# Seminar Report

## Biology Seminar on May 27, 2020

2020-06-01

On 27 May, Ayaka Kato, The University of Tokyo, gave a talk at the 6th iTHEMS Biology Seminar. In this seminar, Ayaka talked about the results of the research on mathematical modeling of dopamine-related phenomena. It was not previously known how dopamine is involved in motivation, but in Ayaka's previous studies, the mathematical model from several previous experiments was proposed. In this seminar, Ayaka presented a new model that incorporates learning decay and successfully reproduces the real behavior on a computer simulation based on her new model. Since modeling the relationship between dopamine and motivation is very important both psychologically and medically, I felt that the results of these studies would not only benefit basic research but would also serve as a basis for general-purpose practical science and improve their research motivation.

Forgetting in Reinforcement Learning Links Sustained Dopamine Signals to Motivation

May 27 at 10:00 - 10:45, 2020

# Seminar Report

## QFT-core Seminar by Dr. Ryusuke Hamazaki on May 29, 2020

2020-06-01

The second QFT-core seminar entitled “Localization and universality in non-Hermitian many-body systems” given by Dr. Ryusuke Hamazaki (RIKEN Hakubi/iTHEMS) was held on May 29.

Non-Hermitian physics is now one of the topics studied actively, and he is one of the world-leading physicists of this topic. In the seminar, first, he introduced the basic ideas of thermalization of the isolated quantum systems and non-Hermitian physics with simple examples. After that, some cutting-edge progress of non-Hermitian many-body localization, and universality of non-Hermitian random matrices were introduced.

The seminar was held via the Zoom online conference system. Around 20 people participated in the seminar and joined the active discussion.

Localization and universality in non-Hermitian many-body systems

May 29 at 15:00 - 16:30, 2020

# Seminar Report

## Math Seminar by Dr. Masaki Taniguchi

2020-05-29

The iTHEMS Math seminar entitled "Knotted 2-spheres in the 4-space and Yang-Mills gauge theory," by Dr. Masaki Taniguchi, was held on 27 May.

In the first part, the speaker reviewed that classical knot theory and history of knot. Especially, he introduced that one and two dimensional knot theory, and gave many examples. For one dimensional knot theory, he explained the fundamental problem of knot theory, i.e., the problem of classifying 1-knots up to equivalent. As an example, he introduced a knot invariant coming from 3-colorings. For two dimensional knot theory, he explained the problem of how we write diagrams of 2-knots in four dimensional Euclidean space. Then he introduced the motion picture.

In the second part, the speaker focuses on a problem considered in differential topology. First, he explained that the fundamental problem in differential topology. Next, he introduced gauge theory and some examples. Finally, as the main result of the talk, he explained his theorem about the difference between continuous and smooth two dimensional knots. He then introduced that the proof uses Yang-Mills gauge theory for 4-manifolds obtained by the surgery of 2-knots.

Knotted 2-spheres in the 4-space and Yang-Mills gauge theory

May 27 at 16:00 - 18:10, 2020

# Upcoming Events

## Seminar

### The effect of the early kinetic decoupling in a fermionic dark matter model

June 12 at 10:00 - 11:00, 2020

Dr. Tomohiro Abe (Assistant Professor, Division of Theoretical Studies, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University)

*Detailed information about the seminar refer to the email

Venue: via Zoom

Event Official Language: English

## Seminar

### Dark Matter Heating vs. Rotochemical Heating in Old Neutron Stars

June 22 at 16:00 - 17:00, 2020

Prof. Koichi Hamaguchi (Associate professor, School of Science, The University of Tokyo)

*Detailed information about the seminar refer to the email

Venue: via Zoom

Event Official Language: English

# Paper of the Week

## Week 1 of June

2020-06-04

Title: Probing the Universality of Topological Defect Formation in a Quantum Annealer: Kibble-Zurek Mechanism and Beyond

Author: Yuki Bando, Yuki Susa, Hiroki Oshiyama, Naokazu Shibata, Masayuki Ohzeki, Fernando Javier Gómez-Ruiz, Daniel A. Lidar, Adolfo del Campo, Sei Suzuki, Hidetoshi Nishimori

arXiv: http://arxiv.org/abs/2001.11637v3

Title: Effective quantum kinetic theory for spin transport of fermions with collsional effects

Author: Di-Lun Yang, Koichi Hattori, Yoshimasa Hidaka

arXiv: http://arxiv.org/abs/2002.02612v2

Title: Entanglement of Local Operators and the Butterfly Effect

Author: Jonah Kudler-Flam, Masahiro Nozaki, Shinsei Ryu, Mao Tian Tan

arXiv: http://arxiv.org/abs/2005.14243v1

Title: Clustering of conditional mutual information for quantum Gibbs states above a threshold temperature

Author: Tomotaka Kuwahara, Kohtaro Kato, Fernando G. S. L. Brandão

arXiv: http://arxiv.org/abs/1910.09425v2

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