Seminar
615 events

Seminar
Dynamics of the very early universe: towards decoding its signature through primordial black hole abundance, dark matter, and gravitational waves.
July 5 (Fri) at 14:00  15:15, 2024
Riajul Haque (Postdoctoral Researcher, Department of Physics, Indian Institute of Technology, India)
I will start my talk with a brief overview of the standard reheating scenario. Then, I will discuss reheating through the evaporation of primordial black holes (PBHs) if one assumes PBHs are formed during the phase of reheating. Depending on their initial mass, abundance, and inflaton coupling with the radiation, I discuss two physically distinct possibilities of reheating the universe. In one possibility, the thermal bath is solely obtained from the decay of PBHs, while inflaton plays the role of the dominant energy component in the entire process. In the other possibility, PBHs dominate the total energy budget of the universe during evolution, and then their subsequent evaporation leads to a radiationdominated universe. Furthermore, I will discuss the impact of both monochromatic and extended PBH mass functions and estimate the detailed parameter ranges for which those distinct reheating histories are realized. The evaporation of PBHs is also responsible for the production of DM. I will show its parameters in the background of reheating obtained from two chief systems in the early universe: the inflaton and the primordial black holes (PBHs). Then, I will move my discussion towards stable PBHs and discuss the effects of the parameters describing the epoch of reheating on the abundance of PBHs and the fraction of cold dark matter that can be composed of PBHs. If PBHs are produced due to the enhancement of the primordial scalar power spectrum on small scales, such primordial spectra also inevitably lead to strong amplification of the scalarinduced secondary gravitational waves (GWs) at higher frequencies. I will show how the recent detection of the stochastic gravitational wave background (SGWB) by the pulsar timing arrays (PTAs) has opened up the possibility of directly probing the very early universe through the scalarinduced secondary gravitational waves. Finally, I will conclude my talk by elaborating on the effect of quantum correction on the Hawking radiation for ultralight PBHs and its observational signature through dark matter and gravitational waves.
Venue: via Zoom
Event Official Language: English

Seminar
Finding and understanding diseasecausing genetic mutations
June 20 (Thu) at 16:00  17:00, 2024
Kojima Shohei (Special Postdoctoral Researcher, Genome Immunobiology RIKEN Hakubi Research Team, RIKEN Center for Integrative Medical Sciences (IMS))
Disease is caused by genetic factors and environmental factors. Genomewide association study (GWAS) is a powerful method to find genetic factors associated with disease and human complex traits. One conceptual finding GWAS revealed is that many common diseases are caused by a combination of multiple genetic factors (polygenic), rather than a single causal mutation (monogenic). I have been working on finding genetic factors causing polygenic diseases by developing software that accurately finds sequence insertions and deletions from human populationscale sequencing datasets. In this talk, first, I will introduce some examples of diseasecausing variants we recently discovered. Next I will also introduce my current research theme aiming to untangle how multiple genetic factors coordinately change cellular homeostasis, which I would like to have a collaboration with mathematical scientists.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
On the volume conjecture for the Teichm ̈uller TQFT
May 31 (Fri) at 15:00  17:00, 2024
Soichiro Uemura (Junior Research Associate, iTHEMS / Student Trainee, iTHEMS)
The ChernSimons theory is a topological quantum field theory (TQFT) on the principal Gbundle and has been studied in both mathematics and physics. When G is SU(2), which is compact, Witten conjectured that its path integral gives the topological invariant of the base 3manifold. This invariant was formulated rigorously and is known as the WRT invariant. In addition, it is known that the expectation value of the Wilson loop along the hyperbolic knot in S3 gives the invariant of knots, which is called the colored Jones polynomial. Invariants of knots and manifolds derived from the path integral are called quantum invariants. There is an open conjecture called the volume conjecture, which states that the complete hyperbolic volume of the knot complement appears in the asymptotic expansion of the colored Jones polynomial. The volume conjecture suggests a close connection between quantum invariants and hyperbolic geometry. On the other hand, ChernSimons theory with the noncompact G such as SL(2,C) also appears in duality in string theory called the 3d3d correspondence but has not been well formulated mathematically. Andersen and Kashaev constructed a TQFTlike theory called the Teichm ̈uller TQFT by quantizing the Teichm ̈uller space, which is the deformation space of the hyperbolic structures on a surface. The Teichm ̈uller TQFT is expected to correspond to the SL(2,C) ChernSimons theory. In this theory, a conjecture similar to the volume conjecture has been proposed and proven for several hyperbolic knots. In this talk, I will introduce the outline of the Teichm ̈uller TQFT and explain our results on the volume conjecture and its proof using techniques in hyperbolic geometry by Thurston, Casson, Rivin, and others.
Venue: via Zoom / Seminar Room #359
Event Official Language: English

Introduction to homotopy theory
May 24 (Fri) at 15:00  17:00, 2024
Junnosuke Koizumi (Special Postdoctoral Researcher, iTHEMS)
In a narrow sense, homotopy theory is a framework for capturing the essential structures of shapes and has long been used as a powerful tool in topology. On the other hand, the concept of homotopy is so universal that it appears even in purely algebraic settings and has recently had a significant impact on other fields such as number theory and algebraic geometry. This talk aims to introduce homotopy theory in this broader sense from multiple perspectives. If time permits, I will also touch upon recent developments in the homotopy theory of algebraic varieties.
Venue: via Zoom / Seminar Room #359
Event Official Language: English

The collective order of human corneal endothelial cells as a unified biomarker for in vitro cultured cells and in vivo regenerated tissue
May 23 (Thu) at 16:00  17:00, 2024
Akihisa Yamamoto (Research Scientist, iTHEMS)
Approximately 200,000 corneal transplantations are performed worldwide yearly, and more than half of them are applied to patients with corneal endothelial dysfunction. Recently, the restoration of functional corneas by injecting cultureexpanded cells has developed in contrast to the conventional transplantation which relies on a limited number of donors’ corneas. This novel treatment opens up the potential to cure more patients with less surgical invasion and allows the utilization of cells with consistent and controlled quality. In this talk, I will introduce a unified physical biomarker for the quality assessment of corneal endothelial cells in in vitro culture and the predictive diagnosis of in vivo tissues using a single equation based on the collective order of cells. Taking an analogy to the twodimensional colloidal assembly, the spatial arrangement of cells is generalized in terms of manybody interactions, and the “spring constant” of the underlying interaction potential is calculated from microscopy images. I also would like to discuss our recent approach to characterize the local structure of the arrangement of cells based on the topological data analysis.
Venue: via Zoom
Event Official Language: English

Seminar
Prefactorization algebra and theta term
May 21 (Tue) at 16:00  17:30, 2024
Masashi Kawahira (Ph.D. Student, Yukawa Institute for Theoretical Physics, Kyoto University)
Quantum field theories (QFTs) describe a lot of physical phenomena in our world. And giving a mathematical definition of QFTs is a longstanding problem. There are several mathematical formulations: Wightman formulation, Osterwalder–Schrader formulation and AtiyahSegal formulation. And each of them cover different aspects of QFTs. Recently, Costello and their collabolators formulate QFTs by using prefactorization algbras. This formulaion cover a lot of classes of QFTs: TQFTs, 2d CFTs and perturbative QFTs. And they reproduce various results such as asymptotic freedom in nonAbelian gauge theories. Prefactorization algbras can be given by Batalin–Vilkovisky quantization (BV quantization) of the Lagrangian. However the original BV quantizations are perturbative and they do not have nonperturbative effects like instantons. In this talk, we propose the way to include Abelianinstanton effects. In modern language, it is the same as ℤgauging.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Introduction to operator algebras
May 17 (Fri) at 15:00  17:00, 2024
Kan Kitamura (Special Postdoctoral Researcher, iTHEMS)
I will give a quick introduction to operator algebras. Operator algebras in this talk consist of linear operators over some Hilbert space. Their study was initiated by Murray and von Neumann, motivated partially by the mathematical foundation of quantum mechanics. Starting from the definitions of a few basic notions, I will explain that commutative operator algebras can be interpreted as spaces. On the other hand, simple operator algebras (i.e., those without nontrivial ideals) form a class of operator algebras opposite to commutative ones and have attracted many operator algebraists. I will try to introduce several examples of simple operator algebras, some of which appear in mathematical physics. If time permits, I will also give recent results on ideals in C*algebras. People with any scientific background are welcome.
Venue: via Zoom / Seminar Room #359
Event Official Language: English

Seminar
Exploring the impact of environments on flower color differentiation: A metaanalytical approach
May 16 (Thu) at 16:00  17:00, 2024
Masaru Bamba (Assistant Professor, Graduate School of Science, Tohoku University)
Flower color is one of the most diverse phenotypes in angiosperms, yet the initial processes of its differentiation remain unclear. Flower color is primarily expressed through the accumulation of pigment compounds in the petals, which are also associated with various stress responses. While it is conceivable that the environmental conditions during plant evolution could contribute to the differentiation of flower color, few studies have examined this hypothesis. Therefore, I conducted a metaanalysis using plant flower color information and growth environment data to elucidate the relationship between flower color differentiation and growth environments. Flower color data was extracted using LLM from botanical descriptions, and growth environment data was acquired by aligning GBIF occurrence information with WorldClim and ISRIC databases. Integrating approximately 30,000 flower color data points and 35 million occurrence records revealed trends such as a predominance of red flowers at higher altitudes and white flowers in arid areas. This study is still preliminary, so I would welcome discussions on more suitable analytical methods and models.
Venue: via Zoom
Event Official Language: English

Seminar
Black hole graviton and quantum gravity
May 16 (Thu) at 15:00  16:30, 2024
Yusuke Kimura (Research Scientist, Analytical quantum complexity RIKEN Hakubi Research Team, RIKEN Center for Quantum Computing (RQC))
Drawing from a thought experiment that we conduct, we propose that a virtual graviton gives rise to a black hole geometry when its momentum surpasses a certain threshold value on the Planck scale. This hypothesis implies that the propagator of a virtual graviton, that possesses momentum surpassing this threshold, vanishes. Consequently, a Feynman diagram containing this type of graviton propagator does not add to the overall amplitude. This mechanism suggests the feasibility of formulating an ultravioletfinite fourdimensional quantum gravitational theory. The elementary particles including the gravitons are treated as point particles in this formulation.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Boundaryinduced transitions in Möbius quenches of holographic BCFT
May 15 (Wed) at 16:00  17:30, 2024
Dongsheng Ge (Project Researcher, Department of physics, Osaka University)
Boundary effects play an interesting role in finitesize physical systems. In this work, we study the boundaryinduced properties of 1+1dimensional critical systems driven by inhomogeneous Möbiuslike quenches. We focus on the entanglement entropy in BCFTs with a large central charge and a sparse spectrum of lowdimensional operators. We find that the choice of boundary conditions leads to different scenarios of dynamical phase transitions. We also derive these results in a holographic description in terms of intersecting branes in AdS3, and find a precise match.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Quantum Computing in Omics Medicine
May 10 (Fri) at 16:00  17:15, 2024
Tatsuhiko Tsunoda (Professor, Department of Biological Sciences, Graduate School of Science, The University of Tokyo)
(The speaker is also the team leader of Laboratory for Medical Science Mathematics, RIKEN Center for Integrative Medical Sciences. This is a joint seminar with the iTHEMS Biology Group.) In medical science, the recent explosive development of omics technologies has enabled the measurement not only of bulk data from entire tissues, but also data for individual cells and their spatial location information, and even allowed collection of such information in realtime. Meaningful interpretation of these rich data requires an ability to understand highorder and complex relationships that underpin biological phenomena such as drug response, simulating their dynamics, and selecting the optimal treatment for each patient based on these results. While these data are largescale and of ultrahigh dimensionality, they are also often sparse, with many missing values in the measurements and frequent higherorder interactions among variables, making them hard to handle with conventional statistics. To make further progress, machine learning – especially deep learning – is emerging as one of the promising ways forward. We have developed a method to transform omics data into an imagelike representation for analysis with deep learning (DeepInsight) and have successfully used it to predict drug response and to identify original cell types from singlecell RNAseq data. However, anticipation of the vast amount of medical data being accumulated gives particular urgency to addressing the problems of the time it actually takes to train deep learning models and the complexity of the necessary computational solutions. One possible way to resolve many of these problems is “quantum transcendence”, which is made possible by quantum superposition computation. Among all the different ways to apply quantum computation to medical science, we are particularly interested in quantum deep learning based on optimization and search problems, quantum modeling of single nucleotide detection by observational systems and statistical techniques such as regression analysis by inverse matrix computation and eigenvalue computation. In this seminar, I will first present an overview of how quantum machine learning and quantum deep learning can be used to formulate treatment strategies in medicine. We will discuss how to implement the quantum DeepInsight method, the challenges of noise in quantum computation when training QCNNs, feature mapping issues, problems of pretraining in quantum deep learning, and concerns relating to handling sensitive data such as genomic sequences. I hope this seminar will enhance our understanding of how to effectively facilitate medical research with quantum computing.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Surrogate Modeling for Supernova Feedback toward StarbyStar Simulations of MilkyWaysized Galaxies
May 10 (Fri) at 14:00  15:15, 2024
Keiya Hirashima (Ph.D. Student, Department of Astronomy, Graduate School of Science, The University of Tokyo)
Galaxy simulations have found the interdependence of multiscale gas physics, such as star formation, stellar feedback, inflow/outflow, and so on, by improving the physical models and resolution. The mass resolution remains capped at around 1,000 solar masses (e.g., Applebaum et al. 2021). To overcome the limitations, we are developing a new Nbody/SPH code, ASURAFDPS, to leverage exascale computing (e.g., Fugaku), handle approximately one billion particles, and simulate individual stars and stellar feedback within the galaxy. However, the emergence of communication costs hinders scalability beyond one thousand CPU cores. One of the causes is short timescale events localized in tiny regions, such as supernova explosions. In response, we have developed a surrogate model using machine learning to duplicate supernova feedback quickly (Hirashima et al., 2023a,b). In the presentation, I report the fidelity and progress of the simulations with our new machinelearning technique.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Deep Learning for Estimating TwoBody Interactions in MixedSpecies Collective Motion
May 9 (Thu) at 16:00  17:00, 2024
Masahito Uwamichi (Project Researcher, Graduate School of Arts and Sciences, The University of Tokyo)
(This is a joint seminar with the Information Theory Study Group.) Collective motion is a fundamental phenomenon observed in various biological systems, characterized by the coordinated movement of individual entities. Such dynamics are especially crucial in understanding cellular behaviors, which can now be observed at an individual level in complex tissue formations involving multiple types of cells, thanks to recent advancements in imaging technology. To harness this rich data and uncover the hidden mechanisms of such dynamics, we developed a deep learning framework that estimates equations of motion from observed trajectories. By integrating graph neural networks with neural differential equations, our framework effectively predicts the twobody interactions as a function of the states of the interacting entities. In this seminar, I will first introduce the structure and hyperparameters of our framework. Subsequently, I will detail two numerical experiments. The first is a simple toy model that was employed to generate data for testing our framework to refine the hyperparameters. The second explores a more complex scenario mimicking the collective motion of cellular slime molds, highlighting our model's ability to adapt to mixedspecies interactions.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Role of selfgravity on the central halo structure of fuzzy dark matter
April 30 (Tue) at 13:30  15:00, 2024
Yusuke Manita (Affiliated Scientist, Yukawa Institute for Theoretical Physics, Kyoto University)
Fuzzy dark matter (FDM) is a dark matter model that is characterized by the ultralight masses around 10−22 eV. As FDM has the wavelike nature, the selfgravitating structure is described by the SchrödingerPoisson equation. Previous simulations based on the SchrödingerPoisson equation have demonstrated that solitonlike structure having a highdensity flat core is formed at the central region of the FDM halos, and the size of such a core is typically determined by the de Broglie wavelength. Away from the central core, the density profile of the FDM halos resembles that of the cold dark matter halos on average, and is shown to be described by the NavarroFrenkWhite (NFW) profile. In this paper, we study the role of the selfgravity of the soliton core, and its relation to the bulk halo properties by solving the SchrödingerPoisson equation in a simplified setup. The findings indicate that the contribution from the soliton selfgravity must dominate over the NFW potential in order to sustain the soliton.
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
How Stars End Their Lives
April 26 (Fri) at 14:00  15:15, 2024
Philipp Podsiadlowski (Professor, University of Oxford, UK)
While the basic evolution of stars has been understood for many decades, there are still major uncertainties in our overall understanding of how stars end their lives, both in the context of low and intermediatemass stars (including the Sun) and massive stars. I will first review some of key principles that govern the structure and evolution of stars and then present recent progress that has been made for both groups of stars. I will argue and present numerical simulations that show that all stars become dynamically unstable when they become large giant stars, which leads to sporadic, dynamical mass ejections. Low and intermediatemass stars may lose all of their envelopes as a consequence, leaving whitedwarf remnants. More massive stars experience core collapse, leaving a neutronstar or blackhole remnant, possibly associated with a supernova explosion. I will show how the dramatic recent progress on understanding the corecollapse process, for the first time, allows us to connect the late evolution of massive stars with the resulting supernova explosions and the final remnants and discuss how observations with current gravitationalwave detectors (such as LIGO) will allow us to test this theoretical connection.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Tracing link of cell ageing and disease progression: Joining factors and facilitators
April 25 (Thu) at 16:00  17:00, 2024
Rajkumar Singh Kalra (Staff Scientist, Immune Signal Unit, Okinawa Institute of Science and Technology Graduate University (OIST))
Cell ageing is an inevitable biological process. It marks declined homeostatic processes in a cell, the impact of which is reflected in the organism’s function/physiology. Ageing, thus, raises risks of disease progression in elderly people and compromises their immunity. Progression of cancer and neurodegenerative diseases and weak immune response against a pathogen(s) represent cases of ageingrelated diseases. What molecular factors/signaling could be associated with disease progression or take part in governing such decisions in aging? – remained a key focus of my research so far. In my talk, I shall shed light on the part characterizing key proteins and their signalling in ageingrelated diseases with an emphasis on cancer, neurodegenerative disease, and immunity. Taking advantage of wet lab and system biology studying gene networks, and genomic, proteomic, and metabolomic readouts, I investigated the molecular expression and processes impacted and compromised by ageing. I shall be discussing new knowledge from my work on the linkage of cell ageing and disease progression and therein role of key factors and facilitators I studied.
Venue: via Zoom
Event Official Language: English

Seminar
A night out with ghosts
April 24 (Wed) at 16:00  17:30, 2024
Veronica Errasti Diez (Research Fellow, Faculty of Physics, LudwigMaximiliansUniversität München, Germany)
Field theories are the chief theoretical framework for physics. For instance, the Standard Model and General Relativity are widely accepted as accounting for subatomic particle and gravitational behavior, respectively. Nonetheless, even such acclaimed field theories have their limitations, such as the mysterious neutrino masses and dark sector. A natural and popular way around the hurdles consists in generalizations of field theories, via the inclusion of nonlinear and/or higherorder corrections. Unless painstakingly avoided, these corrections lead to the propagation of negative kinetic energy modes, or ghosts for short. Ghosts have earned an appalling fame: kill, exorcise, avoid… No efforts are spared to guarantee their absence. In this talk, we will delve into the root causes for the ill name of ghosts. As a result, we will take up the cudgels for ghosts. While they do have a strong tendency to yield illbehaved theories, ghosts are not intrinsically pathological. As we will see, goodnatured ghosts open the door to multidisciplinary tantalizing opportunities…! And ghosts make excellent partygoers, so make sure not to miss this appointment!
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Zooming into the ancient world by reconstructing the joint genealogies of modern and ancient humans
April 18 (Thu) at 16:00  18:00, 2024
Leo Speidel (Senior Research Fellow, Genetics Institute, University College London, UK)
In recent years, we have gone from databases that store the genetic differences observed between hundreds of thousands of sequenced people to using this information to build the actual genetic trees that relate individuals through their shared ancestors back in time. These genetic trees describe how our genomes have evolved up to millions of years into the past. Additionally, sequencing of DNA from ancient human bone has enabled the direct observation of genomic change over past millennia and has unlocked numerous previously hidden genetic histories. In this talk, I will illustrate how we can unearth the human past from these data, ranging from ancient migrations out of Africa and subsequent mixtures with now extinct Neanderthals to waves of ancestry transformations in a nation’s recent past.
Venue: via Zoom
Event Official Language: English

Seminar
Quantum FineGrained Complexity
April 18 (Thu) at 10:30  12:00, 2024
Harry Buhrman (Chief Scientist for Algorithms and Innovation, Quantinuum, UK)
(The speaker is also a professor at University of Amsterdam & QuSoft. This is a joint seminar with the iTHEMS Quantum Computation Study Group.) One of the major challenges in computer science is to establish lower bounds on the resources, typically time, that are needed to solve computational problems, especially those encountered in practice. A promising approach to this challenge is the study of finegrained complexity, which employs special reductions to prove time lower bounds for many diverse problems based on the conjectured hardness of key problems. For instance, the problem of computing the edit distance between two strings, which is of practical interest for determining the genetic distance between species based on their DNA, has an algorithm that takes O(n^2) time. Through a finegrained reduction, it can be demonstrated that a faster algorithm for edit distance would imply a faster algorithm for the Boolean Satisfiability (SAT) problem. Since faster algorithms for SAT are generally considered unlikely to exist, this implies that faster algorithms for the edit distance problem are also unlikely to exist. Other problems used for such reductions include the 3SUM problem and the All Pairs Shortest Path (APSP) problem. The quantum regime presents similar challenges; almost all known lower bounds for quantum algorithms are defined in terms of query complexity, which offers limited insight for problems where the bestknown algorithms take superlinear time. Employing finegrained reductions in the quantum setting, therefore, represents a natural progression. However, directly translating classical finegrained reductions to the quantum regime poses various challenges. In this talk, I will present recent results in which we overcome these challenges and prove quantum time lower bounds for certain problems in BQP, conditioned on the conjectured quantum hardness of, for example, SAT (and its variants), the 3SUM problem, and the APSP problem. This presentation is based on joint works with Andris Ambainis, Bruno Loff, Florian Speelman, and Subhasree Patro.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Sustainable Organic Synthesis with Abundant Resources
April 15 (Mon) at 13:00  14:00, 2024
Sobi Asako (Senior Scientist, Advanced Organic Synthesis Research Team, RIKEN Center for Sustainable Resource Science (CSRS))
The sustainable development of modern society necessitates technologies that harness earthabundant metals and organic resources, minimizing reliance on scarce materials. This presentation will introduce our recent efforts towards this goal. We have developed sustainable organic synthesis using sodium dispersion, a molybdenumquinone species for the diazofree generation of carbene species from stable and readily available compounds, and a SpiroBpy ligand that enables the siteselective functionalization of arenes under remote steric control. I will also share some of the challenges we face in developing these reactions in order to ensure reproducibility.
Venue: 3rd floor public space, Main Research Building
Event Official Language: English
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