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Chiral effects on lepton transport in core-collapse supernovae

December 13 (Tue) 13:30 - 15:00, 2022

Di-Lun Yang (Assistant Research Fellow, Institute of Physics, Academia Sinica, Taiwan)

Dynamics of leptons such as electrons and neutrinos play an important role in the evolution of core-collapse supernovae (CCSN). Nevertheless, chirality as one of fundamental microscopic properties that could affect lepton transport, through e.g. weak interaction, has been mostly overlooked. In this talk, I will discuss how chiral effects such as the renowned chiral magnetic effect (CME), generating an electric charge current along magnetic fields with chirality imbalance, could result in the unstable modes of magnetic fields and inverse cascade, which potentially influence the matter evolution in CCSN and pulsar kicks. I will also show how an effective CME could be realized via the backreaction from neutrino radiation even in the absence of an axial charge characterizing an unequal number of right- and left-handed electrons.

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

Event Official Language: English

Quantum kinetics of neutrinos in high-energy astrophysical phenomena

December 9 (Fri) 14:00 - 15:00, 2022

Hiroki Nagakura (Specially Appointed Assistant Professor (NAOJ Fellow), Division of Science, NAOJ)

Neutrinos are the most mysterious and elusive particles in the standard model of particle physics. They play important roles in core-collapse supernovae and binary neutron star mergers as driving mass-ejection, synthesizing heavy elements including r-process nuclei, and neutrino signals from these sources. This exhibits the importance of accurate modeling of neutrino radiation field in these phenomena, which will be used to connect neutrino physics to multi-messenger astronomy. It has recently been suggested that neutrino-flavor conversion (or neutrino-oscillation) can ubiquitously occur in these astrophysical environments, exhibiting the requirement of quantum kinetic treatments in the modeling of neutrino transport. In this seminar, I will give an overview of the quantum kinetics neutrino transport and then introduce its recent progress, paying a special attention to the connection to astrophysics. I will also present the latest results of our numerical simulations of collective neutrino oscillations, which can be properly accounted for only by quantum kinetic framework.

Venue: via Zoom

Event Official Language: English

Carrollian hydrodynamics near the black hole horizon

December 8 (Thu) 16:00 - 17:30, 2022

Puttarak Jai-akson (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

The membrane paradigm provides a fascinating bridge between gravitational dynamics near black hole horizons (null boundaries) and fluid dynamics. One question naturally follows: what type of fluids and hydrodynamics emerged at the horizon? Contrary to the longstanding belief, it turns out that the horizon fluid is Carrollian, rather than the Galilean (Navier-Stokes) fluid. The Carroll geometries and Carrollian physics, arising originally when the speed of light goes to zero (c to 0 limit), have recently gained increasing attention in the fields of black hole physics and flat holography. In this presentation, I will talk about the Carrollian limit and the resulting Carroll geometries and this unusual kind of hydrodynamics, the Carrollian hydrodynamics. I will then present the geometrical construction of the membrane (also known as the stretched horizon) in a way that a Carroll geometry manifest, therefore allowing us to spell out precisely the dictionary between gravitational degrees of freedom on the membrane and the Carrollian fluid quantities. I will also show that the Einstein’s equations projected onto the horizon are the Carrollian hydrodynamic conservation laws. Lastly, I will discuss the covariant phase space of the horizon, symmetries, and conservation laws. The talk is based on arXiv:2209.03328 and arXiv:2211.06415.

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

Event Official Language: English

Efficient encoding of the Schrodinger equation on quantum computers

December 5 (Mon) 14:00 - 15:30, 2022

Ermal Rrapaj (Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

The continuous space Schrödinger equation is reformulated in terms of spin Hamiltonians. For the kinetic energy operator, the critical concept facilitating the reduction in model complexity is the idea of position encoding. A binary encoding of position produces a spin-1/2 Heisenberg-like model and yields exponential improvement in space complexity when compared to classical computing. Encoding with a binary reflected Gray code (BRGC), and a Hamming distance 2 Gray code (H2GC) reduces the model complexity down to the XZ and transverse Ising model respectively. Any real potential is mapped to a series of k-local Ising models through the fast Walsh transform. As a first step, the encoded Hamiltonian is simulated for quantum adiabatic evolution. As a second step, the time evolution is discretized, resulting in a quantum circuit with a gate cost that is better than the Quantum Fourier transform. Finally, a simple application on an ion-based quantum computer is provided as proof of concept.

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

Event Official Language: English

Community assembly and species coexistence in the heterogeneous world

November 28 (Mon) 16:00 - 17:00, 2022

Naoto Shinohara (Assistant Professor, Graduate School of Life Sciences, Tohoku University)

How ecological communities are assembled and maintained is a fundamental question in community ecology. To tackle this challenge in the heterogeneous world, we need to understand how community assembly patterns change with environmental gradients and how species coexist in temporally fluctuating environments. In the first of my talk, I introduce our study on how plant community assembly patterns change along with the largest global environmental gradient, the latitudinal gradient. Then, I will present how the seasonal variability of environments contributes to the coexistence of phytoplankton species in a lake. These results altogether uncover how spatiotemporal heterogeneity of environments forms ecological communities in nature.

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

Event Official Language: English

Tropical methods in Enumerative Geometry and Mirror Symmetry

November 25 (Fri) 14:00 - 16:00, 2022

Michel Van Garrel (Assistant Professor, School of Mathematics, University of Birmingham, UK)

Abstract for the 1st hour: Enumerative Geometry has been a feature of mathematics from its beginnings, just think about the number of lines in the plane passing through 2 points. I will take you on a history of the subject and its relationship to other areas of mathematics and physics. Abstract for the 2nd hour: Many problems in mathematics are solved by taking a limit and solving the limiting problem. Tropical geometry is a key technique that allows us to do this systematically. I will talk about the following problem. Take the complex projective plane S and an elliptic curve E in S. Count algebraic maps from the affine line into the complement S \ E. This counting problem is solved via tropical geometry as I will describe in this talk.

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

Event Official Language: English

RNA-Puzzles - the evaluation and automation of RNA 3D structure

November 24 (Thu) 16:00 - 17:00, 2022

Zhichao (Chichau) Miao (Principal Investigator, Guangzhou Laboratory, China / Guangzhou Medical University, China)

RNA-Puzzles is a collective endeavour dedicated to the advancement and improvement of RNA 3D structure prediction. With agreement from crystallographers, the RNA structures are predicted by various groups before the publication of the crystal structures. Systematic protocols for comparing models and crystal structures are described and analyzed. In RNA-Puzzles, we discuss a) the capabilities and limitations of current methods of 3D RNA structure based on sequences; b) the progress in RNA structure prediction; c) the possible bottlenecks that hold back the field; d) the comparison between the automated web server and human experts; e) the prediction rules, such as coaxial stacking; f) the prediction of structural details and ligand binding; g) the development of novel prediction methods; and h) the potential improvements to be made. Till now, 37 RNAs with crystal structures have been predicted, while many of them have achieved high accuracy in comparison with the crystal structures. We have summarized part of our results in three papers and two community-wide meetings. With the results in RNA-Puzzles, we illustrate that the current bottlenecks in the field may lie in the prediction of non-Watson-Crick interactions and the reconstruction of the global topology. Correct coaxial stacking and tertiary contacts are key for the prediction of RNA architecture, while ligand binding modes can only be predicted with low resolution. For the model evaluation, we present RNA-Puzzles toolkit, a computational resource including (i) decoy sets generated by different RNA 3D structure prediction methods, (ii) 3D structure normalization, analysis, manipulation, visualization tools and (iii) 3D structure comparison metric tools. With the increasing number of RNA structures being solved as well as the high-throughput biochemical experiments, RNA 3D structure prediction is becoming routine and accurate. Structure modelling may effectively help in understanding the viral RNA structures, including the SARS-CoV-2.

Venue: via Zoom

Event Official Language: English

Energy partition in Weibel-mediated shock waves: from Supernova Remnants to Gamma-Ray Bursts

November 24 (Thu) 14:00 - 15:00, 2022

Arno Vanthieghem (Princeton-NINS Postdoctoral Research Fellow, Department of Astrophysical Sciences, Princeton University, USA)

Gamma-ray bursts and supernovae provide ideal environments for efficient energy channeling between different plasma species through collective processes such as collisionless shock waves. Extensively studied in astrophysical and laboratory environments, observations and kinetic simulations indicate strong electron heating in the precursor of collisionless shock waves propagating in unmagnetized electron-ion plasmas. We outline a theoretical model accounting for electron heating via a Joule-like process through the interplay between pitch-angle scattering in the microturbulence and the coherent electrostatic field induced by the difference in inertia between species. Using analytical kinetic estimates, semi-analytical Monte Carlo methods, and ab-initio Particle-In-Cell simulations, we demonstrate the validity of this model in the relativistic regime relevant to the afterglow emission of gamma-ray burst and extend it to characterize the electron-to-ion-temperature ratio in the downstream of nonrelativistic high-Mach numbers shock waves relevant for supernova remnants and laboratory experiments.

Venue: via Zoom

Event Official Language: English

Tetra and pentaquarks with multi-flavor contents

November 22 (Tue) 13:30 - 15:00, 2022

Atsushi Hosaka (Professor, Research Center for Nuclear Physics, Osaka University)

Recent hadron experiments keep providing evidences of exotic hadrons with multi-quark components. These multiquarks are self-arranged into various configurations such as diquarks, hadronic molecules and so on. In this seminar, we discuss possible structures of tetra and pentaquarks with multi-flavor contents including recently observed T_cc, Pc and P_cs. Based on our recent studies in the quark model and hadron models, we discuss where and how different quark structures emerge.

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

Event Official Language: English

Mathematics of Post-Quantum Cryptography

November 18 (Fri) 14:00 - 16:30, 2022

Yusuke Aikawa (Researcher, Information Technology R&D Center, Mitsubishi Electric Corporation)

Cryptography keeps our everyday information communications secure. Cryptography based on key sharing have been used mainly for military purposes since ancient times in human history, but with the advent of the Internet, cryptography that does not require key sharing has become necessary. In 1976, Diffie and Hellman proposed the concept of public key cryptography, which does not require key sharing among communicators. Since then, research on public key cryptography has progressed, involving not only computer science but also mathematics, and has become an essential technology for the society we live in. The security of public key cryptography is supported by computational hardness of problems derived from mathematics. For example, the integer factoring problem is a basis for the security of RSA cryptography, and the discrete logarithm problem is for elliptic curve cryptography. However, in 1994, Shor proposed an efficient quantum algorithm that solves these problems. This means that emergence of large-scale quantum computers will break RSA and elliptic curve cryptography we use today. For this reason, research on next-generation cryptography, so-called Post-Quantum Cryptography (PQC for short), is currently underway to prepare for a future in which quantum computers will emerge. In this talk, without assuming any knowledge of cryptography, I will give a brief overview of cryptography and the progress of PQC. The first half of the talk will mainly outline the relationship between mathematics and cryptography, while the second half will discuss isogeny-based cryptography, one of the promising PQC, with our recent results.

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

Event Official Language: English

Emergence of growth and dormancy from a kinetic model of the Escherichia coli central carbon metabolism

November 17 (Thu) 18:00 - 19:00, 2022

Yusuke Himeoka (Assistant Professor, Universal Biology Institute, The University of Tokyo)

Physiological states of bacterial cells exhibit a wide spectrum of timescale. Under nutrient-rich conditions, most of the cells in an isogenic bacterial population grow at certain rates, while a small subpopulation sometimes stays in a dormant state where the growth rates slow down by orders of magnitude. For revealing the origins of such heterogeneity of timescales, we studied the kinetic model of Escherichia coli central carbon metabolism. We found that the model robustly exhibits both the growing- and the dormant state. Performing the model reduction, we have revealed the necessary conditions for the distinct behaviour, namely, the depletion of energy due to the futile cycle and its non-uniform impact on the kinetics because of the coexistence of the energy currency-coupled and uncoupled reactions as well as branching of the network.

Venue: via Zoom

Event Official Language: English

MCME SYMPOSIUM 2022

November 16 (Wed) - 17 (Thu) 2022

Takemasa Miyoshi (Team Leader, Data Assimilation Research Team, RIKEN Center for Computational Science (R-CCS))
Hidetoshi Taya (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
Hidetoshi Nishimori (Specially Appointed Professor, Tokyo Institute of Technology)

"MCME SYMPOSIUM 2022" will be held at the Musashino Center of Mathematical Engineering (MCME), Musashino University. This symposium is free of charge and open to everyone. Colleagues of iTHEMS will also be speaking. Below is an excerpt from the program. Wednesday, November 16, 13:30 - 14:40 Takemasa Miyoshi Thursday, November 17, 10:00 - 11:10 Hidetoshi Taya Thursday, November 17, 14:50 - 16:00 Hidetoshi Nishimori Registration is open until November 14. Please register from the related links below. Organized by Musashino Center of Mathematical Engineering (MCME), Musashino University Co-organized by RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS)

Venue: Hybrid Format (Room 301, Building 5, Ariake Campus, Musashino University and Zoom)

Merger and post-merger of binary neutron stars with a quark-hadron crossover equation of state

November 15 (Tue) 15:00 - 17:01, 2022

Yongjia Huang (Ph.D. Student, University of Science and Technology of China, China)

The state of the ultra-dense matter remains one of the long-standing open questions. Neutron star (NS), as it cools down the eons ahead after the birth in the supernova explosion, provides an astrophysical laboratory to investigate the dense, strongly interacting nuclear matter at zero temperature. On the other hand, the most intense gravitational wave(GW) radiation is produced in regions of the strong gravitational field by coherent movements of masses with large compactness. Therefore, GW from binary neutron star(BNS) merger naturally contains the information from the ultra-dense matter. In this talk, I will introduce our recent work, "Merger and post-merger of binary neutron stars with a quark-hadron crossover equation of state ."Quark-hadron crossover(QHC) is one way of hadron-quark transition, which generally predicts a peak in sound speed vs. density, and so releases more pressure during the hadron-quark transition. I will first briefly summarize the features of QHC EOS and the BNS merger. I will then focus on how information on the hadron-quark transition shows in the GW and its spectrum during the BNS merger.

Venue: via Zoom

Event Official Language: English

Expanding Edges of Quantum Hall Systems in a Cosmology Language - Hawking Radiation from de Sitter Horizon in Edge Modes

November 11 (Fri) 16:00 - 17:30, 2022

Masahiro Hotta (Assistant Professor, Department of Physics, Graduate School of Science, Tohoku University)

Expanding edge experiments are promising to open new physics windows of quantum Hall systems. In a static edge, the edge excitation, which is described by free fields decoupled with the bulk dynamics, is gapless, and the dynamics preserve conformal symmetry. When the edge expands, such properties need not be preserved. We formulate a quantum field theory in 1+1 dimensional curved spacetimes to analyze the edge dynamics. We propose methods to address the following questions using edge waveforms from the expanding region: Does the conformal symmetry survive? Is the nonlinear interaction of the edge excitations induced by edge expansion? Do the edge excitations interact with the bulk excitations? We additionally show that the expanding edges can be regarded as expanding universe simulators of two-dimensional dilaton-gravity models, including the Jackiw-Teitelboim gravity model. As an application, we point out that our theoretical setup might simulate emission of analog Hawking radiation with the Gibbons-Hawking temperature from the future de Sitter horizon formed in the expanding edge region.

Venue: #345-347, 3F, Main Research Building (Main Venue) / via Zoom

Event Official Language: English

Sociogenesis: motivations and first steps

November 10 (Thu) 16:00 - 17:00, 2022

Cédric Ho Thanh (Postdoctoral Researcher, Prediction Science Laboratory, RIKEN Cluster for Pioneering Research (CPR))

Sociogenesis is a project that aims to study emergent social behaviors of multi-agent systems. In its simplest form, and agent simply seeks to survive by consuming food and maximizing some happiness score. In this presentation, I will discuss some motivations and inspirations of this project, as well as the challenges to get an agent to survive on its own. I will then showcase some methods to evaluate the quality of agents and their underlying architecture beyond simply looking at their lifespan. I will then conclude with some potential applications. No prior knowledge in reinforcement/deep learning is required to attend this presentation. This work is still mostly at an exploratory stage, so discussions and inputs from the audience are more than welcome!

Venue: via Zoom

Event Official Language: English

Tensor renormalization group approach to quantum fields on a lattice

November 8 (Tue) 13:30 - 15:00, 2022

Shinichiro Akiyama (Specially Appointed Assistant Professor, Quantum Software Project, The University of Tokyo)

Tensor renormalization group (TRG) approach is a variant of the real-space renormalization group to evaluate the path integral defined on the thermodynamic lattice, without resorting to any probabilistic interpretation for the given Boltzmann weight. Moreover, since the TRG can directly deal with the Grassmann variables, this approach can be formulated in the same manner for the systems with bosons, fermions, or both. These advantages of the TRG approach have been confirmed by the earlier studies of various lattice theories, which suggest that the TRG enables us to investigate the parameter regimes where it is difficult to access with the standard stochastic numerical methods, such as the Monte Carlo simulation. In this talk, explaining our recent applications of the TRG approach to several lattice models, we demonstrate the efficiency of the TRG as a tool to investigate lattice theories particularly in higher dimensions and future perspective.

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

Event Official Language: English

UHECR anisotropy: effects of the Galactic magnetic field on the UHECR correlation studies

November 4 (Fri) 14:00 - 15:00, 2022

Ryo Higuchi (Special Postdoctoral Researcher, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))

Telescope Array (TA) and Auger experiments reported anisotropies in the arrival direction of ultra-high-energy cosmic rays (UHECRs). In the current correlation studies between UHECRs and source candidates, the Auger experiment reported a correlation between the flux model of assumed sources and UHECR events and suggested a 10% contribution of starburst galaxies (SBGs) to the anisotropy of UHECRs. However, they do not consider the effect of coherent deflection by the galactic magnetic field (GMF), and they should significantly affect the results of the correlation studies. In this talk, we introduce a current study of UHECR anisotropy and the effect of GMF on them.

Venue: via Zoom

Event Official Language: English

Measuring diversity: species similarity

October 28 (Fri) 16:00 - 17:00, 2022

Tom Leinster (Professor, University of Edinburgh, UK)

Traditional measures of the diversity of an ecological community depend only on how abundant the species are, not the similarities or differences between them. To better reflect biological reality, species similarity should be incorporated. Mathematically, this corresponds to moving from probability distributions on sets to probability distributions on metric spaces. I will explain how to do this and how it can change ecological judgements. Finally, I will describe a surprising theorem on maximum diversity (joint with Meckes and Roff), which reveals close connections between maximum diversity and invariants of geometric measure.

Venue: via Zoom

Event Official Language: English

Migration dynamics and model of cells crawling on a matrix with cell-scale stiffness heterogeneity

October 27 (Thu) 16:00 - 17:00, 2022

Hiroyuki Ebata (Assistant Professor, Graduate School of Science, Kyushu University)

In living tissues where cells migrate, spatial distribution of mechanical properties, especially matrix stiffness, are generally heterogenous with cell-scales ranging from 10 to 1000 μm. Since the cell migration in our body plays critical role in morphogenesis, wound healing, and cancer metastasis, it is essential to understand the migratory dynamics on the matrix with cell-scale stiffness heterogeneity. However, while cellular responses to homogeneous matrix have been extensively explored, studies of the cell motility with stiffness heterogeneity have been limited to the directional movement (durotaxis) driven by a simple stiffness gradient. Thus, we need to elucidate how cell migration is determined through the interaction among cell-scale stiffness heterogeneity and cellular responses such as dynamics of the cell-matrix adhesion site, the intracellular prestress, and cell shape. In this talk, we introduce our experiments on cell motility, shaping, adhesion, and traction forces at long time scales using microelastically patterned hydrogels that enable us to systematically control the cell-scale heterogeneity of the matrix-stiffness. Using microelastically patterned hydrogels, we showed that the cell exhibited a general mode of durotaxis depending on the shape and size of the stiff domains, which was coincided with the extraordinarily large fluctuation of the traction force. We proposed a cell migration model based on equations of a deformable self-propelled particle adopting an amoeboid swimmer-like velocity-shape relationship. By considering the cellular response to stiffness gradients, the model can reproduce general durotaxis driven by cell-scale heterogeneity of the matrix-stiffness.

Venue: via Zoom

Event Official Language: English

Measuring diversity: the axiomatic approach

October 21 (Fri) 16:00 - 17:00, 2022

Tom Leinster (Professor, University of Edinburgh, UK)

Ecologists have been debating the best way to measure diversity for more than 50 years. The concept of diversity is relevant not only in ecology, but also in other fields such as genetics and economics, as well as being closely related to entropy. The question of how best to quantify diversity has surprising mathematical depth. I will argue that the best approach is axiomatic: to enable us to reason logically about diversity, the measures we use must satisfy certain mathematical conditions, and those conditions dramatically limit the choice of measures. This point will be illustrated with a theorem: using a simple model of ecosystems, the only diversity measures that behave logically are the Hill numbers, which are very closely related to the Rényi entropies of information theory.

Venue: via Zoom

Event Official Language: English