3rd QGG Intensive Lectures: Spinfoam path integrals for Quantum Gravity

July 26 (Wed) - 28 (Fri), 2023

Etera Livine (Research Director CNRS, Ecole Normale Supérieure de Lyon, France)

At the crossroads of several approaches to quantum gravity, Spinfoams propose a discrete path integral for quantum general relativity built from topological field theory. With the spectrum of geometric operators directly read from the representation theory of the local symmetry group, they can be interpreted as a quantized version of Regge calculus and can be understood as implementing the dynamics of quantum states geometry in loop quantum gravity. I will explain the basics of the formalism, the motivations, the mathematical framework and the main tools. In three space-time dimensions, the spinfoam quantization of 3d gravity is given by the Turaev-Viro topological invariant, which is intimately related to the quantization of Chern-Simons theory. I will explain in particular how the spinfoam amplitudes solve the Wheeler-de Witt equation, implement the invariance under 3d diffeomorphisms (despite being formulated in a discretized space-time) and lead to a quasi-local version of holography. In four space-time dimensions, general relativity can be formulated as an almost-topological theory and I will explain how the existing spinfoam models introduce a sea of topological defects to re-create the gravitational degrees of freedom from a topological path integral. Finally, I will show how spinfoams are naturally defined in terms of group field theory, which are generalized tensor models, and the prospects that this opens. I will conclude with the main challenges and open lines of research of the field. Program: July 26 10:00 - 10:15 Registration and reception 10:15 - 11:45 Lecture 1 11:45 - 13:30 Lunch & coffee break 13:30 - 15:00 Lecture 2 15:00 - 16:00 Coffee break 16:00 - 17:00 Lecture 3 17:10 - 18:30 Short talk session July 27 10:00 - 11:45 Lecture 4 11:45 - 13:30 Lunch & coffee break 13:30 - 15:00 Lecture 5 15:00 - 16:00 Coffee break 16:00 - 17:00 Lecture 6 17:30 - 20:00 Banquet July 28 10:00 - 11:45 Lecture 7 11:45 - 13:30 Lunch & coffee break 13:30 - 15:00 Lecture 8 15:00 - 16:00 Coffee break 16:00 - 17:30 Lecture 9 & Closing

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

Event Official Language: English

Exploring interior magnetic-field in neutron stars

July 25 (Tue) at 10:00 - 12:00, 2023

Yasufumi Kojima (Emeritus Professor, Hiroshima University)

Neutron stars are well known as a good laboratory to test high-density material. Magnetic field on the stars is relevant to some astrophysical phenomena, and understanding the effect is crucial to extract information of the stellar interior. In this talk, I start with discussing some evidence and implications for intense magnetic field, and focus on the magneto-elastic equilibrium in the solid crust. The study leads to upper limit of deformation, and beyond a threshold crustal fracture observed burst on strongly magnetized neutron stars. The model is still primitive, and further development is desirable to connect micro-physics with astrophysical observation.

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

Event Official Language: English

Electronic instabilities emerging from higher-order van Hove singularities

July 24 (Mon) at 17:00 - 18:15, 2023

Xinloong Han (Postdoctoral Fellow, Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, China)

Time: 5pm ~ 6:15pm (JST); 10am ~ 11:15am (CET); 4pm ~ 5:15pm (Taiwan) Field: condensed matter physics Keywords: topological superconductor, Van Hove singularity, Hubbard model, Kagome lattices Abstract: Competing correlated electronic states are a central topic in condensed matter physics. A typical example is the close competition between spin density wave and d-wave superconductivity in the Hubbard model on the square lattice near half filling where the band structures have saddle points at which the Fermi surface topology changes from hole type to electron type. The saddle points are called van Hove singularity (VHS) points, and host diverging density of states with power-law behavior in the two dimensions. Recently, another type of VHS, namely the higher-order VHS was investigated in ABC-stacked trilayer graphene and twisted bilayer graphene. In this talk, I will first introduce the higher-order VHS, and make comparisons to the conventional VHS. Then I will discuss the enhanced nematicity driven by large flavor number with higher-order VHSs on the square and Kagome lattices. Finally, I will show that robust topological superconductivity can emerge on the square lattice due to interplay of spin-orbital coupling and higher-order VHSs.

Venue: Hybrid Format (Common Room 246-248 and Zoom)

Event Official Language: English

The 23rd MACS Colloquium

July 14 (Fri) at 14:45 - 18:00, 2023

Tetsushi Ito (Associate Professor, Division of Mathematics and Mathematical Sciences, Graduate School of Science, Kyoto University)
Aya Ishihara (Professor, International Center for Hadron Astrophysics / Institute for Advanced Academic Research, Chiba University)

14:45-15:00 Teatime discussion 15:00-16:00 Talk by Dr. Tetsushi Ito (Associate Professor, Division of Mathematics and Mathematical Sciences, Graduate School of Science, Kyoto University) 16:15-17:15 Talk by Prof. Aya Ishihara (Professor, International Center for Hadron Astrophysics / Institute for Advanced Academic Research, Chiba University) 17:15-18:00 Discussion

Venue: Maskawa Hall, 1F, Maskawa Building for Education and Research

Event Official Language: Japanese

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

July 13 (Thu) at 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) at 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

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

July 11 (Tue) at 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

Searching for dark matter subhalos in the Fermi-LAT catalog with Bayesian neural networks

July 10 (Mon) at 16:30 - 18:00, 2023

Slivia Manconi (Marie Skłodowska-Curie Fellow, Laboratoire d'Annecy-Le-Vieux de Physique Theorique (LAPTh), CNRS, France)

Machine learning techniques are powerful tools to tackle diverse tasks in current astroparticle physics research. For example, Bayesian neural networks provide robust classifiers with reliable uncertainty estimates, and are particularly well suited for classification problems that are based on comparatively small and imbalanced data sets, such as the gamma-ray sources detected by Fermi-Large Area Telescope (LAT). About one third of the gamma-ray sources collected in the most recent catalogs remain currently unidentified. Intriguingly, some of these could be exotic objects such as dark subhalos, which are overdensities in dark matter halos predicted to form by cosmological N-body simulations. If they exist in the Milky Way, they could be detected as gamma-ray point sources due to the annihilation or decay of dark matter particles into Standard Model final states. In this talk I will discuss our recent work* in which, after training on realistic simulations, we use Bayesian neural networks to identify candidate dark matter subhalos among unidentified gamma-ray sources in Fermi-LAT catalogs. Our novel framework allows us to derive conservative bounds on the dark matter annihilation cross section, by excluding unidentified sources classified as astrophysical-like.

Venue: 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) at 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

Introduction to braid groups

July 5 (Wed) at 14:00 - 16:30, 2023

Haru Negami (Ph.D. Student, Graduate School of Science and Engineering, Chiba University)

Part 1 (14:00-15:00): Introduction to braid groups Braid groups are groups that are defined by figures formed by the entanglement of n strings. Besides this geometric realization, it is a very interesting field where algebra and analysis intersect. In the first half of this seminar, aimed mainly at those unfamiliar with braid groups, we will introduce three aspects of braid groups and review the history of the research. In particular, in the area of its relation to analysis, the relationship between KZ equations and braid groups will be introduced. Part 2 (15:30-16:30): Representations of braid groups and the relationship between monodromy representations of KZ equations In the second half of the talk, after a brief introduction to representation theory, we will introduce the Katz-Long-Moody construction, a method of constructing infinite series of representations of the semi-direct product of braid group and free group. We will also show that its special case is isomorphic to multiplicative middle convolution, a method for constructing monodromy representations of KZ equations. Lastly, we will also discuss the connection between representations of braid groups and knot invariants. The talk includes joint work with Kazuki Hiroe.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

6th Workshop on Virus Dynamics

July 4 (Tue) - 6 (Thu), 2023

Catherine Beauchemin (Deputy Program Director, iTHEMS)
Shingo Iwami (Professor, Graduate School of Science, Nagoya University)

The Workshop on Virus Dynamics is an international meeting held every 2 years. It brings virologists, immunologists, and microbiologists together with mathematical and computational modellers, bioinformaticians, bioengineers, virophysicists, and systems biologists to discuss current approaches and challenges in modelling and analyzing different aspects of virus and immune system dynamics, and associated vaccines and therapeutics. This 6th version of the workshop builds on the success of previous ones held in Frankfurt (2013), Toronto (2015), Heidelberg (2017), Paris (2019) and virtually (2021). It is supported by the Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program at RIKEN, by Nagoya University, and by the Japan Science and Technology Agency. Up-to-date information and registration is available via the website. The workshop is for in-person participation only (no virtual or hybrid option).

Venue: Noyori Conference Hall, Higashiyama Campus, Nagoya University

Event Official Language: English

Maximum Force Conjecture and Black Hole Thermodynamics

June 30 (Fri) at 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) at 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) at 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

The role of fluid dynamics in microbial ecology

June 22 (Thu) at 14:00 - 15:00, 2023

Douglas R. Brumley (Senior Lecturer, Applied Mathematics, University of Melbourne, Australia)

Bacterial motility, symbioses, and marine nutrient cycling unfold at the scale of individual microbes, and are inherently dynamic. In this talk, I will discuss the role that fluid flows play in shaping the ecology of microbes, both in the open ocean as well as around coral surfaces. In each case, I will demonstrate how iteratively combining video-microscopy, image processing and mathematical modelling can resolve features of microbial lifestyles that are difficult or impossible to see otherwise, and show how single-cell measurements can be connected to bulk processes at the population-level.

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

Event Official Language: English

Matrix estimation via singular value shrinkage

June 21 (Wed) at 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

Introduction to statistical decision theory and Stein’s paradox

June 21 (Wed) at 14:00 - 15:00, 2023

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

Statistical decision theory is a general framework for discussing optimality of statistical procedures such as estimation, testing and prediction. In 1956, Charles Stein found a counter-intuitive phenomenon in estimation of the mean parameter of a multivariate normal distribution. He showed that a ``shrinkage estimator” attains better estimation accuracy (smaller mean-squared error) than the maximum likelihood estimator when the dimension is greater than or equal to three. This phenomenon is related to several mathematical fields such as Markov processes and potential theory. The idea of shrinkage estimation has been employed in many statistical methods such as regularization, empirical Bayes and model selection. In this talk, I will introduce the statistical decision theory and illustrate Stein’s paradox.

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

Event Official Language: English

2nd QGG Intensive Lectures: Large gauge transformation and infrared regularity in the inflationary universe

June 19 (Mon) - 20 (Tue), 2023

Takahiro Tanaka (Professor, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

In this lecture we will start with the general framework to analyse the density perturbation in the inflationary universe. Then, we will introduce various infrared (IR) phenomena, including IR divergences, delta N formalism and consistency relation. The underlying symmetry originally coming from 3D diffeomorphism invariance leads us to a harmonic and unified understanding of these phenomena. Program: June 19 10:00 - 10:15 Registration and reception (with coffee) 10:15 - 11:45 Lecture 1 11:45 - 13:30 Lunch & coffee break 13:30 - 15:00 Lecture 2 15:00 - 16:00 Coffee break 16:00 - 17:30 Lecture 3 17:45 - 18:30 Short talk session June 20 10:00 - 10:15 Reception (with coffee) 10:15 - 11:45 Lecture 4 11:45 - 13:30 Lunch & coffee break 13:30 - 15:00 Lecture 5 15:00 - 16:00 Coffee break 16:00 - 17:30 Lecture 6 17:30 - 18:30 Discussions & Closing

Venue: #535-537, 5F, Main Research Building

Event Official Language: English