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

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

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

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

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

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

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

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

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

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

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

Warming reduces the density-dependent divergence in emergence time for two competing parasitoid species

March 23 (Thu) 16:00 - 17:00, 2023

Midori Tuda (Associate Professor, Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University)

Climate change is expected to directly affect ectothermic species through their sensitivity to temperature, with cascading effects on populations and communities. Here we experimentally tested predictions from two non-exclusive hypotheses concerning the impacts of elevated temperature (+2°C) on interactions between a single host species (the azuki bean beetle) and two species of parasitoid wasps. We hypothesized that increasing temperature shortens the time that the host is vulnerable to parasitoid attack. This change in available resource should heighten intra- and interspecific competition among parasitoids, which could induce divergence in emergence times. We found that intraspecific competition of both parasitoid species was more intense than interspecific competition irrespective of temperature. The difference (d) in the emergence times of the two parasitoid species increased with the density of each parasitoid but decreased at the elevated temperature. Both parasitoids emerged sooner at the elevated temperature and experienced a reduction in body size. Thus, high levels of intraspecific competition (along with the consequent reduction in body size) may have attenuated the intensity of interspecific competition at the elevated temperature despite a reduction in the differentiation of emergence times.

Venue: via Zoom

Event Official Language: English

Lab-Theory Standing Talks #1

March 16 (Thu) 13:00 - 13:30, 2023

Hideshi Ooka (Research Scientist, Biofunctional Catalyst Research Team, RIKEN Center for Sustainable Resource Science (CSRS))

Venue: 3rd floor public space, Main Research Building

Event Official Language: English

Towards S-matrix theory of unstable particles

March 15 (Wed) 13:30 - 15:00, 2023

Katsuki Aoki (Research Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)

The S-matrix is one of the central objects in quantum field theory and gains renewed interest recently to understand the possible structures of low-energy effective field theories and quantum gravity. However, most of the particles have finite decay widths and thus do not appear in asymptotic states. Therefore, the standard S-matrix arguments may not be directly applied to scatterings of such unstable particles and we need to formulate “the S-matrix theory of unstable particles” to properly understand the availability of the S-matrix arguments in realistic systems. In this talk, I will talk about the first steps towards this goal. In particular, I will discuss non-perturbative consequences of unitarity in a scattering amplitude of unstable particles and its analytic properties.

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

Event Official Language: English

Neutrinos from the big bang: probing cosmic gravitational inhomogeneities & magnetic fields in the early universe

March 13 (Mon) 13:30 - 15:00, 2023

Gordon Baym (Professor Emeritus, University of Illinois, USA)

Primordial neutrinos from the Big Bang are about 100 times more prevalent than solar neutrinos, and at least two-thirds of them are now non-relativistic. These relic neutrinos, which have never been detected, decoupled in the early universe predominantly in helicity eigenstates. As I will discuss, their subsequent propagation through gravitational inhomogeneities and even background gravitational radiation, as well as cosmic and galactic magnetic fields partially flips their helicities, and can produce noticeable effects in their eventual detection. I will briefly mention future detection of relic neutrinos.

Venue: Common Room #246-248 (Main Venue) / via Zoom

Event Official Language: English

Cosmic magnetism and its effects on the observed properties of ultra high-energy cosmic rays

March 10 (Fri) 14:00 - 15:00, 2023

Ellis Owen (JSPS International Research Fellow, Theoretical Astrophysics Group, Department of Earth and Space Science, Graduate School of Science, Osaka University)

Ultra high-energy (UHE) cosmic rays (CRs) from distant sources interact with intergalactic radiation fields, leading to their spallation and attenuation through photo-hadronic processes. Their deflection and diffusion in large scale intergalactic magnetic fields (IGMFs), in particular those associated with Mpc-scale structures, alter the cumulative cooling and interactions of a CR ensemble to modify their spectral shape and composition observed on Earth. In this talk, I will demonstrate the extent to which IGMFs can affect observed UHE CRs, and show that source population models are degenerate with IGMF properties. Interpretation of observations, including the endorsement or rejection of any particular UHE CR source classes, needs careful consideration of the structural properties and evolution of IGMFs. Future observations providing tighter constraints on IGMF properties will significantly improve confidence in assessing UHE CR sources and their intrinsic CR production properties.

Venue: via Zoom / Common Room #246-248

Event Official Language: English

Feynman’s proof of integrability of Calogero system from a modern point of view

March 10 (Fri) 10:00 - 11:30, 2023

Yehao Zhou (Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)

In his last year of life Feynman was interested in integrable system, and in his study of Calogero models he came up with his own proof of the commutativity of integrals of motions of these models, which remains unpublished until it was transcribed by Polychronakos in 2018. His idea is to organize integrals of motions of a Calogero model into a generating function of differential operators which look like a correlation function in a certain free theory, then he showed that the generating function of differential operators commute for all spectral values, which leads to a proof of commutativity of integrals of motions. He commented on his proof “I learn nothing, no real clue as to why all this works, and what it means”. Recently in a joint work with Davide Gaiotto and Miroslav Rapcek we identify Feynman’s generating function as the correlation function of Miura operators in a W-algebra of type A, and in the rational and trigonometric cases we show that they equal to certain elements in the Dunkl representation of corresponding spherical Cherednik algebras in type A, which make the commutativity self-evident. This progress is a byproduct of a project in the study of M2-M5 brane junction in the M-theory.

Venue: Common Room #246-248 / via Zoom

Event Official Language: English

Reproductive interference can affect trait diversity of closely related animal species

March 9 (Thu) 16:00 - 17:00, 2023

Keiichi Morita (Ph.D. Student, School of Advanced Sciences Department of Evolutionary Studies of Biosystems, The Graduate University for Advanced Studies (SOKENDAI))

Previous theoretical studies have considered that evolution driven by resource competition is important for the creation and maintenance of biodiversity. Recently, reproductive interference caused by misrecognition of sexual traits such as calling between closely related species has been increasingly important for the creation and maintenance of diversity, but the impact of reproductive interference on trait diversity between closely related species remains unresolved. In this study, we combined population dynamics model with reproductive interference in two closely related species with an evolutionary model of traits related to reproduction to examine the impact of reproductive interference on the evolutionary consequences of reproductive traits in the two closely related species. The model assumed a trade-off in which reproductive interference weakens as reproductive traits diverge between the two species, but predation pressure increases as the reproductive traits diverge from their optimum traits in their habitat. For simplicity, we assumed that only one species evolves. Our model analysis revealed that convergence and divergence of traits of two closely related species occurs depending on initial trait divergence. Also, under the parameter condition where trait convergence occurs, large mutation makes trait divergence possible. Our model will provide a new framework for understanding evolutionary dynamics in ecological communities containing closely related species.

Venue: via Zoom

Event Official Language: English

Topological Kondo superconductors

March 2 (Thu) 17:00 - 18:15, 2023

Yung-Yeh Chang (Postdoctoral Researcher, National Center for Theoretical Sciences & National Chiao Tung University, Taiwan)

Spin-triplet p-wave superconductors are promising candidates for topological superconductors. They have been proposed in various heterostructures where a material with strong spin-orbit interaction is coupled to a conventional s-wave superconductor by proximity effect. However, topological superconductors existing in nature and driven purely by strong electron correlations are yet to be studied. Here we propose a realization of such a system in a class of Kondo lattice materials in the absence of proximity effect. Therein, the odd-parity Kondo hybridization mediates ferromagnetic spin-spin coupling and leads to spin-triplet resonant-valence-bond (t-RVB) pairing between local moments. Spin-triplet p±p’ wave topological superconductivity is reached when Kondo effect co-exists with t-RVB [1]. We identify the topological nature by the non-trivial topological invariant and the Majorana zero modes at edges. Our results on the superconducting transition temperature, Kondo coherent scale, and onset temperature of Kondo hybridization not only qualitatively but also quantitatively agree with the observations for UTe2, a U-based ferromagnetic heavy-electron superconductor. *This work is supported by the National Science and Technology Council, Taiwan. Field: condensed matter physics Keywords: strongly correlated systems, topological superconductor, Kondo effect, resonant valence bond, heavy-fermion compounds

Venue: via Webex

Event Official Language: English

How to sit Maxwell and Higgs on the boundary of AdS

February 28 (Tue) 13:30 - 15:00, 2023

Matteo Baggioli (Associate Professor, School of Physics and Astronomy, Shanghai Jiao Tong University, China)

Within the holographic correspondence, boundary conditions play a fundamental role in determining the nature of the dual field theory. In this talk, I will show how to exploit mixed boundary conditions to obtain dynamical electromagnetism in the boundary theory. This is necessary to apply AdS-CFT to many real-world applications, e.g., magnetohydrodynamics, plasma physics, superconductors, etc. where dynamical gauge fields and Coulomb interactions are fundamental. As a proof of concept, I will show two emblematic cases. First, I will prove that the results from the 4-dimensional Einstein-Maxwell bulk theory with these deformed boundary conditions are in perfect agreement with relativistic magneto-hydrodynamics in 2+1 dimensions. Second, I will discuss the collective excitations of a bona-fide holographic superconductor and prove the existence of the Anderson-Higgs mechanism therein.

Venue: Room 6209, Korakuen Campus, Chuo University (Main Venue) / via Zoom

Event Official Language: English