Seminar

Forming primordial black holes

November 11 (Mon) at 14:00 - 15:30, 2024

Zachary Picker (Postdoctoral Researcher, University of California, Los Angeles, USA)

Primordial black holes (PBHs) are black holes which form in the early universe. Not only are PBHs good dark matter candidates, but they have a wide range of fascinating phenomenology (even if they are only a fraction of the dark matter). In this talk I will review a somewhat under-discussed aspect of the PBH gospel---their formation mechanisms. In fact, there is a wide variety of ways to form PBHs of different sizes and abundances, and many of our favorite BSM theories can have PBHs in their spectra. I will then discuss some of our particular upcoming research on PBH formation, where attractive Yukawa forces in a dark sector can lead to the early formation of dense dark structures called Fermi balls which can collapse to black holes, with novel cosmological implications.

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

Event Official Language: English

Mathematical modeling of circadian rhythm: temperature compensation and after effect

November 7 (Thu) at 16:00 - 17:00, 2024

Yuta Kitaguchi (Ph.D. Student, Graduate School of Natural Science & Technology, Kanazawa University)

Almost all organisms have a circadian clock. This circadian clock consists of negative transcriptional-translational feedback loops (TTFLs) between various circadian clock genes in cells. Collective gene expression rhythms in the central circadian pacemaker tissue regulate nearly 24-hour behavioral rhythms of organisms. The circadian clock has three characteristics: (1) autonomous oscillation, (2) temperature compensation of the period, and (3) entrainment to external cycles such as a light-dark cycle. In this presentation, I will talk about theoretical studies on temperature compensation, and the entrainment to light-dark cycles. For temperature compensation, I will show that only a few temperature-insensitive reactions in the complex TTFLs of the circadian clock are sufficient to maintain the circadian period under increasing temperature. For entrainment to the light-dark cycle, I will show the mechanism for after-effect where the period of the circadian clock in constant darkness correlates with that of a previously entrained light-dark cycle for several months.

Venue: via Zoom

Event Official Language: English

Heterostyly and the evolution of mating system in plants

October 31 (Thu) at 16:00 - 17:00, 2024

Jeffrey Fawcett (Senior Research Scientist, iTHEMS)

Many organisms exhibit various strategies to avoid self-fertilization and promote outcrossing (mating with different individuals). Such strategies have repeatedly evolved and been disrupted throughout evolution, resulting in a remarkable diversity of mating systems. The most well-known strategy is sexual dimorphism, in which mating is only successful between opposite sexes (e.g. male and female) which exhibit different morphology (e.g. males and females look different). However, some plants, including buckwheat that I have been studying, have evolved a strategy where all individuals either have flowers with long or short styles (female organ), referred to as heterostyly or distyly, and mating is typically only successful between individuals with long-styled flowers and those with short-styled flowers, i.e., outcrossing is promoted by floral dimorphism that is not associated with sexes. While how such a system evolves and its genetic basis are still largely unknown, the genomic region responsible for heterostyly has been identified in many different species within the past year or two, revealing some interesting parallels between independently evolved systems. In this seminar, I will introduce these recent findings and discuss how heterostyly may be linked to the diverse mating systems observed in plants. I will also introduce what we have been doing and are planning/hoping to do in buckwheat and its related species.

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

Event Official Language: English

Quantum signature kernels

October 30 (Wed) at 14:00 - 15:00, 2024

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

Arising from rough path theory, the signature transform captures features of time-series data by constructing a so-called path signature. This feature has proven valuable for various machine learning tasks. However, computing the associated signature kernel classically remains computationally intensive. In this talk, I will present recent developments in generalising the signature kernel to randomised Lie group path developments. I will discuss a quantum approach via matrix models with an associated unitary quantum signature kernel to propose a quantum algorithm for its computation.

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

Event Official Language: English

Holographic Gubser flow

October 29 (Tue) at 13:30 - 14:30, 2024

Sukrut Mondkar (Postdoctoral Researcher, Harish-Chandra Research Institute, India)

Gubser flow is an evolution with cylindrical and boost symmetries, which can be best studied by mapping the future wedge of Minkowski space ℝ^{(3,1)} to dS_3 × ℝ in a conformal relativistic theory. Here, we sharpen the analytic results of Banerjee, Mitra, Mukhopadhyay Soloviev, EPJC (2024) and validate them via the first numerical exploration of the Gubser flow in a holographic conformal field theory. Remarkably, the leading generic behavior at large de Sitter time is free-streaming in transverse directions and the sub-leading behavior is that of a color glass condensate. We also show that Gubser flow can be smoothly glued to the vacuum outside the future Minkowski wedge generically given that the energy density vanishes faster than any power when extrapolated to early proper time or to large distances from the central axis. We find that at intermediate times the ratio of both the transverse and longitudinal pressures to the energy density converge approximately to a fixed point which is hydrodynamic only for large initial energy densities. We argue that our results suggest that the Gubser flow is better applied to collective behavior in jets rather than the full medium in the phenomenology of heavy ion collisions and can reveal new clues to the mechanism of confinement. The talk will be based on Mitra, Mondkar, Mukhopadhyay, Soloviev, arxiv:2408.04001/hep-th (accepted for publication in JHEP).

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

Event Official Language: English

Asymmetries in Stripped Envelope Supernovae

October 25 (Fri) at 14:00 - 15:15, 2024

Thomas Maunder (Ph.D. Student, Department of Astronomy, Monash University, Australia)

The explosion mechanism of supernovae is not yet fully understood. In order to better understand the inner-workings of the explosion we need to be able to test our models with observations. Current hydrodynamic simulations of stellar explosions often do not provide photometry or spectroscopy as this requires a treatment of the radiation transport of the ejecta. This project takes hydrodynamic simulations of Type Ib/c (stripped-envelope) supernovae and then performs Monte Carlo Radiative Transport simulations on the ejecta to obtain results we can compare with observations. We choose stripped-envelope supernovae because the lack of Hydrogen shell provides a more direct view into the core and the asymmetries of the explosion mechanism. Through these comparisons between models and observations we can improve our understanding of the explosion mechanism in core-collapse supernovae.

Venue: via Zoom

Event Official Language: English

The hidden language of light: Polarization signals in cuttlefish courtship

October 24 (Thu) at 16:00 - 17:00, 2024

Arata Nakayama (Postdoctoral Fellow, Atmosphere and Ocean Research Institute, The University of Tokyo)

The most conspicuous signals are generally the most attractive; this principle underlies the evolution of sexual signal. While the sexual signal design and its exceptional diversity have primarily explored on the color (wavelength) of light, various animals utilize a different property of light for signaling: polarization. In short, polarization is a third physical property of light, alongside color and intensity, and refers to the orientation of light waves' vibrations. While most vertebrate species, including humans, cannot perceive polarized light, some invertebrate species, such as crustaceans and cephalopods (e.g., octopus, squid, and cuttlefish), can detect the polarization of light and reflect polarized light from their body surfaces, suggesting that the polarization of light might function as a communication signal. In our study, by focusing on the sexually ornamented trait and the courtship behavior of specific cephalopod species, we found an polarization courtship signal, which is extremely conspicuous from the perspective of cephalopod polarization vision. Additionally, we conducted morphological observations and optical analyses of their polarization-reflective body surfaces, uncovering a novel mechanism for generating complex polarization patterns. In this gethering, I will provide a general introduction to the role of polarization as a visual cue and signal, followed by an overview of our study on the unique courtship behavior involving polarization signaling in the cuttlefish Sepia andreana.

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

Event Official Language: English

Young's convolution inequality on locally compact groups

October 18 (Fri) at 15:00 - 17:00, 2024

Takashi Satomi (Special Postdoctoral Researcher, iTHEMS)

Young's convolution inequality is one of the elementary inequalities in functional and harmonic analysis, and this inequality is related to various theories in mathematics, physics, and computer theory. In addition, it is known that Young's inequality can be generalized to any locally compact group. In this talk, we introduce the definition of locally compact groups and the statement of Young's inequality with several examples. Finally, we see the speaker's recent results about refining Young's inequality for several locally compact groups, including the special linear groups.

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

Event Official Language: English

Open Effective Field Theories for primordial cosmology

October 18 (Fri) at 13:30 - 15:00, 2024

Thomas Colas (Postdoc, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK)

Imprints of new physics on observable cosmology may require the modelling of dissipation and noise. In this talk, I will present an open effective field theory for primordial cosmology where the inflaton sector interacts with an unknown environment. The approach recovers the usual effective field theory of inflation in a certain limit and extends it to account for local dissipation and noise. Non-Gaussianities are generated that peak in the equilateral configuration for large dissipation and in the folded configurations for small dissipation. The construction provides an embedding for local dissipative models of inflation and a framework to study dissipative and stochastic effects in cosmology.

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

Event Official Language: English

Digital Twinning of Plant Internal Clocks for Robotics and Virtual Reality Enhancements in Agriculture

October 17 (Thu) at 16:00 - 17:00, 2024

Hirokazu Fukuda (Professor, Graduate School of Engineering, Osaka Metropolitan University)

Digital twinning, widely used in fields like industrial and agricultural engineering, creates digital replicas of physical systems. When applied to plant circadian clocks, these digital twins simulate physiological processes governed by circadian rhythms. This technology aids in predicting and optimizing plant growth and productivity in controlled environments, such as greenhouses and plant factories (vertical farms). By understanding key processes like photosynthesis and nutrient uptake, researchers can more effectively manage environmental factors, boosting crop yields and reducing waste. The integration of robotics and virtual reality further enhances these systems, enabling precise automation and real-time optimization. This presentation will explore these advancements, with a focus on mathematical models for controlling circadian clocks.

Venue: via Zoom

Event Official Language: English

Foliation Matter Phase and Godbillon-Vey Invariant

October 16 (Wed) at 15:00 - 17:00, 2024

Taiichi Nakanishi (Ph.D. Student, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)

It has been a main topic in today's physics to classify matter phases. Especially, topologically ordered phases are attracting much attension from broad perspective. However, most of mathematical structures other than the topology are not investigated yet in physics. In this talk, we present a physical model which is strongly connected to the foliation structure of the space manifold, and its field theoretical description. In such a foliation field theory, we can see the structure is highly connected to the mathematical invariant of foliation structures called Godbillon-Vey invariant. This work would be a fiest step toward shining a light on mathematical structures used in physics. This work is based on arXiv:2408.05048 with Hiromi Ebisu, Masazumi Honda, and Soichiro Shimamori.

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

Event Official Language: English

The laser light shed on Darwin’s ‘Abominable mystery’

October 10 (Thu) at 16:00 - 17:00, 2024

Chiharu Kato (Ph.D. Student, Department of Biological Sciences, Graduate School of Science, The University of Tokyo)

Reproductive isolation is the inability of a species to breed with related species and thus is a key to evolution of new species in flowering plants. In interspecific crosses between closely related species, a stage of pollen tube reception by female tissues of the pistil act as a pivotal hybridization barrier. Within the genus Arabidopsis, pistils of Arabidopsis thaliana can be fertilized by pollen from its relative species, but about half of the ovules reject the release of sperm from heterospecific pollen tubes and these rejected pollen tubes continue growing inside the embryo sacs (referred to as pollen tube overgrowth). A loss-of function mutant line of ARTUMES gene, encoding a subunit of the oligosaccharyltransferase complex, pollinated with heterospecific pollen shows a higher overgrowth rate than the wild type, suggesting that ARTUMES is involved in interspecific pollen tube reception. However, its molecular mechanism is largely unknown. Here, we report that some knockout lines of receptor kinases show ARTUMES mutant-like impairment in interspecific pollen tube reception, indicating that these receptor kinases might be potentially the target proteins of ARTUMES. We anticipate these receptors recognize the ligands from conspecific (self) pollen and heterospecific pollen either in the presence of ARTUMES, thus they can lead successful interspecific fertilization. We also identified ARTUMES mutant shows abnormal calcium dynamics in their female tissue during pollen tube reception. In this talk, I would like to briefly mention about how mathematical modeling can be promoting to pursue the questions regarding calcium dynamics reflecting male-female communication during fertilization. We anticipate these mechanisms that enable interspecific fertilization contribute to rapid development and diversification of flowering plants in recent geological time.

Venue: via Zoom

Event Official Language: English

Joint Seminar on cosmology and related topics

October 10 (Thu) at 14:00 - 18:00, 2024

Koki Tokeshi (Postdoctoral Researcher, Institute for Cosmic Ray Research (ICRR), The University of Tokyo)
Misako Tatsuuma (Research Scientist, iTHEMS)
Puttarak Jai-akson (Postdoctoral Researcher, iTHEMS)

Joint Seminar is a seminar series that is held regularly in Tokyo and its vicinity. The topics are on cosmology and related areas. The seminar venue alternates among the universities and research institutes in the Kanto area, and this time it is held at RIKEN. Among the 3 speakers in the event, Dr. Misako Tatsuuma and Dr. Puttarak Jai-akson from iTHEMS will give talks, together with an external speaker Dr. Koki Tokeshi (ICRR, U. Tokyo). The time table of the event is as follows: Date: October 10th (Thu), 14:30. (room will open at 14:00) Place: RIKEN iTHEMS Wako Campus, Okochi Hall Program: 14:00 Room open 14:30 Koki Tokeshi’s talk（ICRR, 45 min） 15:15 Break & free discussion（15 min） 15:30 Misako Tatsuuma’s talk（RIKEN iTHEMS, 45 min） 16:15 Break & free discussion（15 min） 16:30 Puttarak Jai-akson’s talk（RIKEN iTHEMS, 45 min） 17:15 Free Discussion（15 min） 17:30 Close (go to dinner) Titles and abstracts: 1st Speaker: Koki Tokeshi (ICRR) Title: Exact solutions in stochastic inflation Abstract: The stochastic formalism of inflation, or stochastic inflation for short, enables us to study the dynamics of large-scale primordial fluctuations in a non-perturbative way. I will present a class of all the possible exact expressions for statistical quantities such as distribution and correlation functions of a test field in the expanding universe, given that the significance of exact solutions in cosmology cannot be overemphasised. To this aim, a sequence of isospectral Hamiltonians and an underlying symmetry called shape invariance are exploited. 2nd Speaker: Misako Tatsuuma (RIKEN iTHEMS) Title: Numerical Simulations of the Strengths of Dust Aggregates in Planet Formation Abstract: Planet formation is the growth process from sub-micrometer-sized dust grains to planets larger than 10,000 km. This growth process can be broadly divided into two phases: the initial growth to kilometer-sized planetesimals, which involves the adhesion of dust grains through intermolecular forces such as van der Waals forces and hydrogen bonds, and the subsequent growth to planets, driven by gravitational forces. Currently, no unified planetesimal formation theory can fully explain both observations of protoplanetary disks, where planet formation takes place, and the exploration results of small bodies in the solar system, such as asteroids and comets, which are considered remnants of planetesimals. Constructing such a theory is the ultimate goal of planet formation studies. To investigate planetesimal formation based on the exploration results of small solar system bodies, we have used the discrete element method (DEM) to calculate the tensile and compressive strengths of dust aggregates, constructing their physically-based models that we have compared to the properties of small solar system bodies. This talk will focus on the methodologies used in these studies. 3rd Speaker: Puttarak Jai-akson (RIKEN iTHEMS) Title: Null Surfaces Through The Looking-Glass Abstract: Carrollian physics has recently become a prominent topic in theoretical physics, especially in gravitational studies and flat-space holography. Understanding Carrollian geometries and symmetries is essential to the modern interpretation of null surfaces, whether at finite distances or asymptotic infinities. In this talk, I will introduce Carrollian geometries as intrinsic to any generic null surface, and highlight the profound analogy between gravitational dynamics on null surfaces and Carrollian hydrodynamics. Additionally, I will discuss the phase space structure and symmetries associated with these geometries, shedding light on their implications for gravitational theories and potentially for holographic dualities.

Venue: Okochi Hall

Event Official Language: English

Understanding Diffusion Models by Feynman's Path Integral

October 9 (Wed) at 15:00 - 16:30, 2024

Yuji Hirono (Assistant Professor, Department of Physics, Graduate School of Science, Osaka University)

Diffusion models have emerged as powerful tools in generative modeling, especially in image generation tasks. In this talk, we introduce a novel perspective by formulating diffusion models using the path integral method introduced by Feynman for describing quantum mechanics. We find this formulation providing comprehensive descriptions of score-based diffusion generative models, such as the derivation of backward stochastic differential equations and loss functions for optimization. The formulation accommodates an interpolating parameter connecting stochastic and deterministic sampling schemes, and this parameter can be identified as a counterpart of Planck's constant in quantum physics. This analogy enables us to apply the Wentzel-Kramers-Brillouin (WKB) expansion, a well-established technique in quantum physics, for evaluating the negative log-likelihood to assess the performance disparity between stochastic and deterministic sampling schemes.

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

Event Official Language: English

Dynamics of Phase Transitions: Between First and Second Order

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

Catherine Beauchemin (Deputy Program Director, 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

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

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