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Interactions between Algebraic Topology and Representation Theory by Toric Code

October 2 (Mon) - 4 (Wed) 2023

Minkyu Kim (Research Fellow, School of Mathematics, Korea Institute for Advanced Study (KIAS), Republic of Korea)

Toric code is an error correction code designed by Kitaev in late 1990’s, which contributes to the birth of topological quantum computation. The goal of these lectures is to introduce toric code and related mathematics. We will explain an interaction between low-dimensional topology and representation of Drinfeld double. Especially, we will encode several operations (e.g. braidings) on representations into topology and geometry on surfaces. If time allows, we will give an overview of how toric code arises from chain complexes, which will be the prequel of our talk at Tokyo-Seoul Conference on Oct 6. These lectures will be fundamental and concrete. We hope that the audience are familiar with basic concepts of finite groups and Hopf algebras. These lectures will be held from Oct 2 to Oct 4, each from 13:30 to 15:00, for a total of 3 lectures. Oct 2 (mon) Introduction to toric code. Oct 3 (tue) Introduction to non-abelian toric code. Oct 4 (wed) Further studies on toric code.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

The 4th "Medicine and Mathematics" Workshop

September 29 (Fri) - 30 (Sat) 2023

We will have the 4rd workshop on "Medicine and Math" in Sendai (hybrid style) on Sep.29-30, 2023. Please join if you are interested in this interdisciplinary subject. Most of the talks are in Japanese except for session 4. For more information and registration, please visit the related links. For more information and registration, please visit the related links. Co-organized by: Center for Integrative Medicine and Physics, Kyoto University Institute for Advanced Study (KUIAS) Center for Science Adventure and Collaborative Research Advancement (SACRA), Kyoto University Tohoku Forum of Creativity, Tohoku University RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS)

Venue: TOKYO ELECTRON House of Creativity, Katahira Campus, Tohoku University / via Zoom

Response to sounds in the cochlea of the inner ear

September 26 (Tue) 16:00 - 17:00, 2023

Takeru Ota (Assistant Professor, Division of Glocal Pharmacology, Department of Pharmacology, Graduate School of Medicine, Osaka University)

We hear sounds. The acoustic wave passes through the ear canal and oscillates the ear drum. The middle ear bones conduct the mechanical input into the cochlea, the primary sensory organ of hearing. A sensory epithelium, a sheet-like tissue inside the snail-like structure, decomposes the sound frequencies into each component along the coil. The sound stimulation evokes nanometer-scale motions in the epithelium which contains hair cells. The cells expose their hair bundles to endolymph, the extracellular solution characterized by high [K+]. The epithelium vibration changes the open probability of mechanosensitive channels on the bundles and modulates the ion entering from the fluid. Inner hair cells release neurotransmitters to the auditory nerves and outer hair cells shrink and elongate their soma depending on the receptor potentials. The electromotive response amplifies the vibration of the sensory epithelium and contributes to the faint sound sensitivity and sharp frequency selectivity. With developed technique, we observed the sound-evoked vibrations in the sensory epithelium. In this seminar, I will introduce the physiological background of the cochlear physics and the recent results.

Venue: via Zoom

Event Official Language: English

First X-ray polarimetry of neutron stars with strong magnetic fields

September 25 (Mon) 13:30 - 15:00, 2023

Toru Tamagawa (Chief Scientist, High Energy Astrophysics Laboratory, RIKEN Cluster for Pioneering Research (CPR))

We launched the world's first highly sensitive X-ray polarimetry satellite, IXPE, in December 2021. IXPE began observations in January 2022 and detected significant X-polarization from objects in all categories. The IXPE observations have opened a new window in astrophysics. In this talk, I will introduce IXPE and present the results of X-ray polarimetry observations of neutron stars with strong magnetic fields (magnetars and neutron star binaries). The neutron star observations show results quite different from our prior expectations and await further theoretical interpretation.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Induced gravitational waves from inflaton oscillons

September 22 (Fri) 14:00 - 15:30, 2023

Kaloian Dimitrov Lozanov (Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)

We present a new way to study cosmic inflation with gravitational waves. The gravitational signal is generated thanks to nonlinear structures in the inflaton field, called oscillons. This novel probe allows us to test models of inflation which are challenging to test with CMB experiments.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

Predicting future biodiversity with species distribution models: current applications, persistent issues, and where to go from here

September 19 (Tue) 16:00 - 17:00, 2023

Jamie M. Kass (Associate Professor, Graduate School of Science, Tohoku University)

There is much current interest in macroecology to make predictions of future biodiversity patterns in order to inform both regional and global priorities for conservation and sustainability of ecosystem functions and services. Species distribution models use data on species' occurrence records, environmental predictor variables, and sometimes other data sources to estimate niche relationships and distribution extents—these models can also be combined to make biodiversity estimates. As the field of species distribution modeling has grown considerably over the past two decades, many approaches now exist to build models, evaluate their performance, and use them to make predictions for unsampled areas and times. I will provide an overview of current techniques to predict future distributions of species and biodiversity, detail some issues with these techniques concerning uncertainty and realism of predictions, and contribute my humble thoughts on where the field should go from here.

Venue: via Zoom

Event Official Language: English

Classification of Meromorphic Spin 2-dimensional Conformal Field Theories of Central Charge 24

September 19 (Tue) 15:00 - 16:30, 2023

Möller Sven (Group Leader, Department of Mathematics, University of Hamburg, Germany)

We classify the self-dual (or holomorphic) vertex operator superalgebras (SVOAs) of central charge 24, or in physics parlance the purely left-moving, spin 2-dimensional conformal field theories with just one primary field. There are exactly 969 such SVOAs under suitable regularity assumptions and the assumption that the shorter moonshine module VB^# is the unique self-dual SVOA of central charge 23.5 whose weight-1/2 and weight-1 spaces vanish. Additionally, there might be self-dual SVOAs arising as "fake copies" of VB^# tensored with a free fermion F. We construct and classify the self-dual SVOAs by determining the 2-neighbourhood graph of the self-dual (purely bosonic) VOAs of central charge 24 and also by realising them as simple-current extensions of a dual pair containing a certain maximal lattice VOA. We show that all SVOAs besides VB^# x F and potential fake copies thereof stem from elements of the Conway group Co_0, the automorphism group of the Leech lattice. By splitting off free fermions F, if possible, we obtain the classification for all central charges less than or equal to 24. This is based on joint work with Gerald Höhn (arXiv:2303.17190)

Venue: Seminar Room #359

Event Official Language: English

Quasi-BPS categories

September 13 (Wed) 10:00 - 11:30, 2023

Yukinobu Toda (Professor, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)

In this talk, I will explain the notion of "Quasi-BPS category". This is the (yet to be defined) category which categorifies BPS invariants on Calabi-Yau 3-folds, and plays an important role in categorical wall-crossing in Donaldson-Thomas theory. I will explain the motivation of quasi-BPS categories, give definition in the case of symmetric quivers with potential (a local model of CY 3-folds), and their properties. If time permits, I will explain quasi-BPS categories for local K3 surfaces and their relation to derived categories of hyperkahler manifolds. This is a joint work in progress with Tudor Padurariu.

Venue: Seminar Room #359

Event Official Language: English

Parameter Fitting for Glucose Homeostasis - Searching for Methods to Predict and Diagnose

September 12 (Tue) 16:00 - 17:00, 2023

Gabriel Gress (Specially Appointed Research Fellow, Mathematical Science Group, Advanced Institute for Materials Research (AIMR), Tohoku University)

The human body regulates glucose through a complex web of biological interactions, for which state-of-the-art models require dozens of variables and parameters to even emulate. But while we've had devices to measure glucose levels as far back as the 1980's, nearly all of the remaining variables and parameters cannot be measured directly to this day. While continuous glucose monitors have greatly improved the health of diabetic patients, there are still many barriers in the diagnosis of at-risk patients as well as accurately dispersing insulin to counteract future trends in glucose levels. While glucose readings are only a small window into one of many factors of how the human body maintains glucose homeostasis, we search for ways to leverage the high-frequency and high-volume data to improve the state of diagnosis and prediction in diabetic patients.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

The Cosmic Gravitational Microwave Background

September 6 (Wed) 15:00 - 16:30, 2023

Jan Schuette-Engel (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

The thermal plasma in the early universe produced a guaranteed stochastic gravitational wave (GW) background, which peaks today in the microwave regime and was dubbed the cosmic gravitational microwave background (CGMB). I show that the CGMB spectrum encodes fundamental information about particle physics and gravity at ultra high energies. In particular, one can determine from the CGMB spectrum the maximum temperature of the universe and the effective degrees of freedom at the maximum temperature. I also discuss briefly how quantum gravity effects arise in the CGMB spectrum as corrections to the leading order result.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

MNISQ: A Large-Scale Quantum Circuit Dataset for Machine Learning on/for Quantum Computers in the NISQ era

August 29 (Tue) 14:00 - 15:30, 2023

Leonardo Placidi (Ph.D. Student, Graduate School of Engineering Science, Osaka University)

We introduce the first large-scale dataset, MNISQ, for both the Quantum and the Classical Machine Learning community during the Noisy Intermediate-Scale Quantum era. MNISQ consists of 4,950,000 data points organized in 9 subdatasets. Building our dataset from the quantum encoding of classical information (e.g., MNIST dataset), we deliver a dataset in a dual form: in quantum form, as circuits, and in classical form, as quantum circuit descriptions (quantum programming language, QASM). In fact, also Machine Learning research related to quantum computers undertakes a dual challenge: enhancing machine learning by exploiting the power of quantum computers, while also leveraging state-of-the-art classical machine learning methodologies to help the advancement of quantum computing. Therefore, we perform circuit classification on our dataset, tackling the task with both quantum and classical models. In the quantum endeavor, we test our circuit dataset with Quantum Kernel methods, and we show excellent results with up to 97% accuracy. In the classical world, the underlying quantum mechanical structures within the quantum circuit data are not trivial. Nevertheless, we test our dataset on three classical models: Structured State Space sequence model (S4), Transformer, and LSTM. In particular, the S4 model applied on the tokenized QASM sequences reaches an impressive 77% accuracy. These findings illustrate that quantum circuit-related datasets are likely to be quantum advantageous, but also that state-of-the-art machine learning methodologies can competently classify and recognize quantum circuits. We finally entrust the quantum and classical machine learning community.

Venue: #345, 3F, Main Research Building, RIKEN Wako Campus (Main Venue) / via Zoom

Event Official Language: English

Landscape structure drives eco-evolution in host parasite systems

August 24 (Thu) 16:00 - 17:00, 2023

Jhelam Deshpande (Ph.D. Student, Biodiversity: dynamics, interactions and conservation team, Institute of Evolutionary Science of Montpellier, France)

As all biological and many artificial systems, hosts and their parasites are most often spatially structured. Besides this highly relevant spatial context, parasites may change through time due to to evolutionary processes, including mutation and selection. These facts imply that we must study host-parasite systems taking into account space and evolution. Past work has mainly focused on simple spatial structures, but how parasites evolve in realistically complex landscapes remains unclear, hampering the translation of theoretical predictions to real ecological systems.Therefore, we here develop an eco-evolutionary metapopulation model of host-parasite interactions in which hosts and parasites disperse through realistically complex spatial graphs. Parasite virulence, a parasite life-history trait of central importance that here impacts host reproduction, is able to evolve. Our model therefore captures the eco-evolutionary feedback loop between host demography and parasite evolution in space. In order to gain a general understanding of parasite eco-evolution in space, we analyse our model for spatial networks that represent terrestrial (represented by random-geometric graphs; RGG) and riverine aquatic (represented by optimal channel networks; OCN) landscapes. We find that evolved virulence is generally a function of host dispersal, with a unimodal relationship in aquatic and a saturating relationship in terrestrial landscape, and this is driven by higher order network properies. Consistent with previous work, we show that our results are driven by kin selection, because dispersal and landscape structure impact both patterns of relatedness and availability of susceptible hosts. Our model yields readily testable predictions, including that terrestrial parasites should be more virulent than aquatic parasites are low dispersal rates and vice versa as dispersal increases. These differences in evolved virulence directly lead to differences in system stability, with more virulent parasites more often leading to host extinction. Thus, in this study we highlight the role of landscape structure in driving eco-evolutionary dynamics of parasites.

Venue: via Zoom

Event Official Language: English

Exploring 2D Quantum Spacetime Based on Causal Dynamical Triangulations

August 21 (Mon) - 23 (Wed) 2023

Yuki Sato (Associate Professor, National Institute of Technology (KOSEN), Tokuyama College)

This is the fourth event by the Quantum Gravity Gatherings (QGG) Study Group at RIKEN iTHEMS. For this event we have invited Prof. Yuki Sato, National Institute of Technology, Tokuyama College, to give pedagogical lectures on the causal dynamical triangulations approach to quantum gravity. We wish this event to provide insights to researchers in related fields. The causal dynamical triangulations formalism appears to be one of the most promising constructive approaches to quantum gravity: possessing deep links with the asymptotic safety programme and Hořava-Lifshitz gravity, causal dynamical triangulations appears to avoid many of the well-known pathologies characteristic of its Euclidean analogue. As an example the emergence of spacetime geometry remains possible in various spacetime dimensions. While many of the results in higher dimensions are understood only at the numerical level, the analytical study of the approach in two spacetime dimensions is relatively well developed; Yuki Sato is a leading expert on these latter developments and we are very lucky he has agreed to present the understanding of 2D causal spacetime coming from this approach in a manner consistent with the Quantum Gravity Gatherings philosophy. This intensive lecture series is intended to be a lively and participatory event, not just a listening experience. For this reason, the number of participants will be limited to about 30 with priority given to graduate students and young post-docs; the intensive talk will be given in a face-to-face blackboard style (in English, no online streaming) to allow for informal and lively Q&A discussions. The program will also include short talk sessions, where interested participants can give a 5 min talk on a topic of their choice (their research, reviews on some works, what they want to study in the future, etc.). Registration is available via the dedicated website.

Venue: #435-437, 4F, Main Research Building

Event Official Language: English

Mating system of buckwheat

August 17 (Thu) 16:00 - 17:00, 2023

Jeffrey Fawcett (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

Buckwheat (soba in Japanese) has a slightly unusual mating system called heterostylous self-incompatibility where two types of individuals coexist, one that produces flowers with a long style (female part of the flower) and short stamen (male part of the flower), and the other that produces flowers with a short style and long stamen. Mating is only successful when it occurs between the different types of individuals. It is a bit similar to sexual dimorphism where males and females coexists but in this case all individuals have both male and female organs. In this talk, I will introduce the basics of this mating system in buckwheat and some work we have been doing. In particular, I will talk about its genetic architecture and some parallels observed with other plants in which a similar mating system evolved independently. The talk will be aimed at non-experts so non-biologists are also welcome to attend.

Venue: via Zoom

Event Official Language: English

Dark matter heating vs vortex creep heating in old neutron stars

August 7 (Mon) 13:30 - 15:00, 2023

Motoko Fujiwara (Postdoctoral Researcher, Theoretical Particle Physics Group, Technical University of Munich, Germany)

Old isolated neutron stars have been gathering attention as targets to probe Dark Matter (DM) through temperature observations. DM will anomalously heat neutron stars through its gravitational capture and annihilation process, which predicts surface temperature as T_s ~ (1 − 3) × 10^3 K for t > 10^6 years. We may put constraints on DM-nucleon scattering cross section by finding even colder neutron stars. This story, however, assumed that there is no relevant heating source for old neutron stars. In this talk, we discuss the creep motion of vortex lines in the neutron superfluid of the inner crust as the heating mechanism. This creep mechanism is inherent in the structure of neutron stars. The heating luminosity is proportional to the time derivative of the angular velocity of the pulsar rotation, and the proportional constant J has an approximately universal value for each neutron star. If this vortex creep heating is quantitatively relevant against DM heating, this mechanism may cause a serious background to probe DM. The J parameter can be determined from the temperature observation of old neutron stars because the heating luminosity is balanced with the photon emission in the late time. We study the latest data of neutron star temperature observation and find that these data indeed give similar values of J, in favor of the assumption that these neutron stars are heated by the frictional motion of vortex lines. Besides, these values turn out to be consistent with the theoretical calculations of the vortex-nuclear interaction. Integarting all the results, we evaluate the vortex creep heating and conclude its significance against DM heating.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Evidence against a strong first-order phase transition in neutron star cores: impact of new data

August 1 (Tue) 13:30 - 15:00, 2023

Len Brandes (Ph.D. Student, Technical University of Munich, Germany)

Information on the phase structure of strongly interacting matter at high baryon densities can be gained from observations of neutron stars and their detailed analysis. Bayesian inference methods are used to set constraints on the speed of sound in the interior of neutron stars, based on recent multimessenger data in combination with low-density constraints based on chiral effective field theory and perturbative QCD constraints at asymptotically high densities. A detailed re-analysis is performed in order to clarify the influence of the latter constraints on the inference procedure. The impact of the recent new heavy (2.35 M_sol) black widow pulsar PSR J0952-0607 and of the unusually light supernova remnant HESS J1731-347 is inspected. One of the consequences of including PSR J0952-0607 in the database is a further stiffening of the equation-of-state, resulting in a 2.1 solar-mass neutron star in a reduced central density of less than five times the equilibrium density of normal nuclear matter. A systematic Bayes factor assessment quantifies the evidence (or non-evidence) for small sound speeds, necessary for a strong first-order phase transition, within the range of densities realized in the core of neutron stars. Given the presently existing database, it can be concluded that the occurrence of a strong first-order phase transition in the core of even a 2.1 solar-mass neutron star is unlikely, while a continuous crossover cannot be ruled out.

Venue: via Zoom (Main Venue) / Seminar Room #132

Event Official Language: English

Evolution of dormant egg production and their hatching rate in Aedes albopictus

July 13 (Thu) 16:00 - 17:00, 2023

Yusuke Kuwano (Ph.D. Student, The Graduate University for Advanced Studies (SOKENDAI))

Mosquitoes are important insect vectors of infectious diseases in humans, and knowledge of their population dynamics is pivotal in disease control. Some mosquito species have dormancy in their life history to survive harsh environments. However, the population dynamics of mosquitoes have not yet been well understood due to the lack of field and experimental data on dormancy. For that reason, I modeled the population dynamics of mosquitoes that face environmental fluctuations and examine the evolution of egg dormancy strategy to survive harsh periods. I found that the ESS dormancy fraction monotonically increases with the period of environmental fluctuation. Next, I analyzed evolutionary traits of the dependence of the dormancy rate and the hatching rate from dormant egg on soil moisture content and conducted evolutionary simulations using actual weather measurement in Tokyo. The results of the hatching rate from dormant egg showed that two mosquito phenotypes having distinctly different responses to soil moisture were selected.

Venue: via Zoom

Event Official Language: English

Conserved charges in the quantum simulation of integrable spin chains

July 12 (Wed) 13:30 - 15:00, 2023

Juan William Pedersen (Ph.D. Student, Graduate School of Arts and Sciences, The University of Tokyo)

In this talk, we present the result of the quantum simulation of the spin-1/2 Heisenberg XXX spin chain. We implement the integrable Trotterization algorithm, which allows us to control the Trotter error with conserved charges remaining conserved, on a real quantum computer and classical simulators. We study the effects of quantum noise on the time evolution of several conserved charges and specifically observe the decay of the expectation values. Our work improves our understanding of quantum noises and can potentially be applied to benchmark quantum devices and algorithms.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English