# Research News

## Dr. Nagisa Hiroshima and Dr. Yoshiyuki Inoue were highlighted in an article of RIKEN 2020 about Dark Matter Search

2020-09-02

It is our great pleasure to inform you that our iTHEMS colleagues, Nagisa Hiroshima and Yoshiyuki Inoue, are highlighted in RIKEN Annual Report 2020 for their leading role in organizing the iTHEMS "Dark Matter Working Group". This working group aims at creating a new domestic and international network of theoretical and experimental physicists who are interested in dark matter search.

# Award

## Dr. Martin Skrodzki received the best slammer award at GAIN20 Science Slam on Aug. 28, 2020.

2020-08-31

The GAIN Science Slam is all about science communication. The objective is to impart current research results to a diverse audience in an understandable and entertaining way. Science Slams started in German university towns in the mid-2000s: Darmstadt, Braunschweig, Hamburg. Today, Science Slams are held all over Germany on a weekly basis. The virtual GAIN20 Science Slam took place in the Auditorium of the virtual GAIN20 conference on August 28, 2020. The annual GAIN conference is the largest German science and research career fair in the US. Early career researchers and representatives from all areas of the German research landscape come together for two days of exchange, learning and networking in a virtual space.

Seven international researchers from various fields presented their findings in a five-minute pitch in front of the virtual audience. This virtual GAIN audience was the Science Slam Jury. The best slammer received a cash prize of $3,000, proudly presented by the German Center for Research and Innovation (DWIH). This year's winner is Dr. Martin Skrodzki from RIKEN iTHEMS. He gave a talk on seeing, recognizing, and self-driving cars. The talk is available on YouTube.

# Hot Topic

## Dr. Jason Chang was ranked in the list of the most downloaded physics papers published in Scientific Reports in 2019

2020-09-02

It is our great pleasure to inform you that the paper on quantum annealing by our iTHEMS colleague, Jason Chang, was ranked No.14 of the most downloaded physics papers published in Scientific Reports in 2019.

# Seminar Report

## iTHEMS Math-Phys joint seminar was held on August 31 and September 1, 2020

2020-09-03

The iTHEMS Math-Phys joint seminar was held on August 31st and September 1st, inviting Makiko Sasada from University of Tokyo and Kenichi Bannai from Keio university / RIKEN AIP. This was a series of lectures entitled “Geometric Perspective for the Theory of Hydrodynamic Limits”. They explained to us their recent joint work with Yukio Kametani on hydrodynamic limits from algebraic/geometric view point.

On Day 1, Sasada-san gave an introduction to hydrodynamic limits, and explained the motivation of the joint work and the key ideas. One of the goals of the theory of hydrodynamic limits is to derive macroscopic dynamics from microscopic evolution equations rigorously. There have been many results to this problem, but all of them depend on specific microscopic models. The long term goal of this joint work is to construct an abstract and universal theory of hydrodynamic limits. One of the most important ingredients of the theory of hydrodynamic limits is the “decomposition of closed forms”, which have been obtained by Varadhan and other people using very technical argument depending on models. One of the aims of this work is to give a more general and clear understanding of this type of decompositions. Their strategy is as follows: the microscopic data can be divided into topological (geometric) part and stochastic (analytic) part. For discrete models, the former one is modeled by a directed graph, the set of states at each vertex, and the interaction through edges. A typical analytic datum is the jump rate, i.e., the frequency of interaction. They observed that some important feature of hydrodynamic limits depends only on the geometric data, and as a consequence, they could avoid ad-hoc analytic estimations. Moreover, they obtain a version of Varadhan’s decomposition in a very general setting.

On Day 2, Bannai-san gave a precise mathematical formulation of their main results and proofs. As explained above, the geometric part of microscopic model is given by a directed graph, a pointed set of states, and a function which represents the interaction through edges. From this set of data, we can form a configuration space, each point of which corresponds to a possible state on the graph (The interaction data induce the transition structure on the configuration space). On the configuration space, they consider a special type of functions / forms called “uniformly local functions / forms”, and construct a cohomology theory (uniformly local cohomology) associated to them. Surprisingly, the uniformly local cohomology captures all conserved quantities (macroscopic observables). Moreover, from this fact, they can derive a local form version of Varadhan’s decomposition. An important ingredient of the proof is the group cohomology, which is often used in the field of number theory. They assume the existence of a free group action on the graph (which is valid in many important examples), and apply a general theory of group cohomology. It is very surprising that a fundamental result in hydrodynamic limits is derived from an abstract algebraic theory, and it will provide us a new and clear understanding of this field.

Geometric Perspective for the Theory of Hydrodynamic Limits

August 31 - September 1, 2020

# Seminar Report

## Biology Short Talk by Dr. Ryosuke Iritani on September 2, 2020

2020-09-03

On September 2, Ryosuke Iritani gave a lecture at iTHMES Biology Seminar. In this seminar, Ryo explained the principles of evolution in an easy-to-understand way, using examples such as the diversification of pet dogs and cruciferous plants, and changes in the structure of the gecko's hands. Especially, the formulation of adaptive evolution using Fokker planck equarion was introduced. His seminar will be very useful as a basic knowledge of evolutionary biology and mathematical biology that will be covered in future seminars.

The hitch-hiker’s guide to
the concept of
adaptive dynamics

September 2 at 10:00 - 10:30, 2020

# Upcoming Events

## 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

## Workshop

### The 2nd Heidelberg-Kyoto-RIKEN Workshop, Medicine and Math

September 18 - 19, 2020

Dr. Tetsuo Hatsuda (Program Director, iTHEMS)

Prof. Takashi Sakajo (Senior Visiting Scientist, iTHEMS / Professor, Department of Mathematics, Kyoto University / Senior Visiting Scientist, Prediction Science Laboratory, RIKEN Cluster for Pioneering Research (CPR))

Prof. Motomu Tanaka (Professor, Heidelberg University / Professor, Center for Integrative Medicine and Physics, Kyoto University Institute for Advanced Study (KUIAS))

Venue: via Online

Event Official Language: Japanese

## 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, RIKEN Astrophysical Big Bang Laboratory)

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

Dr. Ryosuke Iritani (Research Scientist, iTHEMS)

Dr. Ai Niitsu (Postdoctoral Researcher, Theoretical Molecular Science Laboratory, RIKEN)

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

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 1 of September

2020-09-03

Title: Untangling the complexity of market competition in consumer goods -A complex Hilbert PCA analysis

Author: Makoto Mizuno, Hideaki Aoyama, Yoshi Fujiwara

arXiv: http://arxiv.org/abs/2008.11327v1

Title: Parity operation for Majorana neutrinos

Author: Kazuo Fujikawa

arXiv: http://arxiv.org/abs/2008.11390v1

Title: Barthelonids represent a deep-branching metamonad clade with mitochondrion-related organelles predicted to generate no ATP

Author: Euki Yazaki, Keitaro Kume, Takashi Shiratori, Yana Eglit, Goro Tanifuji, Ryo Harada, Alastair G. B. Simpson, Ken-ichiro Ishida, Tetsuo Hashimoto, Yuji Inagaki

URL: https://royalsocietypublishing.org/doi/10.1098/rspb.2020.1538

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