# Coffee Meeting Log

2024-04-12

## Singularity Theorems

Shigehiro Nagataki (Deputy Program Director, iTHEMS / Chief Scientist, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))

I am happy to introduce the Singularity Theorem, which was proved by Roger Penrose in 1965. He won the Nobel Prize in Physics in 2020 by the proof. I hope you will feel the outline of the proof and understand that the Singularity corresponds to a point outside of spacetime. If there is 1 minute left in my presentation, I would like to mention that Roger Penrose and Stephen Hawking proved the existence of (a) singularity(ies) in natural conditions at the beginning of our universe. Einstein's equation for general relativity is a kind of God's equation, but singularity theorems strongly suggest the limitation of general relativity. I want to thank Prof. Fujikawa, who requested that I give a presentation on the Singularity Theorems. His request motivated me to prepare for my presentation (originally, I was planning to give a short talk on stellar physics using a part of my notebook that I used in my lecture course at OIST).

2024-03-29

## Quantum channel characterization

Shunji Matsuura (Visiting Scientist, iTHEMS / Senior Researcher, Hardware Inovation Lab, 1QBit, Canada)

The greatest challenge in building a quantum computer is noise. Suppressing noise in quantum systems is extremely difficult, which has led to a long-standing skepticism about the feasibility of quantum computers. So, what exactly is noise in the context of quantum computers? How is it characterized, and how is it measured? In this talk, we will discuss the nature of noise and, as specific examples of methods for characterizing it, we will talk about randomized benchmarking and tomography.

2024-03-22

## ORCID to auto-report your research contributions & manage your online visibility

Catherine Beauchemin (Deputy Program Director, iTHEMS / Professor, Department of Physics, Toronto Metropolitan University, Canada)

We all have to report our papers (and grants) activities at least once per year to the institutions we work for. Different employers have different systems (e.g. RIKEN has RARS) and it is tiresome to fill these forms again and again. We also want to share or make this information visible to the wider scientific community, as part of looking for a new jobs or for new collaborators. Again a lot of different tools and databases exist (Scopus, Web of Science, Dimensions, Google Scholar, ResearchGate, Pubmed, etc.). In this talk I want to tell you about ORCID: what it is and what it can do for you. Especially, how it can help you solve the problems of reporting and widely disseminating your research accomplishments to the community across the different platforms, while managing it in just one place: your ORCID record. I'll demonstrate some of nice applications.

2024-03-15

## What is a Mathematical Model to Replicate Filtration Phenomena?

Ken Furukawa (Postdoctoral Researcher, iTHEMS / Postdoctoral Researcher, Prediction Science Laboratory, RIKEN Cluster for Pioneering Research (CPR))

I will discuss a mathematical model concerning filtration of water and air. I will demonstrate how filtration phenomena can be mathematically replicated using special (less known) boundary conditions. I will also explain why these boundary conditions are necessary and discuss future possibilities.

2024-03-08

## Kin selection and social evolution

Thomas Hitchcock (Special Postdoctoral Researcher, iTHEMS)

All of life is social, yet the evolution of social traits posed a problem to classical Darwinian thinking for over a century. I will introduce the concepts of kin selection, relatedness, and inclusive fitness and talk about how these resolved the puzzle of altruistic behaviours and revolutionised behavioural ecology in the process. I will then discuss how the scope of social evolution has expanded over the years to tackle a wider set of questions, including the origins of individuality itself.

2024-03-01

## Molecular evolution and the neutral theory

Jeffrey Fawcett (Senior Research Scientist, iTHEMS)

Understanding how biological diversity is created is one of the most fundamental goals in biology. While the work of Charles Darwin formed the basic framework of Evolution, especially by highlighting the role of natural selection, it was the work of Motoo Kimura, who proposed the Neutral Theory and highlighted the role of stochastic processes, that formed the theoretical framework of molecular (i.e., DNA/RNA/protein) evolution. Here, I will explain the basic ideas of the Neutral Theory and the processes involved in creating the diversity at the molecular level.

2024-02-16

## Welcome to the new world, "Particle Zoo 2.0"

Takumi Doi (Senior Research Scientist, iTHEMS)

In 1960s, many new "fundamental" particles were found and called "Particle Zoo". Their systematic classification lead to the discovery of elementary particles, quarks. Since the beginning of 21c, however, a new kind of mysterious (exotic) particles are unexpectedly being discovered. In this talk, I will introduce this new world of "Particle Zoo 2.0" and its impact.

2024-02-09

## The undervalued and misunderstood importance of taxonomy in century 21th

José Said Gutiérrez-Ortega (Special Postdoctoral Researcher, iTHEMS)

Taxonomy, the branch of biology that classifies the living beings and give them scientific names, is not a hypothesis-driven science but a descriptive discipline that suffers of a great undervaluation in century 21th. Taxonomic papers will never be published in high impact journals, they won’t get many citations (if any), and getting funding for pure taxonomic research is basically impossible. Furthermore, taxonomy is often criticized for its apparent arbitrariness on how researchers decide to give name to a species, and attaching a scientific name to a group of organisms often seems trivial in a moment when in biology the definition of “species" is heavily discussed. Certainly, this is not a good moment for a biologist to specialize in taxonomy. (Un)fortunately, my research line somehow directed me to become a “part-time taxonomist”, which compels me to try to understand and overcome the challenges of this discipline. I will tell a few of my experiences as a taxonomist and will tell you about, in my opinion, the hottest topic in the modern history of taxonomy: should taxonomy be reinvented by updating its conventional rules?

2024-02-02

## Do Mathematicians Dream of Quantum Field Theory?

Yuto Moriwaki (Special Postdoctoral Researcher, iTHEMS)

Leibniz discovered differentiation independently of "classical mechanics" and Riemann discovered Riemannian geometry independently of "theory of gravity". Let's ask: "Will Quantum field theory (a fundamental theory of physics) be reconstructed from pure mathematics?". Here I will talk about what I feel quantum field theory looks like as future mathematics based on my current understanding and expectations. One mathematician said that "quantum field theory is the mathematics of the 22nd century." So this is an extremely incomplete and informal talk, so please listen with an easy mind and a cup of coffee :)

2024-01-26

## What is a path integral?

Christy Koji Kelly (Special Postdoctoral Researcher, iTHEMS)

Path integrals are an important technical tool in physics for describing quantum systems. We will try to provide an intuitive account of why they appear in quantum theory and show why they are mathematically difficult to understand.

2024-01-19

## How were elements synthesized？

Tomoya Naito (Special Postdoctoral Researcher, iTHEMS)

I will explain how elements were synthesized in the Universe, which is a important topic in nuclear physics.

2024-01-05

## Brane Tiling: a bridge between geometry and gauge theory

Dongwook Ghim (Postdoctoral Researcher, iTHEMS)

I will quickly overview the story of brane tiling, also known as dimer model, involving its relation with supersymmetric gauge theory and toric Calabi-Yau geometries.

2023-12-15

## Resurgence: making sense out of non-convergent series

Masazumi Honda (Senior Research Scientist, iTHEMS)

Interesting problems are often difficult to solve and this is why they are interesting. For such problems, we often aprroximate the answers by considering perturbation around solvable cases. Perturbative series obtained in such a way are often not convergent and their naive summation to all orders are divergent. In this talk, I will introduce techniques to make sense out of non-convergent perturbative series.

2023-12-08

## How can we use a quantum computer to study the ground state of the hydrogen molecule?

Steffen Backes (Senior Research Scientist, iTHEMS / Senior Research Scientist, First-Principles Materials Science Research Team, RIKEN Center for Emergent Matter Science (CEMS))

Quantum computers differ fundamentally from classical computers, since their main computing unit, the "Qubit", is a quantum-mechanical object. But how can we actually exploit this "quantumness" to study or simulate a physical system? In this coffee talk I want to discuss the basic principles of Quantum computing and present just the smallest set of tools we need to obtain the ground state wave function and ground state energy of (a simplified model of) the hydrogen molecule.

2023-12-01

## Asymptotics of period integrals

Yuto Yamamoto (Special Postdoctoral Researcher, iTHEMS)

A period integral is one of the most fundamental quantities of complex manifolds. In the talk, I will explain a technique of tropical geometry to compute the asymptotics of period integrals for a one-parameter family of complex plane curves.

2023-11-24

## Surface interaction between dust grains: an introduction to JKR theory

Misako Tatsuuma (Research Scientist, iTHEMS)

The planet formation process is the growth from sub-micrometer-sized cosmic dust grains to thousand-kilometer-sized planets. This growth process has broadly two phases: the growth from dust grains to kilometer-sized planetesimals, mainly driven by intermolecular forces like van der Waals forces and hydrogen bonds, and the subsequent growth from planetesimals to planets, governed by gravitational forces. In the aggregation process of dust grains, the interactions between their surfaces play a fundamental role. In the interaction model known as Johnson-Kendall-Roberts (JKR) theory, we treat dust grains as elastic spheres with sticky force caused by intermolecular forces and parameterized by surface energy. In this talk, I will provide an overview of the estimation of elastic forces and surface sticking forces.

2023-11-17

## Elements of majorization and its properties

Ryosuke Iritani (Senior Research Scientist, iTHEMS)

I will explain about the basics of majorization and Schur-convexity. Specifically, I will first talk about the definition of majorizaiton. Second, I will explain about Schur-convexit functions as a class of majorization-monotone functions. Finally I will talk about the applications, including how the second law of thermodynamics can prove the arithmetic-geometric means inequality.

2023-11-10

## Introduction to symmetry and band topology

Seishiro Ono (Special Postdoctoral Researcher, iTHEMS)

The last decade has seen significant advances in the understanding of topological materials. In this talk, I will briefly discuss what topological insulators are and how they can be efficiently distinguished from atomic insulators.