iTHEMS Theoretical Physics Seminar
128 events
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Seminar
Gradient flow exact renormalization group 2
July 6 (Wed) 13:30 - 17:00, 2022
Hiroshi Suzuki (Professor, Graduate School of Science, Kyushu University)
Wilson’s exact renormalization group (ERG), which tells how a system changes under the scale transformation, provides a fundamental framework to define quantum field theory even beyond the perturbation theory. It has however been known that it is difficult to preserve a manifest gauge symmetry in ERG because of the usage of the momentum cutoff in ERG. Here, we propose a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gauge-covariant diffusion equation. I explain the basic idea and properties of GFERG. If time permits, I want to present a possible application of GFERG to the consideration of the axial anomaly.
Venue: via Zoom
Event Official Language: English
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Seminar
Gradient flow exact renormalization group 1
July 5 (Tue) 13:30 - 17:00, 2022
Hiroshi Suzuki (Professor, Graduate School of Science, Kyushu University)
Wilson’s exact renormalization group (ERG), which tells how a system changes under the scale transformation, provides a fundamental framework to define quantum field theory even beyond the perturbation theory. It has however been known that it is difficult to preserve a manifest gauge symmetry in ERG because of the usage of the momentum cutoff in ERG. Here, we propose a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gauge-covariant diffusion equation. I explain the basic idea and properties of GFERG. If time permits, I want to present a possible application of GFERG to the consideration of the axial anomaly.
Venue: via Zoom
Event Official Language: English
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Seminar
Dress code for infrared safe S-matrix in QED
June 22 (Wed) 13:30 - 15:00, 2022
Sotaro Sugishita (Designated Assistant Professor, Institute for Advanced Research (IAR), Nagoya University)
We consider the infrared (IR) aspects of the gauge invariant S-matrix in QED. I will review the problem of IR divergences in QED, and introduce the dressed state formalism to obtain IR-safe S-matrix elements. I will show a condition for dressed states to obtain IR-safe S-matrix elements, and explain that this condition can be interpreted as the memory effect and is related to asymptotic symmetry. I also explain that IR divergences are necessary to prohibit the violation of asymptotic symmetry. We also argue that the difference between dressed and undressed states can be observed, even if we are able to observe an inclusive cross-section summing over soft photons.
Venue: Hybrid Format (Common Room 246-248 and Zoom)
Event Official Language: English
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Seminar
Is the Standard Model in the Swampland? Consistency Requirements from Gravitational Scattering
November 2 (Tue) 14:30 - 16:00, 2021
Katsuki Aoki (Research Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
Underlying assumptions on ultraviolet completion can impose constraints on its low-energy effective field theories (EFTs). The swampland program aims to clarify consistent and inconsistent EFTs with quantum gravity and aims to understand quantum gravity from low-energy physics and vice versa. One of the most well-established constraints is called positivity bounds, provided that general assumptions such as Poincare invariance and unitarity are satisfied at all scales. I will first explain how these consistency conditions arise especially in the presence of gravity. I will then show that the positivity bound is violated if the Standard Model of particle physics coupled to General Relativity is extrapolated up to 10^16 GeV, requiring new physics there or below. The precise value of the cutoff is determined by hadronic physic while it is insensitive from non-gravitational physics beyond the Standard Model. This is a signal from established physics for the necessity of quantum gravity below 10^16 GeV.
Venue: Hybrid Format (Common Room 246-248 and Zoom)
Event Official Language: English
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Seminar
S-matrix Unitarity toward UV Completion
September 13 (Mon) 13:30 - 15:00, 2021
Keisuke Izumi (Assistant Professor, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Application of AdS/CFT to non-equilibrium phenomena in external electric fields
August 16 (Mon) 13:00 - 15:00, 2021
Shunichiro Kinoshita (Collaborative Researcher, Faculty of Science and Engineering, Chuo University)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Non-Unitary TQFTs from 3d N=4 Rank-0 SCFTs
July 5 (Mon) 13:00 - 14:30, 2021
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Toward QCD-based description of dense baryonic matter
June 29 (Tue) 13:00 - 14:30, 2021
Yuki Fujimoto (Postdoctoral Scholars, Department of Physics, University of Washington, USA)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Black Hole Information Paradox and Wormholes
June 21 (Mon) 13:00 - 14:30, 2021
Kanato Goto (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
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.
Venue: via Zoom
Event Official Language: English
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Seminar
iTHEMS-phys Intro Meeting on June 7, 2021
June 7 (Mon) 13:00 - 14:30, 2021
Tomoya Naito (Ph.D. Student, Department of Physics, Graduate School of Science, The University of Tokyo)
Takeru Yokota (Postdoctoral Researcher, The Institute for Solid State Physics (ISSP), The University of Tokyo)
Naomi Tsuji (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))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
Venue: via Zoom
Event Official Language: English
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Seminar
iTHEMS-phys Intro Meeting on June 1, 2021
June 1 (Tue) 13:00 - 15:00, 2021
Kengo Kikuchi (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Enrico Rinaldi (Research Fellow, Physics Department, University of Michigan, USA)
Hiroshi Yokota (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))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
Venue: via Zoom
Event Official Language: English
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Seminar
iTHEMS-phys Intro Meeting on May 31, 2021
May 31 (Mon) 13:00 - 15:00, 2021
Ryo Namba (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Naritaka Oshita (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Yuki Yokokura (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Shigehiro Nagataki (Chief Scientist, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))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
Venue: via Zoom
Event Official Language: English
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Seminar
iTHEMS-phys Intro Meeting on May 25, 2021
May 25 (Tue) 13:00 - 15:00, 2021
Takuya Sugiura (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Takumi Doi (Senior Research Scientist, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))
Shoichiro Tsutsui (Special Postdoctoral Researcher, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))
Kanato Goto (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))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
Venue: via Zoom
Event Official Language: English
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Seminar
iTHEMS-phys Intro Meeting on May 24, 2021
May 24 (Mon) 13:00 - 14:30, 2021
Hidetoshi Taya (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Yuta Sekino (Visiting Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Ching-Kai Chiu (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))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
Venue: via Zoom
Event Official Language: English
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Seminar
iTHEMS-phys Intro Meeting on May 18, 2021
May 18 (Tue) 13:00 - 14:30, 2021
Masaru Hongo (Postdoctoral Research Associate, Physics Department, The University of Illinois at Chicago (UIC), USA)
Etsuko Itou (Contract Researcher, Strangeness Nuclear Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))
Nobuyuki Matsumoto (Special Postdoctoral Researcher, Computing Group, RIKEN BNL Research Center, RIKEN Nishina Center for Accelerator-Based Science (RNC))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
Venue: via Zoom
Event Official Language: English
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Seminar
iTHEMS-phys Intro Meeting on May 17, 2021
May 17 (Mon) 13:00 - 14:30, 2021
Tetsuo Hatsuda (Program Director, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Akira Harada (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Tsukasa Tada (Vice Chief Scientist, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))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
Venue: via Zoom
Event Official Language: English
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Seminar
Quantum mechanical description of energy dissipation and application to heavy-ion fusion reactions
February 16 (Tue) 13:00 - 14:30, 2021
Masaaki Tokieda (Ph.D. Student, Department of Physics, Graduate School of Science, Tohoku University)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Quantum kinetic theory for chiral and spin transport in relativistic heavy ion collisions and core-collapse supernovae
February 4 (Thu) 13:00 - 14:30, 2021
Di-Lun Yang (Assistant Professor, Faculty of Science and Technology, Keio University)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Many body problems from quarks to stellar evolutions
January 28 (Thu) 13:30 - 15:00, 2021
Nobutoshi Yasutake (Associate Professor, Chiba Institute of Technology)
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.
Venue: via Zoom
Event Official Language: English
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Seminar
Classical liquids and functional renormalization group
December 17 (Thu) 13:00 - 14:30, 2020
Takeru Yokota (Postdoctoral Researcher, The Institute for Solid State Physics (ISSP), The University of Tokyo)
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.
Venue: via Zoom
Event Official Language: English
128 events