# Seminar Report

## iTHEMS Theoretical Physics Seminar by Prof. Keisuke Izumi on September 13, 2021

2021-10-11

At the seminar organized by the iTHEMS-physics study group, Prof. Keisuke Izumi discussed the S-matrix unitarity toward UV completion. Einstein gravity is not renormalizable and does not hold perturbative unitarity at high energy. This is the main reason why the construction of quantum gravity is difficult. A conjecture was proposed by Llewellyn Smith, "renormalizablility and tree-unitarity at high energy give the same conditions". This conjecture would be important because it shows that, if a theory is constructed such that unitarity is satisfied, renormalizablility holds automatically, and vice versa.

Unfortunately, a counterexample was pointed out. If a theory involves higher derivatives, there exists a theory which is renormalizable but does not satisfy tree-unitarity. A candidate of quantum gravity, the quadratic gravity (R_{\mu\nu}^2 gravity), is one of the examples. Therefore, Llewellyn Smith's conjecture would not be useful for the discussion of quantum gravity. Then, Prof. Izumi and his collaborators introduced a new conjecture, "renormalizablility and S-matrix unitarity (or often called pseudo-unitarity) at high energy give the same conditions".

In his talk, Prof. Izumi explained Llewellyn Smith's conjecture and his contribution to it. Then, he introduced his new conjecture. Finally, he showed that his conjecture works well even in theories with higher derivatives.

Reported by Ryo Namba

S-matrix Unitarity toward UV Completion

September 13 at 13:30 - 15:00, 2021

# Seminar Report

## Quantum Matter SG seminar by Prof. Bohm-Jung Yang on October 7, 2021

2021-10-12

The Quantum Matter study group had the honor to invite Prof. Bohm-Jung Yang to give a talk on October 7th. He talked about wave function geometry and anomalous Landau levels of flat bands. He started with a heuristic introduction by explaining the geometry matters in a flat band, including the notion of the (Hilbert-Schmidt) quantum distance and the quantum metric. Particularly, he used a Kagome lattice as an example of the singular touching point of the flat band and quadratic band locked by the geometry. Furthermore, in the presence of a magnetic field, the singular flat band evolves into very dense anomalous Landau levels. Remarkably, the relation between the Landau level spreading and the maximum of the quantum distance can be described by a universal formula, independent of material parameters. In consequence, deducing the Landau level spreading in (spectroscopic) experiments would allow for the measurement of the quantum distance, thus probing the quantum geometry of the wave functions. The study was extended to the (spin-orbit-coupled) Lieb lattice with one flat band sandwiched by two dispersive bands. In this case, the Landau level spreading of the isolated flat band is determined by the fidelity tensor. This talk showed us the interesting and subtle interplay between the band flatness and the Landau levels.

Reported by Ching-Kai Chiu and Chen-Hsuan Hsu (CEMS, RIKEN)

Wave function geometry and anomalous Landau levels of flat bands

October 7 at 16:00 - 17:15, 2021

# Award

## Nagisa Hiroshima received the Award for Female Researchers of the University of Toyama

2021-10-13

University of Toyama has announced that Nagisa Hiroshima (Visiting Scientist, iTHEMS) received "The Award for Female Researchers of the University of Toyama". Congratulations!

# Upcoming Events

## Conference

### Can social issues be solved by mathematical science? -attempts and challenges

October 26 at 10:00 - 17:00, 2021

Dr. Tetsuo Hatsuda (Program Director, iTHEMS)

Dr. Masato Wakayama (Fundamental Mathematics Research Principal, NTT Institute for Fundamental Mathematics)

Prof. Takashi Sakajo (Professor, Department of Mathematics, Kyoto University)

Prof. Shingo Iwami (Professor, Division of Biological Science, Graduate School of Science, Nagoya University)

Dr. Hirotaka Irie (Assistant Manager, DENSO Corporation)

In recent years, the importance of mathematical sciences has been increasingly recognized in various fields, as exemplified by the rapid progress of AI technology and the development of DX (Digital Transformation) in companies.

In academia, research centers have been established in fields such as space, materials, life, and medicine, where experts in the mathematical sciences play an important role in research activities in their respective fields.

At the same time, the universality of mathematics and the quantitative and predictive nature of data analysis are also being considered useful in industry, and some companies are actively using mathematical science in their own business. Some companies are actively utilizing mathematical science in their business.

In this symposium, researchers who are conducting research with the mission of returning research using mathematical science to society and implementing it will gather to discuss, based on the results of their cutting-edge research, "Can social issues be solved with mathematical science? -Attempts and Challenges" and discuss the role of mathematical science in society.

Venue: Hybrid Format (Noyori Conference Hall, Nagoya University and Zoom)

Event Official Language: Japanese

## Colloquium

### High-Energy Neutrino Astrophysics in the Multimessenger Era

October 28 at 15:00 - 16:30, 2021

Prof. Kohta Murase (Associate Professor, Pennsylvania State University, USA)

The discovery of high-energy cosmic neutrinos opened a new window of astroparticle physics. Their origin is a new mystery in the field, which is tightly connected to the long-standing puzzle about the origin of cosmic rays. I will give an overview of the latest results on high-energy neutrino and cosmic-ray observations, and demonstrate the power of "multimessenger" approaches. In particular, I will show that the observed fluxes of neutrinos, gamma rays, and extragalactic cosmic rays can be understood in a unified manner. I will also highlight the recent developments about astrophysical neutrino emission from supermassive black holes and violent transient phenomena. Possibilities of utilizing high-energy neutrinos as a probe of heavy dark matter may be discussed.

Venue: via Zoom

Event Official Language: English

# Person of the Week

## Self-introduction:Gilberto Nakamura

2021-10-13

My name is Gilberto Nakamura and I joined iTHEMS as a postdoctoral researcher in Oct 2021, after working as a postdoctoral fellow at IJCLab/CNRS in France.

I'm interested on the role of noise and correlations in biologically inspired systems. The relation between fluctuations and correlations lies at the heart of the theory of critical phenomena, with ramifications in Statistical Physics and Quantum Field Theory. Fluctuations in biological systems are further exacerbated by the innate variability of organisms, adding richness to the dynamics and promoting the emergence of complex behavior. More recently, I have worked on disease-spreading dynamics, viral infections, and migration of cancer cells, all of which have a significant impact on human health and require continued interdisciplinary efforts across Mathematics, Physics, and Biology.

My current focus has been on bottom-up approaches, starting from microscopic stochastic models and working them out into the hydrodynamic limit, with support from numerical Monte Carlo simulations, followed by parameter extraction from data. I am sure the interdisciplinary environment fostered by iTHEMS will promote new collaborations and further advance my research goals.

# Paper of the Week

## Week 3, October 2021

2021-10-14

Title: The genome of Shorea leprosula (Dipterocarpaceae) highlights the ecological relevance of drought in aseasonal tropical rainforests

Author: Kevin Kit Siong Ng, Masaki J. Kobayashi, Jeffrey A. Fawcett, Masaomi Hatakeyama, Timothy Paape, Chin Hong Ng, Choon Cheng Ang, Lee Hong Tnah, Chai Ting Lee, Tomoaki Nishiyama, Jun Sese, Michael J. O’Brien, Dario Copetti, Mohd Noor Mat Isa, Robert Cyril Ong, Mahardika Putra, Iskandar Z. Siregar, Sapto Indrioko, Yoshiko Kosugi, Ayako Izuno, Yuji Isagi, Soon Leong Lee, Kentaro K. Shimizu

Journal Reference: Commun Biol 4, 1166 (2021)

doi: https://doi.org/10.1038/s42003-021-02682-1

Title: Effect of advancing age on the reproductive performance of Japanese Thoroughbred broodmares

Author: Jeffrey A. FAWCETT, Hideki INNAN, Takeru TSUCHIYA, Fumio SATO

Journal Reference: J. Equine Sci. Vol. 32, No. 2, pp. 31–37 (2021)

doi: https://doi.org/10.1294/jes.32.31

Title: Universal relation for supernova gravitational waves

Author: Hajime Sotani, Tomoya Takiwaki, Hajime Togashi

arXiv: http://arxiv.org/abs/2110.03131v2

Title: Topology and symmetry of circular photogalvanic effect in the chiral multifold semimetals: a review

Author: Congcong Le, Yan Sun

doi: https://doi.org/10.1088/1361-648X/ac2928

arXiv: http://arxiv.org/abs/2110.03434v1

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