理論物理学セミナー
135 イベント
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セミナー
Exotic Pairing Nature and Charge Ordering in Kagome Superconductor
2025年6月5日(木) 15:00 - 16:15
Wu Xianxin (Associate Professor, CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, China)
Abstract：Recent experimental investigations have identified fascinating electronic orders in kagome metals, such as intriguing superconductivity, charge density wave (CDW) and nematicity. Notably, there is various evidence of spontaneous time-reversal symmetry (TRS) breaking within the CDW phase, pointing to a long-pursued loop current order, though its underlying mechanism remains elusive. In this talk, I will first review the exotic properties of these kagome superconductors. Then, I will discuss the effective model and the unique sublattice texture associated with van Hove singularities in the kagome lattice [1], which turns out to have significant effect on correlated states. Finally, I will present our scenario for realizing a TRS breaking CDW within the kagome lattice and discuss loop-current fluctuation induced unconventional pairing [2-4]. Potential experimental implications will be also discussed.
会場: via Zoom / 研究本館
イベント公式言語: 英語
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セミナー
Generalized symmetry from Type IIB superstring theory
2025年5月27日(火) 16:00 - 17:00
川平 将志 (神戸大学 大学院理学研究科 物理学専攻 博士研究員)
Recently, generalized symmetries have enabled the systematic analysis of various quantum systems. In this talk, we focus on global generalized symmetries that appear in the low-energy effective theory of type IIB superstring theory (i.e., type IIB supergravity). Specifically, we highlight the SL(2,ℤ) gauge symmetry (self-duality) in type IIB supergravity. We see that a global ℤ₁₂ eight-form symmetry arises as the quantum symmetry of the SL(2,ℤ) gauge symmetry. And we discuss its topological operator and its relation to 7-branes. This talk is based on joint work with Hiroki Wada (Tohoku University) and Naoto Kan (Osaka University).
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
2d Cardy-Rabinovici model with the modified Villain lattice formulation
2025年5月9日(金) 14:00 - 15:00
片山 颯 (京都大学 基礎物理学研究所 博士課程)
One of the most famous scenarios of the quark confinement problem is the dual superconductor picture. In this picture, the quark confinement is induced by monopole condensation, but in the theory with a θ term, we expect that not only monopole but also dyon condensation is induced, as suggested by Cardy and Rabinovici through their intuitive arguments. In this study, the Witten effect of the theory of two-dimensional compact bosons with the θ term is examined using a modified Villain-type lattice theory that can treat the θ term and dion in a rigorous manner. In addition, we construct the 2d Cardy-Rabinovici model and analyze the phase diagram through the scaling dimension argument and the anomaly matching constraint.
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
Supernova axion emissivity with Δ(1232) resonance in heavy baryon chiral perturbation theory
2025年5月1日(木) 16:00 - 17:30
Shu-Yu Ho (Postdoctoral Researcher, Institute of Physics, Academia Sinica, Taiwan)
Abstract: In this talk, we evaluate the energy loss rate of supernovae induced by the axion emission process π− + p → n + a with the Δ(1232) resonance in the heavy baryon chiral perturbation theory for the first time. Given the axion-nucleon-∆ interactions, we include the previously ignored Δ-mediated graphs to the π− + p → n + a process. In particular, the Δ_0-mediated diagram can give a resonance contribution to the supernova axion emission rate when the center-of-mass energy of the pion and proton approaches the Δ(1232) mass. With these new contributions, we find that for the typical supernova temperatures, compared with the earlier work with the axion-nucleon (and axion-pion-nucleon contact) interactions, the supernova axion emissivity can be enhanced by a factor of ∼ 4(2) in the Kim-Shifman-Vainshtein-Zakharov model and up to a factor of ∼ 5(2) in the Dine-Fischler-Srednicki-Zhitnitsky model with small tanβ values. Remarkably, we notice that the Δ(1232) resonance gives a destructive contribution to the supernova axion emission rate at high supernova temperatures, which is a nontrivial result in this study.
会場: 研究本館 3階 345−347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
On IR/UV divergence of inflationary decoherence
2025年4月22日(火) 14:00 - 15:30
佐野 文哉 (東京科学大学 博士課程)
Supported by observational evidence indicating that cosmological scalar perturbations were nearly Gaussian at the beginning of the universe, it is anticipated that the origin of these perturbations is quantum fluctuations. Consequently, cosmic inflation provides a valuable laboratory for testing the quantum nature with/of gravity. Evaluation of the quantumness of the primordial perturbations is an inevitable step for the purpose. However, quantum states of the perturbations are suffered from IR/UV divergence, resulting in fully classical states. In this presentation, I will first review the evaluation of the quantum coherence in de Sitter spacetime as a measure of quantumness, and then show how to regularize the divergence.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
A Strategy for Proving the Strong Eigenstate Thermalization Hypothesis: Chaotic Systems and Holography
2025年4月3日(木) 16:00 - 17:00
川本 大志 (京都大学 基礎物理学研究所 博士課程／日本学術振興会 特別研究員 DC)
The strong eigenstate thermalization hypothesis (ETH) provides a sufficient condition for thermalization and equilibration. Although it is expected to hold in a wide class of highly chaotic theories, there are only a few analytic examples demonstrating the strong ETH in special cases, often through methods related to integrability. In this talk, I will explore sufficient conditions for the strong ETH that may apply to a broad range of chaotic theories. These conditions are expressed as inequalities involving the long-time averages of real-time thermal correlators. Specifically, I will discuss bottom-up holographic models that satisfy these conditions under certain assumptions, which are expected to hold in such models. This talk is based on the preprint 2411.09746 [hep-th].
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
How to define a Majorana fermion?
2025年2月20日(木) 13:00 - 14:30
藤川 和男 (東京大学 名誉教授)
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.
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
New topological quantum order in 2D lattices from non-invertible symmetries
2025年2月18日(火) 15:00 - 16:00
Ayan Mukhopadhyay (Associate Professor, Valparaiso University, Chile)
I will introduce an exactly solvable 2D lattice model which reveals a large number of distinct topological phases with non-invertible (generalized) symmetries. In all these topological phases, which have topological ground state degeneracy, a commutative stabilizer monoid of Hermitian operators leave the ground state invariant and can also distinguish *all* local excitations, (These symmetries are indeed symmetry operations.) There exists novel confined fractonic excitations which change the nature of deconfined excitatons profoundly. The fusion rules form an associative but noncommutative. non-Abelian and non-unital category, and are distinct for each of these phases. A class of these phases are adiabatically connected to a limit which can be described in terms of generalized free field theories. I will describe systematic ways to construct such phases. I will also discuss phases which do not have generalized free field limits. These phases have novel forms of non-local entanglement as many of them share the same topological entanglement entropy. They also violate the entanglement bootstrap axioms. When the phases do not have a generalized free field limit, the violation of the entanglement bootstrap axioms can happen for arbitrary large subregions signifying new forms of long-range entanglement.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Linking quantum error correction and gauge theories with quantum reference frames
2025年2月14日(金) 10:30 - 11:30
Philipp Hoehn (沖縄科学技術大学院大学 (OIST) 助教)
Redundancy is the hallmark of both quantum error correction and gauge theories. In this talk, I will show that this analogy is not merely a coincidence but that there is a deeper underlying structural relationship. The key ingredient to this observation is quantum reference frames (QRFs), which constitute a universal tool for dealing with symmetries in quantum systems. They define a split between redundant and physical information in gauge systems, thereby establishing a notion of encoding in that context. This leads to an exact dictionary between (group-based) quantum error correcting codes and QRF setups. In stabilizer codes, this uncovers a correspondence between errors and QRFs: every maximal set of correctable errors generates a unique QRF, and each QRF is associated with a unique class of correctable errors. This allows for a reinterpretation of the Knill-Laflamme condition and novel insights into the relation between correctability and redundancy. The dictionary also reveals a novel error duality, based on Pontryagin duality, and somewhat akin to electromagnetic duality. Time permitting, I will illustrate these findings in surface codes, which can be understood as both codes and lattice gauge theories. These findings may find use in code design and quantum simulations of gauge theories.
会場: 研究本館 3階 345−347号室
イベント公式言語: 英語
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セミナー
Reheating after a cosmological constant relaxation and gravitational waves lensed by a supermassive black hole
2025年1月30日(木) 14:00 - 15:30
Paul Martens (Postdoctoral Fellow, Department of Physics, The Chinese University of Hong Kong, China)
This presentation will be articulated in two parts. In a first part, I will present the a reheating mechanism that follows a dynamically relaxed cosmological constant. The latter is achieved by the dynamics of a scalar field whose kinetic term is modulated by an inverse power of spacetime curvature. While it is at work against radiative corrections to the dark energy, this process alone would wipe out not only the vacuum energy, but also all other matter contents. A reheating phase is thus introduced, which exploits a null-energy-condition violating sector. In a second part, I shall present a more recent and still ongoing project to describe and characterize the lensing of gravitational waves by an active galactic nuclei (or any supermassive black hole), in the geometric limit. Such systems are simple enough for constraints to be derived with only few assumptions. Yet, they present interesting features that could provide information on e.g. on binary black hole formation mechanisms and quasinormal modes.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Krylov subspace method for quantum dynamics
2024年12月23日(月) 14:00 - 15:00
高橋 和孝 (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.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Perturbative unitarity of Higgs inflation in the Riemannian and generalized geometry
2024年12月13日(金) 16:00 - 17:30
三倉 祐輔 (名古屋大学 高等研究院理学研究科C研 博士課程)
In a simple Higgs inflation model in metric-affine gravity, it is known that its UV cutoff is much smaller than the Planck scale. While it calls for UV completion, a concrete example has not yet been found, even with the large-N limit known as a successful technique to complete an original Higgs inflation defined on the Riemannian geometry. In this talk, after a review of the unitarity issue and previous attempts to complete Higgs inflation models, we investigate how small deformation of the simple Higgs inflation affects the emergence and properties of dynamical fields particularly in the large-N limit.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Dark matter from inflationary quantum fluctuations
2024年12月9日(月) 14:00 - 15:30
Mohammad Ali Gorji (Junior Faculty, Center for Theoretical Physics of the Universe, Institute for Basic Science, Republic of Korea)
We explore a scenario in which dark matter is a massive bosonic field, arising solely from quantum fluctuations generated during inflation. In this framework, dark matter exhibits primordial isocurvature perturbations with an amplitude of O(1) at small scales that are beyond the reach of current observations, such as those from the CMB and large-scale structure. Assuming a monochromatic initial power spectrum, we identify the viable parameter space defined by dark matter mass and the length scale of perturbations. A key prediction of this scenario is copious formation of subsolar dark matter halos at high redshifts.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Nuclear clustering phenomena revealed by knockout reaction
2024年11月20日(水) 15:30 - 17:00
吉田 数貴 (大阪大学 核物理研究センター 助教)
Nuclear clustering is one of the unique phenomena in the nucleon many-body system. Historically, alpha formation has been known since the very early years of the nuclear physics, in the light and heavy mass regions. The former is known as the alpha clustering and its threshold rule, which was introduced by the Ikeda diagram in 1968. The latter has been known since the beginning of the nuclear physics as the alpha decay phenomena; the formation of alpha particles and their tunneling through the Coulomb barrier. Recently, the alpha clustering has been experimentally confirmed in the medium mass nuclei, 112-124Sn (Tin isotopes), using the alpha knockout reaction. Triggered by the experimental observation, the alpha knockout reaction is used as a reaction probe for the alpha clustering phenomena. In this talk, I will give an overview of the clustering phenomena and its reaction observables, in particular I will introduce the idea that the alpha knockout reaction can be a probe for the alpha formation on the alpha decay nuclei. In general, this idea can be applied to probe the particle trapped in the potential resonance.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Forming primordial black holes
2024年11月11日(月) 14:00 - 15:30
Zachary Picker (Postdoctoral Researcher, University of California, Los Angeles, USA)
Primordial black holes (PBHs) are black holes which form in the early universe. Not only are PBHs good dark matter candidates, but they have a wide range of fascinating phenomenology (even if they are only a fraction of the dark matter). In this talk I will review a somewhat under-discussed aspect of the PBH gospel---their formation mechanisms. In fact, there is a wide variety of ways to form PBHs of different sizes and abundances, and many of our favorite BSM theories can have PBHs in their spectra. I will then discuss some of our particular upcoming research on PBH formation, where attractive Yukawa forces in a dark sector can lead to the early formation of dense dark structures called Fermi balls which can collapse to black holes, with novel cosmological implications.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Quantum signature kernels
2024年10月30日(水) 14:00 - 15:00
Samuel Crew (Postdoctoral Fellow, Imperial College London, UK)
Arising from rough path theory, the signature transform captures features of time-series data by constructing a so-called 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.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Holographic Gubser flow
2024年10月29日(火) 13:30 - 14:30
Sukrut Mondkar (Postdoctoral Researcher, Harish-Chandra 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 free-streaming in transverse directions and the sub-leading 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/hep-th (accepted for publication in JHEP).
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
Open Effective Field Theories for primordial cosmology
2024年10月18日(金) 13:30 - 15:00
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.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Application of Complex Scaling Method to Scattering Calculations of Atomic Systems
2024年10月8日(火) 13:30 - 15:00
佐野 大志 (早稲田大学 理工学研究科 物理学及応用物理学専攻 辻川研究室 修士課程)
Based on our paper [1], this presentation will show the application of complex scaling method(CSM) to scattering calculations of atomic systems. While CSM has been extensively used to study resonance states, the application of CSM to scattering calculations was proposed recently with applications in nuclear physics. In our study, we apply the CSM scattering calculation to atomic systems and propose an effective correction to avoid the problem of slow convergence to the number of complex eigen energies. Our results with the effective correction agree well with those reported in the literature for positron scattering with the targets Ne, Ar, Kr, Xe, H, He, He+, and Li2+. In this presentation, we introduce the framework of phase-shift calculation using the CSM together with the examples of the positron scattering, and advantages and features of this approach. [This seminar is co-hosted by Few-body Systems in Physics Laboratory, RIKEN Nishina Center.]
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
135 イベント