238件のイベント / 2025年
-
講演会・レクチャー
Lectures on Neutron Star Structure III
2025年10月21日(火) 15:30 - 17:00
Mark Alford (Professor, Washington University in St. Louis, USA)
This is a lecture series by Prof. Mark Alford (Washington University in St. Louis) on the structure of neutron stars. Oct. 7 (Tues), 15:30-17:00 Lecture I : Quark matter: the high-density frontier The densest predicted state of matter is color-superconducting quark matter, which has some affinities to electrical superconductors, but a much richer phase structure because quarks come in many varieties. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is currently proceeding. I will review the nature of color-superconducting quark matter, and discuss some ideas for finding it in nature. Oct. 14 (Tues), 15:30-17:00 Lecture II: Solid quark matter I will review three ways in which quark matter can occur in a solid phase, where translational invariance is broken by some sort of crystalline structure. These include a color superconductor of the Fulde-Ferrell-Larkin-Ovchinnikov type, mixed phases that can arise at a nuclear/quark matter interface, and the strangelet crystal crust of a strange star. Oct. 21 (Tues), 15:30-17:00 Lecture III: Dissipation in neutron star mergers In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on flavor equilibration and its consequences such as bulk viscosity and damping of oscillations. Oct. 28 (Tues), 15:30-17:00 Lecture IV: Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.
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
-
セミナー
Simulating nonequilibirum quantum dynamics on Reimei
2025年10月21日(火) 10:00 - 12:00
早田 智也 (慶応義塾大学 医学部 准教授)
This is the third quantum computing gathering hold by quantum computing study group.
会場: via Zoom / セミナー室 (359号室)
イベント公式言語: 英語
-
セミナー
Compact Association Schemes and Fourier Analysis
2025年10月17日(金) 15:00 - 17:00
中田 彬文 (広島大学 大学院先進理工系科学研究科 博士課程／日本学術振興会 特別研究員 DC)
Error-correcting codes are a fundamental tool in information and communication technologies. They can be viewed as collections of points in a space that are sufficiently far apart to allow error detection and correction. More broadly, coding theory studies good arrangements of points in spaces. This theory has been particularly developed in the frameworks of association schemes and compact homogeneous spaces, where harmonic analysis plays a central role. In this talk, we will begin with an introduction to error-correcting codes and then present compact association schemes, which we define as a generalization of these spaces in which harmonic analysis can be developed.
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
-
セミナー
Bonded Knotted Structures and Applications
2025年10月16日(木) 16:00 - 18:00
Sofia Lambropoulou (Professor, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Greece)
We present the theory of bonded knots and bonded knotoids, as well as their algebraic counterparts, the theory of bonded braids and bonded braidoids. We also discuss some applications to the topological study of proteins.
会場: via Zoom / セミナー室 (359号室)
イベント公式言語: 英語
-
セミナー
Particle-in-Cell Simulations on Collisionless Shocks and Particle Acceleration in Black Hole Coronae
2025年10月16日(木) 14:00 - 15:15
Nhat-Minh Ly (大阪大学 大学院理学研究科 博士課程)
Multiple nearby Active Galactic Nuclei have been reported as sources of high-energy neutrinos detected by the IceCube observatory. These results strongly suggest efficient proton acceleration to (sub-)PeV energies, likely within Black Hole (BH) coronae, given the lack of γ-ray counterparts. The acceleration mechanisms remain unconfirmed due to limited understanding of coronal environments and challenges in modeling hot, relativistic plasmas. Although diffusive shock acceleration (DSA) has been proposed, a self-consistent treatment incorporating detailed kinetic plasma effects has been lacking. In this study, we present the particle-in-cell (PIC) method as a first-principles approach to investigate particle acceleration by collisionless shocks under conditions inferred from multi-wavelength observations of BH coronae. Using large-scale 1D3V simulations, we surveyed shock parameters, focusing on underexplored effects such as initial ion–electron temperature ratios and trans-relativistic shock velocities, and found that collisionless shocks can form even in hot, low-Mach plasmas. These shocks accelerate protons up to ~100 TeV, consistent with the energies required for IceCube neutrino detections, across a wide range of coronal conditions. The shocks partition ~10% of dissipated energy into nonthermal protons and <1% into electrons, providing critical, observationally testable constraints on the plasma state of BH coronae.
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
-
セミナー
Why complexity persists: Evolutionary dynamics of the amylase locus in primates
2025年10月16日(木) 12:30 - 13:45
Charikleia Karageorgiou (Postdoctoral Fellow, University at Buffalo, USA)
The amylase locus is among the most structurally variable regions of the human genome, frequently linked to starch digestion, metabolic traits, and dietary adaptation. Yet the causes of its recurrent duplication and exceptional variability remain unresolved. Why is this locus particularly prone to structural change? To address these questions, we analyzed 98 modern human genomes using long-read sequencing and optical mapping, alongside 53 high-quality primate assemblies. We identified 30 distinct amylase haplotypes in humans and documented more than 15 lineage-specific expansions and contractions across primates. Structural complexity appears to have been initiated by lineage-specific LTR insertions and subsequently shaped by non-allelic homologous recombination, with occasional contributions from microhomology-mediated break-induced replication. Independent duplications and salivary expression gains evolved repeatedly across primate lineages, but extensive within-species structural polymorphism is largely unique to humans. We further detected signatures of positive selection among primate paralogs, and dietary correlations with copy number suggest recurrent adaptive roles for amylase variation. The persistence of structural variation in this locus points to a unique combination of elevated mutational input, relaxed constraint, and ongoing selection, highlighting broader principles in the evolution of structurally unstable loci.
会場: via Zoom / セミナー室 (359号室)
イベント公式言語: 英語
-
セミナー
Topological Field Theory Coupled to Parameter Spaces
2025年10月15日(水) 13:30 - 15:00
安藤 貴政 (京都大学 基礎物理学研究所 博士課程)
Topological quantum field theories (TQFTs) describe the IR fixed points of wide classes of gapped theories and are useful for studying many-body quantum phases of matter. In this talk, I will talk about TQFTs coupled to parameter spaces. I first explain the motivation for studying such TQFTs with parameter spaces from two perspectives: generalizing the description of the partition function with background gauge fields, and generalizing to invariants of many-body gapped phases over parameter spaces, known as the Berry phase. Then I will explain how these two are related by showing two physically motivated maps that connect them. The construction of these maps provides physical evidence for the Cobordism Hypothesis. I also discuss other related topics, such as the bulk-boundary correspondence. The talk is based on my ongoing work with Ryan Thorngren (UCLA).
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
-
講演会・レクチャー
Lectures on Neutron Star Structure II
2025年10月14日(火) 15:30 - 17:00
Mark Alford (Professor, Washington University in St. Louis, USA)
This is a lecture series by Prof. Mark Alford (Washington University in St. Louis) on the structure of neutron stars. Oct. 7 (Tues), 15:30-17:00 Lecture I: Quark matter: the high-density frontier The densest predicted state of matter is color-superconducting quark matter, which has some affinities to electrical superconductors, but a much richer phase structure because quarks come in many varieties. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is currently proceeding. I will review the nature of color-superconducting quark matter, and discuss some ideas for finding it in nature. Oct. 14 (Tues), 15:30-17:00 Lecture II: Solid quark matter I will review three ways in which quark matter can occur in a solid phase, where translational invariance is broken by some sort of crystalline structure. These include a color superconductor of the Fulde-Ferrell-Larkin-Ovchinnikov type, mixed phases that can arise at a nuclear/quark matter interface, and the strangelet crystal crust of a strange star. Oct. 21 (Tues), 15:30-17:00 Lecture III: Dissipation in neutron star mergers In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on flavor equilibration and its consequences such as bulk viscosity and damping of oscillations. Oct. 28 (Tues), 15:30-17:00 Lecture IV: Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.
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
-
セミナー
Temporal Evolution of Crustal Stress at Volcanoes During Periods of Unrest
2025年10月14日(火) 10:30 - 12:00
Eric Newland (Research Fellow, Faculty of Mathematical & Physical Sciences, University College London, UK)
Eruptions that occur at volcanoes after periods of quiescence are difficult to forecast. Pathways that connect the source to the surface may have become sealed. The pressurisation of the source leads to the deformation of the crust. Initially the crust deforms elastically, strain is accommodated via ground movement and elastic strain energy is stored to the crust. Then, the deformation transitions to inelastic where strain is accommodated via brittle failure (volcano-tectonic event), and elastic strain energy is transferred from the crust. We present a novel method to estimate the temporal evolution of elastic strain energy and bulk stress during periods of unrest. We consider the transfer of energy using measurements of surface deformation and seismic activity. We evaluate the temporal evolution of crustal bulk stress and investigate the progression of deformation in the crust. We apply our method to the unrest at the Campi Flegrei caldera, Italy from 2011-2024, and the eruption of Sierra Negra, Galapagos, 2018. Our calculations reveal that the bulk stress follows a characteristic progression, in which the stress initially increases linearly with time prior to the onset of significant seismicity, consistent with elastic deformation. We then observe a transition to inelastic deformation, when rate of elastic strain energy lost via fracturing increases and eventually exceeds the rate of elastic strain energy transferred to the crust. This results in a decrease in the bulk stress stored in the crust with time, indicating a progressive weakening of the crustal material due to seismicity-induced damage. Comparison with laboratory experiments show the behaviour is consistent with bulk failure in extension and the potential formation of new pathways in the crust. Finally, we demonstrate how our method, along with the understanding of eruption precursors gained from the results, can be used to constrain deformation regimes at reawakening volcanoes after extended repose and to evaluate the hazard posed during periods of unrest.
会場: Hybrid Format (RIKEN R-CCS room 107 and Zoom)
イベント公式言語: 英語
-
コロキウム
Why do we sleep? — The Role of Calcium and Phosphorylation in Sleep
2025年10月10日(金) 15:30 - 17:00
上田 泰己 (東京大学 大学院医学系研究科 システムズ薬理学教室 教授 / 久留米大学 分子生命科学研究所 個体システム生物学研究部門 教授)
Sleep remains one of greatest remaining mysteries. At the Sleep 2012 conference, we conceived a shift from the concept of “sleep substances” to “wake substances” such as calcium, suggesting that sleep homeostasis may arise from the integration of wake-related activity. Inspired by Dr. Setsuro Ebashi’s work on calcium signaling, we investigated calcium’s role in sleep regulation. Using our Triple-CRISPR method (Sunagawa et al. 2016), we screened 25 genes related to calcium channels and pumps, revealing calcium as a brake on brain activity to promote sleep (Tatsuki et al. 2016). We also developed a tissue-clearing method CUBIC (Susaki et al. 2014; Tainaka et al. 2014) to visualize calcium’s effects on neural circuits. Further work showed that calcium-dependent enzymes, CaMKIIα/β kinases, act as calcium “memory” devices, with phosphorylation sites controlling sleep onset, duration, and termination (Tone et al. 2022). Other direct and indirect calcium-dependent phosphatases, Calcineurin and PP1 (sleep-promoting), and opposing kinases, PKA (wake-promoting), function as synaptic sleep switches (Wang et al. 2024). We also identified the ryanodine receptor 1, a calcium channel, as a molecular target of inhalational anesthetics, hinting at shared pathways between anesthesia and sleep (Kanaya et al. 2025). Lastly, we proposed the WISE (Wake Inhibition Sleep Enhancement) mechanism, where quiet wakefulness suppresses and deep sleep strengthens synaptic connections, explaining links between sleep, depression, and antidepressant effects (Kinoshita et al. 2025).
会場: 大河内記念ホール (メイン会場) / via Zoom
イベント公式言語: 英語
-
その他
Mathematical Application Research Team Meeting #9
2025年10月10日(金) 13:30 - 14:30
アントワーヌ・ディエズ (理化学研究所 数理創造研究センター (iTHEMS) 数理展開部門 数学応用研究チーム 研究員)
In this meeting, Antoine Diez will give a talk entitled "Mean-field limits a la Tanaka and large deviations for particle systems with network interactions." Feel free to join if you are interested.
会場: 研究本館 3階 359号室 (メイン会場) / via Zoom
イベント公式言語: 英語
-
セミナー
Algebraic structures in QFT in the presence of a quantum reference frame
2025年10月9日(木) 14:00 - 15:00
Kasia Rejzner (Professor, Department of Mathematics, University of York, UK)
In this talk I will show how operational description of measurement with the use of quantum reference frames (QRF) affects the algebraic structure of quantum field theory (QFT). I will focus on the example of a quantum clock coupled to a QFT on de Sitter spacetime, previously discussed by Chandrasekaran, Longo, Pennington and Witten. This talk is based on my recent work with Chris Fewster, Daan Janssen, Leon Loveridge and James Waldron.
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
-
セミナー
Homo lupo lupus est: Man is a wolf to wolves.
2025年10月9日(木) 14:00 - 15:00
Carlos Sarabia (Postdoctoral Researcher, Evolutionary Population Genetics Lab, Institute of Evolutionary Biology (IBE-CSIC), Spain)
The gray wolf (Canis lupus) is one of the most emblematic wild species in human history: revered as a symbol of strength and wildness, although unforgivably persecuted as a competitor and pest. Across Europe and much of Eurasia, wolves would still dominate as apex predators... were it not for millennia of human pressure. Today, their evolutionary trajectory is shaped not only by climate fluctuations and habitat loss, but also by a uniquely flexible species boundary. Due to their unique karyotype, canids can admix freely with other related species, a capacity that both threatens the genetic integrity of wild canids like wolves and enriches our understanding of hybridization as a driver of adaptation. In this talk, we will explore recent studies on wolf demography under human pressure and climatic change, with particular attention to admixture with domestic dogs and the consequences for their survival in increasingly anthropized environments. Finally, we will observe how the wolf's distinctive genomic architecture makes it a powerful model for testing population genetics theoretical frameworks and for applying state-of-the-art computational tools, offering new insights into the understanding of evolution as a force for change.
会場: via Zoom
イベント公式言語: 英語
-
講演会・レクチャー
Lectures on Neutron Star Structure I
2025年10月7日(火) 15:30 - 17:00
Mark Alford (Professor, Washington University in St. Louis, USA)
This is a lecture series by Prof. Mark Alford (Washington University in St. Louis) on the structure of neutron stars. Oct. 7 (Tues), 15:30-17:00 Lecture I: Quark matter: the high-density frontier The densest predicted state of matter is color-superconducting quark matter, which has some affinities to electrical superconductors, but a much richer phase structure because quarks come in many varieties. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is currently proceeding. I will review the nature of color-superconducting quark matter, and discuss some ideas for finding it in nature. Oct. 14 (Tues), 15:30-17:00 Lecture II: Solid quark matter I will review three ways in which quark matter can occur in a solid phase, where translational invariance is broken by some sort of crystalline structure. These include a color superconductor of the Fulde-Ferrell-Larkin-Ovchinnikov type, mixed phases that can arise at a nuclear/quark matter interface, and the strangelet crystal crust of a strange star. Oct. 21 (Tues), 15:30-17:00 Lecture III: Dissipation in neutron star mergers In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on flavor equilibration and its consequences such as bulk viscosity and damping of oscillations. Oct. 28 (Tues), 15:30-17:00 Lecture IV: Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.
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
-
数学レクチャー
On ℓ_p-Vietoris-Rips complexes and blurred magnitude homology
2025年10月7日(火) 11:00 - 13:00
Sergei O. Ivanov (Professor, Beijing Institute of Mathematical Sciences and Applications, China)
One of the main tools in topological data analysis is the notion of a persistence module. The most prominent example is the persistence module associated with the Vietoris–Rips complex of a finite metric space. On the other hand, the concept of magnitude has become increasingly well known in data analysis. Recently, Nina Otter introduced blurred magnitude homology, which is also a persistence module associated with a metric space. Govc and Hepworth showed that the magnitude of a finite metric space can be uniquely recovered from its blurred magnitude homology. For 1 ≤ p ≤ ∞, we define the ℓ_p-Vietoris–Rips complexes and the associated ℓ_p-persistent homology of metric spaces, and we study their fundamental properties. We show that for p=∞ this theory recovers the classical theory of Vietoris–Rips complexes and their persistent homology, while for p=1 it recovers the theory of blurred magnitude homology.
会場: 研究本館 3階 セミナー室(345-347) (メイン会場) / via Zoom
イベント公式言語: 英語
-
セミナー
Discovering and harnessing symmetry with machine learning
2025年10月6日(月) 16:00 - 17:30
Escriche Santos Eduardo (Ph.D. Student, Department of Computer Science, Technical University of Munich, Germany)
Incorporating symmetry-inspired inductive biases into machine learning models has led to many significant advances in the field, especially for its application to scientific data. However, recently, a trend has emerged that favors implicitly learning relevant symmetries from data instead of designing constrained equivariant architectures. In this talk, I will first introduce these different modelling alternatives, together with their associated benefits and limitations. Then, I will describe some examples of automatic symmetry discovery methods as a way of mitigating some of those limitations. Finally, I will present our recent work that integrates symmetry discovery and the definition of an equivariant model into a joint learnable end-to-end approach, which further alleviates some of the limitations of current equivariant modelling approaches.
会場: via Zoom
イベント公式言語: 英語
-
講演会・レクチャー
Lectures on General Probabilistic Theories: From Introduction to Research Participation
2025年10月6日(月) - 9日(木)
荒井 駿 (東京大学 大学院総合文化研究科 JSPS特別研究員)
(The deadline of the registration is on Sep 30.) 100 years have passed since quantum mechanics was born. The mathematical model has been describing the physical world remarkably well. However, the foundations of this model still remain unclear. A comprehensive understanding of quantum theory, including its foundations, is becoming even more important in an era where the demands of realizing quantum information technologies pose significant theoretical and experimental challenges. The framework of General Probabilistic Theories (GPTs) is a modern approach to the foundations of quantum theory. It deals with mathematical generalizations of both classical and quantum theories and has attracted increasing attention in recent years. Roughly speaking, research on GPTs has three major objectives: characterizing the models of classical and quantum theories, investigating the fundamental limits of physical and information-theoretic properties arising from operational requirements, and deepening our understanding of the mathematical structures underlying classical and quantum theories. The studies of GPTs have provided many new perspectives on these topics. However, at the same time, there remain many important open problems in the field. For this reason, more researchers are encouraged to enter and contribute to research on GPTs. This intensive three-day lecture series is designed to provide researchers and graduate students with the essential knowledge necessary for research on GPTs, starting from an introduction to the subject. The lectures will cover the mathematical foundations, physical and information-theoretic concepts, and both the established results and future directions of GPT research. The 1st day will present the necessary mathematical structures, including convex geometry, positive cones, and the operational formulation of probabilistic models. The 2nd day will explore composite systems, information-theoretic quantities, symmetries, and Euclidean Jordan algebras. The 3rd day will survey key results on discrimination and communication tasks, the characterization of classical and quantum theories, and open problems that connect GPTs to quantum information science and beyond. Note: The content of each lecture may extend into the next slot or be covered earlier, depending on the pace of discussion and participant questions. The 1st day (6th Oct.): Mathematical Introduction to GPTs Venue: Large Meeting Room, 2F, Wako Welfare & Conference Building 10:30-12:00 Lecture 1 (Introduction and Mathematics on Positive Cones) 12:00-13:30 Lunch time 13:30-15:00 Lecture 2 (Mathematics on Positive Cones) 15:00-15:30 Coffee break 15:30-17:00 Lecture 3 (Introduction to General Models and Relation between Operational Probability Theories) The 2nd day (7th Oct.): Physical and Information Theoretical Concepts in GPTs Venue: Large Meeting Room, 2F, Wako Welfare & Conference Building 10:30-12:00 Lecture 4 (Composite Systems in GPTs) 12:00-13:30 Lunch time 13:30-15:00 Lecture 5 (Information Quantities) 15:00-15:30 Coffee break 15:30-17:00 Lecture 6 (Dynamics, Symmetry, and Euclidean Jordan Algebras) The 3rd day (8th Oct): Previous and Future Studies in GPTs Venue: Meeting Room 435-437, 4F, Wako Main Research Building 10:30-12:00 Lecture 7 (Discrimination and Communication Tasks) 12:00-13:30 Lunch time 13:30-15:00 Lecture 8 (Characterization of Classical and Quantum Theories) 15:00-15:30 Coffee break 15:30-17:00 Lecture 9 (Other Topics, Open Problems, and Future Directions) 18:00- Dinner The day of no lecture (9th Oct): Open Discussion and Q&A Research discussions will take place between the lecturer and participants in areas such as the hallways on the 3rd and 4th floors of the Main Research Bldg, RIKEN Wako Campus.
会場: 理化学研究所 和光キャンパス 統合支援施設2階会議室 / 研究本館 435-437号室
イベント公式言語: 英語
-
数学レクチャー
Bousfield-Kan completion as a codensity ∞-monad
2025年10月3日(金) 15:00 - 17:00
Sergei O. Ivanov (Professor, Beijing Institute of Mathematical Sciences and Applications, China)
In this talk we recall the theory of codensity monads in ordinary category theory and tell about its generalization to the ∞-category setting. In particular, we show that the codensity ∞-monad of a full subcategory D of an ∞-category C satisfies a universal property: it is the terminal D-preserving ∞-monad. As an application, we show that the classical Bousfield-Kan R-completion functor can be described as the codensity ∞-monad of the full subcategory K(R) in the ∞-category of spaces spanned by the empty space and the products of Eilenberg-MacLane spaces of R-modules. As a corollary, we obtain that the Bousfield-Kan R-completion is the terminal K(R)-preserving ∞-monad.
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
-
セミナー
Quantum tunneling in the curved spacetime
2025年10月2日(木) 13:30 - 15:00
山口 昌英 (Director, Center for Theoretical Physics of the Universe, Institute for Basic Science, Republic of Korea)
False vacuum decay is theorized to have occurred frequently throughout the history of the universe, particularly during first-order phase transitions associated with spontaneous symmetry breaking. The decay rate of such a vacuum is governed by Euclidean bounce solutions, which can exhibit a wide range of configurations, even under fixed boundary conditions. In the absence of gravitational effects, it was established over four decades ago—under reasonable assumptions—that the most symmetric bounce solution, namely the O(4)-symmetric one, minimizes the Euclidean action. This renders it the dominant tunneling path in flat spacetime. However, when gravitational effects are taken into account—as is essential in cosmological settings—all prior studies have assumed, without rigorous proof, that the O(4)-symmetric bounce continues to minimize the action. This has remained a longstanding unresolved problem for more than forty years. In this work, we address this issue by employing the anti-de Sitter/conformal field theory (AdS/CFT) correspondence to determine the configuration with the lowest Euclidean action in a metastable AdS false vacuum. Within the Euclidean formalism of Callan and Coleman, we identify the most probable decay channel of the AdS vacuum. The AdS/CFT duality enables us to sidestep the technical challenges intrinsic to metastable gravitational systems. We demonstrate that the Fubini bounce in conformal field theory—which is dual to the Coleman–de Luccia (CdL) bounce in AdS—indeed minimizes the Euclidean action among all finite bounce solutions in a conformal scalar field theory. Consequently, under certain conditions, we establish that the CdL bounce yields the lowest action among all relevant configurations, including both large and thin-wall limits. Time permitting, we also discuss the prefactor of the decay rate, as obtained from one-loop quantum corrections.
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
-
セミナー
What constitutes a gravitational wave in an expanding universe?
2025年10月1日(水) 16:00 - 17:30
Yi-Zen Chu (Professor, Department of Physics, National Central University, Taiwan)
Our understanding of gravitational waves produced by isolated astrophysical systems is primarily based on gravitational perturbation theory off a flat spacetime background. This leads to the common identification of gravitational radiation with massless spin-2 waves. In this talk, I will argue that gravitational waves may no longer be solely "spin-2" in character once the background spacetime is our expanding universe instead. As a result of the mixing between gravitational and other degrees of freedom, scalar "spin-0" gravitational waves may exist during the radiation-dominated epoch of our universe; as well as during its current accelerated expansion phase -- provided the main driver is not the cosmological constant, but some extra "Dark Energy" field. Moreover, during the radiation-dominated era, spin-0 Cherenkov gravitational waves may even be generated if its material source were traveling faster than 1/\sqrt{3}.
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
238件のイベント / 2025年