Organizational meeting 4

September 26 (Thu) at 16:00 - 17:00, 2024

This the semi-regular opportunity for iTHEMS Biology members to discuss their current research progress and/or difficulties and/or research questions. Anyone is welcome to join. It will be held in hybrid form.

Venue: via Zoom / Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Evolution and origin of complex genetic organisms

September 19 (Thu) at 16:00 - 17:00, 2024

Thomas Hitchcock (Special Postdoctoral Researcher, iTHEMS)

Whilst the standard Mendelian rules of inheritance are the most familiar to most researchers, and common across many groups of organisms, a large minority of animals diverge from this. Included in this are eusocial groups such as ants, wasps, bees and termites. These creatures can be thought of not only as groups of individuals (workers, queens, kings), but also as a single complex genetic organism (a “superorganism”). Amongst these groups a wide array of genetic and mating systems have also emerged. I first describe some of the variation in some of the genetic systems we see, and then outline some plans for models of molecular evolution in these species. I'll discuss how these groups may enable some non-standard forms of meiotic drive, which in turn may help explain the origin of some of the unusual genetic features and systems that we observe.

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

Event Official Language: English

Renormalization Group Approach for Machine Learning Hamiltonian

September 10 (Tue) at 15:00 - 17:00, 2024

Misaki Ozawa (CNRS Researcher, Laboratory for Interdisciplinary Physics (LIPhy), Université Grenoble Alpes, France)

We develop a multiscale approach to estimate high-dimensional probability distributions. Our approach applies to cases in which the energy function (or Hamiltonian) is not known from the start. Using data acquired from experiments or simulations we can estimate the underlying probability distribution and the associated energy function. Our method—the wavelet-conditional renormalization group (WCRG)—proceeds scale by scale, estimating models for the conditional probabilities of “fast degrees of freedom” conditioned by coarse-grained fields, which allows for fast sampling of many-body systems in various domains, from statistical physics to cosmology. Our method completely avoids the “critical slowing-down” of direct estimation and sampling algorithms. This is explained theoretically by combining results from RG and wavelet theories, and verified numerically for the Gaussian and φ4-field theories, as well as weak-gravitational-lensing fields in cosmology. Misaki Ozawa obtained his Ph.D. in 2015 from the University of Tsukuba. He did his first postdoc at the University of Montpellier in France. He then moved to Ecole Normale Supérieure (ENS) Paris as the second postdoc. Currently, he is a CNRS permanent researcher at Grenoble Alpes Univeristy in France. His background is in the physics of disordered systems such as glasses and spin glasses. He is also working on interdisciplinary studies between statistical physics and machine learning.

Venue: #359, 3F, Seminar Room #359 / via Zoom

Event Official Language: English

A model to unify the theory of speciation

September 5 (Thu) at 16:00 - 17:00, 2024

José Said Gutiérrez-Ortega (Special Postdoctoral Researcher, iTHEMS)

Speciation, the process by which new species originate, occurs due to geographic (physical distance), ecological (different background environments), and historical (divergence time) factors that promote reproductive isolation among lineages. However, we don’t know how these factors interplay; therefore, our empirical and theoretical knowledge about speciation is limited, fragmented, and lacks unification. To fill this knowledge gap, I propose a model and an experiment that treats speciation as a continuum of the interplay between geographic and ecological factors. Empirical evidence has shown that the extremes of this continuum produce high evolutionary rate (faster speciation), while I expect that intermediate values in the interplay continuum would produce reduced evolutionary rates. I expect this seminar can open opportunities for collaboration.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

RIKEN - LBNL Workshop on Quantum Information Science

September 3 (Tue) - 6 (Fri), 2024

This international workshop will bring together researchers worldwide to discuss and collaborate on the latest developments in quantum technologies and quantum computing. Other focus areas will be algorithms, hybrid classical - quantum computing, error mitigation, and applications in physics and chemistry. With an emphasis to galvanize the participants into future collaborations, in addition to presentations on recent trends, the workshop will dedicate time in the afternoons for facilitated brainstorming and planning sessions.

Venue: Lawrence Berkeley National Laboratory (Berkeley, California)

Event Official Language: English

Visit by MACS SG Students

September 2 (Mon) - 3 (Tue), 2024

Monday, September 2nd 13:20–13:30: Opening 13:30–13:40: Self-introductions 13:40–14:10: Introduction to iTHEMS 14:10–14:30: Coffee Break 14:30–15:30: Seminar by iTHEMS Researcher (Dr. Moriwaki) 16:30–18:00: Laboratory Visit (Kazama Lab) 18:30–20:00: Research Presentation/ Discussion Session Tuesday, September 3rd 10:00–10:20: Tour of iTHEMS Facilities 10:40–12:10: Laboratory Visit (Tatara Lab) 12:20–13:20: Lunch/Coffee Break 13:30–15:00: Laboratory Visit (Tamagawa Lab) 15:30–17:00: Laboratory Visit (Isomura Lab) 17:20–17:30: Closing

Venue: Seminar Room #359

Event Official Language: Japanese

NCTS-iTHEMS Joint Workshop on Matters to Spacetime: Symmetries and Geometry

August 26 (Mon) - 29 (Thu), 2024

The National Center for Theoretical Sciences (NCTS) and the Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS) at RIKEN have long maintained a collaborative relationship, even before the Memorandum of Understanding was signed in December, 2022. This partnership has successfully facilitated joint activities in high energy physics over recent years. As the impact of the COVID-19 pandemic wanes, we are excited to announce the inaugural joint workshops focusing on condensed matter physics and (quantum) gravity. These workshops are designed to foster international collaborations and stimulate interdisciplinary research. We are pleased to invite you to the 2024 NCTS-iTHEMS Workshop on Matters to Spacetime: Symmetries and Geometry, to be held from August 26 (Monday) to August 29 (Thursday), at the National Center for Theoretical Sciences, located on the campus of National Taiwan University (NTU) in Taipei, Taiwan. This workshop will feature presentations on the latest research findings, foster discussions to spark new ideas, and provide opportunities for initiating collaborative projects. While we strongly encourage in-person attendance to maximize engagement and interaction, an online platform will also be available to accommodate participants who are unable to attend physically.

Venue: NCTS Physics Lecture Hall, 4th Floor, Cosmology Hall, National Taiwan University

Event Official Language: English

Chromatophore patterns, packing, and scaling on a growing squid

August 20 (Tue) at 16:00 - 17:00, 2024

Robert Ross (Interdisciplinary Postdoctoral Researcher, Biological Complexity Unit / Computational Neuroethology Unit, Okinawa Institute of Science and Technology Graduate University (OIST))

Many biological patterns are formed during growth, and various modeling approaches have repeatedly shown that growth can substantially impact pattern formation. However, experimental testing of these ideas has been limited, largely due to the difficulty in precisely measuring organism growth while simultaneously tracking the dynamics of pattern formation. To address this, we turned to the skin of the oval squid. The oval squid grows rapidly, hatching with a length of approximately 16mm and reaching 90mm within 3 months. Throughout development, its skin is populated by pigment-filled cells called chromatophores. Following insertion into the skin, chromatophores do not move. This means that squid chromatophores, besides being the constitutive elements of a point pattern, can also function as reference points to precisely determine skin growth. For the more biologically-minded, I will explain how the chromatophore pattern emerges through the interplay of growth and decreasing chromatophore growth rates. For those who lean physics, I will talk about how due to the combination of volume exclusion and growth, chromatophores exhibit a scaling in which relative density fluctuations grow with spatial scale, akin to a critical system.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

What will Happen to iTHEMS⊗Masason Foundation Members?

August 2 (Fri) at 13:30 - 17:30, 2024

Venue: Seminar Room #359

Event Official Language: English

Social behavior and social engineering in bacteria

August 1 (Thu) at 16:00 - 17:00, 2024

Ashleigh Griffin (Professor, Department of Biology, University of Oxford, UK)

This year is the 60th anniversary of WD Hamilton’s seminal paper in which he outlined his theory of inclusive fitness and showed how it could be used to understand altruism in the social insects. In this talk, I will describe efforts made to use his theory to understand social behavior in bacteria. And I’ll go on to explore the potential of using these insights to tackle problems of antibiotic resistance in infections.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

Algebraic curves and parametric resurgence

July 29 (Mon) at 16:30 - 17:45, 2024

Samuel Crew (Postdoctoral Fellow, Imperial College London, UK)

In this talk I will discuss recent work together with Ines Aniceto (Southampton) on algebraic examples of parametric resurgence. We discuss a simple example to elucidate the so-called higher order Stokes phenomena and discuss how a Borel inner-outer matching procedure allows us to view parametric resurgence as a series of non-parametric resurgence problems.

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

Event Official Language: English

RIKEN iTHEMS & AIPmath Special Lecture: Contact geometry in 3-dimensional space and higher

July 29 (Mon) at 15:30 - 16:30, 2024

Emmy Murphy (Professor, Princeton University, USA)

In mathematics, contact geometry is a type of geometry describing a variety of dynamical systems. They are the phase spaces of systems arising in geometric optics, semi-classical quantum systems, classical dynamics, and control theory. On the mathematical side, contact geometry relates to a variety of other geometric structures, such as Kahler geometry, smooth topology, and foliation theory. It can be especially interesting to look at contact geometry in 3-dimensional space, because we can explicitly visualize the spaces. Additionally, by connecting contact geometry with our understanding of 3-D topology, mathematicians have the ability to understand the large-scale structure of these spaces like never before. The talk will introduce the basics of contact geometry and its applications. We'll particularly focus on the 3-dimensional case, while also mentioning some of the unique properties of higher-dimensional spaces which are recently being explored. Registration required: Register before Wednesday, July 24, 15:00.

Venue: RIKEN Tokyo Liaison Office (Nihonbashi) (Main Venue) / via Zoom

Event Official Language: English

Lectures on Black Holes, Holography and Quantum Gravity

July 29 (Mon) - August 1 (Thu), 2024

Yasunori Nomura (Director, Berkeley Center for Theoretical Physics, University of California, Berkeley, USA)

The information problem of black holes has evolved modern physics and led to the holographic principle, considered the fundamental principle of quantum gravity. Through a series of four lectures (blackboard style), including naive questions from the audience and lively discussions, I will introduce these fundamental ideas as well as the current state of the art and problems in cutting-edge research. Lecture 1: July 29 (Mon) 13:30~15:00 (Lecture 2: July 30 (Tue) 13:30~15:00 was canceled) Lecture 3: July 31 (Wed) 13:30~15:00 Lecture 4: Aug 1 (Thu) 13:30~15:00 (+ A possible lecture )

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Stringy Nonlocality: Operator Formalism and Implications

July 26 (Fri) at 14:00 - 15:30, 2024

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

Nonlocality is a fundamental property of string theory, where point-like particles are replaced by extended strings. This feature is especially evident in string field theories, where field components interact through form factors containing spacetime derivatives of infinite order. The usual approach to canonical quantization is no longer applicable, and thus a non-perturbative treatment of nonlocal effects at the quantum level remains unclear. In this seminar, I will discuss a recent attempt to construct an operator formalism for stringy nonlocal field theories, and explore the potential implications for black hole radiation and primordial fluctuations in the early universe.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Multi-Agent Reinforcement Learning for Exploring Collective Behavior

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

Kazushi Tsutsui (Assistant Professor, Graduate School of Arts and Sciences, The University of Tokyo)

Humans and other organisms develop collective behaviors through interactions with diverse environments and various species. These behaviors are significant topics across multiple research fields, including evolutionary biology, behavioral ecology, and animal sociology. Unraveling the decision-making mechanisms of individuals in groups within cooperative and competitive contexts has captured the attention of many researchers but remains a complex challenge. This seminar will present research cases that employ multi-agent reinforcement learning, a machine learning technique, to investigate the decision-making processes underlying collective behavior. Through this approach, we aim to provide deeper insights into the dynamics and mechanisms that drive group behaviors in various biological systems.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Symmetries and Generalization for Machine Learning on a Lattice

July 23 (Tue) at 15:00 - 16:30, 2024

Andreas Ipp (Senior Scientist, Institute for Theoretical Physics, TU Wien, Austria)

Symmetries such as translations and rotations are crucial in physics and machine learning. The global symmetry of translations leads to convolutional neural networks (CNNs), while the much larger space of local gauge symmetry has driven us to develop lattice gauge equivariant convolutional neural networks (L-CNNs). This talk will discuss how the challenges of simulating the earliest stage of heavy ion collisions led us to use machine learning and how these innovations could improve lattice simulations in the future. Andreas Ipp is a Senior Scientist at the Institute for Theoretical Physics at TU Wien. He received his PhD in 2003 and held postdoctoral positions at ECT* in Trento and the Max-Planck-Institute in Heidelberg before returning to TU Wien in 2009. He completed his habilitation on "Yoctosecond dynamics of the quark-gluon plasma" in 2014. His current research focuses on symmetries in machine learning for applications in lattice gauge theory and heavy ion collisions.

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

Event Official Language: English

Probing Majorana excitations in the Kitaev magnet α-RuCl3 through bulk heat capacity measurements

July 22 (Mon) at 10:30 - 11:45, 2024

Kumpei Imamura (Ph.D. Student / JSPS Research Fellow DC, Department of Advanced Materials Science, The University of Tokyo)

Recently, the layered honeycomb material α-RuCl3 exhibits several anomalous features that are consistent with expectations of the Kitaev quantum spin liquid (KQSL) under in-plane magnetic field. Most remarkably, finite planar thermal Hall conductivity has been observed, whose magnitude is close to the half-integer quantization value expected for the chiral edge currents of Majorana fermions[1]. However, it has been reported that the thermal Hall conductivity shows strong sample dependence. Also, there are attempts to offer a different explanation by the bosonic edge excitations due to topological magnons or phonon. A key to distinguishing between fermionic and bosonic origins of unusual features in the high-field state of α-RuCl3 is the difference in the field angle dependence of the excitation gap. Therefore, we distinguish these origins from combined low-temperature measurements of high-resolution specific heat and thermal Hall conductivity with rotating magnetic fields within the honeycomb plane. A distinct closure of the low-energy bulk gap is observed for the fields in the Ru-Ru bond direction, and the gap opens rapidly when the field is tilted. Notably, this change occurs concomitantly with the sign reversal of the Hall effect. General discussions of topological bands show that this is the hallmark of an angle rotation–induced topological transition of fermions, providing conclusive evidence for the Majorana-fermion origin of the thermal Hall effect in α-RuCl3[2]. Furthermore, to understand the nature of the high-field state, it is crucial to elucidate the effects of disorder, which inevitably exists in real materials. We artificially introduce point defects by electron irradiation and compare the low-energy excitations in the pristine and irradiated sample by high-resolution specific heat measurements. We observed an additional in-gap T-linear term in C/T, whose coefficient shows distinct field-sensitive behaviors suggestive of Majorana physics in the KSL. This can be interpreted by the weak localization of Majorana fermions, which is induced by the disorder[3]. Moreover, recently, we succeed in synthesizing very high-quality crystals of α-RuCl3[4].

Venue: via Zoom / Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

iTHEMS NOW & NEXT 2024

July 19 (Fri) at 9:30 - 18:00, 2024

9:30-10:00 Keynote by Lucy Mcneill 10:00-10:30 Keynote by Jose Said Gutierrez Ortega 10:35-11:05 Keynote by Puttarak Jai-akson 11:05-11:35 Keynote by Kannaka Kazuki 11:35-12:30 Lunch Time Session 12:30-13:30 Working Group / Study Group Report 
13:30-15:30 Flash Talk & Poster Presentation Part 1 
15:30-17:30 Flash Talk & Poster Presentation Part2 17:30 Concluding Remarks by the Director 18:00 reception

Venue: RIKEN Wako Campus, Head Quarter Build., 2F Large Conference Room (Main Venue) / via Zoom

Event Official Language: English

Optimal control of stochastic reaction networks

July 18 (Thu) at 16:00 - 17:00, 2024

Shuhei Horiguchi (JSPS Postdoctoral Research Fellow, Nano Life Science Institute, Kanazawa University)

Optimal control problems for the population of interacting particles arise in various fields, including pandemic management, species conservation, cancer therapy, and chemical engineering. When the population size is small, the time evolution of the particle numbers is inherently noisy and modeled by stochastic reaction networks, a class of jump processes on the space of particle number distributions. However, compared to deterministic and other stochastic models, optimal control problems for stochastic reaction networks have not been extensively studied. In this talk, I will review a formulation of stochastic reaction networks and present a new class of optimal control problems that are efficiently solvable and widely applicable. The optimal solution can be efficiently obtained using the Kullback–Leibler divergence as a control cost. We apply this framework to the control of interacting random walkers, birth-death processes, and stochastic SIR models. Both numerical and analytical solutions will be presented, highlighting the practical applications and theoretical significance of this approach.

Venue: via Zoom

Event Official Language: English

Thermal radiation exchange in primordial gravitational waves

July 18 (Thu) at 13:30 - 15:00, 2024

Atsuhisa Ota (Postdoctoral Fellow, Institute for Advanced Study, Hong Kong University of Science and Technology, China)

The radiation-dominated universe is a key component of standard Big Bang cosmology. Radiation comprises numerous quantum elementary particles, and its macroscopic behavior is described by taking the quantum thermal average of its constituents. The dynamics of gravitational waves are considered in this smooth fluid. While interactions between individual particles and gravitational waves are often neglected in this context, it raises the question of whether such a hydrodynamical approximation is reasonable. To address this question, we explored the quantum mechanical aspects of gravitational waves in a universe dominated by a massless scalar field, whose averaged energy-momentum tensor serves as background radiation. We computed thermal loop corrections for the gravitational wave power spectrum using the Schwinger-Keldysh formalism. Interestingly, we found that the loop effect enhances the super-horizon primordial gravitational wave spectrum, indicating that the inflationary spectrum is not conserved, contrary to conventional wisdom. These findings have significant implications for our understanding of the early universe. In this talk, I will begin with the basics of cosmology and explain the significance of these results and their relevant observational consequences.

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

Event Official Language: English