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The eyes have it: Influenza virus infection beyond the respiratory tract

July 11 (Tue) 14:00 - 15:30, 2023

Jessica Belser (Research Microbiologist, Influenza Division, US Centers for Disease Control and Prevention (CDC), USA)

Influenza viruses are typically considered a respiratory pathogen, but are nonetheless capable of causing ocular complications in infected individuals and establishing a respiratory infection following ocular exposure. While both human and zoonotic influenza A viruses can replicate in ocular tissue and use the eye as a portal of entry, many H7 subtype viruses possess an ocular tropism in humans, though the molecular determinants that confer a non-respiratory tropism to a respiratory virus are poorly understood. In this presentation, I will discuss the establishment of several mammalian models to study ocular exposure and ocular tropism, ongoing investigations conducted in vitro and in vivo to elucidate properties associated with ocular-tropic viruses, and ways in which this information can improve efforts to identify, treat, and prevent human infection following ocular exposure to influenza viruses. Continued investigation of the capacity for respiratory viruses to gain entry to the respiratory tract and to cause ocular complications will improve understanding of how these pathogens cause human disease, regardless of the virus subtype or exposure route.

Venue: Okochi Hall / via Zoom

Event Official Language: English

A dynamical model for IRAS 00500+6713: the remant of a type Iax supernova SN1181 hosting a double degenerate merger product WD J005311

July 7 (Fri) 14:00 - 15:15, 2023

Takatoshi Ko (Ph.D. Student, Research Center for the Early Universe (RESCEU), The University of Tokyo)

Iras 00500+6713 is a bright nebula in the infrared, and X-ray observations show it consists of diffuse region and strong illuminated central region. In addition, optical spectral observations have recently revealed that fast wind with about 15,000 km/s is blowing from the massive white dwarf at the center. The properties of this nebula and white dwarf are very similar to those theoretically predicted by the binary white dwarf merger. In addition, its position on the celestial sphere and the extent make it a prime candidate for the remnant of SN 1181, a historical supernova. In this study, we propose that such a multilayered structure is formed by the collision between the remnant of SN 1181 and the stellar wind blowing from the central white dwarf, and succeeded in constructing a model that is consistent with the multi-wavelength observations. The results show that the progenitor of SN 1181 is a binary white dwarf with 1.3-1.9 solar mass and that their merger triggered an explosion that ejected mass with 0.2-0.6 solar mass to form the present object. The extent of the X-ray source concentrated in the center reveals that these winds began blowing within the last 30 years, and we will discuss this property as well.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

NU-Q-iTHEMS-YITP Lecture: Applications of Quantum Computation in Quantum Field Theory

July 6 (Thu) - 7 (Fri) 2023

Masazumi Honda (Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)

This lecture aims to provide an introductory explanation of the application of quantum computation in numerical simulations of quantum field theory. We will begin by covering the fundamental aspects of quantum computation, followed by a discussion on its application to simulating spin systems. Subsequently, we will delve into introductory explanations of continuous field quantum theory and lattice field quantum theory, and discuss their simulation methods. Additionally, practical exercises utilizing IBM Qiskit for quantum simulations will be conducted. Important Notice for Participants: Please note that loaner laptops for the practical exercises will not be provided, so please bring your own laptops. Prior to the lecture, please ensure that you have set up your environment to use Jupyter Notebook, for example, by installing Anaconda. Organizers: Quantum Research Center (NU-Q), Niigata University / Yukawa Institute for Theoretical Physics (YITP), Kyoto University Co-organizer: RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS)

Venue: #A317, Building A, Faculty of Science, Niigata University / via Zoom

Event Official Language: Japanese

Maximum Force Conjecture and Black Hole Thermodynamics

June 30 (Fri) 14:00 - 15:30, 2023

Yen Chin Ong (Professor, Center for Gravitation and Cosmology, College of Physical Science and Technology, Yangzhou University, China)

I review the current controversial status of the so-called "maximum force conjecture" in general relativity, whose validity has recently been debated. Then I will discuss how maximum force conjecture can nevertheless be relevant for black hole thermodynamics.

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

Event Official Language: English

Journal Club: Inference of hydrodynamic equations for active matter

June 29 (Thu) 16:00 - 17:00, 2023

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

Event Official Language: English

The classical equations of motion of quantised gauge theories

June 23 (Fri) 13:30 - 15:00, 2023

Tom Melia (Associate Professor, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)

The Einstein and Maxwell equations are the jewels in the crown of classical physics. But classical physics is only an approximation to nature, arising as a limit of the underlying quantum mechanical description. And in the case of both general relativity and electromagnetism, owing to their gauge theory nature, the full set of classical equations of motion are not guaranteed to follow from the quantum theory. The time-time and time-space components of the Einstein equations in GR and Gauss’ law in EM are enforced ‘by hand' in the quantisation procedure—a choice so as to make the classical-like states behave as per our classical belief. But what if our universe was actually described by another classical-like state? For GR, the resulting modification of the Einstein equations can be packaged as the inclusion of an auxiliary energy-momentum tensor describing a ’shadow’ matter that adds no additional degrees of freedom to the theory. The homogeneous and isotropic background piece of this auxiliary matter contributes to expansion of the universe identical to cold dark matter, and the inhomogeneous components source curvature perturbations that grow linearly at linear order.

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

Event Official Language: English

Matrix estimation via singular value shrinkage

June 21 (Wed) 15:30 - 16:30, 2023

Takeru Matsuda (Unit Leader, Statistical Mathematics Collaboration Unit, RIKEN Center for Brain Science (CBS))

In this talk, I will introduce recent studies on shrinkage estimation of matrices. First, we develop a superharmonic prior for matrices that shrinks singular values, which can be viewed as a natural generalization of Stein’s prior. This prior is motivated from the Efron–Morris estimator, which is an extension of the James–Stein estimator to matrices. The generalized Bayes estimator with respect to this prior is minimax and dominates MLE under the Frobenius loss. In particular, since it shrinks to the space of low-rank matrices, it attains large risk reduction when the unknown matrix is close to low-rank (e.g. reduced-rank regression). Next, we construct a theory of shrinkage estimation under the “matrix quadratic loss”, which is a matrix-valued loss function suitable for matrix estimation. A notion of “matrix superharmonicity” for matrix-variate functions is introduced and the generalized Bayes estimator with respect to a matrix superharmonic prior is shown to be minimax under the matrix quadratic loss. The matrix-variate improper t-priors are matrix superharmonic and this class includes the above generalization of Stein’s prior. Applications include matrix completion and nonparametric estimation.

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

Event Official Language: English

g-RIPS-Sendai 2023

June 19 (Mon) - August 8 (Tue) 2023

The Research in Industrial Projects for Students (RIPS) program has been held at the Institute for Pure & Applied Mathematics (IPAM) of the University of California, Los Angeles. In 2018, the Advanced Institute for Materials Research (AIMR) at Tohoku University in Sendai launched the g-RIPS-Sendai program in collaboration with IPAM, targeting graduate-level students in mathematical science and related disciplines. Participants from the U.S. and Japan will work on cross-cultural teams on research projects designed by industrial partners. The projects are expected to be of great interest to the partners and offer stimulating challenges to students. For more information on this year's g-RIPS-Sendai 2023, please visit the program website at the related link. Organizers: Research Alliance Center for Mathematical Science (RACMaS), Tohoku University Tohoku Forum for Creativity (TFC), Tohoku University Advanced Institute for Materials Research (AIMR), Tohoku University In cooperation with the following organizations: RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) Institute for Pure & Applied Mathematics (IPAM), UCLA

Venue: Advanced Institute for Materials Research (AIMR), Tohoku University

Phase reduction beyond the Kuramoto model

June 15 (Thu) 14:00 - 15:00, 2023

Iván León (Research Scientist, Department of Systems and Control Engineering, Tokyo Institute of Technology)

Many biological, engineering and natural systems can be modeled as populations of coupled oscillators where each oscillator behaves periodically. When these units are coupled to each other, emergent phenomena, as synchronization, appears. However, dealing with those systems is usually difficult due to the large number of degrees of freedom. Conditionality reduction techniques to obtain simple tractable models are usually considered. The most common method is "phase reduction" that allows to capture the dynamics of each oscillator with just one variable, the phase. The succeed of the method was clear when the Kuramoto model, derived through phase reduction, gave a simple explanation to collective synchronization. Despite this success, phase reduction is often limited to the Kuramoto model because of the challenge to obtain analytical expressions. The porpoise of this talk is to make clear that phase reduction beyond Kuramoto model is possible. On the first part of the talk we introduce phase reduction and its limitations. Then we show how it is possible to obtain analytical phase reduced model for weakly nonlinear oscillators. Finally, we talk about second order phase reduction where higher order corrections are included to capture the qualitative dynamics and improve accuracy.

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

Event Official Language: English

Deciphering speciation processes: a mathematical modelling approach to biodiversity patterns

June 8 (Thu) 10:00 - 11:00, 2023

Ryo Yamaguchi (Assistant Professor, Department of Advanced Transdisciplinary Sciences, Faculty of Advanced Life Science, Hokkaido University / Postdoctoral Research Fellow, Biodiversity Research Centre, University of British Columbia, Canada)

The grandeur and complexity of Earth’s biodiversity present a challenge to comprehend the intricate mechanisms underlying speciation. Once dubbed by Darwin as the “mystery of mysteries,” speciation remains a frontier in biology, with much still cloaked in obscurity. Applying mathematical models inspired by population genetics and individual-based simulations, I aim to shed light on the complex mechanisms underlying speciation. In this talk, I focus on the concept of a “speciation cycle,” a recurring pattern integral to the formation of biodiversity. In contrast to traditional views that focus solely on a single speciation event, our approach argues for the necessity of multiple intertwined processes. These include the coexistence of closely related species, ongoing diversification, and the accumulation of new species, all while avoiding extinction. By overviewing mathematical models of each evolutionary and ecological process, I will introduce their basic ideas, and examine under what conditions the formation and coexistence of new species are promoted. Then we further explore the temporal and spatial dimensions of speciation, looking closely at the intervals between speciation events and the steady buildup of biodiversity over geological timescales. By bridging the gap between microevolutionary processes and macroevolutionary patterns, I hope to enable the prediction of biodiversity patterns based on a deeper understanding of speciation mechanisms.

Venue: via Zoom

Event Official Language: English

Around homogeneous spaces of complex semisimple quantum groups

June 7 (Wed) 14:00 - 16:30, 2023

Kan Kitamura (Ph.D. Student, Graduate School of Mathematical Sciences, The University of Tokyo)

Murray and von Neumann initiated the study of operator algebras motivated by the mathematical foundations of quantum physics. Operator algebras give good language to treat quantum symmetries, such as quantum groups. In this talk, I would like to give an overview of this topic first. Then, I discuss the q-deformations of complex semisimple Lie groups. From an operator algebraic viewpoint, we can treat them as "locally compact" quantum groups. Especially, I will focus on its homogenous spaces coming from discrete quantum subgroups with a motivation toward the quantum analog of lattices. Unlike the classical setting, we can obtain a complete classification of its discrete quantum subgroups.

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

Event Official Language: English

Termination of Superradiance from a Binary Companion

June 6 (Tue) 13:30 - 15:00, 2023

Huiyu Zhu (Ph.D. Student, Department of Physics, Hong Kong University of Science and Technology, Hong Kong)

We study the impact of a binary companion on black hole superradiance at orbital frequencies away from the gravitational-collider-physics (GCP) resonance bands. A superradiant state can couple to a strongly absorptive state via the tidal perturbation of the companion, thereby acquiring a suppressed superradiance rate. Below a critical binary separation, this superradiance rate becomes negative, and the boson cloud gets absorbed by the black hole. This critical binary separation leads to tight constraints on GCP. Especially, a companion with mass ratio q > 10^−3 invalidates all GCP fine structure transitions, as well as almost all Bohr transitions except those from the |211> state. Meanwhile, the backreaction on the companion manifests itself as a torque acting on the binary, producing floating/sinking orbits that can be verified via pulsar timing. In addition, the possible termination of cloud growth may help to alleviate the current bounds on the ultralight boson mass from various null detections.

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

Event Official Language: English

Modelling radiation cancer treatment with ordinary and fractional differential equations

June 1 (Thu) 10:00 - 11:00, 2023

Kathleen Wilkie (Associate Professor, Department of Mathematics, Toronto Metropolitan University, Canada)

Fractional calculus has recently been applied to mathematical modelling of tumour growth, but its use introduces complexities that may not be warranted. Mathematical modelling with differential equations is a standard approach to study and predict treatment outcomes for population-level and patient-specific responses. Here we use patient data of radiation-treated tumours to discuss the benefits and limitations of introducing fractional derivatives into three standard models of tumour growth. The fractional derivative introduces a history-dependence into the growth function, which requires a continuous death-rate term for radiation treatment. This newly proposed radiation-induced death-rate term improves computational efficiency in both ordinary and fractional derivative models. This computational speed-up will benefit common simulation tasks such as model parameterization and the construction and running of virtual clinical trials.

Venue: via Zoom

Event Official Language: English

Quantum uncertainty of fields and its effect on entanglement generation in quantum particles

May 31 (Wed) 14:00 - 15:15, 2023

Yuki Sugiyama (Ph.D. Student, Department of Physics, Graduate School of Science, Kyushu University)

The unification of gravity and quantum mechanics is one of the important problems. To elucidate the theory of quantum gravity, it is becoming more and more important to get any hint of the quantum nature of gravity. In particular, the quantum-gravity-induced-entanglement of masses (QGEM) scenario, which is expected to observe the quantum nature of non-relativistic gravity, has recently attracted great attention. In this talk, we show the effect of relativistic fields on entanglement generation based on quantum field theory. We also discuss the relationship between the entanglement generation and quantum uncertainty of the fields.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

Spectral correlations and scrambling dynamics in Sachdev-Ye-Kitaev type models

May 30 (Tue) 13:30 - 15:00, 2023

Masaki Tezuka (Assistant Professor, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

Note: Due to unexpected trouble, we have made the decision to postpone the seminar scheduled for February 21 to May 30. Sorry for the trouble. Abstract: The Sachdev-Ye-Kitaev (SYK) model, proposed in 2015, is a quantum mechanical model of N Majorana or complex fermions with all-to-all random four-body interactions. The model has attracted significant attention over the years due to its features such as the existence of the large-N solution with maximally chaotic behavior at low temperatures and holographic correspondence to low-dimensional gravity. The sparse version of the SYK model reproduces essential features of the original model for reduced numbers of disorder parameters. We recently proposed [1] a further simplification, where we set the nonzero couplings to be +1 or -1 rather than sampling from a continuous distribution such as Gaussian. This binary-coupling model exhibits strong correlations in the spectrum, as observed in the spectral form factor, more efficiently in terms of the number of nonzero terms than in the Gaussian distribution case. We also discuss the scrambling dynamics with the binary-coupling sparse SYK model, comparing the model with the original model as well as the SYK model with random two-body terms [2], where the localization of the many-body eigenstates in the Fock space has been quantitatively studied [3,4].

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

Event Official Language: English

Molecular and evolutionary bases of Pieris butterflies for overcoming diverse chemical defenses in their host plants

May 25 (Thu) 16:00 - 17:00, 2023

Yu Okamura (JSPS Research Fellow PD, Department of Biological Sciences, Graduate School of Science, The University of Tokyo)

In terrestrial ecosystems, plants and herbivorous insects account for more than half of the described species and play quite important ecological roles. Plants and herbivorous insects have strong chemical interaction as plants defend themselves with various defense compounds such as secondary metabolites and herbivores adapt to it by evolving detoxification mechanisms. Larvae of Pieris butterflies feed on Brassicaceae plants as the main host. Brassicaceae plants contain diverse glucosinolates (GLS) as a main chemical defense, which can be rapidly hydrolyzed into toxic isothiocyanates by a plant enzyme called myrosinase upon tissue damage. Larvae of Pieris butterflies are known to express nitrile-specifier protein in their gut and this can redirect toxic breakdown products of GLSs to less toxic metabolites. Although NSP is considered an evolutionary key innovation for Pieridae that enabled these butterflies to colonize GLS-containing plants, it has been largely unclear whether NSP is enough for Pieris butterfly larvae to overcome the diverse types of GLS they encounter in their host plants. In this seminar, I would like to introduce our recent findings showing that Pieris butterfly larvae not only use NSP but also use its ortholog major allergen (MA) to overcome the diverse types of GLS in their Brassicaceae host plants. We found that Pieris larvae show fine-tuned regulation of those two adaptive genes depending on the chemical profiles of their host plants. Furthermore, those two adaptive genes have different evolutionary trajectories in macro- and micro-evolutionary scales among Pieris species or populations associated with their pattern of host plant usage. Moreover, with an approach using CRISPR/Cas9 genome editing, we showed that both NSP and MA have different but complementary roles in disarming GLS-based defenses in their host plants and that both genes are crucial for Pieris in overcoming their host plant’s major chemical defense. Those highlight that having both NSP and MA is a key for Pieris butterflies to overcome the diverse types and GLS and, consequently, adapt to a wider range of Brassicaceae hosts. Our results illuminate that gene duplication, functional differentiation, and the evolution of gene regulation mechanisms are all crucial for herbivorous insects to overcome co-evolving chemical defenses in their host plants.

Venue: via Zoom

Event Official Language: English

Hydrodynamic limit and the fluctuating hydrodynamics for large-scale interacting systems

May 24 (Wed) 14:00 - 16:30, 2023

Kohei Hayashi (Visiting Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

In these decades, a great deal of works has been devoted to understand macroscopic phenomena, such as diffusion, aggregation or pattern formation, from the viewpoint of microscopic systems. Hydrodynamic limit, or fluctuating hydrodynamics, is a fundamental framework to explain the macroscopic behavior of physical quantities in mathematically rigorous ways from a system of the vast numbers of microscopic agents under random interactions, which system is called the large-scale interacting system. In this framework, our central aim is to derive partial differential equations (PDEs) which describe time evolution of some macroscopic quantities, starting from the large-scale interacting systems; hydrodynamic limit is a procedure to derive deterministic PDEs with help of the law of large numbers, whereas stochastic PDEs are derived under the scale of the central limit theorem by fluctuating hydrodynamics. In this talk, I would like to explain basic concepts of hydrodynamic limit and fluctuating hydrodynamics, through some simple models. In the first part, I will give a concise exposition on Markov processes as preliminaries and then state some results on scaling limits of simple exclusion processes as a pedagogical example. In the second part, I will talk about recent progress on universality which appears in fluctuating hydrodynamics. Especially, I would like to talk about the universality of the Kardar-Parisi-Zhang equation, and its mathematical background.

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

Event Official Language: English

Statistical methods to probe binary stellar evolution with ZTF and LISA data

May 23 (Tue) 13:30 - 15:00, 2023

Lucy McNeill (JSPS Fellow, Department of Physics, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

The Laser-Interferometer-Space-Antenna (LISA) will be capable of detecting all galactic double neutron star binaries (DNSBs) with orbital periods < 20 minutes, as well as 10-100’s of thousands of double white dwarf binaries. I will present our method to use LISA detections to constrain the formation frequencies of galactic DNSBs, which are determined by supernova physics and various mass exchange processes. Next, I summarise the key differences in DNSBs and white dwarf binaries (WDBs) in the context of future LISA observations, as well as the current Zwicky Transient Facility (ZTF) for the latter. Then we will examine the current catalogue of short period white dwarf binaries (orbital periods < 1 hour) detected by ZTF so far, including the first ever measurement (Burdge et al. 2023) of the temperature of a mass transferring white dwarf in a binary. Here I will make the case that taken together, these observations are in conflict with the theoretical picture commonly used in Galactic modelling- specifically related to cooling and mass transfer leading to WDB mergers. However, heating from tidal interactions may explain and mediate this inconsistency. Finally I will put these results into context regarding preparing for the unprecedented data set of galactic white dwarf binaries from LISA in the 2030s.

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

Event Official Language: English

X-ray study on the synchrotron emission in Kepler's SNR

May 19 (Fri) 14:00 - 15:15, 2023

Vincenzo Sapienza (Ph.D. Student, Department of Physics, Graduate School of Science, The University of Tokyo)

Synchrotron X-ray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high energy electrons accelerated at the shock front. We performed a spatially resolved spectral analysis of the young Kepler's SNR, where we identify two different regimes of particle acceleration. In the north, where the shock interacts with a dense circumstellar medium (CSM), we found a more efficient acceleration than in the south, where the shock velocity is higher and there are no signs of shock interaction with dense CSM. We also studied the temporal evolution of the synchrotron flux, from 2006 to 2014. A number of regions show a steady synchrotron flux and equal cooling and acceleration times. However, we found some regions where we measured a significant decrease in flux from 2006 to 2014. Our results display a coherent picture of the different regimes of electron acceleration observed in Kepler's SNR. Also If I will have time during the seminar it will be nice to present also some preliminary results I will have in the SN 1987A project.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

Excursion Theory, Galton Watson Trees and their Scaling Limits

May 18 (Thu) 16:00 - 17:00, 2023

Christy Koji Kelly (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

In this talk we aim to introduce a recent perspective in probability theory that views random trees as random excursions with additional data. This perspective is particular suited to the study of the scaling limit of tree-valued random processes. Excursion theory is a useful and relatively elementary tool allowing one to derive rather explicit information about the local and global geometry of the resultant continuum trees which in turn can be used to derive information about large random trees. We illustrate these ideas in the context of the Brownian continuum random tree, the scaling limit of critical Galton-Watson trees and a structure that arises naturally in various contexts in physics; in particular the Brownian continuum random tree is a pathological model of quantum spacetime. Despite the fundamentally mathematical nature of the talk, the aim is to keep the presentation essentially heuristic emphasising key intuitions over rigorous proof. The content itself should be relevant to biologists interested in the theory of branching processes or coalescent theory.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English