe the gravitational effect induced by a spatially superposed mass source, particularly gravity-induced entanglement. This experiment is expected to be the first step in exploring the quantum nature of gravity. Also, there are ongoing efforts to extend their proposal to the relativistic region to observe the unique quantum nature of gravity. In this talk, I will investigate gravitational lensing in a weak gravitational field induced by a spatially superposed mass source. I will show the Einstein ring image of a quantum scalar field propagated on a superposed curved spacetime and compare it with the image of the semi-classical gravity case. This work is currently in progress and is a collaboration with Yasusada Nambu.
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Bayesian mechanics of classical, neural, and quantum systems
2024年1月17日(水) 16:30 - 17:45
磯村 拓哉 (理化学研究所 脳神経科学研究センター (CBS) 脳型知能理論研究ユニット ユニットリーダー)
(This is a joint seminar with iTHEMS Biology group.) Bayesian mechanics is a framework that addresses dynamical systems that can be conceptualised as Bayesian inference. However, the elucidation of requisite generative models is required for empirical applications to realistic self-organising systems. This talk introduces that the Hamiltonian of generic dynamical systems constitutes a class of generative models, thus rendering their Helmholtz energy naturally equivalent to variational free energy under the identified generative model. The self-organisation that minimises the Helmholtz energy entails matching the system's Hamiltonian with that of the environment, leading to an ensuing emergence of their generalised synchrony. In short, these self-organising systems can be read as performing variational Bayesian inference of the interacting environment. These properties have been demonstrated with coupled oscillators, simulated and living neural networks, and quantum computers. This notion offers foundational characterisations and predictions regarding asymptotic properties of self-organising systems exchanging with the environment, providing insights into potential mechanisms underlying emergence of intelligence.
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
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セミナー
Methods for neural decoding using machine learning, deep learning, and quantum-inspired algorithms
2024年1月17日(水) 15:00 - 16:15
間島 慶 (量子科学技術研究開発機構 (QST) 研究員)
Note: The format of this event has changed from hybrid to Zoom only. However, you will still be able to watch it on the screen in Room #359 of the Main Research Building. (This is a joint seminar with iTHEMS Biology group.) Recent advances in machine learning have enabled the extraction of intrinsic information from neural activities, a field known as neural decoding. In this presentation, I will introduce several machine learning methods recently developed for neural decoding analysis: 1) a method for visualizing subjective images in the human mind based on brain activity [1], 2) a supervised algorithm designed for predicting discrete ordinal variables [2], and 3) a fast classical algorithm algorithm inspired by quantum computation for approximating principal component analysis (PCA) and canonical correlation analysis (CCA), potentially allowing for the analysis of vast-dimensional neural data [3]. Following these presentations, I am eager to engage in discussions with participants at the RIKEN Quantum Seminar regarding potential collaborations.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Dust-driven instabilities in protoplanetary disks: toward understanding formation of planetesimals
2024年1月17日(水) 10:30 - 11:30
冨永 遼佑 (理化学研究所 開拓研究本部 (CPR) 坂井星・惑星形成研究室 基礎科学特別研究員)
Planet formation starts from collisional growth of sub-micron-sized dust grains in a gas disk called a protoplanetary disk. They are expected to grow toward km-sized objects called planetesimals. The resulting planetesimals further coalesce by gravity and form planets. However, there are some barriers preventing planetesimal formation, which includes fast radial drift and collisional fragmentation of dust grains. To circumvent the barriers and to explain planetesimal formation, previous studies have proposed hydrodynamic instabilities of dusty-gas disks. The instabilities can cause dust clumping, and planetesimals form if the resulting clumps collapse self-gravitationally. We have been investigating the linear/nonlinear development of these dust-gas instabilities. We also found a new instability driven by collisional growth of dust, which can bridge a potential gap between the first dust growth and the later planetesimal formation via the previous instabilities. In this talk, I will introduce our work on the dust-driven instabilities and their impact on planetesimal formation.
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Does horizontal gene transfer stabilize cooperation in bacteria?
2024年1月16日(火) 16:00 - 17:00
Anna Dewar (Postdoctoral Researcher, Department of Biology, University of Oxford, UK)
Bacteria are highly social. Much of this sociality occurs through the production of cooperative ‘public goods’. Unlike in animals, bacterial genes are able to transfer horizontally between individuals, in addition to vertically via descendants. This widespread horizontal gene transfer has implications for the concept of relatedness and how cooperation is maintained in bacteria. It has been suggested that horizontal gene transfer, particularly via small segments of DNA called plasmids, could stabilize cooperation in bacteria. Transfer of a cooperative gene could turn non-cooperative ‘cheats’ into cooperators, preventing cheats from invading and destabilizing cooperation. We tested this with a comparative analysis across bacterial species. In contrast to the predictions of the hypothesis, we found that genes for cooperative traits were not more likely to be carried on either: (1) plasmids compared to chromosomes; or (2) plasmids that transfer at higher rates. Our results were supported by theoretical modelling which showed that, while horizontal gene transfer can help cooperative genes initially invade a population, it has less influence on the longer-term maintenance of cooperation.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Probing structure of neutron stars through X-ray bursters
2024年1月12日(金) 14:00 - 15:15
土肥 明 (理化学研究所 開拓研究本部 (CPR) 長瀧天体ビッグバン研究室 基礎科学特別研究員)
Type-I X-ray bursts are rapidly brightening phenomena triggered by the nuclear burning of light elements near the surface of accreting neutron stars. Most of the X-ray bursters show irregular behavior of light curves. However, some X-ray bursters are somehow quite regular, i.e., constant recurrence time and constant shaper of light curves, and are often called Clocked bursters, which are powerful sites to probe uncertainties of many model parameters such as accretion rate, the composition of accreted matter, reaction rates, neutron star structure, and temperature. In this study, we focus on the uncertainties of the equation of states, which determines the latter two properties. Based on our numerical models covering whole areas of neutron stars, we will present their impact on X-ray burst light curves. Furthermore, we will discuss the possibility of constraining the equation of states from Clocked bursters such as GS 1826-24 and 1RXS J180408.9-342058.
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
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セミナー
Symmetry Topological field theory for Subsystem symmetry
2024年1月9日(火) 15:00 - 16:00
Qiang Jia (Research Fellow, School of Physics, Korea Institute for Advanced Study (KIAS), Republic of Korea)
We generalize the idea of symmetry topological field theory (SymTFT) to subsystem symmetry. We propose the 2-foliated BF theory with level N in (3+1)d as subsystem SymTFT for subsystem Z_N symmetry in (2+1)d. Focusing on N=2, we investigate various topological boundaries. The subsystem Kramers-Wannier and Jordan-Wigner dualities can be viewed as boundary transformations of the subsystem SymTFT and are included in a larger duality web from the subsystem SL(2,Z_2) symmetry of the bulk foliated BF theory.
会場: via Zoom / セミナー室 (359号室)
イベント公式言語: 英語
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セミナー
Application of Modular tensor category to Lattice gauge theory
2023年12月29日(金) 10:30 - 16:00
早田 智也 (慶應義塾大学 経済学部 助教)
Inspired by the recent development in quantum computers, much efforts have been devoted to exploring their potential applications in lattice gauge theories. However, in contrast to condensed matter systems, we face many challenges in applications of quantum computations to lattice gauge theories, where one of the major obstructions lies in implementation of gauge symmetries in quantum computations. In this seminar, I talk about a possible solution to the problem based on a unitary modular tensor category, expressing the Hamiltonian of lattice gauge theories in terms of the so called F moves, and implementing the F moves on quantum computers. References: TH, Y. Hidaka, JHEP 09 (2023) 126; JHEP 09 (2023) 123.
会場: セミナー室 (359号室)
イベント公式言語: 英語
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セミナー
Oscillatory data analysis using the extended Hilbert transform method
2023年12月26日(火) 16:00 - 17:00
松木 彩星 (北海道大学 先端生命科学研究院 博士研究員)
Oscillatory phenomena are observed in various biological systems, such as spinal nervous systems and circadian rhythms. These macroscopic oscillatory phenomena appear as a result of synchronization of microscopic oscillators, such as pacemaker cells. The first step in the analysis of synchronization is to reconstruct the "phase" from the observed signal. The Hilbert transform method is one of the popular methods for phase reconstruction, but it is known that it can only accurately reconstruct the phase from a limited class of signals such as narrowband signals. In this study, we show that the Hilbert transform method has a low-pass filter-like effect on the phase modulation and propose an "extended Hilbert transform method" that can be applied to a wider class of signals. In this talk, I will introduce the extended Hilbert transform method, and its application to phase shift detection and coupling network inference.
会場: via Zoom
イベント公式言語: 英語
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A symmetry principle for gauge theories with fractons
2023年12月22日(金) 17:00 - 18:15
広野 雄士 (京都大学 大学院理学研究科 物理学・宇宙物理学専攻 物理学第二教室 特定准教授)
Fractonic phases are emergent quantum phases of matter that host excitations with restricted mobility. Although these phases have been considered to be of “beyond Landau” order, we show that a certain class of gapless fractonic phases are realized as a result of spontaneous breaking of generalized symmetries. The corresponding symmetries are continuous higher-form symmetries whose conserved charges do not commute with spatial translations, and we refer to them as nonuniform higher-form symmetries. For a given set of nonuniform symmetries, the effective theory associated with the spontaneous breaking of them can be constructed. At low energies, the theories reduce to known higher-rank gauge theories such as scalar/vector charge gauge theories, and the gapless excitations in these theories are interpreted as Nambu–Goldstone modes for higher-form symmetries. Due to the nonuniformity of the symmetry, some of the modes acquire a gap, which is the higher-form analogue of the inverse Higgs mechanism of spacetime symmetries. In this formulation, the mobility restrictions are fully determined by the choice of the commutation relations of charges with translations. This approach allows us to view existing (gapless) fracton models such as the scalar/vector charge gauge theories and their variants from a unified perspective and enables us to engineer theories with desired mobility restrictions. Field: condensed matter physics Keywords: fractonic phases, higher-form symmetries, Nambu-Goldstone modes, Higgs mechanism, gauge theories
会場: via Zoom
イベント公式言語: 英語
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セミナー
Inflationary Cosmology with a scalar-curvature mixing term $\frac{1}{2} \xi R \phi^2$
2023年12月20日(水) 16:00 - 17:30
Payel Sarkar (京都大学 客員研究員)
We use the PLANCK 2018 and the WMAP data to constraint inflation models driven by a scalar field $\phi$ in the presence of the non-minimal scalar-curvature mixing term $\frac{1}{2}\xi R \phi^2$. We consider four distinct scalar field potentials $\phi^p e^{-\lambda\phi},~(1 - \phi^{p})e^{-\lambda\phi},~(1-\lambda\phi)^p$ and $\frac{\alpha\phi^2}{1+\alpha\phi^2}$ to study inflation in the non-minimal gravity theory. We calculate the potential slow-roll parameters, predict the scalar spectral index $n_s$, tensor-to-scalar ratio $r$, leading and higher order non-Gaussianity parameters ($f_{NL},~\tau_{NL}$ and $g_{NL}$) and the amplitude of the scalar spectrum $A_s$ in the parameter ($\lambda, p, \alpha$) space of the potentials corresponding to different values of the non-minimal coupling parameter $\xi$. We have compared our results with the ones existing in the literature, and this indicates the present status of non-minimal inflation after the release of the PLANCK 2018 data.
会場: 研究本館 3階 359号室とZoomのハイブリッド開催 (メイン会場) / via Zoom
イベント公式言語: 英語
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セミナー
Application of mathematical models to the COVID-19 cohort study
2023年12月19日(火) 16:00 - 17:00
西山 尚来 (名古屋大学 大学院理学研究科 博士課程)
The COVID-19 pandemic, which began in 2019, has caused widespread morbidity and mortality across the globe. In response, a multitude of studies focusing on SARS-CoV-2 have been undertaken. Among these, cohort studies have been particularly significant. These studies, as a key observational research method, play a crucial role in exploring the links between various factors and the onset of diseases, offering valuable insights for disease control. Mathematical model, applied within these studies, provide essential quantitative data. In my talk, I will introduce how mathematical models are instrumental in cohort studies, drawing on two of my own COVID-19 cohort studies as examples.
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Energy spectrum and time evolution of a SU(2) pure gauge lattice theory on a quantum annealer
2023年12月18日(月) 14:00 - 15:00
Emanuele Mendicelli (Postdoctoral Research Associate, Department of Mathematical Sciences, University of Liverpool, UK)
Lattice gauge theory is an indispensable tool for non-Abelian fields, such as those in quantum chromodynamics where lattice results have been of central importance for several decades. Recent studies suggest that quantum hardware could extend the reach of lattice gauge theory to inaccessible phenomena due to the need for an exponentially large amount of resources, the so-called sign problem. Among the available quantum hardware gate-based quantum computer are well know but less common quantum annealer can play a role too. In this talk we briefly report one of the first use of D-Wave quantum annealer to study the energy spectrum and the time evolution of a SU(2) pure gauge lattice theory in its Hamiltonian formulation. In particular we present how to extract the energy spectrum using the quantum Quantum Annealer Eigensolver algorithm and perform the time evolution using the Kitaev-Feynman clock states. Despite the nosy hardware, no error mitigation techniques were needed but the usability of the D-Wave hardware was extended by simply block-diagonalizing the Hamiltonian.
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
1011 イベント