# Hot Topic

## Anew Calculation of Penguin Pooing Pressure by Hiroyuki Tajima

2020-08-28

As posted in the Ig Nobel Prize web page, our iTHEMS friend Hiroyuki Tajima (Kochi Univ., former member of RIKEN Nishina Center) has published an interesting work "Projectile Trajectory of Penguin’s Faeces and Rectal Pressure Revisited" with Fumiya Fujisawa (Katsurahama Aquarium). Find how the gauge/gravity duality in particle physics is useful to find out the incredible power of penguin’s rectum!

# Seminar Report

## iTHEMS Theoretical Physics Seminar by Dr. Takuya Shimazaki on August 21, 2020

2020-08-22

On August 21st (Fri.), Takuya Shimazaki (The University of Tokyo) gave an iTHEMS-phys seminar on an application of the Lefschetz thimble method to the Schwinger mechanism, or a particle production problem caused by strong electric fields. In the seminar, he has demonstrated a new formulation to estimate the particle production rate. The new formulation gives a good result even in some regimes where one cannot use the Dykhne–Davis–Pechukas (DDP) formula (a commonly used approximation in a two-level quantum system equivalent to the Schwinger mechanism). There were a lot of lively discussions, and the audience looked enjoying the 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

# Seminar Report

## Biology Seminar by Dr. Gen Kurosawa on August 26, 2020

2020-08-27

On August 26th, Gen Kurosawa gave a talk at the iTHEMS Biology seminar. The main topic of the talk was biological timing, and he introduced his work on mathematical modelling of circadian rhythm and hibernation. In addition, he also talked about his current effort in trying to apply theories developed in biology to understand the transaction network between companies. He clearly made a lot of effort to make the seminar accessible and enjoyable to people without background knowledge, and I'm sure many people appreciated that.

Modeling biological timing

August 26 at 10:00 - 11:00, 2020

# Upcoming Events

## 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)

Abstract:

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

## Seminar

### Maximal Regularity and Partial Differential Equations

September 8 at 16:00 - 18:10, 2020

Dr. Ken Furukawa (Postdoctoral Researcher, Prediction Science Laboratory, RIKEN Cluster for Pioneering Research (CPR))

The theory of maximal regularity is a powerful tool to get solutions having the best regularity to linear partial differential equations (PDEs) of parabolic type. The theory is also applicable to show well-posedness of various non-linear PDEs.

In the first part, We introduce the history of the development of the theory of maximal regularity and the way to apply non-linear PDEs.

In the second part, We give some applications to PDEs, e. g. the primitive equations, the Navier-Stokes equations, and elliptic equations with dynamic boundary conditions.

Venue: via Zoom

Event Official Language: English

## Seminar

### The Uchuu Simulations: Data Release 1 and Dark Matter Halo Concentrations

October 1 at 14:00 - 15:00, 2020

Dr. Tomoaki Ishiyama (Associate Professor, Institute of Management and Information Technologies)

We introduce the Uchuu suite of large high-resolution cosmological N-body simulations. The largest simulation, named Uchuu, consists of 2.1 trillion dark matter particles in a box of 2.0 Gpc/h. The highest resolution simulation, called Shin-Uchuu, consists of 262 billion particles in a box of 140 Mpc/h. Combining these simulations we can follow the evolution of dark matter haloes (and subhaloes) spanning from dwarf galaxies to massive galaxy cluster hosts. We present basic statistics, dark matter power spectra and halo (subhalo) mass function, to demonstrate the huge dynamic range and superb statistics of the Uchuu simulations. From the analysis of the evolution of the power spectra we conclude that our simulations are accurate enough from the Baryon Acoustic Oscillations up to very small scales. We also provide parameters of a mass-concentration model, which describes the evolution of halo concentrations, that reproduces our simulation data within 5% error for haloes with masses spanning nearly eight orders of magnitude at redshift 0<z<14. We make publicly available various N -body products, as part of Uchuu Data Release 1, on the Skies & Universes site. We also plan to release gravitational lensing maps, mock galaxy, X-ray cluster and active galactic nuclei catalogues in the near future.

Venue: via Zoom

Event Official Language: English

## Lecture

### Forefront of Modern Science: Frontiers in Mathematics, Astronomy, Physics, Biology and Computation

October 2 at 16:20 - 17:50, 2020

Dr. Tetsuo Hatsuda (Program Director, iTHEMS)

Dr. Yuka Kotorii (Visiting Scientist, iTHEMS / Associate Professor, Mathematics Program, Graduate School of Advanced Science and Engineering, Hiroshima University / Visiting Scientist, Mathematical Analysis Team, RIKEN Center for Advanced Intelligence Project (AIP))

Dr. Shigehiro Nagataki (Deputy Program Director, iTHEMS / Chief Scientist, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))

Dr. Makiko Nio (Senior Researcher, RIKEN Nishina Center for Accelerator-Based Science (RNC))

Dr. Ryosuke Iritani (Research Scientist, iTHEMS)

Dr. Ai Niitsu

Dr. Shigenori Otsuka (Research Scientist, iTHEMS / Research Scientist, Data Assimilation Research Team, RIKEN Center for Computational Science (R-CCS))

Dr. Emi Yukawa (Assistant Professor, Department of Physics, Faculty of Science Division I, Tokyo University of Science)

Venue: Changed to Zoom

Event Official Language: Japanese

# Paper of the Week

## Week 4 of August

2020-08-27

Title: Two relativistic Kondo effects from two HQETs

Author: Yasufumi Araki, Daiki Suenaga, Kei Suzuki, Shigehiro Yasui

arXiv: http://arxiv.org/abs/2008.08434v1

Title: Gravitational wave asteroseismology for low-mass neutron stars

Author: Hajime Sotani

arXiv: http://arxiv.org/abs/2008.09839v1

Title: Chirality-driven edge flow and non-Hermitian topology in active nematic cells

Author: Lisa Yamauchi, Tomoya Hayata, Masahito Uwamichi, Tomoki Ozawa, Kyogo Kawaguchi

arXiv: http://arxiv.org/abs/2008.10852v1

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