Seminar
1075 events
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Seminar
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
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Seminar
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
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Seminar
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
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Seminar
Ground-state phases of the one-dimensional SU(N)-symmetric Kondo lattice model
May 11 (Thu) 17:00 - 18:15, 2023
Keisuke Totsuka (Associate Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
The Kondo-lattice model and its variants (e.g., the Kondo-Heisenberg model), in which itinerant fermions interact with immobile magnetic moments via spin-exchange coupling (Kondo coupling), have been playing an important role in understanding the physics of heavy-fermion systems. In this talk, I begin by quickly explaining how the SU(N) Kondo-lattice model, in which the spin SU(2) symmetry is generalized to SU(N), is realized in actual physical systems (e.g., cold fermions and twisted bilayer graphene), and then I focus on the ground-state properties of its one-dimensional version. Specifically, when the Kondo coupling is sufficiently large, we find ferromagnetic metallic phases that can be established rigorously as well as several insulating ones. I also show that the SU(N) Kondo-lattice model provides a natural condensed-matter realization of supersymmetric [i.e., SU(N|1)] models. Various (insulating) phases at small Kondo coupling are then explored using the machinery of bosonization and various conformal field theory (CFT) techniques, and the results are compared with the predictions of the Lieb-Schultz-Mattis-type (or anomaly-matching) argument. Field: condensed matter physics Keywords: Kondo lattice model, SU(N) symmetry, supersymmetry, heavy-fermion systems, bosonization, conformal field theory
Venue: via Webex
Event Official Language: English
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Seminar
Conditions for maintaining pseudo-overdominance
May 11 (Thu) 16:00 - 17:00, 2023
Diala Abu Awad (Associate Professor, Génétique Quantitative et Évolution - Le Moulon, Université Paris-Saclay, France)
Deleterious recessive mutations should purge or fix within inbred populations, yet inbred populations often retain moderate to high segregating load. However, arrays of deleterious recessives linked in repulsion could generate appreciable pseudo-overdominance, mimicking overdominant selection that would sustain segregating load. We use analytical approches and simulations to explore whether and for how long pseudo-overdominant (POD) zones can persist once created (e.g., by hybridization between populations fixed for alternative mildly deleterious mutations). Balanced haplotype loads, tight linkage, and moderate to strong cumulative selective effects all serve to maintain POD zones. Tight linkage is key, suggesting that such regions are most likely to arise and persist in low recombination regions (like inversions). Selection and drift unbalance the load, eventually eliminating POD zones, but this process is quite slow, and could influence short term evolution of populations.
Venue: via Zoom
Event Official Language: English
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Seminar
Quantum transport with cold atoms
May 10 (Wed) 13:30 - 15:00, 2023
Shun Uchino (Researcher, Advanced Science Research Center, Japan Atomic Energy Agency (JAEA))
Quantum transport occurring through a mesoscopic conduction region allows us to extract interesting quantum many-body phenomena. For decades, solid-state systems have been the playground of such transport and revealed nontrivial outcomes such as the conductance quantization in a quantum point contact system and the fractional charge measurement in a fractional quantum Hall system. More recently, cold atoms trapped in the vacuum have served as the complementary system to study the quantum transport phenomena. In this seminar, I wish to discuss the recent progresses of quantum transport with cold atoms. The great advantages of those systems are that one can control quantum statistics, inter-particle interactions, dissipation, and dimensions. I try to show that such controllability enables to explore a regime of quantum transport that has yet to be reached with solid-state materials, including transport of bosons, dissipation effect in transport, and transport with synthetic dimensions.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Generalized AKS scheme of integrability via vertex algebra
May 9 (Tue) 16:15 - 17:15, 2023
Wenda Fang (Ph.D. Student, Research Institute for Mathematical Sciences (RIMS), Kyoto University)
In this talk, we define and study the classical R-matrix for vertex Lie algebra, based on which we propose to construct a new vertex Lie algebra. As an application, using the classical R-matrix we defined, we give a new scheme to construct infinite-dimensional (Liouville) integrable systems via the Feigin-Frenkel center. This seminar is on-site only.
Venue: Seminar Room #359
Event Official Language: English
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Seminar
On the Beem-Nair conjecture
May 9 (Tue) 15:00 - 16:00, 2023
Syun Furihata (Ph.D. Student, Research Institute for Mathematical Sciences (RIMS), Kyoto University)
Given a simple Lie group G, we have an open immersion (constructed by Beem and Nair) from the Kostant-Toda lattice associated to G into the universal centralizer of G. They expected that a free field realization of the chiral universal centralizer of G at the critical level will be obtained by the chiralization of this immersion. In this talk, we will verify this conjecture is true by constructing an embedding from the chiral universal centralizer into an appropriate vertex operator algebra at any level. This seminar is on-site only.
Venue: Seminar Room #359
Event Official Language: English
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Seminar
Introduction to Genomics
April 27 (Thu) 16:00 - 17:00, 2023
Jeffrey Fawcett (Senior Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
A 'genome' is a single set of genetic information of a given individual, which is encoded by the nucleotide sequence of the DNA. For instance, the human genome consists of around 3 billion nucleotide base pairs, although the size and content of the genome differs greatly across species and individuals. Some species such as the budding yeast has a genome as small as 12 million base pairs, whereas other species such as Paris japonica, a flowering plant native to the sub-alpine regions of Japan, is said to have a genome as large as 150 billion base pairs. In this talk, I will give a introduction of what kind of information is contained within a genome, and how that differs across species and individuals. This talk will be introductory and aimed at non-experts including non-biologists.
Venue: via Zoom
Event Official Language: English
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Seminar
Search for TeV-scale WIMP Dark Matter by observing Gamma rays around the Galactic Centre with the MAGIC telescopes and future prospects.
April 25 (Tue) 11:00 - 12:00, 2023
Tomohiro Inada (Shuimu Tsinghua Fellow, Department of Physics, National Tsinghua University, Beijin, China)
Line-like features in TeV γ rays constitute a “smoking gun” for TeV-scale particle dark matter and new physics. Probing the Galactic Centre region with ground-based Cherenkov telescopes enables the search for TeV spectral features in immediate association with a dense dark matter reservoir at a sensitivity out of reach for satellite γ-ray detectors, and direct detection and collider experiments. I will report on about seven years of observations of the Galactic Centre region with the MAGIC stereoscopic telescope system reaching γ-ray energies up to 100 TeV. We constrain the cross-section for dark matter annihilation into two photons, achieving the best limits to date for a dark matter mass above 20 TeV and a cuspy dark matter profile at the Galactic Centre. I would like to discuss how to constrain supersymmetric wino models, which are one of the most popular dark matter candidates in the context of the Lightest Supersymmetric Particles (LSPs).
Venue: via Zoom
Event Official Language: English
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Seminar
Machine learning predicts biological system evolution by gene gains and losses
April 20 (Thu) 16:00 - 17:00, 2023
Naoki Konno (Ph.D. Student, Department of Biological Sciences, Graduate School of Science, The University of Tokyo)
Prediction of evolution is a fundamental goal of biology with a potential impact on strategic pathogen control and genome engineering. While predictability of short-term and sequence-level evolution has been investigated, that of long-term and system-level evolution has not been systematically examined. Here, we show that evolution of metabolic systems by gene gains and losses is generally predictable by applying ancestral gene content reconstruction and machine learning techniques to ~3000 bacterial genomes. Our framework, Evodictor, successfully predicted gene gain and loss events at the branches of the reference phylogenetic tree, suggesting universally shared evolutionary pressures and constraints on metabolic systems. I herein present the mathematical model of Evodictor and our findings on evolutionary rules from physiological and ecological aspects. I will further discuss potential versatility of Evodictor approach to analyze various diversification processes along branching lineage trees, not only evolution, but also developmental processes.
Venue: via Zoom
Event Official Language: English
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Seminar
Towards EeV Neutrino Astronomy with GRAND
April 18 (Tue) 14:00 - 15:15, 2023
Kumiko Kotera (Director of Research, Institute of Astrophysics, France)
We are living exciting times: we are now able to probe the most violent events of the Universe with diverse messengers (cosmic rays, neutrinos, photons and gravitational waves). One challenge to complete the multi-messenger picture resides in the highest energies, as no ultra-high energy neutrinos have been observed yet. This challenge could be undertaken by the GRAND (Giant Radio Array for Neutrino Detection) project, which aims at detecting ultra-high energy particles, with a colossal array of 200'000 antennas over 200'000 km2, split into ~20 sub-arrays of ~10'000 km2 deployed worldwide. In this talk, we will present preliminary designs and simulation results, plans for the ongoing, staged approach to construction, and the rich research program made possible by the proposed sensitivity and angular resolution.
Venue: Common Room #246-248 / via Zoom
Event Official Language: English
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Seminar
Why are cell populations maintained via multiple compartments?
April 13 (Thu) 10:00 - 11:00, 2023
Carmen Molina-París (Researcher, Theoretical Biology and Biophysics, Los Alamos National Laboratory, USA)
We consider the maintenance of “product” cell populations from “progenitor” cells via a sequence of one or more cell types, or compartments, where each cell’s fate is chosen stochastically. If there is only one compartment then large amplification, that is, a large ratio of product cells to progenitors comes with disadvantages. The product cell population is dominated by large families (cells descended from the same progenitor) and many generations separate, on average, product cells from progenitors. These disadvantages are avoided using suitably-constructed sequences of compartments: the amplification factor of a sequence is the product of the amplification factors of each compartment, while the average number of generations is a sum over contributions from each compartment. Passing through multiple compartments is, in fact, an efficient way to maintain a product cell population from a small flux of progenitors, avoiding excessive clonality and minimising the number of rounds of division en route. We analyse the possible descendants of one progenitor cell, families of cells that journey through the sequence of compartments. We find that the ability of product cells to perform their function may be negatively affected by the number of rounds of cell division that separates them from their progenitor, because every round of division brings with it a risk of mutation.
Venue: via Zoom
Event Official Language: English
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Seminar
An overview on the nuclear equation of state studied from ground and collective excited state properties of nuclei
April 12 (Wed) 13:30 - 15:00, 2023
Xavier Roca-Maza (Associate Professor, Department of Physics, University of Milan, Italy)
This contribution reviews a selection of available constraints to the nuclear equation of state (EoS) around saturation density from nuclear structure calculations on ground and collective excited state properties of atomic nuclei [1]. It concentrates on predictions based on self-consistent mean-field calculations, which can be considered as an approximate realization of an exact energy density functional (EDF). Mostly, EDFs are currently derived from effective interactions commonly fitted to nuclear masses, charge radii and, in many cases, also to pseudo-data such as nuclear matter properties. Although in a model dependent way, EDFs constitute nowadays a unique tool to reliablyand consistently access bulk ground state and collective excited state properties of atomic nuclei along the nuclear chart as well as the EoS. The impact on the EoS of the new CREx [2] and PREx [3] measurments of the parity violating asymmetry (ground state observable) in 48Ca and 208Pb, respectively, will be also discussed [4,5] and compared to previously presented results on collective excitations. As the main conclusion, the isospin dependence of the nuclear EoS around saturation density and, to a lesser extent, the nuclear matter incompressibility remain to be accurately determined. Experimental and theoretical efforts in finding and measuring observables specially sensitive to the EoS properties are of paramount importance, not only for low-energy nuclear physics but also for nuclear astrophysics applications.
Venue: 2F Large Meeting Room, RIBF Building, RIKEN Wako Campus (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Quantum modularity of quantum invariants and related techniques
April 11 (Tue) 13:00 - 15:30, 2023
Yuya Murakami (JSPS Research Fellow PD, Faculty of Mathematics, Kyushu University)
In this talk, I will present my recent work[1] and related research. In the first half of the talk, I will provide an overview of the concept of quantum modularity of quantum invariants, and briefly discuss my main result. In the second half, I will provide a more detailed explanation of my main result and the proof.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Frobenius algebras associated with the α-induction for equivariantly braided tensor categories
April 10 (Mon) 14:00 - 16:30, 2023
Mizuki Oikawa (Ph.D. Student / JSPS Research Fellow DC, Graduate School of Mathematical Sciences, The University of Tokyo)
In this talk, I would like to introduce my work https://arxiv.org/abs/2303.11845. In the first half of the talk, I will give an introduction of tensor categories. In the latter half, I will explain about my construction of some tensor categories and Frobenius algebras.
Venue: Seminar Room #359 / via Zoom
Event Official Language: English
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Seminar
Introduction to the Renormalization group method as a powerful reduction method of dynamics
April 10 (Mon) 10:30 - 12:00, 2023
Teiji Kunihiro (Emeritus Professor, Kyoto University)
Extracting effective slow dynamics with fewer degrees of freedom from a complex system with many degrees of freedom is of basic importance in all areas of Science. Typical examples include the derivation of the amplitude and phase dynamics from nonlinear oscillators, that of the Boltzmann equation from Hamilton dynamics, which is further reduced to fluid dynamics and so on. The purpose of this talk is to give an elementary introduction to the renormalization group (RG) method as a powerful reduction method of differential (difference) equations in terms of the notion of envelopes. Some simple examples will be worked out in this method, which include the van der Pol (Rayleigh) equation with its discrete analog and a generic system with a bifurcation. In the final part, we list up various examples to which the RG method has been successfully applied.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Organizational meeting
April 6 (Thu) 16:00 - 17:00, 2023
Catherine Beauchemin (Deputy Program Director, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
The purpose of the organizational meetings is to discuss various topics of interest to the members of iTHEMS in the field of Biology, but also to participants of the iTHEMS BIology Seminar, irrespective of their field. The primary objective of this meeting will be to discuss recruitment of JRAs, SPDRs, and female researchers from Biology into iTHEMS. I hope we can identify the main obstacles and consider together possible solutions. As usual, any additional topic can be brought up spontaneously by participants. Anyone with thoughts about iTHEMS Biology is welcome to join us, no matter their field.
Venue: via Zoom
Event Official Language: English
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Seminar
Gauge-equivariant neural networks as preconditioners in lattice QCD
April 6 (Thu) 13:30 - 15:00, 2023
Tilo Wettig (Professor, Universität Regensburg, Germany)
We demonstrate that a state-of-the-art multi-grid preconditioner can be learned efficiently by gauge-equivariant neural networks. We show that the models require minimal re-training on different gauge configurations of the same gauge ensemble and to a large extent remain efficient under modest modifications of ensemble parameters. We also demonstrate that important paradigms such as communication avoidance are straightforward to implement in this framework.
Venue: Common Room #246-248 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Asymmetric enzyme kinetics of F1-ATPase resulted from asymmetric allosterism
March 30 (Thu) 16:00 - 17:00, 2023
Yohei Nakayama (Assistant Professor, Department of Applied Physics, Graduate School of Engineering, Tohoku University)
Bio-molecular machines play various roles in cells where thermal fluctuation is dominant. Since artificial molecular machines are far behind bio-molecular machines for the present, we should begin with understanding how bio-molecular machines are designed to play their roles. We examine the motion of a bio-molecular machine, F1-ATPase, in single molecule experiments. In particular, we focus on the operation of F1-ATPase as ATP synthase in addition to as molecular motor. In this seminar, I talk about the enzyme kinetics, dependence of reaction rate on substrate concentration, of F1-ATPase in ATP synthesis. The experimental result shows that the enzyme kinetics of F1-ATPase in ATP synthesis exhibits weaker dependence on substrate concentration than the ordinary Michaelis-Menten kinetics, whereas that in ATP hydrolysis follows Michaelis-Menten kinetics. Therefore, the enzyme kinetics of F1-ATPase turned out to be asymmetric between ATP synthesis and hydrolysis. We analyzed this asymmetry based on a potential switching model, totally asymmetric allosteric model, whose characteristic is asymmetry in angular dependence of binding rates of substrates. It was shown that the totally asymmetric allosteric model may reproduce the experimental results, where the asymmetry of binding rates is essential. We also discuss physiological roles that the asymmetry of enzyme kinetics may play.
Venue: via Zoom
Event Official Language: English
1075 events