Seminar
587 events

Seminar
Ultrahighenergy constraints on decaying superheavy dark matter
March 26 (Tue) at 10:18  11:00, 2024
Saikat Das (Postdoctoral Fellows, Yukawa Institute for Theoretical Physics, Kyoto University)
Venue: via Zoom
Event Official Language: English

Seminar
Brane field theory with higherform symmetry
March 12 (Tue) at 14:00  15:30, 2024
Kiyoharu Kawana (Research Fellow, Korea Institute for Advanced Study (KIAS), Republic of Korea)
We propose field theory for branes with higherform symmetry as a generalization of ordinary Landau theory. The field \psi[C_p^{}] becomes a functional of pdimensional closed brane Cp embedded in a spacetime. As a natural generalization of ordinary field theory, we call this theory brane field theory. In order to construct an action that is invariant under higherform transformation, we first generalize the concept of “derivative” for higherdimensional objects. Then, we discuss various fundamental properties of the brane field based on the higherform invariant action. It is shown that the classical solution exhibits the area law in the unbroken phase of U(1) pform symmetry, while it indicates a constant behavior in the broken phase for the large volume limit of Cp. In the latter case, the lowenergy effective theory is described by the pform Maxwell theory. If time permits, we also discuss branefield theories with a discrete higherform symmetry and show that the lowenergy effective theory becomes a BFtype topological field theory, resulting in topological order.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Macroscopic neutrinoless double beta decay: long range quantum coherence
March 6 (Wed) at 15:30  17:30, 2024
Gordon Baym (Professor Emeritus, University of Illinois, USA)
This talk will introduce the concept of ``macroscopic neutrinoless double beta decay" (MDBD) for Majorana neutrinos. In this process an antineutrino produced by a nucleus undergoing beta decay, $X\to Y + e^ + \bar \nu_e$, is absorbed as a neutrino by another identical $X$ nucleus via the inverse beta decay reaction, $\nu_e + X \to e^+Y$. The distinct signature of MDBD is that the total kinetic energy of the two electrons equals twice the endpoint energy of single beta decay. The amplitude for MDBD, a coherent sum over the contribution of different mass states of the intermediate neutrinos, reflects quantum coherence over macroscopic distances, and is a new macroscopic quantum effect. We discuss the similarities and differences between the MDBD and conventional neutrinoless double beta decay, as well as give estimates of the rates of MDBD and backgrounds.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building (Main Venue) / via Zoom
Event Official Language: English

Seminar
Do plants have bones? Silica phytoliths and their role and fate in the development of terrestrial plants and human civilizations
March 1 (Fri) at 14:00  15:15, 2024
Mikhail Blinnikov (Professor, St. Cloud State University, USA)
Silicon is the second most common element in the Earth’s crust. Some families of higher plants evolved mechanisms for soluble silica to be carried by xylem from groundwater and deposited as plant opal in or around plant cells as phytoliths thought to play a role in the structural support and defense against herbivores. While known since the early 19th century, phytoliths remain an intriguing class of microfossils whose formation and role in plants and their preservation in soils and sediments are a subject for a lot of active research. I outline some emerging themes in phytolith analysis including phytoliths’ role in global biogeochemical cycles, plantherbivore interactions, and their tracing of evolution of cultural plants, especially cereals such as rice (Oryza), wild rice (Zizania), maize (Zea), wheat (Triticum) and millet (Panicum), all relevant to global archaeology. Some emerging research on phytoliths connects their changes in shapes to plant taxonomy of some families such as grasses and opens up avenues for further investigation of their active construction in the cells of some taxa by yet undiscovered genetically mediated mechanisms. New image analysis techniques and some advanced microscopy methods will allow us to further the field of phytolith study using deep machine learning algorithms and true 3D analysis of their shapes, something where contribution from other branches of science are most welcome.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Stochastic tunneling in de Sitter spacetime
February 28 (Wed) at 16:00  17:30, 2024
Taiga Miyachi (Ph.D. Student, Institute of Cosmophysics, Department of Physics, Graduate School of Science, Kobe University)
The formulation of tunneling in real time formalism is discussed. In the case of de Sitter spacetime, there is a method called the stochastic approach, which is known to reproduce the tunneling predicted by Hawking and Moss in the imaginary time formalism. In the case of accelerated expansion of space, the shortwavelength modes are stretched and transformed into longwavelength modes. In the stochastic approach, such UVIR transition is incorporated as quantum noise, and the dynamics of the longwavelength modes are described by stochastic differential equations. In this talk, we construct a SchwingerKeldysh path integral that reproduces this stochastic differential equation and reformulate the tunneling probability. We also reproduce the HawkingMoss tunneling probabilities by using the saddle point approximation.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Basic experimental considerations for analyzing gene expression
February 28 (Wed) at 13:00  14:00, 2024
Hirotaka Toh (JSPS PD Researcher, RNA Systems Biochemistry Laboratory, RIKEN Cluster for Pioneering Research (CPR))
Methods such as RNAsequencing and ribosome profiling are indispensable tools for the comprehensive elucidation of the mechanisms underlying gene expression. A fundamental aspect that requires meticulous attention in the execution of these experiment is the extraction of intact RNA and Ribosomes. The integrity and purity of the extracted RNA is critical to ensure the accuracy and reliability of the sequencing data. In this seminar, I will introduce the basic but key points of the extraction process.
Venue: 3rd floor public space, Main Research Building
Event Official Language: English

Using a trapped ion quantum computer for hamiltonian simulations
February 28 (Wed) at 10:30  12:00, 2024
Enrico Rinaldi (Senior Research Scientist, Quantum Machine Learning and Algorithms, Quantinuum K.K.)
Trapped ion quantum computers, like the Hseries quantum hardware by Quantinuum, robustly encode quantum information in long lived and precise qubits. However, utilizing the hardware efficiently requires a fullstack workflow from software libraries to hardware compilers. In this talk we introduce the relevant elements of this stack in the context of solving the quantum dynamics of a spin system on Hseries hardware: we start from the definition of the Hamiltonian operator in the qubit Hilbert space using the opensource pytket python library and we define the quantum circuits in measurements to run, on a simulator first and on hardware later.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Plant hackers: galling insects extend their phenotypes on the trees by novel plant organogenesis
February 27 (Tue) at 16:00  17:00, 2024
Xin Tong (Special Postdoctoral Researcher, Cell Function Research Team, RIKEN Center for Sustainable Resource Science (CSRS))
When it comes to plantinsect interactions, insects are generally seen as pests like caterpillars eating vegetables or fruits. However, one group of insects, the galling insects can induce de novo organogenesis on the host plants which are often woody plants. Each galling insect species ‘designs’ its own gall as the extended phenotype which are socalled speciesspecific gall formation. Different from leaves and roots, galls represent unique plant organs swiftly formed in response to parasitic organisms, observed across diverse plant species. Yet, the precise mechanisms by which normal plant development is interrupted and redirected to form galls by galling organisms remain elusive. During the talk, I will share some discoveries and views related to aphid gall formation on the elm tree, which is the super host plant for more than 30 galling species, and further discussion about why an insect gall is not simple cell mass but wellorganized structure, and how we could systematically understand insect gall formation.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

An Investment Banker’s Journey to the World of Physicists Seeking the Truth in Economics and Finance
February 26 (Mon) at 15:30  17:00, 2024
Irena Vodenska (Professor, Boston University, USA)
I encountered many exciting opportunities to learn, grow intellectually, and teach during my educational, professional, and scientific journey. Life brings chances, and it is up to us to take or leave them. I took my chances, one of the fascinating ones being to embark on a scientific interdisciplinary research collaboration with physicists. My background is in economics and finance, and doing research with physicists has been fascinating from many different points of view, especially in light of being free from any ONE discipline, free to explore research possibilities to answer finance and economic questions based on a boundless horizon of possible solutions. I worked as an investment banker after my first graduate degree before returning to academia to continue chartering new pathways to research. During my work as a hedge fund manager and a NASDAQ market maker, I had an opportunity to witness firsthand, on the trading floor, the US market collapse sparked by the demise of the Long Term Capital Management in 1998 and later the European market plunge during the tragic events of the terrorist attack on New York City on September 11, 2001, when I lived and worked on Manhattan. Most world problems today are complex to solve with one discipline, as multidisciplinary THINKING is needed to cover various aspects of scientific inquiry. Experience is essential, translating realworld knowledge into academia even more so. I was fortunate to be in a position to build the bridge between investment banking and academia. Learning about the pioneer of Econophysics, Boston University Professor H. Eugene Stanley, was like discovering a gold mine for me. After an exciting investment banking experience in the 1990s and early 2000s, I left my investment banking job in New York City to join Professor Stanley’s research laboratory, a time I will cherish and remember as formative, enlightening, and transformative for the rest of my life. One may ask why physicists work with economists on financial economics problems. The answer is simple: physicists are naturally curious, inquisitive, and open to new ideas. Moreover, physicists and economists share the same language, the language of mathematics. The value of the achievement in econophysics research is the results and the empirical outcome based on data obtained with solid models grounded in natural and social science theory. It is not trivial to produce interdisciplinary research, but recognizing its necessity is already prominently featured in many universities’ strategic plans, including Boston University. Let me lay out several studies and results to give you a glimpse into the research I will discuss today. We analyze economic time series and panel data to understand their relationships and investigate whether some economic data could be informative of the behavior of others. We use a novel approach comprised of Complex Hilbert Principal Component Analysis (CHPCA), Rotational Random Shuffling (RRS), and HelmholtzHodge (HH) potential to unearth statistically significant comovements and identify noteworthy economic and geopolitical events that might influence such comovement dynamics. I will present results from four cases studied collaboratively with my international research collaborators over the last decade since 2013.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

A Selective Survey of Ideas, Tools and Results in Constructive Field Theory
February 26 (Mon) at 13:00  14:30, 2024
Christy Koji Kelly (Special Postdoctoral Researcher, iTHEMS)
In this talk we discuss some aspects of constructive field theory with an emphasis on analytical and probabilistic methods and results. In particular after an overview of some points in the history of constructive QFT we plan to discuss some early achievements in axiomatic QFT, some features of the theory of distributions and the basic structure of the Wightman reconstruction theorem. We also introduce the OsterwalderSchrader axioms and overview the strategy for the construction of nontrivial measures describing pathintegrals for interacting QFTs. Depending on time constraints we might also discuss probabilistic tools (weak convergence of measures, the BochnerMinlos theorem etc), Gaussian measures, UV regularity of simple QFTs and the construction of (infinite volume) Euclidean P(phi)_2 measures. The plan is to discuss some of these topics in some detail after the end of the official seminar.
Venue: via Zoom / Seminar Room #359
Event Official Language: English

Seminar
Cellularlevel leftright asymmetry, cell chirality, induces the chiral collective rotation of multicellular colony
February 15 (Thu) at 16:00  17:00, 2024
Tomoki Ishibashi (Special Postdoctoral Researcher, Laboratory for Physical Biology, RIKEN Center for Biosystems Dynamics Research (BDR))
Ryohei Nishizawa (Ph.D. Student, Graduate School of Frontier Biosciences, Osaka University)The leftright (LR) asymmetric morphology of organs is essential for the development and maintenance of their functions in various species. In recent years, it has become clear that the LR asymmetry of organs originates from cell chirality, the LR asymmetric nature at the cellular level [1]. However, it is unclear how the cell chirality generates the LR asymmetry at the multicellular level. Here we show a mechanism of LR asymmetry formation at the multicellular level based on cell chirality. We previously found that Caco2 cells, a typical cultured epithelial cell line derived from human colon cancer, exhibit stereotypical and directional cell chirality; when Caco2 cells are cultured as single cells, their nuclei and cytoplasm rotate in the clockwise direction at a rate of 50°/h [2]. Interestingly, when Caco2 forms multicellular colonies, the colonies also undergo a collective clockwise rotation at 10º/h. We revealed that the actomyosin cytoskeleton is essential for the formation of the collective rotation [2]. We also found that Caco2 cells formed lamellipodia and focal adhesions LR asymmetrically during the collective colony rotation, which may be responsible for the chiral collective motion. Interestingly, the disruption of microtubules reversed the direction of collective rotation. The LR asymmetric formation of lamellipodia and focal adhesions was also reversed by inhibition of microtubule polymerization. We will discuss the possible mechanism and the mathematical model where cell chirality induces multicellular chiral rotation depending on microtubules.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Chemical reaction network theory and the problem of reaction rate
February 8 (Thu) at 16:00  17:00, 2024
Tomoharu Suda (Postdoctoral Researcher, Biofunctional Catalyst Research Team, RIKEN Center for Sustainable Resource Science (CSRS))
A chemical system can be described at different levels. When we focus on the population of chemical species, it is convenient to consider the system as consisting of a number of chemical reactions, which assumes the structure of a (hyper)graph together with the species. The chemical reaction network theory studies chemical systems described in such a way. It aims to elucidate the dynamics of overall chemical composition in terms of the associated graph structure. Notably, it applies not only to chemical systems but also to more general systems as long as the mathematical structure is compatible. In the first part of this talk, we will review the basic concepts and results of the theory, which mainly concern the existence and stability of the equilibrium. From the viewpoint of chemical kinetics, it is interesting to consider the rate of the overall reaction, which may be obtained by the total balance of chemical species. The second part of the talk will be devoted to this topic. Formulation of the problem and some results will be presented. In particular, chemical reaction networks with firstorder reactions will be considered in detail.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Relativistic Jet Simulations and Modeling on Horizon Scale
February 8 (Thu) at 13:00  14:30, 2024
Yosuke Mizuno (T.D. Lee Fellow / Associate Professor, TsungDao Lee Institute, Shanghai Jiao Tong University, China)
Relativistic jets are launched in the vicinity of the central black holes and emit powerful radiation across the electromagnetic spectrum. According to our current understanding, relativistic jets are launched by directly tapping the rotational energy of spinning black holes via the socalled BlandfordZnajek process. In addition to the spin of the black hole, numerical simulations showed the amount of accreted magnetized flux has a major impact on the formation of relativistic jets. We have investigated the radiative signatures of selfconsistently launched relativistic jets using 3D general relativistic magnetohydrodynamical simulations and general relativistic radiative transfer calculations in horizon scale to the connection with largescale structure. We discuss our findings and comparison with observations.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Recent advances in nuclear Density Functional Theory and applications to the nuclear response
February 6 (Tue) at 13:30  15:00, 2024
Gianluca Colò (Professor, Department of Physics, University of Milan, Italy / Professor, Sezione di Milano, INFN, Italy)
In this contribution, I will give an overall (and, of course, biased) view of the general status of DFT. I will stress that, in contrast to ab initio methods, DFT is the only framework that allows the study of excited states, including those lying at relatively high energy. Accordingly, I will focus on the nuclear response. After a reminder on the nuclear Giant Resonances and the link with the nuclear equation of state, I will discuss the projection methods to restore symmetries in the calculations of deformed systems. While symmetryrestored calculations are nowadays of common use in the study of groundstate properties and lowlying excitations, similar realistic investigations for the nuclear response are essentially missing in the literature. Recently, we have implemented an exact Angular Momentum Projection (AMP) on top of SkyrmeRandom Phase Approximation (RPA) calculations in a projection after variation (PAV) scheme, for the first time. The results will be critically analysed in the case of the monopole response, also taking into account the experimental investigations that can be envisioned for welldeformed systems. If time allows, the nuclear response will be also discussed as a way to improve the current density functionals and ground them on ab initio nuclear theory. This seminar is cohosted by Nuclear Manybody Theory Laboratory and Fewbody Systems in Physics Laboratory, RIKEN Nishina Center for AcceleratorBased Science.
Venue: 2F Large Meeting Room, RIBF Building, RIKEN Wako Campus (Main Venue) / via Zoom
Event Official Language: English

Seminar
Nuclear EnergyDensity Functional Approach to Bridging NeutronRich Nuclei and Neutron Stars
February 5 (Mon) at 13:30  15:00, 2024
Kenichi Yoshida (Associate Professor, Research Center for Nuclear Physics, Osaka University)
Understanding the properties of neutronrich nuclei has been a central subject in lowenergy nuclear physics. The great interest lies not only in the pursuit of a variety of structures and the elucidation of the mechanisms of their occurrence but also in obtaining insights into the structure of the inner crust of neutron stars. With advances in neutronstar observation techniques, the structure of neutron stars has been becoming better understood. The data accumulated from these observations unveil properties of neutronrich matter that are otherwise inaccessible through terrestrial experiments. In this talk, I will introduce an attempt to construct a nuclear energydensity functional (EDF) inspired by the observations and then demonstrate its applicability to nuclear structure problems, including mass and deformation. One intriguing aspect of neutron stars is the emergence of superfluidity, especially the occurrence of spintriplet pairing. I will discuss the unconventional pairing in nuclei within the nuclear EDF framework and give perspectives on the study of the phase diagram of the superfluidity in neutron stars. This seminar is cohosted by UKAKUREN.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Competition across scales in biology
January 31 (Wed) at 11:00  12:00, 2024
Sidhartha Goyal (Associate Professor, Department of Physics, University of Toronto, Canada)
Many biological phenomena emerge from interaction and competition between its parts. I will share some examples across biological scales where datadriven theory can reveal new rules of biological competition. At the molecular scale competition between mitochondrial genomes within budding yeast depends on genome architecture; dynamics of adaptive immunity in microbes reveal different modalities of competition and coexistence of bacteria and its phages; in mammals cellular reprogramming may be driven by elite clones, and tumor response to drugs is driven by "epigenetic" switching. Going beyond, I will present some ideas on understanding dynamical systems that govern cell fate dynamics and if competition may play a role in it. Short bio: Sidhartha Goyal got his PhD in Physics at Princeton in 2009 and then moved to Kavli Institute for Theoretical Physics, Santa Barbara for a postdoc. He got his first degree in Electrical Engineering from IIT Bombay. He is now an Associate Professor in the Physics Department at University of Toronto interested in collective phenomena in biology across scales.
Venue: via Zoom
Event Official Language: English

Seminar
Quantum Enhancement in Dark Matter Detection with Quantum Computation
January 22 (Mon) at 16:00  18:00, 2024
Thanaporn Sichanugrist (Ph.D. Student, Graduate School of Mathematical Sciences, The University of Tokyo)
Shion Chen (Project Assistant Professor, International Center for Elementary Particle Physics (ICEPP), The University of Tokyo)Title: Wavelike Dark Matter Search Using Qubits Abstract: The rapid controllability required for quantum computers makes the currently proposed quantum bit modalities also attractive as electromagnetic field sensors. One of the promising applications is wavelike dark matter searches, where the electric field converted from the coherent dark matter excites the qubits, leading to detectable signals [Phys. Rev. Lett. 131, 211001]. The quantum coherence between the qubits can be utilized to enhance the signal rate in a multiqubit system. By designing an appropriate quantum circuit to entangle the qubits, it was found that the signal rate can scale proportionally to $n_q^2$, with $n_q$ being the number of sensor qubits, rather than linearly with $n_q$ [arXiv: 2311.10413]. In the seminar, we overview the theoretical framework of the search, elaborate on the signalenhancing mechanism driven by quantum entanglement with specific examples of the quantum circuits, and discuss how the scheme can be implemented in the platform of future faulttolerant quantum computers. We also provide the introduction of the experimental realization, and report the status of the experimental works carried out in UTokyo/ICEPP.
Venue: via Zoom
Event Official Language: English

Seminar
Knot Theory in Doubly Periodic Tangles and Applications
January 19 (Fri) at 15:00  16:30, 2024
Sonia Mahmoudi (Assistant Professor, Mathematical Science Group, Advanced Institute for Materials Research (AIMR), Tohoku University)
Doubly periodic entangled structures offer an interesting framework for modeling and investigating diverse materials and physical phenomena, from micro to large scales. Specifically, a doubly periodic tangle (DP tangle) is characterized as an embedding of an infinite number of curves in the thickened plane, derived as the lift of a link in the thickened torus to the universal cover. DP tangles play a crucial role in scientific research, particularly in fields such as materials science, molecular chemistry, and biology. Despite their widespread applications, a universally accepted mathematical description of DP tangles is currently lacking. One of the key challenges arises from the infinite possibilities in choosing a periodic cell (referred to as a motif) for a DP tangle, taking into account various periodic boundary conditions. In this presentation, we conduct a comprehensive examination of the concept of topological equivalence of DP tangles, offering insights into potential classifications and applications in the process.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Quantum features in cosmological perturbations?
January 18 (Thu) at 14:15  15:00, 2024
Amaury Micheli (Postdoctoral Researcher, iTHEMS)
The statistical properties of the CMB anisotropies, reflecting the curvature inhomogeneities in the very early Universe, are very well accounted for by assuming that the inhomogeneities come from amplified vacuum fluctuations. This scenario makes the cosmological perturbations a possible observational window on the interplay between quantum degrees of freedom and gravity. I will review the discussions on the current presence or absence of quantum features in the perturbations, emphasising the quantum information approaches to this question, and comment on the observability of these features.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Gravitational lensing on superposed curved spacetime
January 18 (Thu) at 13:30  14:15, 2024
Youka Kaku (Ph.D. Student, Graduate School of Science, Nagoya University)
In 2017, Bose et al. proposed a tabletop experiment to observe the gravitational effect induced by a spatially superposed mass source, particularly gravityinduced entanglement. This experiment is expected to be the first step in exploring the quantum nature of gravity. Also, there are ongoing efforts to extend their proposal to the relativistic region to observe the unique quantum nature of gravity. In this talk, I will investigate gravitational lensing in a weak gravitational field induced by a spatially superposed mass source. I will show the Einstein ring image of a quantum scalar field propagated on a superposed curved spacetime and compare it with the image of the semiclassical gravity case. This work is currently in progress and is a collaboration with Yasusada Nambu.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English
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