Quantum Gravity Gatherings
13 イベント
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講演会・レクチャー
The 11th Intensive Lectures on Quantum Gravity
2026年9月7日(月) - 9日(水)
初田 泰之 (立教大学 理学部 物理学科 准教授)
In the 11th event of the Intensive Lecture Series, organized by the Quantum Gravity Gatherings (QGG) study group at RIKEN iTHEMS, we will have Prof. Yasuyuki Hatsuda from Rikkyo University, who will deliver a three-day lecture series on the analytic methods in black hole perturbation theory. Black hole perturbation theory plays a very important role in the developments of modern physics. For instance, in gravitational wave astronomy, it can describe the ringdown phase during the merger events of binary black holes. As the frequency and decay rate of each quasinormal mode are unique to the remnant black hole, one can test extreme-gravity physics by extracting those modes from the ringdown signal. In addition, the computation of black hole quasinormal modes based on black hole perturbation theory has relations connecting to conformal field theories and even to the computations of tidal Love numbers. With the broad applications, we expect this lecture series to provide fresh perspectives to researchers across a wide range of fields and to inspire new directions in their own research. The lectures will be delivered in a blackboard-style format (in English), designed to foster interaction, active participation, and in-depth Q&A discussions. In addition, short talk sessions will be held, giving participants the opportunity to present briefly on topics of their choice. Through this informal and dynamic setting, we hope to spark active interactions among participants and create an environment where ideas can be shared openly and enthusiastically. This event will take place in person only. Target audience: Senior scholars, early-career researchers, and students are all warmly welcome. Registration deadline: July 31, 2026
会場: 研究本館 4階 435-437号室
イベント公式言語: 英語
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講演会・レクチャーiTHEMS-UTokyo Intensive Lectures on Quantum Gravity
2026年8月31日(月) - 9月2日(水)
川合 光 (大阪公立大学 南部陽一郎物理学研究所 客員教授)
iTHEMS-UTokyo Intensive Lectures on Quantum Gravity (10th Quantum Gravity Gatherings Lecture Series) The 10th QGG Lecture Series is a special three-day installment of the intensive lecture series organized by the Quantum Gravity Gatherings (QGG) study group at RIKEN iTHEMS. This celebratory edition will feature Professor Hikaru Kawai from Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP), who will deliver a series of lectures on themes related to quantum gravity. This lecture series will follow a style similar to Prof. Kawai's first QGG lectures, held three years ago at RIKEN (Wako) as the inaugural QGG event, which explored fundamental questions in quantum gravity, string theory, and the quantum universe. A distinctive feature of this 10th installment is that it will take place on the Komaba campus of The University of Tokyo, where one of the iTHEMS satellite offices is located. This will be the first QGG lecture series held outside Wako, with the aim of making the event more accessible to a broader group of participants. Format: Lectures will be given mainly in blackboard style and in English, encouraging active participation and in-depth Q&A discussions. Poster sessions will also be held, giving participants an opportunity to present their own work or topics of interest. These sessions are intended to foster communication and stimulate the exchange of ideas among participants. This event will take place in person only. Target audience: Senior scholars, early-career researchers, and students are all warmly welcome. Registration deadline: July 31, 2026
会場: 21 Komaba Center for Educational Excellence (21 KOMCEE) East Building, Room K214, Komaba Campus, The University of Tokyo
イベント公式言語: 英語
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講演会・レクチャー
Quantum Gravity and Emergent Cosmology: A Group Field Theory Perspective
2026年7月31日(金) 14:00 - 16:00
Luca Marchetti (カブリ数物連携宇宙研究機構 (Kavli IPMU) 特任研究員)
This seminar is the second part of a two-part mini-seminar series organized by the Quantum Gravity Gatherings study group. It is intended to have a more lecture-style format, with an extended duration of up to two hours. This will allow the speaker sufficient time to introduce the framework in a clear and pedagogical manner, while also leaving ample room for questions and discussion with the audience. Title: Quantum Gravity and Emergent Cosmology: A Group Field Theory Perspective Abstract: I will introduce the Group Field Theory (GFT) approach to quantum gravity, emphasizing its connections with matrix and tensor models, discrete gravity path integrals, and loop quantum gravity. Through these connections, GFTs emerge naturally as quantum field theories of "spacetime atoms". I will then discuss how semiclassical, macroscopic physics can emerge from GFT, touching upon the challenges of defining locality and coarse-graining in quantum gravity, and on how these can be naturally addressed within relational frameworks. I will present a concrete implementation of this relational strategy in GFT and show how a simple relational coarse-graining scheme can be used to extract cosmological physics. Within the resulting cosmological models, the initial singularity is resolved into a quantum bounce, while cosmological perturbations emerge from the quantum entanglement of the underlying quantum-gravity degrees of freedom, with effective dynamics modified on trans-Planckian scales. Finally, I will show that quantum-gravitational interactions alone can generate cosmic acceleration, leading both to dynamical dark energy and to a slow-roll inflationary phase. I will conclude by showing recent observational constraints on such emergent dynamical dark energy models, and by providing an outlook on future research directions.
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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講演会・レクチャー
Quantum Reference Frames for Quantum Gravity
2026年7月30日(木) 14:00 - 16:00
Luca Marchetti (カブリ数物連携宇宙研究機構 (Kavli IPMU) 特任研究員)
This seminar is the first part of a two-part mini-seminar series organized by the Quantum Gravity Gatherings study group. It is intended to have a more lecture-style format, with an extended duration of up to two hours. This will allow the speaker sufficient time to introduce the framework in a clear and pedagogical manner, while also leaving ample room for questions and discussion with the audience. Title: Quantum Reference Frames for Quantum Gravity Abstract: Internal quantum reference frames provide a general framework for handling symmetries in quantum theory, with applications ranging from quantum gravity and gauge theories to quantum information and foundational physics. I will first introduce the formalism in simple mechanical systems, before turning to classical gravity. There, I will motivate the need for internal, dynamical frames in background-independent theories to define relationally local gauge-invariant observables, and show how this framework leads to a relational update of general covariance: frame covariance. I will then move to non-perturbative quantum gravity, showing how quantum reference frames can be used to define a manifestly gauge-invariant relational path integral, which is also invariant under transformations between quantum reference frames. It therefore provides a perspective-neutral description of quantum gravitational physics. I will also discuss the associated relational effective actions. Although effective actions are, in general, not frame-covariant off shell, the on-shell physics they encode is. Finally, I will present several physical consequences of this framework, including the fuzziness of frame-changed local correlators, the non-trivial interplay between quantum-reference-frame transformations and time evolution, and the frame-dependence properties of ground sectors and Hartle-Hawking prescriptions. I will conclude by outlining future directions, with particular emphasis on a relational notion of the renormalization group flow.
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
Stability of nonsingular black holes
2025年3月27日(木) 15:00 - 16:30
辻川 信二 (早稲田大学 理工学術院 先進理工学研究科 物理学及応用物理学専攻 辻川研究室 教授)
We show that nonsingular black holes (BHs) realized in nonlinear electrodynamics are always prone to Laplacian instability around the center because of a negative squared sound speed in the angular direction. This is the case for both electric and magnetic BHs, where the instability of one of the vector-field perturbations leads to enhancing a dynamical gravitational perturbation in the even-parity sector. Thus, the background regular metric is no longer maintained in a steady state. We also generalize our analysis to the case in which a scalar field is present besides the U(1) gauge field and find no explicit examples of linearly stable nonsingular BHs. Our results suggest that the construction of regular BHs without instabilities is generally challenging within the scheme of classical field theories.
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
Asymptotically flat black hole spacetimes with multiple injections
2025年3月14日(金) 15:30 - 17:00
齊藤 佑太 (日本大学 大学院理工学研究科 物理学専攻 博士課程)
In quantum gravity, Hawking radiation presents several fundamental problems. One of the problems is the black hole (BH) information paradox, in which the entanglement entropy (EE), which quantifies quantum entanglement, exceeds its upper bound. In the absence of the paradox, EE follows the Page curve. Recent progress has been made in resolving this paradox using the island formula, a method for computing EE that successfully reproduces the expected Page curve. In this approach, a portion of the black hole interior is treated as part of the radiation region. Meanwhile, an alternative scenario has been proposed where multiple collapsing shells prevent the formation of a well-defined event horizon [1]. In this case, radiation is emitted throughout the collapse process, shifting dynamically the Schwarzschild radius inward, and a surface structure is formed just outside. This leads to a distinction between the conventional event horizon and the surface, introducing an intermediate region between the Schwarzschild radius and the surface. Interestingly, this model also suggests that part of the black hole interior effectively belongs to the radiation region, drawing a possible parallel to the island formula. In this talk, we explore spacetimes with multiple energy injections in asymptotically flat two-dimensional black hole backgrounds and analyze the entanglement entropy in such scenarios. Since considering backreaction in gravitational collapse in two dimensions is difficult, we instead construct a spacetime solution with multiple energy injections and analyze EE within this background. The main focus of this talk is to derive the spacetime and examine its properties. Additionally, we perform EE calculations in parallel with previous studies [2], which consider the case of α single injection, and confirm that the behavior of EE depends on the interval between energy injections.
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 (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
7th QGG Intensive Lectures: Emergence of space-time in matrix models
2024年12月17日(火) - 19日(木)
土屋 麻人 (静岡大学 教授)
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
会場: 研究本館 4階 435-437号室
イベント公式言語: 英語
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セミナー
Global Thermodynamics for Heat Conduction Systems
2024年12月2日(月) 14:00 - 15:30
中川 尚子 (茨城大学 理工学研究科 教授)
Non-equilibrium phenomena are typically addressed through continuum descriptions based on local equilibrium and linear response theory, such as hydrodynamics. While effective, these approaches often overlook global characteristics. We propose Global Thermodynamics as a minimal-variable framework to describe weak non-equilibrium systems, focusing on two-phase coexistence under weak heat flux. By introducing a unique global temperature and extending entropy to non-equilibrium systems with a non-additive term, the framework predicts phenomena like metastable state stabilization—beyond the scope of traditional heat conduction equations. This talk will outline the framework, its key predictions, and validation efforts through numerical simulations and experiments. (This is a joint seminar with Informatin Theory Study Group.)
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
Lectures on Black Holes, Holography and Quantum Gravity
2024年7月29日(月) - 8月1日(木)
野村 泰紀 (Professor/Director, Berkeley Center for Theoretical Physics, University of California, Berkeley, USA)
The information problem of black holes has evolved modern physics and led to the holographic principle, considered the fundamental principle of quantum gravity. Through a series of four lectures (blackboard style), including naive questions from the audience and lively discussions, I will introduce these fundamental ideas as well as the current state of the art and problems in cutting-edge research. Lecture 1: July 29 (Mon) 13:30~15:00 (Lecture 2: July 30 (Tue) 13:30~15:00 was canceled) Lecture 3: July 31 (Wed) 13:30~15:00 Lecture 4: Aug 1 (Thu) 13:30~15:00 (+ A possible lecture )
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
Black hole graviton and quantum gravity
2024年5月16日(木) 15:00 - 16:30
木村 裕介 (理化学研究所 量子コンピュータ研究センター (RQC) 量子複雑性解析理研白眉研究チーム 研究員)
Drawing from a thought experiment that we conduct, we propose that a virtual graviton gives rise to a black hole geometry when its momentum surpasses a certain threshold value on the Planck scale. This hypothesis implies that the propagator of a virtual graviton, that possesses momentum surpassing this threshold, vanishes. Consequently, a Feynman diagram containing this type of graviton propagator does not add to the overall amplitude. This mechanism suggests the feasibility of formulating an ultraviolet-finite four-dimensional quantum gravitational theory. The elementary particles including the gravitons are treated as point particles in this formulation.
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
Coarse-graining black holes out of equilibrium with boundary observables on time slice
2024年4月1日(月) 16:00 - 17:30
竹田 大地 (京都大学 素粒子論研究室 博士課程)
In black hole thermodynamics, defining coarse-grained entropy for dynamical black holes has long been a challenge, and various proposals, such as generalized entropy, have been explored. Guided by the AdS/CFT, we introduce a new definition of coarse-grained entropy for a dynamical black hole in Lorentzian Einstein gravity. On each time slice, this entropy is defined as the horizon area of an auxiliary Euclidean black hole that shares the same mass, (angular) momenta, and asymptotic normalizable matter modes with the original Lorentzian solution. The entropy is shown to satisfy a generalized first law within Einstein theory and, through holography, the second law as well. This second law corresponds to the positivity of the relative entropy in the CFT. Furthermore, by applying this thermodynamics to several Vaidya models in AdS and flat spacetime, we discover a connection between the second law and the null energy condition.
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
Volume complexity of de Sitter bubbles
2023年11月22日(水) 16:00 - 17:30
Nicolò Zenoni (大阪大学 大学院理学研究科 特任研究員)
Holographic complexity is conjectured to probe the evolution of spacetime. For black holes in anti-de Sitter (AdS) spacetime the growth rate of complexity approaches a constant value at late times, while in de Sitter (dS) spacetime it diverges at a finite critical time. In this talk, we consider geometries interpolating between AdS and dS. In particular, we discuss the evolution of volume complexity in a class of three-dimensional asymptotically anti-de Sitter geometries including dynamical bubbles of de Sitter in their interior. According to the dynamics of the bubble, complexity qualitatively behaves either as in the AdS black hole or as in the dS case. We conclude with some remarks about the possible dual interpretation.
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
Quasi-local holography in 3d quantum gravity
2023年8月4日(金) 14:00 - 15:30
Etera Livine (Research Director CNRS, Ecole Normale Supérieure de Lyon, France)
Since the idea appeared in black hole physics, the concept of holography has become a guiding principle for quantum gravity. It is the notion that the dynamics of the geometry of a region of space-time can be entirely encoded in a theory living on its boundary. Although such holographic dualities have been well-developed in an asymptotical context, it remains a challenge to realize it exactly at finite distances. I will draw a possible route in 3d quantum gravity, by showing a duality between the Ponzano-Regge path integral for 3d quantum gravity as a topological field theory and the 2d (inhomogeneous) Ising model. This leads to an intriguing geometrical interpretation of the Ising critical couplings and opens the door to a possibly rich interplay between 3d quantum gravity and 2d condensed matter built out of holographic dualities.
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
13 イベント