# Coffee Meeting Log

2021-05-28

## The basics of topological band theory

Congcong Le (Post-doctoral research scientist, Max Planck Institute for Chemical Physics of Solids, Germany)

I will be a new member of RIKEN iTHEMS and work on theoretical study in condensed matter. In this short coffee meeting, I would like to disuss the topology properties of photocurrent. Firstly, based on band theory, I will discuss the topological classification of crystalline materials. Secondly, Similar to direct current formular I=U/R, the photocurrents will be discussed. Finally, I will discuss the topology properties of photocurrent in the various topological semimetals.

2021-05-21

## Cosmology 101 - expanding universe and inflationary cosmology

Ryo Namba (Senior Research Scientist, iTHEMS)

I am a new member of RIKEN iTHEMS and working on several aspects of theoretical cosmology. As a partial self-introduction and introduction to the field, I would like to discuss some basics of cosmology, making it accessible by the iTHEMS members in different areas of expertise. In this short coffee meeting talk, my main focus is the evolution of the universe and the physics during its earliest period.

2021-05-14

## Reducing complexity and pursuing reality in computational biophysics

Yuji Sugita (Senior Research Scientist, iTHEMS / Chief Scientist, Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research (CPR))

The basic unit of all the living matters is a cell, where huge number of biomolecules exist and express their biological functions. When we aim to study biological systems in computational biophysics, we always encounter many problems originated from the complexity of the systems. Reducing complexity has been one of the most essential issues in computational biophysics, while too much simplifications may lose the reality of biological phenomena. I would like to discuss several key mathematical concepts that have been used in computational biophysics for reducing complexity and pursuing reality of biology in the cell.

2021-04-30

## Computational phases of quantum matter

Shunji Matsuura (Visiting Scientist, iTHEMS / Fundamental Researcher, Quantum Simulation Division, 1QBit, Canada)

I will talked about a connection between measurement-based quantum computing and quantum phases in physics.

2021-04-23

## Building something from nothing: a mathematical framework for aperiodic/amorphous sets

Christopher Bourne (Visiting Scientist, iTHEMS / Assistant Professor, Advanced Institute for Materials Research (AIMR), Tohoku University)

I will introduce a mathematical construction due to Bellissard that allows us to study disordered materials via Delone sets.

2021-04-16

## Density Functional Theory from Functional Renormalization Group

Takeru Yokota (Special Postdoctoral Researcher, iTHEMS / Postdoctoral Researcher, Institute for Solid State Physics, The University of Tokyo)

In this talk, I will give a brief introduction of density functional theory. I will also talk about our recent attempt to improve density functional theory for electron systems by use of the functional renormalization group.

2021-04-02

## Spin transport in ultracold atomic superfluids

Yuta Sekino (Visiting Researcher, iTHEMS)

I will briefly introduce transport phenomena of spin in ultracold atomic gases in a superfluid phase

2021-03-26

## Hunting the standard candles in their own nest

Maria Giovanna Dainotti (NAOJ/Space Science Institute)

I will introduce briefly the concept of Standard candles and how Gamma-Ray Bursts can be used as standardized candles through a new three-dimensional relation among important features of GRBs and how the kilonovae events associated with GRBs form a plane can naturally form a different plane with a much smaller dispersion around the plane.

2021-03-19

## Sensitivity and robustness of chemical reaction network systems

Takashi Okada (Senior Research Scientist, iTHEMS)

In living cellls, many reactions occur and form complex networks, such as metabolic networks. I will discuss how biological functions can emerge from the complex network dynamics, from network topology perspectives.

2021-03-12

## Recent progress in black hole information paradox

Kanato Goto (Special Postdoctoral Researcher, iTHEMS)

2021-02-26

## Fermionic transport under gravity

Kazuya Mameda (QHP)

I will briefly talk about transport phenomena induced by a background gravitational field.

2021-02-19

## information scrambling is growth of wormwhole

Masahiro Nozaki (Special Postdoctoral Researcher, iTHEMS)

I will explain what is the information scrambling, why it is important, and how it is related to the growth of wormhole.

2021-02-12

## Active and Passive Phase Separation in a Lattice Model

Kyosuke Adachi (Special Postdoctoral Researcher, iTHEMS / Special Postdoctoral Researcher, Nonequilibrium Physics of Living Matter RIKEN Hakubi Research Team, RIKEN Center for Biosystems Dynamics Research (BDR))

Phase separation is spontaneous segregation into high-density and low-density phases, observed in a variety of systems, e.g., alloy, polymer solution, and intracellular cytoplasm. In this talk, I will review the phase separation phenomena and introduce a model that connects the equilibrium phase separation to another class of separation driven by motility.

2021-02-05

## Toward the standard model of elementary particles -- a brief history in 15 min. --

Tetsuo Hatsuda (Program Director, iTHEMS)

I will make a very brief overview on the path toward the modern understanding on the law(s) of fundamental particles.

2021-01-29

## Mathematical analysis to smoldering combustion

Shunsuke Kobayashi (Visiting Scientist, iTHEMS / Specially Appointed Assistant Professor, Center for Science Adventure and Collaborative Research Advancement (SACRA), Graduate School of Science, Kyoto University)

Recently, experimental and theoretical study on near-floor flame spreading along a thin solid have been reported. In this talk, I would like to introduce a mathematical model for flame/smoldering fronts, which is equivalent to the Kuramoto--Sivashinsky equation in a scale.

2021-01-22

## Is a vacuum empty?

Tsukasa Tada (Coordinator, iTHEMS / Vice Chief Scientist, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))

Usually, a vacuum is a word associated with nothingness. The modern concept of the vacuum, however, exhibits rich and beautiful structure. I will explain the vacuum is the very foundation of our universe.

2021-01-15

## Revealing the Neutron Star Properties from Gravitional Wave

Yongjia Huang (International Program Associate, iTHEMS / Ph.D. Student, University of Science and Technology of China, China)

The gravitational wave detection brings us new opportunities to measure the neutron stars' properties. In this talk, I will briefly introduce the process of binary neutron star merger and what we could know from gravitational wave.

2020-12-18

## Elucidation of Physics inside Neutron Stars from their Cooling Observations

Akira Dohi (Junior Research Associate, iTHEMS / Ph.D. Student, Department of Physics, Graduate School of Science, Kyushu University)

The densest stars in universe, neutron stars (NSs), cool down due to neutrino losses after their formation. Firstly, I will review about the NS cooling and the representative observations such as Cassiopeia A and possibly NS in supernova 1987A. NS cooling curves are affected by various uncertain physics which may work in NSs. One of the examples is nucleon superfluidty. I will introduce how the neutrons superfluidity can be specified by cooling observations. Another is modified-gravity or beyond-general-relativistic effect. If time is allowed, I also present the possibility to test the theory to describe gravity with use of cooling observations.

2020-12-11

## Quasi-steady problem and maximal regularity

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

I will introduce a brief review of the theory of maximal regularity, and show application to quasi-steady partial differential equations of parabolic type.