# Person of the Week

2021-10-13

## Self-introduction:Gilberto Nakamura

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.

2021-10-04

## Self-introduction:Yixin Guo

My name is Yixin GUO, a Junior Research Associate joined in iTHEMS from October 2021. I come from China, and now study in the Doctoral Course at The University of Tokyo. I am majoring in theoretical nuclear physics. I am mainly interested in (but not only) the quantum many-body problem, nuclear structure theory, density functional theory, and nuclear reaction theory. I also have some experience in the accelerator physics. I look forward to exchanging ideas with various researchers from different fields.

2021-09-08

## Self-introduction: Matthias Berwein

My name is Matthias Berwein and I'm from Germany. I did my undergraduate studies in physics at TU Munich from 2006 to 2011, followed by a PhD 2012-2016 also at TU Munich in the group of Nora Brambilla. Then I came to Japan for my first postdoc at Tohoku University in Sendai under a JSPS fellowship with Yukinari Sumino. Since 2018 I've been at RIKEN, first in the SPDR program at Quantum Hadron Physics Lab, and from 2021 in iTHEMS. The focus of my research lies in theoretical studies of the strong interactions through the theory of quantum chromodynamics and with a special emphasis on heavy quarks. I have worked on several projects on the static quark potential, heavy quarkonium hybrids, and heavy quarks at finite temperature, using perturbative calculations and effective theory methods. Currently, I'm studying properties of the energy-momentum tensor in these environments. I look forward to many fruitful interactions with fellow researchers here at iTHEMS.

2021-08-05

## Self-introduction: Congcong Le

My name is Congcong Le from China, and I join iTHEMS on August 1st 2021 as a Postdoctoral Researcher. After graduation, I came to the Institute of Physics, Chinese Academy of Sciences to study theoretical physics, and obtained my PhD in July 2017. My research focuses on the theoretical study in condensed matter systems, including unconventional superconductivity, strongly correlated system, and novel topological system (topological insulators, Dirac semimetal, Weyl semimetal), and I start to be interested in twisted bilayers and topological phases in the non-Hermitian systems. I have enjoyed using mathematics to explore condensed matter physics and working with theorists and experimenters. In my spare time, I like Chinese chess, badminton, table tennis and climbing.

2021-07-20

## Self-introduction: Yalong Cao

I am a mathematician doing research on algebraic geometry, differential geometry and mathematical physics. I am particularly interested in understanding Yang-Mills theory on Calabi-Yau 4-folds and how it is interacted with enumerative geometry. I am eager to understand how such theory could lead to unexpected relations with other areas. It is my great pleasure to join RIKEN iTHEMS and I am looking forward to having exciting discussions with you.

2021-07-02

## Self-introduction: Etsuko Itou

I'm Etsuko Itou, a Postdoctoral Researcher (Concurrent) since July 2021. I'm interested in quantum field theories, in particular, quantum chromodynamics (QCD) in extreme regimes. Although QCD in the superfluid phase, which occurs in low-temperature and high-density regimes, is still an unsolved area due to the infamous sign problem, a theoretical understanding is urgently needed in relation to neutron star physics. I am working on various numerical approaches to understanding quantum field theories with the sign problem. For example, I utilize the conventional classical supercomputers to study qualitative properties of modified QCD without the sign problem, and I develop quantum computation algorithms based on a new formula where the sign problem does not emerge.

2021-06-11

## Self-introduction: Yantao Wu

My name is Yantao Wu. I joined iTHEMS in June 2021. My research field is in computational and theoretical statistical physics. I'm also interested in quantum computing. I obtained my PhD in physics from Princeton University in May 2021. During graduate school, I have worked on renormalization group of quantum and classical statistical systems in the context of Monte Carlo simulations. I'm also quite familiar with path-integral molecular dynamics. Currently, I'm interested in developing tensor network algorithms for quantum dynamics in one dimension and ground state calculations in two dimensions. In particular, I'm interested in the approximate canonical form of 2D tensor networks, and its associated entanglement structure. I'm also interested in issues related to quantum dynamics, such as entanglement evolution and eigenstate thermalization hypothesis at the edge of the energy spectrum. I'm based in UC Berkeley, and would be glad to host any iTHEMS visitors in the bay area. Based in UC Berkeley, I have recently got interested in the hardware of quantum computing as well. I hope that we can one day see the ENIAC of our generation. In my spare time, I like soccer, climbing, poetry, and Go (not very good though).

2021-05-28

## Self-introduction: Ryo Namba

Pursuit of the fundamental law that governs the evolution of our universe, is the end goal of cosmology. Our universe is known to be expanding. It is not only expanding, but has been, and perhaps will be, expanding. The driving force of the current accelerated expansion, often called dark energy, is still beyond our understanding, despite that the fate of the universe entirely depends on the nature of dark energy. Furthermore, cosmological observations provide indications that an accelerated expansion also took place at the earliest stage of our universe, known as inflation, and that the seeds of all the structures we observe today were encoded during this period. Thus the physics in the inflationary era is of essential importance, fixing the initial conditions of our universe. The forthcoming advancement of multi-messenger (photons, neutrinos, and gravitational wave), multi-frequency observations opens up the possibility of probing such cosmological signals in novel manners. My research focus is encapsulated in the studies of interactions at cosmological scales, ranging from the highest-energy processes at the onset of the universe to the laws of gravity at the largest distances, by making use of the knowledge of quantum field theory, elementary particle physics and gravitational theory as technical tools. Interactions in cosmology are inevitably those in a gravitating system, and they reserve a large domain of unresolved mysteries that provide a fascinating ground to explore. Understanding the physics in both ends of these extremes is necessary to reveal the origin and fate of our universe. Many different branches of physics are involved in this research adventure, and extending the border of scientific disciplines is of essential importance. [Brief academic history] I received my Ph.D. from the University of Minnesota (USA), and continued my research activities as a postdoctoral researcher at Kavli IPMU (Japan), McGill University (Canada), and Tsung-Dao Lee Institute (China), before joining RIKEN iTHEMS in May 2021. I have worked on research projects on particle production in the early universe, thermalization process (reheating), modified gravity theories (scalar-vector-tensor theories, massive/bimetric gravity), etc.

2021-05-21

## Self-introduction: Akira Harada

I'm Akira Harada, a RIKEN SPDR since April 2021. I'm interested in astrophysics, especially supernovae. The core-collapse supernova (CCSN) is the explosive death of a massive star. Because of the extreme environment realized at the center of the CCSN, the explosion mechanism involves a vast field of physics, namely hydrodynamics, nuclear physics, neutrino physics, and gravitational physics. Besides, understanding such a complicated phenomenon requires numerical simulations. I'm trying to reveal the mechanism by exploiting all these pieces of knowledge. I'd like to get stimulated from interdisciplinary conversations with iTHEMS people.

2021-05-17

## Self-introduction: Naritaka Oshita

I am a theoretical physicist who works on gravity, cosmology, and quantum field theory. Quantum fluctuations of mater/gravitational fields in an expanding universe or a black hole exhibit thermal radiation and superradiance. These phenomena are important to understand the thermal nature of the gravitational systems and how information of matter is encoded there. Also, the classical linear perturbations of a black hole are characterized by the quasinormal modes of the black hole. This is useful to test classical/quantum gravity theories by the observation of gravitational waves. Beyond the linear perturbation in gravitational systems, I am also working on non-perturbative phenomena of quantum fields such as vacuum decay in strong gravity. The standard model of particle physics predicts that the Higgs field is metastable, which means that our Universe might eventually undergo a catastrophic vacuum decay and be filled with negative vacuum energy. The vacuum decay process is therefore important to understand the history and fate of the Universe.

2021-05-13

## Self-introduction: Eiji Inoue

I'm Eiji INOUE, a new member of iTHEMS as a special postdoctoral researcher in mathematics. My current interest is Kahler geometry of algebraic variety. Algebraic variety is (locally) the solution set of polynomials, say x^2 + y^2 -1 = 0. While its origins trace back to ancient Greek, it still fascinates many mathematicians: you can find many Fields medalists, including all Japanese medalists, are awarded for their monumental works on algebraic variety. Calabi-Yau variety is a special class of algebraic varieties attracting attention in string theory. A Calabi-Yau variety admits a Kahler-Einstein metric, which can be thought of as a canonical 'shape' of the variety. Though a general variety in other classes does not necessarily admit such canonical metrics, it is gradually believed by not a few specialists that any variety has a unique degeneration to another variety admitting a canonical metric in some sense. My recent study gives a mathematical formulation of this problem. This framework has a special aspect: it naturally possesses a new parameter λ which plays a role analogous to the inverse temperature. When λ is sufficiently low, canonical metrics, which you may see as 'equilibrium states' of the variety, are unique if it exists. On the other hand, when λ is sufficiently high, canonical metrics are not unique and the absolutely stable states may break the symmetry of the variety. It is reminiscent of phase transition. I am looking forward to discussing this phenomenon with researchers in other areas.

2021-05-12

## Self-introduction: Kazuki Kannaka

I’m Kazuki KANNAKA, a special postdoctoral researcher (mathematician) in iTHEMS. I am interested in the global properties of locally homogeneous manifolds, especially those with Lorentzian structures (e.g., anti-de Sitter manifolds) which are used as models of spacetimes. I am currently studying the spectral theory of the hyperbolic Laplacian (the Klein-Gordon operator), which is a differential operator defined “intrinsically” on such manifolds. In iTHEMS, I would like to find interactions with other various research areas.

2021-05-11

## Self-introduction: Michiya Mori

I am Michiya Mori, a new member of iTHEMS as a Special Postdoctoral Researcher. I received my Ph.D. at The University of Tokyo in March 2021. I am working on the mathematical theory of operator algebras. I am interested in examining certain structure of a collection of linear operators acting on a Hilbert space. In particular, I have studied the metric structure and the (lattice) order structure of, e.g., a domain of bounded self-adjoint operators, the collection of self-adjoint projections, the unit sphere. My research is often base on the classical study by, for example, von Neumann, Wigner, Loewner and Kadison, rather than modern operator algebraists. I believe that my research is closely tied with various fields of theoretical sciences. I hope to develop my research in an interdisciplinary direction.

2021-05-11

## Self-introduction: Mizuki Oikawa

I am Mizuki Oikawa, a Junior Research Associate (JRA) student who joined iTHEMS in April 2021. I am interested in the mathematics of two-dimensional conformal field theory, such as vertex operator algebras, conformal nets, and Segal conformal field theories. In particular, my interest includes moonshine phenomena, which connect finite groups and modular forms via conformal field theories. I look forward to interacting with iTHEMS members in different research areas.

2021-05-10

## Self-introduction: Hidetoshi Taya

My name is Hidetoshi Taya. After finishing my Ph. D in The University of Tokyo in 2017, I had several postdoctoral positions at iTHEMS RIKEN (2017-18), Fudan University (2018-20), and Keio University (2020-21) and then come back to iTHEMS, RIKEN from April, 2021 as a special postdoctoral researcher. I am a theoretical physicist working on (but not limited to) particle and nuclear physics. In particular, I am interested in non-perturbative and non-equilibrium phenomena driven by strong fields, and studying their application to, for example, heavy-ion collisions, intense lasers, and condensed-matter systems. I am also interested in application of mathematical methods such as the resurgence theory and the exact WKB method. I look forward to interacting with iTHEMS members and to enjoying something new/interesting together.

2021-05-10

## Self-introduction: Yuya Kusuki

I am Yuya Kusuki. I joined iTHEMS in April 2021. I am studying the theoretical particle physics. My particular interest is conformal field theory in the context of the AdS/CFT. For example, I would like to understand “Which spectrum and which coupling constants are required to reproduce the semiclassical gravity?”, “Whether or not does a pure gravity on AdS exist?”, “What is the precise definition of the quantum chaos in AdS/CFT?” and so on. For this purpose, I mainly utilize (i) some information tools, developed in the interface between quantum gravity and quantum information, and (ii) conformal bootstrap equation. I am looking forward to collaborating with researchers in various fields at iTHEMS. Since my research is based on gravity, conformal field theory, information theory, condensed matter, that is, many topics, I believe such a cross-disciplinary collaboration provides wonderful results.

2021-03-04

## Self-introduction: Yuta Sekino

I am Yuta Sekino, a JSPS fellow who joined iTHEMS on March 1, 2021. I am a theoretical physicist studying physics of ultracold atoms. My main research interest is universal properties of many-body systems as well as transport phenomena. I am currently working on atomic gases in spatially one dimension and spin transport. At iTHEMS, I hope to broaden my research horizon through discussions with researchers in various fields.

2021-03-04

## Self-introduction: Takeru Yokota

My name is Takeru Yokota. I joined iTHEMS in March 2021. My research field is theoretical physics. I have been interested in the development of nonperturbative frameworks to describe many-body systems, such as the functional renormalization group (FRG). In particular, I have challenged to establish a new framework based on the combination of FRG and density functional theory, which is another powerful method used for various systems including nuclear systems and condensed matter systems, and involved in the application to electrons, nucleons, and classical liquids. I am looking forward to new developments of research emerged from the interaction with researchers from various fields in iTHEMS.

2021-02-04

## Self-introduction: Björn Ahlgren

My name is Björn Ahlgren. I joined iTHEMS as a visiting scientist in February 2021 as part of my current postdok, and I'm otherwise based at KTH in Stockholm, Sweden. My field of research is astrophysics, where I work mainly on gamma-ray bursts (GRBs), which are some of the most violent explosions in the Universe. These phenomena are caused by the collapse of particularly massive stars, and by compact object binary mergers, and they can serve both as laboratories for physics under extreme conditions, as well as probes of the early Universe. In my research I focus on the intersection between theory and observations, where I try to develop and reconcile theoretical models for the emission mechanisms of GRBs with the best available observations, using statistical methods. My specialisation lying in applied statistics, I really enjoy interdisciplinary projects where I get to work with new ideas and new data. I'm excited to join iTHEMS and I hope I will get the opportunity to engage in new collaborations across different disciplines.

2020-11-05

## Self-introduction: Tianfeng Hou

My name is Tianfeng Hou and I joined iTHEMS in November 2020. I am originally from a city in the east of China. After I finished my undergraduate study, I moved to the Netherlands (Leiden University) to study applied mathematics. And after that I moved to Belgium (KU Leuven) to continue with my PhD career. Recently, I finished my PhD with a title ’Efficient Probabilistic Assessment of Hygrothermal Performance: sequential Monte Carlo and decomposition methods’. Particularly, two tasks are included in this research. First, a faster surrogate model is developed in order to replace the current time-consuming building simulation models. Second, an efficient sampling strategy that can minimize the needed simulations in the framework of Monte Carlo based probabilistic analysis is set up. All in all, I think mathematics is fun, and I am very enthusiastic about the use of mathematics to solve different engineering problems. During my stay in iTHEMS I hope I can have the opportunity to cooperate with researchers from different disciplines and explore more about the beauty of mathematics.

2020-10-06

## Self-introduction: Maria Giovanna Dainotti

I am originally from a city in South of Italy. After my PhD at the University of Rome La Sapienza in 2008 I moved to Jagiellonian University in 2009 as a research assistant and I have been Visiting Scholar in several places all around the globe. I here mention a few: I was already at RIKEN with the JSPS Fellowship in November 2014-January 2015 in the ABBL group under the direction of Nagataki-san and as a visiting researcher in January and February 2019. I was in US at Stanford University with the Fulbright, Marie Curie’ and the American Astronomical Society Fellowship from 2012-2013, and 2015-2018. In all these years I have been studying Gamma-Ray Bursts, selection biases in treating GRB correlations, their application as cosmological tools and as a tool to discriminate among theoretical physical models. More recently I have started working on machine learning for redshift extraction of GRBs and Active Galactic Nuclei and on the selection effects in SNe cosmology in collaboration with Hatsuda-san and Nagataki-san. Last year I started collaborating with Don Warren and Gilles Ferrand to a project that aims to include virtual reality to show GRBs correlations to a broader audience.

2020-10-01

## Self-introduction: Ken Furukawa

I am Ken Furukawa. My research area is the mathematical theory of partial differential equations related to the fluid dynamics and diffusion phenomena. More specifically, we studied mathematically rigorous justification of the derivation of the primitive equations by the Navier-Stokes equations. The primitive equations have nice properties on well-posedness and have a strong connection with the Navier-Stokes equations. We obtained some results on the well-posedness of the Navier-Stokes equations in this research. Recently, I have been interested in the mathematical aspect of data assimilation. Data assimilation is very useful to obtain a plausible forecast and is also closely related to our lives. However, mathematically rigorous studies of data assimilation from the mathematical theory of PDE are under development. I will study data assimilation from the view PDE point of view.

2020-09-25

## Self-introduction: Catherine Beauchemin

Bonjour! I was already a member of iTHEMS as a Senior Visiting Scientist so probably you already know me. But since September 2020, I became a Deputy Program Director of iTHEMS. I was looking forward to spending more time at RIKEN, working more closely with everyone, but unfortunately, with COVID-19, for now I have to stay in Toronto. As you maybe know, I am a professor of physics, but my research is in the field of virophysics (ヴイルス物理学). I apply the techniques of physics to virology. More generally, I like applying the methods of physics and computational methods to fields where theoretical/quantitative analysis is less common, like biology and health research, or even ergonomics! I think the methodologies developed in physics can translate to many other fields and provide new insights. Most of my work involves/requires direct collaborations with experimental virologists. I also really enjoy convincing other physicists and mathematicians to join in solving these types of problems across disciplines. For me, iTHEMS is an ideal environment to develop such collaborative projects. In my new role as Deputy Program Director, I want to do my best to help support the young researchers in iTHEMS, and make sure they have everything they need to succeed at their goals. I want to help foster new collaborations, through which everyone can learn new skills, or get help to bring their research to the next level. I have a few ideas that I want to share with all of you over time. If you have some thoughts or concerns, or if you want to discuss something with me, please send me an email anytime. I am happy to get to know you better.

2020-08-03

## Self-introduction: Ching-Kai Chiu

Hello, I will officially join iTHEMS on August 1st as a senior research scientist. My name is Ching-Kai Chiu from Taiwan, and I am a condensed matter physicist. Unfortunately, I cannot enter Japan now due to the travel restriction. Hopefully, I can see everyone in person after COVID-19. Please feel to contact me anytime. My research interests are topological states of matter, superconductivity, and quantum computing. Specifically, my works are related to topological insulators, semimetals, superconductors, and non-Hermitian systems, as well as the designing of universal quantum computers. I have enjoyed using mathematics to explore condensed matter physics and collaborating with theorists and experimentalists. However, I don’t want to limit myself in condensed matter physics. I have broad interests in science. When I was in graduate school (the University of Illinois at Urbana-Champaign), I learned general relativity (Sean Caroll’s and Wheeler’s books) and field theory. Recently, I am also interested in (quantum) cryptography and cryptocurrency. It is exciting for me to work in iTHEMS to interact with scientists from different fields. About my personal life, I lived in many countries, such as USA, Canada, Taiwan, Germany, China. I have enjoyed nature and visited around 20 national parks in the United States. You name it. Yellowstone, Yosemite, and Mount Rainier. My wife and I like to travel. We have been at least 25 countries before COVID-19. My favorite habits are rock climbing and playing board games, such as Terraforming Mars and Power Grids.

2020-04-14

## Self-introduction: Kengo Kikuchi

I’m Kengo Kikuchi, a special postdoctoral researcher in iTHEMS. I’m studying the theoretical physics, elementally particle physics and quantum field theory, especially, gradient flow equation. I’d like to take the opportunity working in iTHEMS to broaden research fields, and it would lead to the new interaction with various study regions.

2020-04-13

## Self-introduction: Naomi Tsuji

I am Naomi Tsuji, a postdoctoral researcher at RIKEN/iTHEMS. My major is observational studies of high energy astrophysical phenomena. I have been working on particle acceleration and nonthermal radiation in shock waves of supernova remnants by using X-ray observations. I also analyze TeV gamma-ray data, as a member of H.E.S.S. (High Energy Spectroscopic System) collaboration.

2020-04-13

## Self-introduction: Hui Tong

My name is Hui Tong, a PhD student from School of Physics, Peking University. My main research topic is nuclear theory, including the interactions between nucleons and using the ab-initio nuclear many-body theory to study nuclear matter and neutron star. Now I am studying on how to extract hadron interactions from lattice QCD calculations. In the iTHEMS, I hope to learn more about theoretical, mathematical and computational sciences, this will be a great opportunity to broaden my horizons.

2020-04-09

## Self-introduction: Yukimi Goto

I am Yukimi Goto, a special postdoctoral researcher of iTHEMS. I have been interested in the mathematical study of physical models. For example, I have investigated the following question in my research: How many electrons can an atom bind? This is a fascinating open problem in mathematical physics. Intuitively, this question is related to the size of the system, e.g., the question: Why are the radii of atoms more or less independent of their nuclear charge? Although one might think these are simple consequences of electrostatics alone, the Pauli exclusion principle plays an essential role. My hope is to understand physics. However, to be honest, I’m not a physicist but an applied mathematician. So, I’m happy if you tell me physics.

2020-04-09

## Self-introduction: Euki Yazaki

My name is Euki Yazaki and I joined iTHEMS in April 2020. My research area is biology, and I have been studying evolutionary biology consistently since I started my research career as a student at University of Tsukuba in 2010. I am particularly interested in the molecular phylogeny and molecular evolution of eukaryotic microorganisms (called Protists). Based on large-scale molecular sequence data acquired from many Protists, I have inferred the evolutionary history of genes and phylogenetic relationships of organisms. Ultimately, I hope to elucidate the early evolution of eukaryotes. I'm very excited to be a member of iTHEMS because the mathematical professionals from diverse backgrounds at iTHEMS give me the opportunity to expand my biology and therefore my science.

2020-04-06

## Self-introduction: Akira Dohi

Hello, I am Akira Dohi, the Junior Research Associate (JRA) student. My research interest concentrates on how neutron stars are cooled or heated. A Neutron star is born as a remnant by supernova explosion of a massive star and basically cools down by many neutrino losses. How to cool or heat the neutron star is connected to the temperature or magnetic field of the surface, which can be estimated using the observations of X-ray astronomical satellite. The cooling and heating processes are believed to be caused in a wide range of density regions even with the above nuclear saturation density. I am studying numerical modeling of neutron stars evolution, and combining some observations, I aim to specify the origin of these processes, which would be useful for elucidation of various physics, above all nuclear theory. iTHEMS’s members have different fields from my area and this would broaden our scientific knowledges and views through communications.

2020-04-06

## Self-introduction: Masaki Taniguchi

I am Masaki Taniguchi, a mathematician, who has been working at iTHEMS/RIKEN since April 2020. My interests cover gauge theory, Floer theory and its applications to 3- and 4-dimensional topology. In a mathematical study of gauge theory, we obtain information of 4-manifolds by observing the moduli space of solutions to a certain non-linear partial differential equation for a given 4-manifold. This method enables us to find interesting phenomena of 3- and 4-dimensional topology which are different from that of other dimensions. Currently, I am studying the following topics: 1. gauge theory for a class of non-compact 4-manifolds called 4-manifolds with periodic ends and their applications to existence of codimension-1 embedding of 3-manifolds and positive scalar curvature on spin 4-manifolds, 2. a quantitative formulation of instanton Floer homology and its applications to a study of the homology cobordism group which is related to existence of triangulations of topological manifolds, and 3. a study of 2-dimensional knots in the 4-space using gauge theory. I'm also interested in physical aspects of gauge theory. I'm looking forward to discussing with researchers in various fields at RIKEN.

2020-04-06

## Self-introduction: Ryusuke Hamazaki

My name is Ryusuke Hamazaki. I am a senior research scientist at iTHEMS and also a RIKEN Hakubi leader of a team on nonequilibrium statistical mechanics. So far I have worked on foundation of equilibrium quantum statistical mechanics, namely how isolated quantum many-body systems relax to thermal equilibrium after long time. Extending this framework, I am currently trying to understand laws of nonequilibrium quantum statistical mechanics. Another motivation of mine is to apply the theory to other nonequilibrium science, such as biology or high-energy physics. I am eager to discuss and collaborate with one another to contribute to interdisciplinary fields through universality of statistical mechanics!

2020-01-23

## Self-introduction: Martin Skrodzki

My name is Martin Skrodzki and I was born in Germany. I studied computer science and mathematics from 2008 to 2011 at TU Dortmund University in Germany where I obtained two Bachelor's degrees. Afterwards, I spend two terms on a Fulbright travel grant at the Texas A&M International University in Laredo, Texas, USA continuing with graduate studies in mathematics. I finishes these with a Master's degree at Freie Universität Berlin, Germany in 2014. My focus in the coursework and in my Master's thesis was on discrete geometry and discrete mathematics. In early 2015, I started work on my PhD with Prof. Polthier at Freie Universität Berlin in the group "Mathematical Geometry Processing". My thesis, titled "Neighborhood Data Structures, Manifold Properties, and Processing of Point Set Surfaces" covers three topics all centered in the context of point set processing. Please find the thesis via the link shown below. I graduated with the title of "Dr. rer. nat" (doctor of the natural sciences) in July 2019. Immediately after my graduation, I started a first postdoc at the Institute of Computational and Experimental Research in Mathematics (ICERM), Brown University, Providence, RI, USA. The position was part of the topical semester program "Illustrating Mathematics" which was concerned about finding new, exciting visualizations of mathematical structures and objects, see the link shown below for some of the results obtained. My research interests are set between computer science and mathematics. I am currently very interested in visualization of high-dimensional data via dimension-reduction methods. Memberships in the Society of Applied and Industrial Mathematics (SIAM), the Solid Modeling Association (SMA), and Eurographics (EG) form my professional network. Finally, I am also an associate editor of the Journal of Mathematics and the Arts (JMA).

2020-01-16

## Self-introduction: Hajime Sotani

Understanding neutron star physics is my research topic. Neutron star is provided via supernova explosion, which happens at the last moment of life of massive star. Neutron star is a unique laboratory for understanding the physics in extreme states. In fact, the density inside the neutron star significantly exceeds the nuclear standard density and the magnetic and gravitational fields around/inside the star become much stronger than those observed in our solar system. So, as an inverse problem, one could extract some aspects of physics in such extreme states via the observation of neutron star itself and/or the phenomena associated with neutron stars. For this purpose, (gravitational wave) asteroseismology is a powerful technique, which is similar to seismology in Earth and helioseismology in Sun. With this approach, we are trying to extract the "invisible" neutron star properties. Since our research is not only in astrophysics but also strongly associated with nuclear physics and condensed matter physics, I am very happy if I can make an interdisciplinary collaboration with the members of iTHEMS for solving a problem in neutron stars.

2019-11-13

## Self-introduction: Hidetoshi Nishimori

I am a Professor at the Institute of Innovative Research, Tokyo Institute of Technology. I obtained my degrees, BSc, MSc, and DSc, from the Department of Physics of the University of Tokyo. After a stint as a postdoctoral fellow at Carnegie-Mellon University and Rutgers University in the United States, I returned to Japan and have been working at Tokyo Institute of Technology, mostly at the Physics Department but I recently moved to the Institute of Innovative Research as the head of the Quantum Computing Research Unit. My main interest has been the theory of spin glasses, a typical hard problem of equilibrium statistical mechanics, especially exact results derived by using a special type of symmetry. I am recently more interested in quantum annealing, a quantum-mechanical paradigm to solve combinatorial optimization problems, a typical example of which is the ground-state search of spin glasses. This is a very exciting field not just because of the big attention from the society to quantum computing in general, but also due to the very interdisciplinary characteristics of the field in that very basic theoretical results are sometimes immediately implemented in real devices, typically the D-Wave quantum annealer, thus affecting the performance of the device in real-world industrial applications. I hope the stimulating environment of iTHEMS to further broaden the scope my research activities, leading to unexpected developments that are hard to be achieved elsewhere.

2019-11-11

## Self-introduction: Takashi Sakajo

I am a full professor of Department of mathematics at Kyoto University, and a project professor of Liaison Center in Mathematics in RIMS at Kyoto University. From Nov. 2019, I am appointed to a senior visiting scientist at RIKEN iTHEMS. My educational background in undergraduate/graduate courses at Kyoto University was mathematics, but I have been keeping strong interests in the other fields of sciences. My expertise in research is applied mathematics, especially mathematical fluid dynamics, in which I would like to understand highly nonlinear and complex fluid phenomena observed in the evolutions of incompressible fluid motions from mathematical points of view theoretically as well as numerically. In addition to those academic topics, I am keen to conduct many interdisciplinary studies with people from the other disciplines (meteorology, medical, material science etc.) and industries. I am the chief coordinator of Math Clinic at MACS program in Kyoto University. These interdisciplinary activities are not just for applying existing mathematical theories, but for exploring new future problems for mathematical sciences from modern world. I am very happy to be a member of iTHEMS, where I can share the same interests with the members. Research Topics: • Topological Flow Data Analysis • Dissipative weak solutions of the Euler equations and turbulence theory • Vortex dynamics • Flow control of vortex dominated flows • Singularity formation and long-time behavior of vortex dynamics • Applied and computational complex analysis (ACCA) • Uncertainty Quantification (Data Assimilations) • Interdisciplinary Studies (Meteorology, Medical, Industrial problems)

2019-09-30

## Self-introduction: Enrico Rinaldi

I am Enrico Rinaldi, a part-time researcher in iTHEMS, who was previously a SPDR fellow in RIKEN BNL and Quantum Hadron Physics Laboratory. My expertise is Monte Carlo numerical simulations of quantum field theories, also known as Lattice Field Theory simulations, which use massively parallel supercomputers (CPU and GPU-based) around the world to solve the complex equations hiding the mysteries of particle physics. My research is focused on understanding high energy strongly-coupled gauged theories, in particular in the context of extensions of the Standard Model (SM) of particle physics, like Dark Matter physics or theories of Composite Higgs. New discoveries are hinging on the theoreticians’ ability to make predictions that can be tested by experimentalists, and that is precisely the my goal. I am also engaged in projects related to low-energy nuclear physics, for example calculating nucleon-nucleon interactions or nuclear form-factors directly from the theory of Quantum Chromo-Dynamics (QCD). Moreover, I have been working on matrix models to study the gauge/gravity duality conjecture with the aim of understanding the possible intriguing relation between gauge theories and quantum gravity. I am currently researching new Machine Learning (ML) approaches to physics, mainly based on the promising rise of generative models. The aim is to improve our ability to get access to multi-dimensional parametric distributions describing physical systems with specific models.

2019-09-12

## Self-introduction: Hirotaka Irie

I am Hirotaka Irie, a research scientist in quantum computing team of DENSO Corporation. From this summer of 2019, I also became a visiting scientist here at RIKEN iTHEMS. I received my Ph.D. in Physics (string theory) at Kyoto University in 2008, and worked as postdoc in KEK, National Taiwan University, National Center for Theoretical Physics (NCTS, Taiwan), and Yukawa Institute for Theoretical Physics (Kyoto University), where my research focused on non-perturbative aspects of string theory and mathematical physics. Now I joined DENSO Corporation, working toward real-world applications of quantum mechanical computing machines with combining aspects of mathematical physics and string theory. In fact, recent industrial studies also require highly sophisticated physical and mathematical researches. Here, I hope to discuss and collaborate with people in iTHEMS to jointly achieve new technological breakthrough which changes our daily life and society.

2019-05-18

## Self-introduction: Keita Mikami

I am Keita Mikami, a research scientist at iTHEMS. My research field is partial differential equations and I work on linear Schrödinger equation. Main subject in the research of linear Schrödinger equation is its spectrum. I have studied localization in direction phenomena of Schrödinger operators with homogeneous potentials of order zero. Roughly speaking, this is a phenomena such that a solution to Schrödinger equation with this class of potentials localizes in direction as time goes to infinity. I have used spectral theory and semiclassical(microlocal) analysis to understand this phenomena and its application. Though my interest comes from mathematics, I want to understand physical aspects of Schrödinger equations and find some application of my results in physics since Schrödinger equation is the governing equation in quantum mechanics.

2019-05-11

## Self-introduction: Kanato Goto

My name is Kanato Goto and I have been working at iTHEMS since April 2019. I am a theoretical physicist studying string theory and my main research interests lie in foundational questions about quantum gravity, black hole physics, and supersymmetric quantum field theories. I am currently trying to understand the basic mechanism and the mysteries of the holographic principle, which states that information about gravity and the spacetime contained in our three-dimensional universe can be completely described by the two-dimensional boundary surrounding it, just like a hologram emerges from a sheet of photographic film. At iTHEMS, I hope to broaden my research horizon through discussions with researchers in various fields.

2019-04-26

## Self-introduction: Kenta Sato

Hello, I am Kenta Sato. My major is mathematics, in particular algebraic geometry. In algebraic geometry, we study algebraic varieties, which are defined as the zero sets of polynomial equations. When you hear polynomials, you may imagine polynomials whose coefficients are integers, rational numbers, or complex numbers. But, it sometimes important to consider polynomials whose coefficients are in some other field, for example a field with positive characteristic. I have been studying polynomials, rings and algebraic varieties over a field with positive characteristic. In particular, I am interested in F-singularities and globally F-regular varieties, which are defined in terms of positive characteristic methods. I also hope to find some application of positive characteristic methods to problems in mathematics and other areas.

2019-04-24

## Self-introduction: Hiroshi Yokota

I am Hiroshi Yokota, a physicist, who have joined iTHEMS since April, 2019. For 5 years, I have investigated a polymer physics, especially, theoretical framework of polymer crystallization. The polymer is a string-like large molecules whose characteristics play important roles in crystallization process. In contrast to the conventional crystal such as metals, the polymer crystal is a solid composed of crystal and amorphous regions due to the characteristics of the string-like molecules, where the polymer crystal is applied to production of industrial products, for example, films and threads (stuff of our clothes). In iTHEMS, by using the knowledge of polymer crystallization and of theoretical treatments of the polymer chain, I will investigate biophysics, especially, dynamics of the formation of the chromosomes.

2019-04-15

## Self-introduction: Takuya Sugiura

My name is Takuya Sugiura and I have been working at iTHEMS/RIKEN since April 2019. My main interest is on theoretical hadron physics, including interactions between hadrons, exotic hadrons, and heavy-quark systems. I am currently working on lattice QCD calculations of hadron interactions. Here at RIKEN I hope to see people from many different backgrounds; this will be a great opportunity to broaden my knowledge and scientific views.

2019-04-05

## Self-introduction: Nagisa Hiroshima

Hello, I am Nagisa Hiroshima. I have joined the iTHEMS from April 2019. My research interest covers varieties of topics in the Universe such as dark matter, structures of galaxies, and gamma-ray emitting objects. I am now working on dark matter search in the Universe with gamma-ray observations combining theoretical methods. I would like to have lots of daily discussions and to try much wider topics here.

2019-04-04

## Self-introduction: Hokuto Konno

I have been working in the mathematical study of gauge theory. In particular, I have developed Seiberg-Witten theory and Yang-Mills theory for families of 4-dimensional manifolds, and used them to examine the topology and geometry of such families. One of typical objects studied using gauge theory for families is the space consisting of all symmetries of a given 4-dimensional manifold. The space of symmetries is a natural mathematical object, but at the same time, this space is an infinite-dimensional complicated space in general, and consequently quite hard to attack. Interestingly, some of my recent work with several groups revealed that we can extract information about the space of symmetries of some 4-dimensional manifolds using gauge theory for families. I am trying to go ahead with this direction, and also to develop other aspects of gauge theory, relating to a sort of topological quantum field theory.

2019-03-11

## Self-introduction: Ryosuke Iritani

Hi, what's up! I'm Ryosuke (Ryo) Iritani. I'm originally from Kobe and did my biology and math undergrad at Kyoto University in Japan. I started my Ph.D. with Yoh Iwasa at Kyushu University in 2011 and worked as a research fellow (DC1) from 2013, visiting Lausanne (Switzerland) and Montpellier (France) to improve my theoretical skills. I then received Ph.D. in 2016 and started my postdoc at the University of California, Berkeley (as a fellow at the University of Exeter, the UK). I am broadly interested in the field of evolutionary ecology, with a special focus on evolutionary game theory in structured populations. I usually start with my modelings with a motivation to understand ecological phenomena, but I am really keen on developing the general theory of evolutionary ecology. I believe scientific collaboration is the prerequisite to do "good" science, and am therefore always open to collaboration opportunities. My current office is at Kyoto University, so please come talk to me. I like coffee, soccer, typographical fonts, cooking, math, and living organisms (with a special passion for insects).

2019-02-28

## Self-introduction: Yuki Koyanagi

Hi everyone. My name is Yuki Koyanagi and I am a visiting student at iTHEMS. My research interest is the study of protein structures, specifically how we can predict local structures of a protein from its sequence of amino acid residues. Knowing the structure of protein is important, because we know that a protein's function is highly dependent on its structure. A protein is made up of lots of amino acids connected like a chain, which then folds itself to a three-dimensional structure. One of the important factors that determine the folding is hydrogen bonds, that form at different places along the chain. I am looking into how we can predict the structure around each hydrogen bond. Another related question is finding out how many different hydrogen bond structures are possible for a given sequence of amino acids. I am a mathematician and work at a mathematics research centre, the interdisciplinary environment at iTHEMS is something new to me. I am very excited about the opportunity of meeting people from different fields with different backgrounds.

2019-01-17

## Self-introduction: Hiroyasu Miyazaki

Hello, everyone! My name is Hiroyasu Miyazaki. I am a mathematician. I mainly study algebraic varieties, which are geometric objects formed by the solutions of algebraic equations. To capture some essential information on algebraic varieties, it is useful to consider their group-theoretic incarnations, called (co)homology groups. Among the many versions of cohomologies, there is a universal one: the motive theory. It has been used to study common properties of cohomologies and their relationship. However, it has been observed that the motive theory loses some important arithmetic information of algebraic varieties. I am trying to overcome this problem by generalizing the motive theory. I was a member of iTHES in 2017. After that, I stayed at IMJ-PRG in Paris for one year, and came back to iTHEMS. I am really glad to join you again, and looking forward to many exciting discussions!

2018-11-27

## Self-introduction: Eren Mehmet Kiral

Hello, I am Eren Mehmet Kıral, I am currently a JSPS fellow at Sophia University working with Prof. Nakasuji on Bruhat cell decompositions of various matrix groups with a view towards finding number theoretic applications. I am also a visiting scientist here at ITHEMS. Starting March 2020 I will be an SPDR at RIKEN working at the Mathematical Science team of Advanced Intelligence Project (AIP) with Prof. Bannai. My research interest is in automorphic forms, and their associated L-functions, including the Riemann zeta function. Automorphic forms can be thought of generalizations of harmonics. Just like sin(nx), cos(nx) are the periodic harmonics on the real line, automorphic forms are the harmonics on more general homogeneous spaces. However unlike the real line, the group of transformations on the space forms a non-commutative Lie group, and hence the harmonic analysis (or equivalently the representation theory) on this group is more involved. It is fascinating that simply the setup of a discrete subgroup sitting inside a homogeneous space, spawns objects that are intrinsically related to number theory. I am looking forward to talking to physicists who work with Lie group representations on a regular basis.

2018-11-21

## Self-introduction: Yongjia Huang

I am Yongjia Huang, an International Program Associate (IPA) student studying in iTHEMS. My research interest is to explore what are the new states of matter at exceedingly high density and temperature. In the universe, various compact objects can reach more extreme condition than laboratory, thus they would be ideal candidates. I am studying the GRMHD simulation of binary neutron stars and neutron star-black hole mergers, which would generate various observable outcomes like gravitational wave (GW) radiation, kilonova, outflow and so on. With the GW astronomy era in progress, we would have a good chance to get the information like chirp mass and tidal deformability of the objects. Combining the GW data with the simulation works, then we can determine the equation of state of neutron stars efficiently. I am glad to have colleagues from different fields, and I believe our communication would play an important role in research.