# Event Schedule

## Events for the 2nd week of July 2021

2021-07-01

Monday, July 5, 13:00- iTHEMS Theoretical Physics Seminar
Monday, July 5, 15:00- MACS Colloquium
Thursday, July 8, 10:30- iTHEMS Colloquium
Friday, July 9, 12:30- Coffee Meeting

# Research News

## RIKEN RESEARCH: Physics modeling of viral spread between cells

2021-06-28

Prof. Catherine Beauchemin (Deputy Program Director, iTHEMS) was featured in the summer issue of RIKEN RESEARCH 2021.

Describe your role at RIKEN - I first joined RIKEN in 2016 as a senior visiting scientist at iTHES, the predecessor of the Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program. In 2020, I became one of four iTHEMS deputy program directors. I am in a field I call ‘virophysics’; the application of physics methods to virology. Primarily, I construct computer and mathematical models to explain the experimental observations made when viruses infect cell cultures. In biology, such knowledge is usually advanced through experimental trial and error, but physics modeling can help streamline this process.

# Research News

## RIKEN NEWS: What is the Significance of Basic Research?

2021-06-25

Program Director Tetsuo Hatsuda is interviewed on the RIKEN website and summer issue of RIKEN NEWS 2021.

How did the universe begin? Why does matter exist? What is the origin of life? Basic research, which pursues such fundamental questions, is difficult for the general public to understand because it does not necessarily lead to immediate practical applications. We asked Tetsuo Hatsuda, Program Director (PD) of the Theoretical and Mathematical Sciences Program (iTHEMS), what exactly basic research is.

# Seminar Report

## iTHEMS Theoretical Physics Seminar by Dr. Yuki Fujimoto on June 29, 2021

2021-07-01

On June 29th, Yuki Fujimoto (The University of Tokyo) gave the iTHEMS-physics seminar on the equation of state (EoS) in the dense baryonic matter. The EoS of dense baryonic/quark matter is the crucial ingredient for understanding neutron stars. He nicely reviewed the current state of the high-density matter EoS based on the QCD perspectives. His recent work on the EoS calculated within the pQCD framework with the resummation [Fujimoto & Fukushima, 2011.10891] gives the Hard Dense Loop resummation formula which turns out to reduce the uncertainty compared with the conventional pQCD estimate without resummation. His approach extends the applicability of the QCD-based EoS down to densities realized inside neutron stars and infers a smooth matching with the baryonic EoS. The audience asked a lot of questions and had fruitful discussions.

Reported by Etsuko Itou

# Seminar Report

## iTHEMS Theoretical Physics Seminar by Dr. Kanato Goto on June 21, 2021

2021-06-29

On June 21st, Kanato Goto (RIKEN iTHEMS) gave the iTHEMS-physics seminar on the black hole information paradox. Recently, there is a proposal for the formula for a quantum black hole entropy, called the island formula, which is expected to reconcile the conflict between the thermal and quantum natures of the black hole. One may regard the island formula as a generalization of the so-called Ryu-Takayanagi formula for the entanglement entropy, but its derivation is yet to be clarified. In the talk, after reviewing the current status of the black hole information paradox, Kanato explained their work on a derivation of the island formula based on the replica method for the gravitational path integral. The audience asked a lot of questions and we really enjoyed the talk.

Reported by Masaru Hongo

# Seminar Report

## DMWG Seinar by Dr. Satoshi Shirai on June 24, 2021

2021-06-28

We are now living in the era of precision cosmology. The relic abundance of dark matter (DM) is now observationally well-determined, and its error is smaller than O(1)%. This means that the same or much higher precision is required when we make theoretical predictions.

Weakly Interacting Massive Particle (WIMP) has long been the leading candidate for DM because of its beautiful mechanism to predict the observed relic abundance. WIMP is in the same thermal bath as the Standard Model particles in the beginning. At a certain point when the temperature of the Universe is smaller than the DM mass, it decouples to fix its number density. The yield of the DM is determined by its annihilation cross-section to the Standard Model sector.

It seems that there is no ambiguity in the calculation of this process at first: the cross-section is purely theoretical and all the remainings are described in the Standard Model physics. However, the source of the uncertainty does remain in the Standard Model sector. The dilution of the number density of DM particle depends on the expansion rate of the Universe, which is determined by the Standard Model particles. The effective degree of freedom (d.o.f) of the relativistic species controls this factor. We have to deal with the non-equilibrium dynamics to precisely describe the time-evolution of the d.o.f, in which we need numerical approaches.

In this talk, he introduced his work to update these calculations. By implementing the latest findings in the non-equilibrium dynamics in i) the neutrino decoupling, ii) the QCD phase transition, iii) the electroweak phase transition, and iv) the perturbative calculations, they found that the final d.o.f is smaller than the previous estimate in more than 1%. This is larger than the level of precision in observations. It is also important that the uncertainty is quantified by them.

Another good news is that he makes the calculated d.o.f with its error publically available. With these updates, we now correctly know the points to probe DM!

Reported by Nagisa Hiroshima

# Seminar Report

## Math Seminar by Dr. Kazuki Kannaka on June 18, 2021

2021-06-28

There was a math seminar by Kazuki Kannaka on June 18. He gave an introductory talk on his research fields, representation theory and briefly explained his study.
He first explained some basic definitions in representation theory. He then explained the mathematical tiling problem with the Lie group.
In the second part, he explained how the distribution of the compact pseudo-Riemannian manifolds differs for parameters. He also introduced his example, which has a continuous spectrum.

Reported by Keita Mikami

# Seminar Report

## Information Theory SG Seminar by Prof. Yoshiyuki Kabashima on June 23, 2021

2021-06-25

With great honor, we have invited Prof. Yoshiyuki Kabashima to our information theory seminar to give a stimulating talk about “introduction to the replica method” on 23rd June. Replica method is a physics-based technique developed for analyzing disordered many-body problems, which is now becoming popular more in information science using the structural similarity between problems from these two different fields. Prof. Yoshiyuki Kabashima is a master of the replica method. He applied this method to many problems in information theory, such as CDMA, compressed sensing, clustering of networks, error correcting codes, etc.

The talk contains two parts. In the first part, as an example of the concept, he explained the mathematical similarity of three problems whose origins are unrelated with one another--random energy model (Physics), error correcting codes (information theory) and random k-SAT problem (theoretical computer science). A unified perspective is the common structure of the three examples is the conditional distribution, and the key to solve the problems is the assessment of the average free energy. The replica method provides a systematic way to performing the configurational average. Even the mathematical justification is still an open problem, there is no known example to which the replica method leads to wrong results by appropriately taking into account the replica symmetry breaking if necessary.
In the second part, Prof. Yoshiyuki Kabashima demonstrated the calculation of replica method using an example of random energy model of spin glass. This simple model has an exact solution without using the replica method. One can see how replica method can provide the correct solution by taking care of the assumptions of replica symmetry and 1-step replica symmetric breaking (1RSB) in different temperature ranges. In the end, he gave an expert perspective of large deviation statistics of replica method and 1RSB solution.

Many excellent questions and stimulating discussions have happened during the 2.5-hour seminar. We absorbed by the world of “replicas”. We thank to Prof. Yoshiyuki Kabashima for giving us this great opportunity and hope new ideas of applications of the replica method appear in iTHEMS.

Report by Yingying Xu

# Upcoming Events

## Seminar

iTHEMS Theoretical Physics Seminar

### Non-Unitary TQFTs from 3d N=4 Rank-0 SCFTs

July 5 at 13:00 - 14:30, 2021

Dr. Myungbo Shim (Kyung Hee University, Republic of Korea)

We propose a novel procedure of assigning a pair of non-unitary topological quantum field theories (TQFTs), TFT_\pm[T_0], to a (2+1)D interacting N=4 superconformal field theory (SCFT) T_0 of rank 0, i.e. having no Coulomb and Higgs branches. The topological theories arise from particular degenerate limits of the SCFT. Modular data of the non-unitary TQFTs are extracted from the supersymmetric partition functions in the degenerate limits. As a non-trivial dictionary, we propose that F = max{ -log |S^{(+)}_{0\alpha}| } = max{ -log |S^{(-)}_{0\alpha}| }, where F is the round three-sphere free energy of T_0 and S^{(\pm)}_{0\alpha} is the first column in the modular S-matrix of TFT_\pm. From the dictionary, we derive the lower bound on F, F > -log(\sqrt{(5-\sqrt{5})/10}) \simeq 0.642965, which holds for any rank 0 SCFT. The bound is saturated by the minimal N=4 SCFT proposed by Gang-Yamazaki, whose associated topological theories are both the Lee-Yang TQFT. We explicitly work out the (rank 0 SCFT)/(non-unitary TQFTs) correspondence for infinitely many examples. Before going to the technical part, we provide some background materials including some peculiar features in 3d gauge theories, some supersymmetries, anyons, and some modular data of MTC in this talk.

Venue: via Zoom

Event Official Language: English

## Colloquium

MACS ColloquiumCo-hosted by iTHEMSSUURI-COOL (Kyoto)

### The 16th MACS Colloquium

July 5 at 15:00 - 18:00, 2021

Prof. Yoshitaka Tanimura (Professor, Department of Biophysics, Kyoto University, Graduate School of Science)
Prof. Hidetoshi Nishimori (Senior Visiting Scientist, iTHEMS / Specially Appointed Professor, Tokyo Institute of Technology)

15:00- Talk by Prof. Yoshitaka Tanimura
16:15- Talk by Prof. Hidetoshi Nishimori
17:15- Discussion

Venue: via Zoom

Event Official Language: Japanese

## Colloquium

iTHEMS Colloquium

### Quantitative Population Dynamics in Interdisciplinary Biology

July 8 at 10:30 - 12:00, 2021

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

Through the course of life, from the moment of birth till death, an organism will achieve various states of equilibrium or ‘homeostasis’ which will inevitably encounter perturbations. The processes of cell growth, differentiation, infection, mutation, evolution and adaptation work together as a coordinated ‘system’, described by mathematical models for population dynamics, to maintain a healthy state. Any disruptions to this system leads to disease including infection, allergy, cancer, and aging. We are conducting interdisciplinary research to elucidate “Quantitative Population Dynamics” through the course of life with original mathematical theory and computational simulation, which are both our CORE approach. Our mathematical model-based approach has quantitatively improved a current gold-standard approach essentially relying on the statistical analysis of “snapshot data” during dynamic interaction processes in life sciences research. In this talk, I will explain how our interdisciplinary approach extends our understanding for complicated clinical data and apply real world problem with an example of the Novel Coronavirus Disease, COVID-19.

Venue: via Zoom

Event Official Language: English

## Workshop

### iTHEMS Science Outreach Workshop 2021

July 11 - 12, 2021

RIKEN iTHEMS, an interdisciplinary Theoretical and Mathematical Sciences Program (RIKEN iTHEMS), was established in November 2016. RIKEN iTHEMS aims to use interdisciplinary methods with a focus on mathematics to elucidate the universe, matter and life, and to solve fundamental problems in society. Building on the achievements of the past exchanges through the Journalist in Residence Program, we will hold an outreach workshop to explore the relevance of the research of the RIKEN iTHEMS to society and to discuss how to build interactive relationships between journalists and researchers in the future. Like last year, this year's workshop will be held as a ZOOM workshop as the seminar house is closed.

Contact: Takashi Tsuboi (iTHEMS Deputy Director)

Venue: via Zoom

Event Official Language: Japanese

# Paper of the Week

## Week 5, June 2021

2021-07-01

Title: Effects of finite-light-speed correction for the Coulomb interaction on nuclear binding energies and radii in spherical nuclei
Author: Tomoya Naito
arXiv: http://arxiv.org/abs/2106.14270v1

Title: Goldstone Boson Scattering with a Light Composite Scalar
Author: T. Appelquist, R. C. Brower, K. K. Cushman, G. T. Fleming, A. Gasbarro, A. Hasenfratz, J. Ingoldby, X. Y. Jin, J. Kiskis, E. T. Neil, J. C. Osborn, C. Rebbi, E. Rinaldi, D. Schaich, P. Vranas, E. Weinberg, O. Witzel
arXiv: http://arxiv.org/abs/2106.13534v1

Title: Quantum hydrodynamics from local thermal pure states
Author: Shoichiro Tsutsui, Masaru Hongo, Shintaro Sato, Takahiro Sagawa
arXiv: http://arxiv.org/abs/2106.12777v1

Title: Modulus sheaves with transfers
Author: Shane Kelly, Hiroyasu Miyazaki
arXiv: http://arxiv.org/abs/2106.12837v1

Title: Unitary $p$-wave Fermi gas in one dimension
Author: Hiroyuki Tajima, Shoichiro Tsutsui, Takahiro M. Doi, Kei Iida
arXiv: http://arxiv.org/abs/2106.12909v1