iTHEMS Theoretical Physics Seminar
76 events

iTHEMSphys Intro Meeting on May 24, 2021
May 24 (Mon) at 13:00  14:30, 2021
Hidetoshi Taya (Special Postdoctoral Researcher, iTHEMS)
Yuta Sekino (Visiting Researcher, iTHEMS)
ChingKai Chiu (Senior Research Scientist, iTHEMS)13:0013:20 [JST] Hidetoshi Taya 13:2013:40 [JST] Yuta Sekino 13:4014:00 [JST] ChingKai Chiu 14:00 Free discussion
Venue: via Zoom
Event Official Language: English

iTHEMSphys Intro Meeting on May 18, 2021
May 18 (Tue) at 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 AcceleratorBased Science (RNC))
Nobuyuki Matsumoto (Special Postdoctoral Researcher, Computing Group, RIKEN BNL Research Center, RIKEN Nishina Center for AcceleratorBased Science (RNC))13:0013:20 [JST] Masaru Hongo 13:2013:40 [JST] Etsuko Itou 13:4014:00 [JST] Nobuyuki Matsumoto 14:00 Free discussion
Venue: via Zoom
Event Official Language: English

iTHEMSphys Intro Meeting on May 17, 2021
May 17 (Mon) at 13:00  14:30, 2021
Tetsuo Hatsuda (Program Director, iTHEMS)
Akira Harada (Special Postdoctoral Researcher, iTHEMS)
Tsukasa Tada (Vice Chief Scientist, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for AcceleratorBased Science (RNC))13:0013:20 [JST] Tetsuo Hatsuda 13:2013:40 [JST] Akira Harada 13:4014:00 [JST] Tsukasa Tada 14:00 Free discussion
Venue: via Zoom
Event Official Language: English

Seminar
Quantum mechanical description of energy dissipation and application to heavyion fusion reactions
February 16 (Tue) at 13:00  14:30, 2021
Masaaki Tokieda (Graduate students, Department of Physics, Tohoku University)
For theoretical description of heavyion 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 coupledchannels method with a few number of internal states has been applied, and it has succeeded in explaining subbarrier fusion reactions. While each method succeeds in each energy range, a unified description of heavyion fusion reactions from subbarrier 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 heavyion 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 heavyion fusion reactions.
Venue: via Zoom
Event Official Language: English

Seminar
Quantum kinetic theory for chiral and spin transport in relativistic heavy ion collisions and corecollapse supernovae
February 4 (Thu) at 13:00  14:30, 2021
DiLun 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 spinorbit interaction. The quark gluon plasmas produced from relativistic heavy ion collisions (HIC) and the corecollapse 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

Seminar
Many body problems from quarks to stellar evolutions
January 28 (Thu) at 13:30  15:00, 2021
Nobutoshi Yasutake (Associate Professor, Chiba Institute of Technology)
The manybody 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 manybody problems, and also hadronic matter as quantum manybody 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 firstprinciple, they are sometimes useful to understand manybody quantum properties. In this talk, we introduce the current status of our color molecular dynamics.
Venue: via Zoom
Event Official Language: English

Classical liquids and functional renormalization group
December 17 (Thu) at 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 manybody 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 higherorder correlation functions to systematically improve the accuracy will be shown. I will also present a numerical demonstration in a onedimensional 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

Seminar
Conserved charges in gravity and entropy
December 10 (Thu) at 13:00  14:30, 2020
Sinya Aoki (Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
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.
Venue: via Zoom
Event Official Language: English

Seminar
KPZ equation, attractive bosons, and the Efimov effect
December 3 (Thu) at 13:00  14:30, 2020
Yusuke Nishida (Associate Professor, Department of Physics, Tokyo Institute of Technology)
The KardarParisiZhang (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 threeboson 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.
Venue: via Zoom
Event Official Language: English

Seminar
Some idea on quantum tunneling via Lefschetz thimbles
November 12 (Thu) at 10:30  12:00, 2020
Yuya Tanizaki (Special Postdoctoral Researcher, Theory Group, RIKEN Nishina Center for AcceleratorBased Science (RNC) / Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
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 realtime path integral for the symmetric doublewell 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.
Venue: via Zoom
Event Official Language: English

Seminar
Toward simulating Superstring/Mtheory on a Quantum Computer
October 23 (Fri) at 17:00  18:00, 2020
Masanori Hanada (Department of Mathematics, University of Surrey, UK)
We present a framework for simulating superstring/Mtheory on a quantum computer, based on holographic duality. Because holographicduality maps superstring/Mtheory to quantum field theories (QFTs), we can study superstring/Mtheory 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 BerensteinMaldacenaNastase (BMN) matrix model. Supersymmetric matrix models have natural applications to superstring/Mtheory and gravitational physics, in an appropriate limit of parameters. Furthermore, for certain states in the BerensteinMaldacenaNastase (BMN) matrix model, several supersymmetric quantum field theories dual to superstring/Mtheory 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 YangMills on quantum computer. If you would like to participate, please register using the form below.
Venue: via Zoom
Event Official Language: English

Seminar
Realistic shell model and chiral threebody force
October 22 (Thu) at 13:30  15:00, 2020
Tokuro Fukui (Researcher, Yukawa Institute for Theoretical Physics, Kyoto University)
We show an evolution to derive the effective Hamiltonian in the shellmodel framework starting from two and threebody interactions based on the chiral effective field theory. A new way to calculate threebody matrix elements of the chiral interaction with the nonlocal regulator is proposed. We apply our framework to the pshell nuclei and perform benchmark calculations to compare our results with those by an ab initio nocore shellmodel. We report that our results are satisfactory and the contribution of the threebody force is essential to explain experimental lowlying spectra of the pshell nuclei. We discuss the contribution of the threebody force on the effective singleparticle energy extracted from the monopole interaction. Next, we investigate the shell evolution on the pfshell nuclei. We show that the monopole component of the shellmodel effective Hamiltonian induced by the threebody force plays an essential role to account for the experimental shell evolution. Moreover, we present our latest results on the investigation of the possible neutron dripline of the Ca isotopes. Finally, we discuss very neutronrich systems, namely, the oxygen isotopes at the dripline and beyond, where the interplay between the threebody force and continuum states plays an important role. If you would like to participate, please register using the form below.
Venue: via Zoom
Event Official Language: English

Seminar
Lefschetzthimble inspired analysis of the Dykhne–Davis–Pechukas method and an application for the Schwinger Mechanism
August 21 (Fri) at 13:00  14:30, 2020
Takuya Shimazaki (Researcher, Hadron Theory Group, The University of Tokyo)
Dykhne–Davis–Pechukas (DDP) method is a common approximation scheme for the transition probability in twolevel quantum systems, as realized in the Landau–Zener effect, leading to an exponentially damping form comparable to the Schwinger pair production rate. We analyze the foundation of the DDP method using a modern complex technique inspired by the Lefschetzthimble method. We derive an alternative and more adaptive formula that is useful even when the DDP method is inapplicable. As a benchmark, we study the modified Landau–Zener model and compare results from the DDP and our methods. We then revisit a derivation of the Schwinger Mechanism of particle production under electric fields using the DDP and our methods. We find that the DDP method gets worse for the Sauter type of shortlived electric pulse, while our method is still a reasonable approximation. We also study the Dynamically Assisted Schwinger Mechanism in two methods.
Venue: via Zoom
Event Official Language: English

Seminar
NambuGoldstone fermion in a BoseFermi mixture with an explicitly broken supersymmetry
August 7 (Fri) at 13:00  14:30, 2020
Hiroyuki Tajima (PhD, Department of Natural Science, Kochi University)
Supersymmetry, which is a symmetry associated with interchange between bosons and fermions, is one of the most important symmetries in highenergy physics but its evidence has never been observed yet. Apart from whether supersymmetric partners such as squark exist or not in our world, it is an interesting problem to explore the consequences of the supersymmetry in an ultracold atomic gas. In this study, we address the NambuGoldstone mode called Goldstino associated with the spontaneous supersymmetry breaking in a BoseFermi mixture. While the explicit supersymmetry breaking is unavoidable even in cold atomic systems, the energy gap in Goldstino spectra can be measured in such atomic systems. By comparing the energy gaps obtained from the GellMannOakesRenner relation and the random phase approximation, we elucidate how the Goldstino acquires the energy gap due to the explicit breakings. We also show effects of Goldstino pole on the fermionic singleparticle spectral functions, which can be measured in the recent experiments.
Venue: via Zoom
Event Official Language: English

Seminar
Complex Langevin study of an attractively interacting twocomponent Fermi gas in 1D with population imbalance
July 10 (Fri) at 13:30  14:30, 2020
Shoichiro Tsutsui (Special Postdoctoral Researcher, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for AcceleratorBased Science (RNC))
We investigate an attractively interacting twocomponent Fermi gas in 1D described by the GaudinYang model with population imbalance. While the GaudinYang model is known as a solvable model based on the thermodynamic Bethe ansatz, the binding energy and mass of poralon at finite temperature and moderate impurity density are still unknown. Moreover, in such a system, quantum Monte Carlo simulation suffers from the sign problem because the population imbalance makes the fermion determinant nonpositive definite. In this study, we apply complex Langevin method, a holomorphic extension of the stochastic quantization to overcome the sign problem. We first confirm our numerical results satisfy a criteria for correct convergence [1], and present how the polaron energy depends on temperature and density of impurity. We also compare our results with a recent study based on a diagrammatic approach [2].
Venue: via Zoom
Event Official Language: English

Field theoretical approach to relativistic hydrodynamics
June 12 (Fri) at 13:00  14:30, 2020
Masaru Hongo (Visiting Scientist, iTHEMS / Postdoctoral Research Associate, Physics Department, The University of Illinois at Chicago (UIC), USA)
Hydrodynamics is a lowenergy effective theory of a conserved charge density, which describes a longdistance and longtime behavior of manybody systems. It is applicable not only to a nonrelativistic weaklyinteracting dilute gas but also a relativistic stronglyinteracting dense liquid like a quarkgluon plasma. The main purpose of this seminar is to explain how we can derive the hydrodynamic equation from the underlying fieldtheoretical description of systems [13]. Our derivation is based on the recent development of nonequilibrium statistical mechanics, and we show that the procedure to derive hydrodynamic equations is similar to the socalled renormalized/optimized perturbation theory. Also, to describe transport phenomena in local thermal equilibrium, we give a pathintegral formula for a thermodynamic functional, which results in the emergence of thermally induced curved spacetime [2]. These results enable us to derive hydrodynamic equation based on quantum field theories.
Event Official Language: English
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