How Stars End Their Lives

April 26 (Fri) at 14:00 - 15:15, 2024

Philipp Podsiadlowski (Professor, University of Oxford, UK)

While the basic evolution of stars has been understood for many decades, there are still major uncertainties in our overall understanding of how stars end their lives, both in the context of low- and intermediate-mass stars (including the Sun) and massive stars. I will first review some of key principles that govern the structure and evolution of stars and then present recent progress that has been made for both groups of stars. I will argue and present numerical simulations that show that all stars become dynamically unstable when they become large giant stars, which leads to sporadic, dynamical mass ejections. Low- and intermediate-mass stars may lose all of their envelopes as a consequence, leaving white-dwarf remnants. More massive stars experience core collapse, leaving a neutron-star or black-hole remnant, possibly associated with a supernova explosion. I will show how the dramatic recent progress on understanding the core-collapse process, for the first time, allows us to connect the late evolution of massive stars with the resulting supernova explosions and the final remnants and discuss how observations with current gravitational-wave detectors (such as LIGO) will allow us to test this theoretical connection.

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

Event Official Language: English

Tracing link of cell ageing and disease progression: Joining factors and facilitators

April 25 (Thu) at 16:00 - 17:00, 2024

Rajkumar Singh Kalra (Staff Scientist, Immune Signal Unit, Okinawa Institute of Science and Technology Graduate University (OIST))

Cell ageing is an inevitable biological process. It marks declined homeostatic processes in a cell, the impact of which is reflected in the organism’s function/physiology. Ageing, thus, raises risks of disease progression in elderly people and compromises their immunity. Progression of cancer and neurodegenerative diseases and weak immune response against a pathogen(s) represent cases of ageing-related diseases. What molecular factors/signaling could be associated with disease progression or take part in governing such decisions in aging? – remained a key focus of my research so far. In my talk, I shall shed light on the part characterizing key proteins and their signalling in ageing-related diseases with an emphasis on cancer, neurodegenerative disease, and immunity. Taking advantage of wet lab and system biology studying gene networks, and genomic, proteomic, and metabolomic readouts, I investigated the molecular expression and processes impacted and compromised by ageing. I shall be discussing new knowledge from my work on the linkage of cell ageing and disease progression and therein role of key factors and facilitators I studied.

Venue: via Zoom

Event Official Language: English

A night out with ghosts

April 24 (Wed) at 16:00 - 17:30, 2024

Veronica Errasti Diez (Research Fellow, Faculty of Physics, Ludwig-Maximilians-Universität München, Germany)

Field theories are the chief theoretical framework for physics. For instance, the Standard Model and General Relativity are widely accepted as accounting for subatomic particle and gravitational behavior, respectively. Nonetheless, even such acclaimed field theories have their limitations, such as the mysterious neutrino masses and dark sector. A natural and popular way around the hurdles consists in generalizations of field theories, via the inclusion of non-linear and/or higher-order corrections. Unless painstakingly avoided, these corrections lead to the propagation of negative kinetic energy modes, or ghosts for short. Ghosts have earned an appalling fame: kill, exorcise, avoid… No efforts are spared to guarantee their absence. In this talk, we will delve into the root causes for the ill name of ghosts. As a result, we will take up the cudgels for ghosts. While they do have a strong tendency to yield ill-behaved theories, ghosts are not intrinsically pathological. As we will see, good-natured ghosts open the door to multi-disciplinary tantalizing opportunities…! And ghosts make excellent party-goers, so make sure not to miss this appointment!

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

Event Official Language: English

iTHEMS x academist Online Event "World of Mathematical Sciences 2024"

April 21 (Sun) at 10:00 - 15:30, 2024

Shingo Gibo (Postdoctoral Researcher, iTHEMS)
Taketo Sano (Special Postdoctoral Researcher, iTHEMS)
Misako Tatsuuma (Research Scientist, iTHEMS)
Tomoya Naito (Special Postdoctoral Researcher, iTHEMS)

Venue: via Zoom

Event Official Language: Japanese

RIKEN DAY: Let's Talk with Researchers! Let's get to know each other through "Mathematics: One S&T poster for Every Household”!

April 19 (Fri) at 18:00 - 18:50, 2024

In this RIKEN DAY, we will introduce various phenomena in the world (all things in the universe) that are understood using "mathematics” and the use of "mathematics", including the latest research, while looking at the annual S&T poster for everyone titlled “Mathematics: One S&T poster for Every Household”. For details, please see the related links.

Venue: via Zoom

Event Official Language: Japanese

The 25th MACS Colloquium

April 19 (Fri) at 14:45 - 18:30, 2024

Wataru Morita (Researcher, Department of Anthropology, National Museum of Nature and Science / Associate Professor, Department of Biological Sciences, Graduate School of Science, The University of Tokyo)

14:45-15:00 Teatime discussion 15:00-16:00 Talk by Dr. Wataru Morita (Researcher, Department of Anthropology, National Museum of Nature and Science / Associate Professor, Department of Biological Sciences, Graduate School of Science, The University of Tokyo) 16:15-17:20 2024 Study Group introduction session 17:30-18:30 Discussion

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

Event Official Language: Japanese

Zooming into the ancient world by reconstructing the joint genealogies of modern and ancient humans

April 18 (Thu) at 16:00 - 18:00, 2024

Leo Speidel (Senior Research Fellow, Genetics Institute, University College London, UK)

In recent years, we have gone from databases that store the genetic differences observed between hundreds of thousands of sequenced people to using this information to build the actual genetic trees that relate individuals through their shared ancestors back in time. These genetic trees describe how our genomes have evolved up to millions of years into the past. Additionally, sequencing of DNA from ancient human bone has enabled the direct observation of genomic change over past millennia and has unlocked numerous previously hidden genetic histories. In this talk, I will illustrate how we can unearth the human past from these data, ranging from ancient migrations out of Africa and subsequent mixtures with now extinct Neanderthals to waves of ancestry transformations in a nation’s recent past.

Venue: via Zoom

Event Official Language: English

Quantum Fine-Grained Complexity

April 18 (Thu) at 10:30 - 12:00, 2024

Harry Buhrman (Chief Scientist for Algorithms and Innovation, Quantinuum, UK)

(The speaker is also a professor at University of Amsterdam & QuSoft. This is a joint seminar with the iTHEMS Quantum Computation Study Group.) One of the major challenges in computer science is to establish lower bounds on the resources, typically time, that are needed to solve computational problems, especially those encountered in practice. A promising approach to this challenge is the study of fine-grained complexity, which employs special reductions to prove time lower bounds for many diverse problems based on the conjectured hardness of key problems. For instance, the problem of computing the edit distance between two strings, which is of practical interest for determining the genetic distance between species based on their DNA, has an algorithm that takes O(n^2) time. Through a fine-grained reduction, it can be demonstrated that a faster algorithm for edit distance would imply a faster algorithm for the Boolean Satisfiability (SAT) problem. Since faster algorithms for SAT are generally considered unlikely to exist, this implies that faster algorithms for the edit distance problem are also unlikely to exist. Other problems used for such reductions include the 3SUM problem and the All Pairs Shortest Path (APSP) problem. The quantum regime presents similar challenges; almost all known lower bounds for quantum algorithms are defined in terms of query complexity, which offers limited insight for problems where the best-known algorithms take super-linear time. Employing fine-grained reductions in the quantum setting, therefore, represents a natural progression. However, directly translating classical fine-grained reductions to the quantum regime poses various challenges. In this talk, I will present recent results in which we overcome these challenges and prove quantum time lower bounds for certain problems in BQP, conditioned on the conjectured quantum hardness of, for example, SAT (and its variants), the 3SUM problem, and the APSP problem. This presentation is based on joint works with Andris Ambainis, Bruno Loff, Florian Speelman, and Subhasree Patro.

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

Event Official Language: English

Sustainable Organic Synthesis with Abundant Resources

April 15 (Mon) at 13:00 - 14:00, 2024

Sobi Asako (Senior Scientist, Advanced Organic Synthesis Research Team, RIKEN Center for Sustainable Resource Science (CSRS))

The sustainable development of modern society necessitates technologies that harness earth-abundant metals and organic resources, minimizing reliance on scarce materials. This presentation will introduce our recent efforts towards this goal. We have developed sustainable organic synthesis using sodium dispersion, a molybdenum-quinone species for the diazo-free generation of carbene species from stable and readily available compounds, and a SpiroBpy ligand that enables the site-selective functionalization of arenes under remote steric control. I will also share some of the challenges we face in developing these reactions in order to ensure reproducibility.

Venue: 3rd floor public space, Main Research Building

Event Official Language: English

Short-Lived Hawking Radiation Under Stringy Effects

April 11 (Thu) at 13:30 - 15:00, 2024

Wei-Hsiang Shao (Ph.D. Student, Department of Physics, National Taiwan University, Taiwan)

A UV theory is required in order to describe the origin of late-time Hawking radiation. In this talk, I will explore Hawking radiation in a non-local model of the radiation field inspired by Witten's open string field theory. An attempt at extracting the correlators of this theory will be discussed, which leads to a space-time uncertainty relation. As a result, the characteristics of trans-Planckian field modes differ significantly from that in the standard low-energy effective theory, and I will argue that this ultimately results in the termination of Hawking radiation around the scrambling time of the black hole.

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

Event Official Language: English

A socio-ecological and genomic approach to mixed-species formation of African forest guenons

April 4 (Thu) at 16:00 - 17:00, 2024

Haruka Kitayama (Ph.D. Student, Graduate School of Environmental Science, Hokkaido University)

While many animal groups consist of a single species, some species have been observed forming mixed-species groups (MSGs). It is thought that by forming groups with different species, animals may reduce predation risk, improve foraging efficiency, and even gain social and reproductive benefits. Red-tailed monkeys and blue monkeys, African forest guenons (Tribe Cercopithecini), are known to form MSGs in several regions in Africa, despite the large niche overlap. The underlying mechanisms driving the formation of MSGs in red-tailed monkeys and blue monkeys are still unclear. One reason is that previous studies have been limited to behavioral ecological approaches. By combining field observations with genomic analyses in the laboratory, we seek to shed light on the role of genetic factors in mediating interspecies interactions within MSGs. In this talk, I will introduce our studies on genomic introgression and gut microbiome sharing within the mixed-species population of red-tailed monkeys and blue monkeys in the Kalinzu Forest Reserve, Uganda.

Venue: via Zoom

Event Official Language: English

Quantum simulation of QCD matter: from hadronic scattering to gauge field qubit encoding

April 3 (Wed) at 10:00 - 11:00, 2024

Tianyin Li (Ph.D. Student, Institute of Quantum Matter, South China Normal University, China)

Recently, quantum computing (QC) has become a new method for solving non-perturbative problems in high-energy physics. Compared to traditional Monte Carlo simulations, the QC method does not encounter the sign problem, making it an effective approach for solving dynamical and finite density problems. The first part of this talk focuses on the quantum simulation of the hadronic scattering process, including the initial state parton distribution functions, intermediate state partonic scattering amplitudes, and final state hadronization. The second part of this talk concentrates on the qubit encoding of Hamiltonian formalism in lattice gauge field theory with a Coulomb gauge. As a preliminary attempt, the qubit encoding of (3+1)-dimensional Coulomb gauge QED will be discussed.

Venue: via Zoom

Event Official Language: English

TadaFest 2024: Toward understanding of the Origin of Spacetime

April 2 (Tue) at 14:00 - 18:00, 2024

Tsukasa Tada (Deputy Program Director, iTHEMS)

Program 14:00-14:05 Welcome address T. Hatsuda (RIKEN iTHEMS) 14:05-15:35 T. Tada (RIKEN iTHEMS) "Toward understanding of the origin of spacetime" (This talk is in English) 15:35-16:00 coffee break 16:00-16:30 Shin Nakamura (Chuo Univ.) "Application of gauge/gravity duality: application to non-equilibrium physics" (This talk is in Japanese) 16:30-17:00 Kinya Oda (Tokyo Woman's Chiristian Univ.) "Gaussian formalism: From Hesenberg's Uncertainty Principle to Time-Boundary Effect and Lorentz-Covariant Complete Basis for Spinors" (This talk is in Japanese) 17:00-17:30 Gen Tatara (RIKEN, CEMS) "Some topics of spintronics" (This talk is in Japanese) 17:30-18:00 Asato Tsuchiya (Shizuoka Univ.) "Recent progress in the studies of the emergence of space-time in the type IIB matrix model" (This talk is in Japanese) 18:15- informal discussion @ Common space on 3F of the main research building

Venue: Okochi Hall (Main Venue) / via Zoom

Event Official Language: English

Coarse-graining black holes out of equilibrium with boundary observables on time slice

April 1 (Mon) at 16:00 - 17:30, 2024

Daichi Takeda (Ph.D. Student, Theoretical Particle Physics Group, Kyoto University)

In black hole thermodynamics, defining coarse-grained entropy for dynamical black holes has long been a challenge, and various proposals, such as generalized entropy, have been explored. Guided by the AdS/CFT, we introduce a new definition of coarse-grained entropy for a dynamical black hole in Lorentzian Einstein gravity. On each time slice, this entropy is defined as the horizon area of an auxiliary Euclidean black hole that shares the same mass, (angular) momenta, and asymptotic normalizable matter modes with the original Lorentzian solution. The entropy is shown to satisfy a generalized first law within Einstein theory and, through holography, the second law as well. This second law corresponds to the positivity of the relative entropy in the CFT. Furthermore, by applying this thermodynamics to several Vaidya models in AdS and flat spacetime, we discover a connection between the second law and the null energy condition.

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

Event Official Language: English

A Selective Survey of Ideas, Tools and Results in Constructive QFT II

April 1 (Mon) at 13:00 - 14:30, 2024

Christy Koji Kelly (Special Postdoctoral Researcher, iTHEMS)

In this talk we continue to discuss the constructive programme in rigorous QFT. Our aim is discuss a few points on difficulties in relation to the definition of Euclidean path integrals and the general strategy of constructive field theory from a constructive perspective. This will motivate a discussion of the fundamental results in probability theory which are the main tools for the construction of Euclidean path integral measures. We might also discuss some points in relation to free fields, including in particular difficulties in the characterisation of massless fields.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

Kyoto University SACRA-RIKEN iTHEMS Special Lecture by Prof. Tadashi Tokieda

March 28 (Thu) at 13:30 - 16:30, 2024

Tadashi Tokieda (Professor, Department of Mathematics, Stanford University, USA)

This event will be conducted in Japanese.

Venue: Large Conference Room, The Kyoto University Tokyo Office

Event Official Language: Japanese

Fast Rotating Neutron Stars: Spectra, Stability and Universal Relations

March 27 (Wed) at 11:00 - 12:30, 2024

Christian Krueger (Postdoctoral Researcher, University of Tuebingen, Germany)

In this talk, we study rapidly rotating relativistic stars which are present in various astrophysical systems. First, we study their oscillations and instabilities by taking into account the contribution of a dynamic space-time. The study is based on the linearised version of Einstein’s equations and via this approach the oscillation frequencies as well as the critical values for the onset of a secular instability are determined. We show asteroseismological relations for the fundamental eigenfrequency which are crucial for tackling the inverse problem. Further, we provide universal relations that allow to estimate the moment of inertia (and other bulk quantities) from the knowledge of the triple mass, radius and moment of inertia of an associated non-rotating star. The proposed universal relations facilitate computationally cheap EOS inference codes that permit the inclusion of observations of rotating neutron stars. As a demonstration, we deploy them into a recent Bayesian framework for equation of state parameter estimation that is now valid for arbitrary, uniform rotation. The results are important for all stages of a neutron star’s life but particularly interesting in pre- and post-merger cases. This seminar is held by GW-EOS WG in iTHEMS.

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

Event Official Language: English