iTHEMS Weekly News Letter


Prof. Gordon Baym thumbnail

Prof. Gordon Baym received 2021 APS Medal for Exceptional Achievement in Research


Prof. Gordon Baym (iTHEMS Senior Visiting Scientist / UIUC) has received 2021 APS Medal for Exceptional Achievement in Research. This is the largest Society prize to recognize the achievement of researchers from across all fields of physics. This prize was established to recognize contributions of the highest level that advance our knowledge and understanding of the physical universe in all its facets. It is intended to celebrate scientific inquiry and the pursuit of knowledge. The citation says "For major discoveries in theoretical condensed matter and many-body physics, neutron star structure and composition, quark matter and quark-gluon plasma physics, and in atomic physics and ultracold quantum gases." Many congratulations, Gordon san!!


Prof. Christopher Bourne thumbnail

Dr. Chris Bourne received Best Paper Prize 2020, Journal of Physics A: Mathematical and Theoretical


It is our great pleasure to inform you that our iTHEMS colleague, Chris Bourne (Tohoku AIMR/ RIKEN iTHEMS), received Best Paper Prize 2020: Journal of Physics A (Mathematical and Theoretical). The Journal of Physics A Best Paper Prize has been awarded annually since 2009. All original research articles from 2018 and 2019 were eligible for consideration this year 2020. The publisher says "Nominations were assessed by the Section Editors and Editor-in Chief using the criteria of novelty, achievement, potential impact and presentation. your article was highly recommended and was considered to have excelled in all of these categories." Many congratulations, Chris!

Upcoming Events


iTHEMS Theoretical Physics Seminar

Lefschetz-thimble inspired analysis of the Dykhne–Davis–Pechukas method and an application for the Schwinger Mechanism

August 21 at 13:00 - 14:30, 2020

Dr. 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 two-level 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 Lefschetz-thimble 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 short-lived 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

Special Lecture

Tetsuo Hatsuda × Yoshinori Ohsumi × Sayaka Oki Online Discussion: "The Usefulness of 'Useless' Knowledge" Presented by iTHEMS & academist

August 22 at 13:00 - 15:30, 2020

Dr. Tetsuo Hatsuda (Program Director, iTHEMS)
Prof. Yoshinori Ohsumi (Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology)
Prof. Sayaka Oki (Graduate School of Economics, Department of Socio-Economic System, Nagoya University)



Venue: via Zoom

Event Official Language: Japanese


Math-Phys Joint Seminar

Geometric Perspective for the Theory of Hydrodynamic Limits

August 31 - September 1, 2020

Dr. Makiko Sasada (Associate Professor, Graduate School of Mathematical Sciences, The University of Tokyo)
Prof. Kenichi Bannai (Professor, Faculty of Science and Technology Department of Mathematics, Keio University)

This is a series of lectures on "Geometric Perspectives for Fluid Dynamic Limit Theory" by the following speakers:
[DAY 1: Aug 31] Dr. Makiko Sasada (University of Tokyo)
[DAY 2: Sept 1] Prof. Kenichi Bannai (Keio University)

One of the fundamental problems in the natural and social sciences is to explain macroscopic phenomena that we can observe from the rules governing the microscopic system giving rise to the phenomena. Hydrodynamic limit provides a rigorous mathematical method to derive the deterministic partial differential equations describing the time evolution of macroscopic parameters, from the stochastic dynamics of a microscopic large scale interacting system.

In the article "Topological Structures of Large Scale Interacting Systems via Uniform Locality" joint with Yukio Kametani, we introduce a general framework encompassing a wide variety of interacting systems in order to systematically investigate various microscopic stochastic large scale interacting systems in a unified fashion. In particular, we introduced a new cohomology theory called the uniformly local cohomology to investigate the underlying geometry of the interacting system. Our theory gives a new interpretation of the macroscopic parameters, the role played by the group action on the microscopic system, and the origin of the diffusion matrix associated to the macroscopic deterministic partial differential equation obtained via the space-time scaling limit of the microscopic system.

The purpose of the series of lectures is to introduce to the audience the theory of hydrodynamic limits, especially the relation between the macroscopic observables and the microscopic interacting system. We then explain our new perspective of how geometry comes into play in investigating the interacting system, and introduce the ideas and results of our article.

Venue: via Zoom

Event Official Language: English

Paper of the Week

Week 3 of August


Title: Gaussian concentration bound and Ensemble equivalence in generic quantum many-body systems including long-range interaction
Author: Tomotaka Kuwahara, Keiji Saito

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