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.

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.

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.

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