# Coffee Meeting Log

2021-11-19

## A Tale of Two Spaces

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

2021-11-05

## Gravitational wave asteroseismology on protoneutron stars

Hajime Sotani (Research Scientist, iTHEMS / Research Scientist, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))

Focusing on the supernova gravitational waves, we are considering to extract the EOS inofrmation for dense matter with asteroseismology.

2021-10-29

## Nuclear physics from lattice QCD

Takumi Doi (Senior Research Scientist, iTHEMS / Senior Research Scientist, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))

The interactions between nucleons (and in general, hadrons) govern the structure of matter, such as nuclei and neutron stars. I will talk about first-principles calculations to determine the interactions from the fundamental theory of quarks and gluons, QCD.

2021-10-22

## Physics of Relativistic Radiation Mediated Shocks

Hirotaka Ito (Research Scientist, iTHEMS / Research Scientist, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))

2021-10-15

## Annoucement of Super Smash Problems (SSP) workshop

Hiroyasu Miyazaki (Senior Research Scientist, iTHEMS)

I will make an annoucement of the forthcoming Super Smash Problems workshop on Novermber 24-26.

2021-10-08

## Cooper triples in atomic fermi gas: Implication for dense quark matter

Shoichiro Tsutsui (Special Postdoctoral Researcher, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))

I propose a microscopic mechanism to reproduce the peak structure of the speed of sound of within a cold atomic model. This would be useful to understand equations of state of neutron star.

2021-09-24

## GRB afterglows and you

Don Warren (Research Scientist, iTHEMS / Research Scientist, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))

2021-09-17

## Localization in the directions of Schrödinger equations

Keita Mikami (Research Scientist, iTHEMS)

For a particular class of Schrödinger equations, the solutions to the equation localize in the directions as time goes infinity. In this small talk, we review some known results on this subject.

2021-09-10

## An invitation to algebraic quantum field theory

Mizuki Oikawa (Junior Research Associate, iTHEMS / Student Trainee, iTHEMS / Ph.D. Student, Graduate School of Mathematical Sciences, The University of Tokyo)

I am a new member of RIKEN iTHEMS and working on mathematics of conformal field theory. In this talk, noninteger dimensions in tensor categories and their relationship to algebraic quantum field theory will be introduced.

2021-08-27

## Toward quantum computation of quantum field theory

Etsuko Itou (Postdoctoral Researcher, iTHEMS / Contract Researcher, Strangeness Nuclear Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))

2021-08-06

## Message-passing algorithms for graphical models

Yingying Xu (Special Postdoctoral Researcher, iTHEMS)

Inference problems like marginalization and maximization are NP-hard to solve exactly and approximately in a graphical model. The complexity can be reduced dramatically when the underlying factor graph has some special structure. One extreme case is that of tree factor graphs, in which marginals can be computed in a number of operations which grows linearly with number of notes. This can be done by a ‘dynamic programming’ procedure often called as message passing or belief propagation algorithms. The update rules have been discovered independently in several different contexts: statistical physics (‘Bethe-Peierls approximation’), coding theory (the ‘sum-product’ algorithm), and artificial intelligence (‘belief propagation’, BP). The time evolution of the message’s distributions is known under the name of ‘density evolution’, and the fixed-point analysis of them is done by the replica-symmetric cavity method.

2021-07-30

## Conformal Bootstrap in AdS/CFT

Yuya Kusuki (Special Postdoctoral Researcher, iTHEMS / Burke Fellow, Burke Institute, California Institute of Technology, USA)

A consistency condition for a given theory is a very vague concept, but in conformal field theories it can be formulated explicitly, known as the "conformal bootstrap equation". The main applications of the conformal bootstrap in recent years can be roughly classified into two categories: "deriving universality (of energy spectrum, etc.)" and "excluding impossible theories". Here I will introduce an application of the conformal bootstrap in the context of understanding quantum gravity.

2021-07-16

## Ringing Black Holes

Naritaka Oshita (Special Postdoctoral Researcher, iTHEMS)

I will provide a brief review of the quasinormal modes of black holes. The study of black hole perturbations is important to model the waveform of ringdown gravitational waves emitted from binary black hole mergers or coalescences of compact objects leading to the formation of black holes. In the latter part of my talk, I will discuss the "ease of excitation" of quasinormal modes. This is indeed important to test the no-hair theorem of balck holes.

2021-07-09

## Von Neumann algebras and their projections

Michiya Mori (Special Postdoctoral Researcher, iTHEMS)

The theory of von Neumann algebras began in a work by von Neumann in 1929. A von Neumann algebra is widely regarded as a noncommutative measure space. I am particular interested in the structure of projections of a von Neumann algebra, which play the role of measurable sets in measure theory. In this talk I will invite the audience to the mysterious world of the geometry of noncommutative measurable sets.

2021-07-02

## Exact WKB and its applications to physics

Hidetoshi Taya (Special Postdoctoral Researcher, iTHEMS)

I explain the exact WKB method, which is a method to solve ordinary differential equations and has been developed (mainly) in mathematics since 1980's. I also discuss its applications to physics, including nonperturbative particle production by strong fields, and mention open problems in this field.

2021-06-25

## The wave operator and the Oppenheim conjecture

Kazuki Kannaka (Special Postdoctoral Researcher, iTHEMS)

I am a new member of iTHEMS and working on spectral analysis of a Lorentzian manifold in mathematics.In this talk, we will discuss the eigenvalue distribution of a wave operator on flat tori as the simplest case. Through the Oppenheim conjecture about the distribution of values at integer points of indefinite quadratic forms, I would like to explain mathematically interesting aspects of spectral analysis of a wave operator. I don't know the physical meaning of this study, but I hope this talk will be an opportunity to discuss it.

2021-06-18

## Phase transtion' in Kahler geometry

Eiji Inoue (Special Postdoctoral Researcher, iTHEMS)

I am a new member of RIKEN iTHEMS and working on Kahler geometry in mathematics. As I cannot overview my study in this short time, I would like to explain a strange phenomenon now I am facing in Kahler geometry with a specific example. It is reminiscent of `phase transition' or `spontaneous symmetry breaking'. I hope it makes a chance of discussion with researchers in other areas.

2021-06-11

## The death of a star: the theory of the supernova explosion

Akira Harada (Special Postdoctoral Researcher, iTHEMS)

At the end of the stellar evolution, the star explodes as bright as a galaxy and leaves a neutron star. This explosion is known as the supernova. Understanding the supernova explosion mechanism is crucial because it plays a vital role in the stellar and cosmic matter evolutions. The explosion mechanism includes a variety of physical processes, and hence it is a challenging problem. In this coffee talk, I would like to introduce the basic features of supernovae and the current understanding of the explosion mechanism.

2021-06-04

## Canonical form of tensor networks in one and two dimensions

Yantao Wu (Postdoctoral Researcher, iTHEMS)

I will be a new member of RIKEN iTHEMS and work on computational study in condensed matter physics. In this short coffee meeting, I would like to discuss the basics of tensor networks. I will be pedagogical and not assume knowledge of quantum mechanics. I will assume basic linear algebra at the level of singular value decomposition. I will introduce the graphical notation of a tensor network, and the notion of a canonical form in one dimension. If time permits, I will also discuss the canonical form in two dimensions.