理論物理学セミナー

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理論物理学セミナー

S-matrix Unitarity toward UV Completion

2021年9月13日13:30 - 15:00

泉 圭介 (名古屋大学 素粒子宇宙起源研究所 助教)

Einstein gravity is not renormalizable and does not hold perturbative unitarity at high energy. This is the main reason why the construction of quantum gravity is difficult. A conjecture was proposed by Llewellyn Smith, "renormalizablility and tree-unitarity at high energy give the same conditions for theories". This conjecture would be important because it shows that, if a theory is constructed s.t. unitarity is satisfied, renormalizablility holds automatically, and vice versa. Unfortunately, a counterexample was pointed out. If a theory involves higher derivatives, there exists a theory which is renormalizable but does not satisfy tree-unitarity. A candidate of quantum gravity, the quadratic gravity (R_{\mu\nu}^2 gravity), is one of the examples. Therefore, Llewellyn Smith's conjecture would not be useful for the discussion of quantum gravity. Then, we introduce a new conjecture, "renormalizablility and S-matrix unitarity (or often called pseudo-unitarity) at high energy give the same conditions for theories". In this talk, Llewellyn Smith's conjecture and our contribution to it will be explained. Then, our new conjecture will be introduced. Finally, it will be shown that our conjecture works well even in theories with higher derivatives.

会場: via Zoom

イベント公式言語: 英語

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Application of AdS/CFT to non-equilibrium phenomena in external electric fields

2021年8月16日13:00 - 15:00

木下 俊一郎 (中央大学 理工学部 共同研究員)

The AdS/CFT correspondence is a useful tool for studying strongly-coupled gauge theories. According to this correspondence, the D3/D7 brane system in string theory is one of the simplest toy model dual to supersymmetric QCD-like gauge theory. In the dual field theory, the mesons, i.e., the quark-antiquark bound states are stable in vacuum when the quark is massive, while the dielectric breakdown occurs by pair production of quark-antiquark under strong electric fields. In this talk, I will review a series of our works of D3/D7 systems and show time-dependent, non-equilibrium phenomena driven by external electric fields such as suddenly increasing or rotating electric fields.

会場: via Zoom

イベント公式言語: 英語

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Non-Unitary TQFTs from 3d N=4 Rank-0 SCFTs

2021年7月5日13:00 - 14:30

Dr. Myungbo Shim (Kyung Hee University, Republic of Korea)

We propose a novel procedure of assigning a pair of non-unitary topological quantum field theories (TQFTs), TFT_\pm[T_0], to a (2+1)D interacting N=4 superconformal field theory (SCFT) T_0 of rank 0, i.e. having no Coulomb and Higgs branches. The topological theories arise from particular degenerate limits of the SCFT. Modular data of the non-unitary TQFTs are extracted from the supersymmetric partition functions in the degenerate limits. As a non-trivial dictionary, we propose that F = max{ -log |S^{(+)}_{0\alpha}| } = max{ -log |S^{(-)}_{0\alpha}| }, where F is the round three-sphere free energy of T_0 and S^{(\pm)}_{0\alpha} is the first column in the modular S-matrix of TFT_\pm. From the dictionary, we derive the lower bound on F, F > -log(\sqrt{(5-\sqrt{5})/10}) \simeq 0.642965, which holds for any rank 0 SCFT. The bound is saturated by the minimal N=4 SCFT proposed by Gang-Yamazaki, whose associated topological theories are both the Lee-Yang TQFT. We explicitly work out the (rank 0 SCFT)/(non-unitary TQFTs) correspondence for infinitely many examples. Before going to the technical part, we provide some background materials including some peculiar features in 3d gauge theories, some supersymmetries, anyons, and some modular data of MTC in this talk.

会場: via Zoom

イベント公式言語: 英語

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Toward QCD-based description of dense baryonic matter

2021年6月29日13:00 - 14:30

藤本 悠輝 (東京大学)

The equation of state (EoS) of dense baryonic/quark matter is the crucial ingredient for understanding neutron stars. I briefly review the current state of the high-density matter EoS based on the QCD perspectives. In this talk, I particularly focus on the perturbative QCD (pQCD) EoS, which was previously thought to be useless at realistic density because it is plagued by the large uncertainty. I introduce our recent analysis of the EoS calculated within the pQCD framework with the resummation [Fujimoto & Fukushima, 2011.10891]. I discuss our scheme for the Hard Dense Loop resummation, which turns out to reduce the uncertainty compared with the conventional pQCD estimate without resummation. Our result apparently extends the applicability of the QCD-based EoS down to densities realized inside neutron stars and infers a smooth matching with the baryonic EoS.

会場: via Zoom

イベント公式言語: 英語

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Black Hole Information Paradox and Wormholes

2021年6月21日13:00 - 14:30

後藤 郁夏人 (数理創造プログラム 基礎科学特別研究員)

In this talk, I will explain about the recent progress in the black hole information paradox that I am involved with. The information paradox arises when a black hole evaporates by emitting Hawking radiation due to the quantum effects. Time dependence of the entropy of Hawking radiation is diagnosis of information loss caused by the black hole evaporation. If information is not lost, the entropy of Hawking radiation should obey the so-called Page curve. In recent research developments, it was found that “the quantum extremal islands” reproduce the unitary Page curve in an evaporating black hole. I will argue about how the quantum extremal islands are derived from the computation of the entropy of Hawking radiation using the gravitational path-integral.

会場: via Zoom

イベント公式言語: 英語

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iTHEMS-phys Intro Meeting on June 7, 2021

2021年6月7日13:00 - 14:30

内藤 智也 (理化学研究所 仁科加速器科学研究センター (RNC) 量子ハドロン物理学研究室 研修生 / 東京大学 大学院理学系研究科 物理学専攻 博士課程)
横田 猛 (数理創造プログラム 基礎科学特別研究員)
辻 直美 (数理創造プログラム 特別研究員)

13:00-13:20 [JST] Tomoya Naito 13:20-13:40 [JST] Takeru Yokota 13:40-14:00 [JST] Naomi Tsuji 14:00- Free discussion

会場: via Zoom

イベント公式言語: 英語

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iTHEMS-phys Intro Meeting on June 1, 2021

2021年6月1日13:00 - 15:00

菊地 健吾 (数理創造プログラム 基礎科学特別研究員)
エンリコ・リナルディ (Research Fellow, Physics Department, University of Michigan, USA)
横田 宏 (数理創造プログラム 特別研究員)

13:00-13:20 [JST] Kengo Kikuchi 13:20-13:40 [JST] Enrico Rinaldi 13:40-14:00 [JST] Hiroshi Yokota 14:00- Free discussion

会場: via Zoom

イベント公式言語: 英語

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iTHEMS-phys Intro Meeting on May 31, 2021

2021年5月31日13:00 - 15:00

難波 亮 (数理創造プログラム 上級研究員)
大下 翔誉 (数理創造プログラム 基礎科学特別研究員)
横倉 祐貴 (数理創造プログラム 上級研究員)
長瀧 重博 (長瀧天体ビックバン研究室 主任研究員)

13:00-13:20 [JST] Ryo Namba 13:20-13:40 [JST] Naritaka Oshita (10 mins break) 13:50-14:10 [JST] Yuki Yokokura 14:10-14:30 [JST] Shigehiro Nagataki 14:30- Free discussion

会場: via Zoom

イベント公式言語: 英語

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iTHEMS-phys Intro Meeting on May 25, 2021

2021年5月25日13:00 - 15:00

杉浦 拓也 (数理創造プログラム 特別研究員)
土井 琢身 (理化学研究所 仁科加速器科学研究センター (RNC) 量子ハドロン物理学研究室 専任研究員)
筒井 翔一朗 (理化学研究所 仁科加速器科学研究センター (RNC) 量子ハドロン物理学研究室 基礎科学特別研究員)
後藤 郁夏人 (数理創造プログラム 基礎科学特別研究員)

13:00-13:20 [JST] Takuya Sugiura 13:20-13:40 [JST] Takumi Doi (10 mins break) 13:50-14:10 [JST] Schoichiro Tsutsui 14:10-14:30 [JST] Kanato Goto 14:30- Free discussion

会場: via Zoom

イベント公式言語: 英語

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iTHEMS-phys Intro Meeting on May 24, 2021

2021年5月24日13:00 - 14:30

田屋 英俊 (数理創造プログラム 基礎科学特別研究員)
関野 裕太 (数理創造プログラム 訪問研究員)
チンカイ・チウ (数理創造プログラム 上級研究員)

13:00-13:20 [JST] Hidetoshi Taya 13:20-13:40 [JST] Yuta Sekino 13:40-14:00 [JST] Ching-Kai Chiu 14:00- Free discussion

会場: via Zoom

イベント公式言語: 英語

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iTHEMS-phys Intro Meeting on May 18, 2021

2021年5月18日13:00 - 14:30

本郷 優 (イリノイ大学シカゴ校 物理学科 Postdoctoral Research Associate)
伊藤 悦子 (理化学研究所 仁科加速器科学研究センター (RNC) ストレンジネス核物理研究室 協力研究員)
松本 信行 (理化学研究所 仁科加速器科学研究センター (RNC) 理研BNL研究センター 計算物理研究グループ 基礎科学特別研究員)

13:00-13:20 [JST] Masaru Hongo 13:20-13:40 [JST] Etsuko Itou 13:40-14:00 [JST] Nobuyuki Matsumoto 14:00- Free discussion

会場: via Zoom

イベント公式言語: 英語

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iTHEMS-phys Intro Meeting on May 17, 2021

2021年5月17日13:00 - 14:30

初田 哲男 (数理創造プログラム プログラムディレクター)
原田 了 (数理創造プログラム 基礎科学特別研究員)
多田 司 (理化学研究所 仁科加速器科学研究センター (RNC) 量子ハドロン物理学研究室 副主任研究員)

13:00-13:20 [JST] Tetsuo Hatsuda 13:20-13:40 [JST] Akira Harada 13:40-14:00 [JST] Tsukasa Tada 14:00- Free discussion

会場: via Zoom

イベント公式言語: 英語

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Quantum mechanical description of energy dissipation and application to heavy-ion fusion reactions

2021年2月16日13:00 - 14:30

時枝 正明 (東北大学 大学院理学研究科物理学専攻 大学院生)

For theoretical description of heavy-ion fusion reactions, two different models have been used depending on the incident energy. At energies above the Coulomb barrier, importance of energy dissipation and fluctuation has been deduced from scattering experiments. To describe them phenomenologically, the classical Langevin equation has successfully been applied. At energies below the Coulomb barrier, on the other hand, the quantum coupled-channels method with a few number of internal states has been applied, and it has succeeded in explaining sub-barrier fusion reactions. While each method succeeds in each energy range, a unified description of heavy-ion fusion reactions from sub-barrier energies to above barrier energies is still missing. To achieve this, we need to treat dissipation and fluctuation quantum mechanically. In order to describe dissipation and fluctuation quantum mechanically, we have applied ideas of open quantum systems to heavy-ion fusion reactions. I will talk about recent development in this talk. First I will introduce a model Hamiltonian to treat dissipation and fluctuation quantum mechanically, and explain its character and a strategy for numerical studies. I will then apply the model to a fusion problem, and discuss a role of energy dissipation during quantum tunneling. Finally I will discuss a possible future direction for a unified description of heavy-ion fusion reactions.

会場: via Zoom

イベント公式言語: 英語

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Quantum kinetic theory for chiral and spin transport in relativistic heavy ion collisions and core-collapse supernovae

2021年2月4日13:00 - 14:30

Dr. Di-Lun Yang (慶應義塾大学 理工学部 助教)

Recently, the anomalous transport phenomena of relativistic fermions associated with chirality and spin induced by external fields have been greatly explored in different areas of physics. Notably, such phenomena are in connection to various quantum effects such as quantum anomalies and spin-orbit interaction. The quark gluon plasmas produced from relativistic heavy ion collisions (HIC) and the core-collapse supernovae (CCSN) are both the systems in extreme conditions with high temperature or density and the presence of strong magnetic and vortical fields. Meanwhile, the abundance of light quarks and neutrinos as relativistic fermions created therein accordingly makes these two systems ideal test grounds for studying such exotic transport phenomena. Inversely, the anomalous transport may also give rise to unexpected impacts on the evolution of both systems. However, to analyze such dynamical quantum effects, a novel quantum transport theory delineating the evolution of chirality imbalance and spin has to be introduced. In this talk, I will discuss recent developments and applications of the quantum kinetic theory for chiral and spin transport in the context of HIC and CCSN.

会場: via Zoom

イベント公式言語: 英語

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Many body problems from quarks to stellar evolutions

2021年1月28日13:30 - 15:00

安武 伸俊 (千葉工業大学 情報科学部 教育センター 准教授)

The many-body problems are major problems that need to be clarified not only in nuclear physics, but also in astronomy. In this seminar, I introduce stellar evolutions as gravitational many-body problems, and also hadronic matter as quantum many-body problems, based on the Lagrangian schemes. The macroscopic stars and the microscopic hadronic matter look completely different issues. But in this seminar, I introduce the similarities between the two problems. For hadronic matter, we adopt the color molecular dynamics to understand the behaviors and properties of hadronic matter in the framework of QCD. Although molecular dynamics can not be the first-principle, they are sometimes useful to understand many-body quantum properties. In this talk, we introduce the current status of our color molecular dynamics.

会場: via Zoom

イベント公式言語: 英語

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Classical liquids and functional renormalization group

2020年12月17日13:00 - 14:30

横田 猛 (東京大学 物性研究所 特別研究員)

Development of methods for classical statistical mechanics is desired for accurate predictions of the structures and thermodynamic properties of liquids. A powerful framework to describe classical liquids is density functional theory (DFT). In the quantum case, there have been recent attempts to develop accurate methods with combining DFT and the functional renormalization group (FRG), which is another framework to deal with many-body systems utilizing evolution equations, and such approaches are expected to work also in the classical case. In this presentation, I will talk about a new approach for classical liquids aided by FRG. The formalism and some ideas to incorporate higher-order correlation functions to systematically improve the accuracy will be shown. I will also present a numerical demonstration in a one-dimensional exactly solvable system and discuss the results by comparing to other conventional methods such as the hypernetted chain.

会場: via Zoom

イベント公式言語: 英語

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Conserved charges in gravity and entropy

2020年12月10日13:00 - 14:30

青木 愼也 (京都大学 基礎物理学研究所 教授)

We propose a manifestly covariant definition of a conserved charge in gravity. We first define a charge density from the energy momentum tensor with a Killing vector, if exists in the system, and calculate the energy (and angular momentum) of the black hole by a volume integral. Our definition of energy leads to a correction of the known mass formula of a compact star, which includes the gravitational interaction energy and is shown to be 68\% of the leading term in some case. Secondly we propose a new method to define a conserved charge in the absence of Killing vectors, and argue that the conserved charge can be regarded as entropy, by showing the 1st law of thermodynamic for a special case. We apply this new definition to the expanding universe, gravitational plane waves and the black hole. We discuss future directions of our research.

会場: via Zoom

イベント公式言語: 英語

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KPZ equation, attractive bosons, and the Efimov effect

2020年12月3日13:00 - 14:30

西田 祐介 (東京工業大学 理学院 物理学系 准教授)

The Kardar-Parisi-Zhang (KPZ) equation for surface growth has been a paradigmatic model in nonequilibrium statistical physics. In particular, it in dimensions higher than two undergoes a roughening transition from smooth to rough phases with increasing the nonlinearity. It is also known that the KPZ equation can be mapped onto quantum mechanics of attractive bosons with a contact interaction, where the roughening transition corresponds to a binding transition of two bosons with increasing the attraction. Such critical bosons in three dimensions actually exhibit the Efimov effect, where a three-boson coupling turns out to be relevant under the renormalization group so as to break the scale invariance down to discrete one. On the basis of these facts linking the two distinct subjects in physics, we predict that the KPZ roughening transition in three dimensions shows either the discrete scale invariance or no intrinsic scale invariance.

会場: via Zoom

イベント公式言語: 英語

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Some idea on quantum tunneling via Lefschetz thimbles

2020年11月12日10:30 - 12:00

谷崎 佑弥 (京都大学 基礎物理学研究所 助教)

In this talk, I will explain my previous study with Takayuki Koike on a possible approach to quantum tunneling via Lefschetz thimbles. We classified all the complex saddle points for the real-time path integral for the symmetric double-well quantum mechanics. We looked at various properties of those complex solutions, which motivated us to conclude that the computation of tunneling amplitudes for the symmetric double well requires the interference of infinitely many Lefschetz thimbles. I would also like to talk about some speculations, admittingly being very optimistic.

会場: via Zoom

イベント公式言語: 英語

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Toward simulating Superstring/M-theory on a Quantum Computer

2020年10月23日17:00 - 18:00

花田 政範 (Department of Mathematics, University of Surrey, UK)

We present a framework for simulating superstring/M-theory on a quantum computer, based on holographic duality. Because holographicduality maps superstring/M-theory to quantum field theories (QFTs), we can study superstring/M-theory if we can put such QFTs on a quantum computer --- but it still looks like a complicated problem, if we use a usual lattice regularization. Here we propose an alternative approach, which turns out to be rather simple: we map the QFT problems to matrix models, especially the supersymmetric matrix models such as the Berenstein-Maldacena-Nastase (BMN) matrix model. Supersymmetric matrix models have natural applications to superstring/M-theory and gravitational physics, in an appropriate limit of parameters. Furthermore, for certain states in the Berenstein-Maldacena-Nastase (BMN) matrix model, several supersymmetric quantum field theories dual to superstring/M-theory can be realized on a quantum device. It is straightforward to put the matrix models on a quantum computer, because they are just quantum mechanics of matrices, and the construction of QFTs is mapped to the preparation of certain states. We show the procedures are conceptually rather simple and efficient quantum algorithms can be applied. In addition, as a (kind of) byproduct, we provide a new formulation of pure Yang-Mills on quantum computer.

会場: via Zoom

イベント公式言語: 英語