On April 22 (Fri), we had the first iTHEMS colloquium of FY2022 by inviting Hong-Yan Shih from Academia Sinica, Taiwan. After reviewing the turbulent phenomena in various area of science, she discussed how the turbulence occurs by increasing the flow velocity and how one can develop an effective theory to describe the critical region of laminar-turbulent transition. Then she discussed a remarkable mathematical relation between the effective theory with the predator-prey dynamics in ecology and showed a characteristic super exponential scaling law. The topic was an ideal subject for the interdisciplinary talk, and there were many questions from the researchers with different scientific backgrounds.

As the alternative for the lectures at RIKEN’s annual open house, iTHEMS held another online lecture event for the general public with the help of Academist Inc., on April 24th, 2022.
This year, the lectures were Masaki Taniguchi, Hidetoshi Taya, Akira Harada, Yingying and Euki Yazaki, who all gave splendid public lectures accessible even to junior-high school students. Each lecturer also served as a commentator to another lecture, asking questions on behalf of the audience.
During the lunch break, Program Director Hatsuda showed the offices of iTHEMS and around. The event was moderated by Ms. Michibayashi from Academist; Her facilitation with a wit kept the event lively. At one time during the event, more than two hundred audiences participated.

RIKEN physicists have put quantum computing and deep learning through their paces and found that they are powerful tools for gleaning insights into new theories of quantum gravity [1]. They could thus help solve one of the most formidable challenges in modern physics—developing a theory of gravity that jives with quantum physics.

When Einstein nutted out his theory of general relativity in 1915, his only tools were pen and paper. The same was true of the pioneers of quantum theory. But the next major breakthrough in theoretical physics could be made with help from emerging technologies such as quantum computers and machine learning, Enrico Rinaldi of RIKEN Theoretical Quantum Physics Laboratory thinks. “I believe these technologies are poised to transform the way we do theoretical physics,” he says.

To read more, please visit the related link.

Takemasa Miyoshi (R-CCS Team Leader/ iTHEMS Deputy Director) received "2022 MEXT Commendation for Science and Technology" for "Study on Big Data Assimilation to Innovate Numerical Weather Forecasting". Congratulations!

Yuji Sugita (CPR Chief Scientist/ iTHEMS Senior Research Scientist) received "2022 MEXT Commendation for Science and Technology" for "Theoretical Study on Dynamic Structure of Biomolecules in the Intracellular Environment". Congratulations!

In this lecture series, Professor Ozawa gave an introduction to topological insulators which are materials whose wavefunctions show nontrivial topological structures in momentum space. In the first two lectures, he introduced the so-called Su-Schrieffer-Heeger model and the bulk-edge correspondence which links edge states with winding number of certain operator in the Hamitonian. Such correspondence has its origin in mathematics called Toeplitz Index theorem which is a special case of Atiyah-Singer index theorem.

In the last two lectures, Chern insulators and quantum metrics are introduced. Eigenvectors of the Hamiltonian define a map from the momentum space (typically a torus) to a complex projective space. The pullback Fubini-Study metric (and standard Kahler form) defines the so-called quantum metric (and Berry curvature) on the momentum space. Using Chern-Weil theory, Chern classes/characters are then defined. Chern classes which are originally notions from differential geometry/topology play an important role in topological insulators. A necessary and sufficient condition is also given when the above mentioned map is an immersion and realises momentum space as a Kahler submanifold of the projective space.

Reported by Yalong Cao

On April 22, there was a math seminar by Dr. Cédric Ho Thanh. In the first half, he explained the recurrence theorems for the topological Markov chain. In the second half, he explained the sketch of the proof.

Reported by Keita Mikami

Dr. Masahiro Iwamoto gave a presentation on his recent three-dimensional (3D) particle-in-cell (PIC) simulation of relativistic shocks and application of the results of the 3D-PIC simulations to astrophysical phenomena. For example, the origin of fast radio bursts (FRBs; Lorimer et al. 2007) is one of the unsolved problems in astrophysics. Many observations of FRBs indicate that FRBs must be coherent emission in the sense that coherently moving electrons radiate electromagnetic waves. In relativistic shocks, it is well known that coherent electromagnetic waves are excited by synchrotron maser instability (SMI) in the shock transition (Hoshino & Arons 1991). The SMI is also known as the emission mechanism of coherent radio sources such as auroral kilometric radiation at Earth and Jovian decametric radiation. Recently, some models of fast radio burst based on the coherent emission from relativistic shock via the SMI have been proposed (e.g., Lyubarsky 2014; Beloborodov 2017; Plotnikov & Sironi 2019; Metzger et al. 2019) and the SMI in the context of relativistic shocks attracts more attention from astrophysics. In this seminar, by performing the world’s first 3D-PIC simulation of relativistic shocks, he demonstrated that large-amplitude electromagnetic waves are indeed excited by the SMI even in 3D and that the wave amplitude is significantly amplified and comparable to that in pair plasmas due to a positive feedback process associated with ion-electron coupling. Based on the simulation results, he discussed the applicability of the SMI for FRBs.

Reported by Shigehiro Nagataki

Title: Visualizing Lamb Waves From a Volcanic Eruption Using Meteorological Satellite Himawari-8
Author: Shigenori Otsuka
Journal Reference: Geophysical Research Letters, 49, e2022GL098324 (2022)
doi: https://doi.org/10.1029/2022GL098324