Search Event
657 results
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Seminar
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
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Seminar
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
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Seminar
Topological recursion and twisted Higgs bundles
July 16 (Tue) 10:30 - 12:00, 2024
Christopher Mahadeo (Research Assistant Professor, Department of Mathematics, The University of Illinois at Chicago (UIC), USA)
Prior works relating meromorphic Higgs bundles to topological recursion have considered non-singular models that allow the recursion to be carried out on a smooth Riemann surface. I will discuss some recent work where we define a "twisted topological recursion" on the spectral curve of a twisted Higgs bundle, and show that the g=0 components of the recursion compute the Taylor expansion of the period matrix of the spectral curve, mirroring a result of for ordinary Higgs bundles and topological recursion. I will also discuss some current work relating topological recursion to a new viewpoint of quantization of Higgs bundles.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Tensionless Strings in a Kalb-Ramond Background
July 10 (Wed) 16:00 - 17:00, 2024
Ritankar Chatterjee (Ph.D. Student, Indian Institute of Technology Kanpur, India)
We investigate tensionless (or null) bosonic string theory with a constant Kalb-Ramond background turned on. In analogy with the tensile case, we find that the constant Kalb-Ramond field has a non-trivial effect on the spectrum only when the theory is compactified on an S^1 ⊗d background with d ≥ 2. We discuss the effect of this constant background field on the tensionless spectrum constructed on three known consistent null string vacua. We elucidate further on the intriguing fate of duality symmetries in these classes of string theories when the background field is turned on. Based on: https://arxiv.org/abs/2404.01385
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English
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Seminar
The role of demographic stochasticity in the evolution of spite and altruism
July 9 (Tue) 16:00 - 17:00, 2024
Troy Day (Professor, Head of Department, Department of Mathematics and Statistics, Queen's University, Canada)
The evolution of spiteful and altruistic behaviour remains a fascinating and somewhat puzzling phenomenon. In recent years there has been interest in examining how stochasticity arising from a finite population size might affect the evolution of these traits. Some results suggest that such stochasticity can reverse the direction of selection and promote the evolution of traits like altruism and spitefulness that are selected against in very large (deterministic) populations. However, other results seem to call this finding into question. In this talk I will consider a simple but quite general model of spite and of altruistic behaviour and examine how demographic stochasticity affects the evolution of these traits. I will show that stochasticity can indeed affect the direction of evolution but not in the way that previous studies have suggested. The results also help to clarify the broader issue of how and why stochasticity can sometimes reverse the direction of evolution.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Dynamics of the very early universe: towards decoding its signature through primordial black hole abundance, dark matter, and gravitational waves.
July 5 (Fri) 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 radiation-dominated 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 scalar-induced 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 scalar-induced secondary gravitational waves. Finally, I will conclude my talk by elaborating on the effect of quantum correction on the Hawking radiation for ultra-light PBHs and its observational signature through dark matter and gravitational waves.
Venue: via Zoom
Event Official Language: English
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Seminar
Worldline Path Integrals for the Graviton and 1-Loop Divergences in Quantum Gravity
June 28 (Fri) 16:00 - 17:20, 2024
Fiorenzo Bastianelli (Professor, University of Bologna, Italy)
In this talk, I will discuss perturbative quantum gravity at the 1-loop level by reviewing and systematizing old results on UV divergences and presenting new findings along with new methods for their calculation. The traditional approach to this problem employs the Schwinger-DeWitt heat kernel method. We extend this approach by incorporating worldline path integrals to compute the perturbative expansion at small proper time. In addition, we explore a more principled approach that utilizes the BRST path integral quantization of the N=4 spinning particle, which describes the graviton in first quantization. Using these methods, we calculate the one-loop divergences in quantum gravity with a cosmological constant in arbitrary dimensions. When evaluated on-shell, these calculations yield a set of gauge-invariant coefficients that characterize pure quantum gravity with a cosmological constant. These coefficients may serve as benchmarks for comparing various approaches to quantum gravity.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Challenging conventional wisdom in binary evolution
June 28 (Fri) 14:00 - 15:15, 2024
Ryosuke Hirai (Special Postdoctoral Researcher, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))
The majority of massive stars, stars with more than 8 times the mass of the Sun, are known to be born in binary or higher-order multiple systems. During the course of their evolution, the stars can interact in many different ways and cause interesting astrophysical phenomena such as eruptions and explosions or create objects like X-ray binaries, gravitational wave sources, etc. Many studies have been conducted over the last few decades to tie our latest models to these observables in order to refine our understanding of massive binary evolution. However, in some cases "refining" a model is not enough and a paradigm shift is required to explain all the observables in a coherent way. In this talk, I will introduce some topics from my past work where I challenge conventional wisdom to resolve long-standing problems. The topics are as follows: 1. impact of supernova ejecta on companion star evolution, 2. wind accretion onto black holes, 3. common-envelope evolution, 4. neutron star kicks. I will also discuss how these new views impact the overall landscape of binary evolution theory.
Venue: via Zoom
Event Official Language: English
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Seminar
Y-chromosome turnover in Drosophila – Escaping from an evolutionary dead-end?
June 28 (Fri) 14:00 - 16:00, 2024
Masafumi Nozawa (Associate Professor, Tokyo Metropolitan University)
The Y chromosome (Y, hereafter) is degenerated in many organisms but cannot be lost due to their important functions in sex determination and/or male fertility. This is true for Drosophila and an individual without Y become a sterile male. Therefore, the Y has been considered as indispensable in Drosophila as in the case of mammals. However, we recently discovered that Drosophila lacteicornis, endemic to Ryukyu islands, is polymorphic in terms of the presence or absence of the Y; i.e., XY and XO males coexist within species. Unlike other Drosophila species, the XO males of this species are fertile. In this seminar, I will introduce how the Y becomes dispensable in this species. To our surprise, our genome and transcriptome analyses revealed that a novel Y is likely emerging in this species rather than an old Y is being lost. In other words, a turnover of the Y is ongoing in this species. Our results indicate that the Y is not necessarily a static entity in an evolutionary dead-end but can be a dynamic entity, sometimes going back to an autosome or even disappearing. Therefore, I would like to emphasize that we should understand the evolution of sex chromosomes not by a one-way path to dead-end but by a circular process, i.e., “sex-chromosome cycle.”
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English
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Seminar
Inferring collective behavior from social interactions to population coding
June 27 (Thu) 16:00 - 17:30, 2024
Chen Xiaowen (Postdoctoral Researcher, Laboratoire de Physique de l’École normale supérieure, CNRS, France)
(This is a joint iTHEMS Biology Seminar) From social animals to neuronal networks, collective behavior is ubiquitous in living systems. How are these behaviors encoded in interactions, and how do they drive biological functions? Recent insights from statistical physics applied to biological data have offer exciting new perspectives. However, previous research has mostly focused on the statics, i.e. the steady-state distributions of the collective behavior, without taking into consideration of time. In this talk, I will present two recent progresses tapping into the temporal domain. First, I will present a study of collective behavior in social mice from their co-localization patterns. To capture both static and dynamic features of the data, we developed a novel inference method termed the generalized Glauber dynamics (GGD) that can tune the dynamics while keeping the steady state distribution fixed. I will first outline the explanation power of the GGD dynamics, then explain how to infer the dynamics from data. The inferred interactions characterize sociability for different mice strains. In the second example, we studied information flow among neurons in the larval zebrafish hindbrain. By adapting the method of Granger causality to single cell calcium transient data, we were able to detect both a global information flow among neurons, as well as identifying brain regions that are key in locomotion.
Venue: via Zoom
Event Official Language: English
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Seminar
Magnonic spin current and shot noise in an itinerant Fermi gas
June 25 (Tue) 13:30 - 15:00, 2024
Tingyu Zhang (Ph.D. Student, Department of Physics, Graduate School of Science, The University of Tokyo)
Spin transport phenomena at strongly-correlated interfaces play central roles in fundamental physics as well as spintronic applications. Although the spin-flip tunneling process, a key mechanism of spin transport, has been extensively studied in solid-state systems, its behavior in itinerant Fermi gases remains elusive. In this regard we study the spin tunneling in a repulsively interacting ultracold Fermi gas based on the conventional quasiparticle tunneling process. we investigate the spin current induced by quasiparticle and spin-flip tunneling processes to see their bias dependence and interaction dependence. To anatomize spin carriers, we propose the detection of the spin current noise in the system. The Fano factor, which is defined as the ratio between the spin current and its noise can serve as a probe of elementary carriers of spin transport. The change of the Fano factor microscopically evinces a crossover from the quasiparticle transport to magnon transport in itinerant fermionic systems.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Grassmann Tensor Renormalization Group for two-flavor Schwinger model with a theta term
June 24 (Mon) 16:00 - 17:00, 2024
Hayato Kanno (Special Postdoctoral Researcher, Theory Group, RIKEN BNL Research Center, RIKEN Nishina Center for Accelerator-Based Science (RNC))
QCD has been understood through numerical calculations by the Monte Carlo method. However, this method does not work for some parameter regions because of the sign problem. For example, QCD with a theta term has a sign problem, so the nature of QCD with a finite theta parameter is unknown. The theta dependence is also important to axion physics. To reveal such systems, tensor network methods are powerful tools. Tensor network methods have been developed by condensed matter theorists. Furthermore, recently there have been some attempts to apply them to high energy physics. In particular, the tensor renormalization group (TRG) method is remarkable for its applicability to higher dimensions. The Schwinger model is known as a two-dimensional toy model of QCD. It has the chiral symmetry and theta term as the same as QCD. In this study, the free energy of the two-flavor Schwinger model is calculated in a broad range of mass and theta parameters. We use TRG to calculate it, with obvious 2pi periodicity of theta parameter. We check the consistency with analytical values in large and small mass limits.
Venue: via Zoom / Seminar Room #359
Event Official Language: English
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Seminar
Finding and understanding disease-causing genetic mutations
June 20 (Thu) 16:00 - 17:00, 2024
Shohei Kojima (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. Genome-wide 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 population-scale sequencing datasets. In this talk, first, I will introduce some examples of disease-causing 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
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Seminar
The speciation-latitude relationship in ferns
June 6 (Thu) 16:00 - 17:00, 2024
José Said Gutiérrez-Ortega (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS))
The latitudinal gradient of diversity (LGD), the pattern that shows that the highest numbers of species in major taxa are at low latitudes and that they decrease towards high latitudes, is the most conspicuous trend on the relationship between geography, environment, and biodiversity. But there is not a concrete answer of why it exists. Three hypotheses have been proposed so far: 1) tropics contain more species because communities have been climatically stable for longer time than the temperate areas; 2) the tropics receives more energy, which allows groups to diversify at higher rates; 3) the tropics provide a higher diversity of ecological opportunities for new species to specialize. By analyzing the fern community from the American continent, I tested the three hypotheses, and found that the first hypothesis is the most likely. The tropics contain more species not because they produce more species than the temperate areas, but because extinction has been lower historically. These results suggest that the climatic instability (cycles of interglaciation-glaciation) at high latitudes have shaped this curious pattern. I am using this seminar to show you some of my research progress, and to briefly mention some of the problems that I have encounter while trying to test my hypotheses. Maybe we can make some ideas to improve the methodological aspects of this kind of macro-ecological research
Venue: via Zoom
Event Official Language: English
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Seminar
On the volume conjecture for the Teichm ̈uller TQFT
May 31 (Fri) 15:00 - 17:00, 2024
Soichiro Uemura (Ph.D. Student, Graduate School of Mathematical Sciences, The University of Tokyo)
The Chern-Simons theory is a topological quantum field theory (TQFT) on the principal G-bundle 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 3-manifold. 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, Chern-Simons theory with the non-compact G such as SL(2,C) also appears in duality in string theory called the 3d-3d correspondence but has not been well formulated mathematically. Andersen and Kashaev constructed a TQFT-like 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) Chern-Simons 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
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Seminar
Lipid Peroxidation Structure Selectivity: A Clue to Coal Workers' Pneumoconiosis
May 30 (Thu) 16:00 - 17:00, 2024
Cai Tie (Associate Professor, China University of Mining and Technology, China)
Coal workers' pneumoconiosis (CWP), resulting from the inhalation of coal dust mixtures, is one of the leading occupational diseases globally. Despite its seriousness, there is still no effective curative method available for CWP. Therefore, a systemic understanding of CWP's pathogenesis is urgently needed. Peroxidation is an oxidation chain reaction in which lipids (glycerophospholipids and other membrane lipids) are degraded into excretory forms, such as fatty aldehydes. This process involves a series of enzymes that catalyze the reactions leading to lipid degradation. Our previous work identified specific regulatory mechanisms in lipid peroxidation processes triggered by diseases or various interventions. To gain a comprehensive understanding of lipid peroxidation, we developed a systematic profiling strategy that allows for the detailed observation of these oxidative processes. Additionally, we adapted this profiling strategy to investigate risk factors associated with coal workers' pneumoconiosis (CWP). By applying our methods to the study of CWP, we aimed to uncover the metabolic and molecular changes induced by coal dust inhalation, providing insights that could contribute to better prevention and treatment strategies for this occupational disease. To comprehensively investigate the lung alterations associated with CWP, both a cohort of coal miners and a CWP rat model were studied. Through the analysis of lipid peroxidation alterations associated with CWP occurrence, several CYP subtype-specific metabolic processes were identified. These findings suggest that coal-derived polycyclic aromatic hydrocarbons (PAHs) are major risk factors for CWP due to the specific activation of the Aryl Hydrocarbon Receptor (AhR) pathway. Further evidence at the gene level and morphological changes supports the role of coal-derived PAHs as key factors in the development of CWP. Hence, it is crucial to consider the toxicity induced by PAHs in the prevention and treatment of CWP.
Venue: via Zoom
Event Official Language: English
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Colloquium
The New World of Spin Zero - Some Novel Approaches at QUP for Experimental Particle Cosmology -
May 28 (Tue) 13:30 - 15:00, 2024
Masashi Hazumi (Director, Professor, International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (QUP), High Energy Accelerator Research Organization (KEK))
Particle cosmology is a discipline seeking a fundamental understanding of the Universe based on particle physics. Five mysteries drive our research today: cosmic inflation, baryon asymmetry, neutrino properties, dark matter, and dark energy. Resolving any of the five mysteries will revolutionize our picture of the Universe. Numerous interesting theoretical hypotheses have been proposed to this end. Many require new scalar quantum fields, such as inflatons, axions, supersymmetric particles, etc. They are, in a sense, an attempt to expand the role of the vacuum. Since we have not found such spin-zero fields yet, we shall invent new eyes to make an experimental or observational breakthrough. The International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (QUP) was established in December 2021 at KEK under the WPI program of MEXT and JSPS. With its tagline of "bring new eyes to humanity," one of the primary missions of QUP is inventing and developing such new eyes for particle cosmology. In this seminar, after briefly introducing QUP, I focus on research topics I have contributed, including the LiteBIRD satellite to study inflatons and light scalar quantum field searches with novel methods using quantum sensing techniques.
Venue: Okochi Hall / via Zoom
Event Official Language: English
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Seminar
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) 16:00 - 17:00, 2024
Akihisa Yamamoto (Research Scientist, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (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 culture-expanded 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 two-dimensional colloidal assembly, the spatial arrangement of cells is generalized in terms of many-body 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
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Seminar
Introduction to operator algebras
May 17 (Fri) 15:00 - 17:00, 2024
Kan Kitamura (Special Postdoctoral Researcher, RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (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 non-trivial 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
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Seminar
Exploring the impact of environments on flower color differentiation: A meta-analytical approach
May 16 (Thu) 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 meta-analysis 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