Search Event

Dynamics of Phase Transitions: Between First and Second Order

October 8 (Tue) 16:00 - 17:30, 2024

Fumika Suzuki (CNLS Postdoctoral Research Associate, T4 / Center for Nonlinear Studies, Los Alamos National Laboratory, USA)

Phase transitions are typically classified as either first-order or second-order. The formation of topological defects in second-order phase transitions is well described by the Kibble-Zurek mechanism, while nucleation theory addresses first-order phase transitions. However, certain systems, such as superconductors and liquid crystals, can exhibit “weakly first-order” phase transitions that do not fit into these established frameworks. In this presentation, I introduce a new theoretical approach that combines the Kibble-Zurek mechanism with nucleation theory to explain topological defect formation in weakly first-order phase transitions. Additionally, I will discuss nonlinear quantum phase transitions that exhibit behaviors similar to weakly first-order transitions, which can be related to experiments with ultra-cold Rydberg atoms.

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

Event Official Language: English

Application of Complex Scaling Method to Scattering Calculations of Atomic Systems

October 8 (Tue) 13:30 - 15:00, 2024

Taishi Sano (Master's Student, Waseda University)

Based on our paper [1], this presentation will show the application of complex scaling method(CSM) to scattering calculations of atomic systems. While CSM has been extensively used to study resonance states, the application of CSM to scattering calculations was proposed recently with applications in nuclear physics. In our study, we apply the CSM scattering calculation to atomic systems and propose an effective correction to avoid the problem of slow convergence to the number of complex eigen energies. Our results with the effective correction agree well with those reported in the literature for positron scattering with the targets Ne, Ar, Kr, Xe, H, He, He+, and Li2+. In this presentation, we introduce the framework of phase-shift calculation using the CSM together with the examples of the positron scattering, and advantages and features of this approach. [This seminar is co-hosted by Few-body Systems in Physics Laboratory, RIKEN Nishina Center.]

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

Event Official Language: English

Dense Matter Physics and Exotic States in Neutron Stars

October 7 (Mon) 14:00 - 15:15, 2024

Vivek Thapa (Assistant Professor, Bhawanipur Anchalik College, India)

In the presentation, I will discuss the exploration of neutron star matter using phenomenological models, focusing on how exotic particles like antikaons, hyperons as well as Delta-resonances influence the neutron star equation of state (EoS). The discussion will cover how antikaon optical potentials and kaon condensation affect the stability and structure of neutron stars, as well as the potential for hadron-quark phase transitions leading to quark matter cores in massive stars. I will also highlight the study of non-radial oscillation modes which provide insights into the internal structure and composition of neutron stars. These oscillation modes are essential for understanding neutron star asteroseismology and interpreting gravitational wave signals from neutron star mergers. By comparing theoretical predictions with observational data, including mass, radius, cooling rates, and gravitational wave detections, the presentation aims to refine constraints on the EoS and enhance our understanding of dense matter in compact stars.

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

Event Official Language: English

Clinical trials and standards of care: How doctors decide your medical treatment

October 2 (Wed) 16:00 - 17:00, 2024

Catherine Beauchemin (Deputy Program Director, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))

Ever wondered what data is considered sufficient for approval of a new drug or vaccine? In this talk, I will talk about some of the errors and shortcomings with how clinical trials are run and regulated. I will also show how the data and analyses behind clinical trials can be very poorly done. I will show one example of very bad data and analysis, but I will also show an example of the valuable information that can come out of doing a good job in presenting, interpreting, and following the data. I will highlight how the over-reliance on summarizing measures like averages and the Gaussian assumption can lead to overlooking therapies that could otherwise have been extremely effective. This talk should be of critical importance to those working in the fields of health, medical and clinical research. But this talk is about data and its analysis, and as such is also very relevant to physicists and other scientists who generate, present or analyse data as part of their research.

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

Event Official Language: English

iTHEMS Cosmology Forum #2 - Stochastic gravitational waves: fossils from the early universe

September 27 (Fri) 9:00 - 18:00, 2024

Keitaro Takahashi (Professor, Faculty of Advanced Science and Technology, Kumamoto University)
Kazuyuki Sugimura (Assistant Professor, Graduate School of Science, Hokkaido University)
Ryusuke Jinno (Associate Professor, Graduate School of Science, Kobe University)
Yuichiro Tada (Designated Assistant Professor, C-Lab, Department of Physics, Institute for Advanced Research, Nagoya University)

iTHEMS Cosmology Forum Workshop is a series of short workshops, each focused on an emerging topics in cosmology. The targeted audience is cosmologists, high-energy physicists and astronomers interested in learning about the subject, not just those who have already worked on the topic. The goal of the workshop is to provide working knowledge of the topic and leave dedicated time for discussions to encourage mutual interactions among participants. The second workshop is devoted to explanations of the stochastic gravitational wave background (SGWB). The SGWB is a significant detection of GW from pulsar timing arrays. The origin of this background could be either supermassive black holes or primordial. Surprisingly, both of these early Universe mechanisms are not well understood. This one-day workshop gathers both the observational and theoretical aspects of this growing topic. The workshop will be in English. The workshop venue will be either at Main Research Building #435-437 or at Okochi Hall, and we will decide and announce which one will be actually used after the registration is closed. The workshops are organised by the iTHEMS Cosmology Forum working group, which is the successor of the Dark Matter Working Group at RIKEN iTHEMS. Invited Speakers: Keitaro Takahashi (Kumamoto University) TBA Kazuyuki Sugimura (Hokkaido University) Supermassive black hole formation Ryusuke Jinno (Kobe University) First-order phase transitions and gravitational wave production in the early Univers Yuichiro Tada (Nagoya University) Scalar-induced gravitational waves as a cosmological phonograph Time table: 09:00-09:30 -- Opening remarks and coffee 09:30-10:45 -- Takahashi (keynote) 10:45-11:45 -- Sugimura 11:45-13:30 -- Lunch time 13:30-14:30 -- Jinno 14:30-15:30 -- Discussion and coffee 15:30-16:30 -- Tada 16:30-17:30 -- Panel Discussion Organisers: Kohei Hayashi, Nagisa Hiroshima, Derek Inman, Amaury Micheli, Ryo Namba

Venue: #435-437, 4F, Main Research Building

Event Official Language: English

A model to unify the theory of speciation

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

José Said Gutiérrez-Ortega (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (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

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) 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

Social behavior and social engineering in bacteria

August 1 (Thu) 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) 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) 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

Stringy Nonlocality: Operator Formalism and Implications

July 26 (Fri) 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) 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

iTHEMS NOW & NEXT 2024

July 19 (Fri) 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: 2F Large Conference Room, Administrative Headquarters, RIKEN Wako Campus (Main Venue) / via Zoom

Event Official Language: English

Optimal control of stochastic reaction networks

July 18 (Thu) 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) 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

Surface defect in N=4 SYM and integrability

July 17 (Wed) 16:00 - 17:00, 2024

Hiroki Kawai (Ph.D. Student, University of California, Santa Barbara, USA)

In the N=4 super Yang-Mills theory, it is well-known that the one-loop anomalous dimension operator for the single trace operators is equivalent to an integrable spin chain. Recent works have extended the application of integrability to scenarios involving a BPS boundary or defects such as 't Hooft line. One can describe the correlators of the single trace operators as an overlap between the Bethe state and the corresponding defect state. This overlap can be exactly calculated if the defect state is a so-called integrable state. We show that the state corresponding to the Gukov-Witten surface defect is integrable. We also calculate the tree-level one-point function of the single trace operators and set up the perturbation calculation in this defect background for one-loop corrections.

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

Event Official Language: English

Supernovae as Tracers of Massive-Star Evolution

July 17 (Wed) 14:00 - 15:15, 2024

Daichi Hiramatsu (Post-Doctoral fellow, Harvard University, USA)

Supernovae are the terminal explosions of massive stars with influences on every astrophysical scale. Advanced wide-field and high-cadence transient surveys routinely discover supernovae near the moment of explosion. Coupled with prompt and continuous follow-up facilities, these observations have revealed unprecedented features of dense circumstellar medium in various spatial scales as traced by the expanding supernova ejecta. Such circumstellar medium is thought to originate from mass-loss activities in the final years to decades of stellar evolution; however, their inferred densities exceed the expectations from standard theory by many orders of magnitude. In this talk, I will first introduce standard stellar evolution and supernova explosion mechanisms, and then describe novel observational probes and modeling techniques of supernovae interacting with circumstellar medium to reconstruct their explosion properties and progenitor mass-loss histories. Finally, I will discuss our on-going largest sample study of interacting supernovae and emerging pictures of dramatic dying breaths of massive stars.

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

Event Official Language: English

Quantum Error Transmutation

July 17 (Wed) 10:30 - 11:30, 2024

Daniel Zhang (Postdoctoral Fellow, University of Oxford, UK)

We introduce a generalisation of quantum error correction, relaxing the requirement that a code should identify and correct a set of physical errors on the Hilbert space of a quantum computer exactly, instead allowing recovery up to a pre-specified admissible set of errors on the code space. We call these quantum error transmuting codes. They are of particular interest for the simulation of noisy quantum systems, and for use in algorithms inherently robust to errors of a particular character. Necessary and sufficient algebraic conditions on the set of physical and admissible errors for error transmutation are derived, generalising the Knill-Laflamme quantum error correction conditions. We demonstrate how some existing codes, including fermionic encodings, have error transmuting properties to interesting classes of admissible errors. Additionally, we report on the existence of some new codes, including low-qubit and translation invariant examples.

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

Event Official Language: English

Mapping the Phase Space of toric Calabi-Yau 3-folds using Explainable Machine Learning

July 16 (Tue) 13:30 - 14:30, 2024

Rak-Kyeong Seong (Assistant Professor, Department of Mathematical Sciences, Ulsan National Institute of Science and Technology (UNIST), Republic of Korea)

This talk will give a brief introduction on how bipartite graphs on a torus represent 4-dimensional quiver gauge theories and their moduli space which is a toric Calabi-Yau 3-fold - a cone over a Sasaki-Einstein 5-manifold. Under mirror symmetry, the bipartite graph can be identified with the tropical projection of the mirror curve obtained from the Newton polytope associated to the toric Calabi-Yau 3-fold. Changes to the complex structure moduli of the mirror Calabi-Yau determine the overall shape of the bipartite graph on the torus. For certain choices of complex structure moduli, the bipartite graph undergoes a graph mutation which is identified with Seiberg duality of the associated 4-dimensional quiver gauge theory. This talk will discuss recent progress in understanding when such mutations occur from the point of view of Calabi-Yau mirror symmetry with the help of new computational techniques such as machine learning.

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

Event Official Language: English