179件のイベント / 2024年
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セミナー
Thermal radiation exchange in primordial gravitational waves
2024年7月18日(木) 13:30 - 15:00
太田 敦久 (Postdoctoral Fellow, Institute for Advanced Study, Hong Kong University of Science and Technology, China)
The radiation-dominated universe is a key component of standard Big Bang cosmology. Radiation comprises numerous quantum elementary particles, and its macroscopic behavior is described by taking the quantum thermal average of its constituents. The dynamics of gravitational waves are considered in this smooth fluid. While interactions between individual particles and gravitational waves are often neglected in this context, it raises the question of whether such a hydrodynamical approximation is reasonable. To address this question, we explored the quantum mechanical aspects of gravitational waves in a universe dominated by a massless scalar field, whose averaged energy-momentum tensor serves as background radiation. We computed thermal loop corrections for the gravitational wave power spectrum using the Schwinger-Keldysh formalism. Interestingly, we found that the loop effect enhances the super-horizon primordial gravitational wave spectrum, indicating that the inflationary spectrum is not conserved, contrary to conventional wisdom. These findings have significant implications for our understanding of the early universe. In this talk, I will begin with the basics of cosmology and explain the significance of these results and their relevant observational consequences.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語
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Quantum Simulation in High Energy Nuclear Physics
2024年7月18日(木) 10:00 - 11:30
郭 星雨 (Lecturer, Institute of Quantum Matter, South China Normal University, China)
Quantum simulation is a novel method of simulation physical systems with quantum computers. Compared to conventional methods, quantum algorithms have various advantages in doing non-perturvative calculations and real-time evolutions, which makes it very promising to apply them in high energy nuclear physics. We propose a systematic quantum algorithm, which integrates both the hadronic state preparation and the evaluation of real-time light-front correlators. This algorithm can be applied to the calculation of a wide range of quantities in high energy nuclear physics. As a demonstration, we calculate the parton distribution functions, the light-cone distribution amplitudes and scattering amplitudes in the 1+1 dimensional NJL model. The results are qualitatively consistent with QCD calculations.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語
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セミナー
Surface defect in N=4 SYM and integrability
2024年7月17日(水) 16:00 - 17:00
河井 大輝 (Ph.D. Student, University of California, Santa Barbara, USA)
In the N=4 super Yang-Mills theory, it is well-known that the one-loop anomalous dimension operator for the single trace operators is equivalent to an integrable spin chain. Recent works have extended the application of integrability to scenarios involving a BPS boundary or defects such as 't Hooft line. One can describe the correlators of the single trace operators as an overlap between the Bethe state and the corresponding defect state. This overlap can be exactly calculated if the defect state is a so-called integrable state. We show that the state corresponding to the Gukov-Witten surface defect is integrable. We also calculate the tree-level one-point function of the single trace operators and set up the perturbation calculation in this defect background for one-loop corrections.
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Supernovae as Tracers of Massive-Star Evolution
2024年7月17日(水) 14:00 - 15:15
平松 大地 (Post-Doctoral fellow, Harvard University, USA)
Supernovae are the terminal explosions of massive stars with influences on every astrophysical scale. Advanced wide-field and high-cadence transient surveys routinely discover supernovae near the moment of explosion. Coupled with prompt and continuous follow-up facilities, these observations have revealed unprecedented features of dense circumstellar medium in various spatial scales as traced by the expanding supernova ejecta. Such circumstellar medium is thought to originate from mass-loss activities in the final years to decades of stellar evolution; however, their inferred densities exceed the expectations from standard theory by many orders of magnitude. In this talk, I will first introduce standard stellar evolution and supernova explosion mechanisms, and then describe novel observational probes and modeling techniques of supernovae interacting with circumstellar medium to reconstruct their explosion properties and progenitor mass-loss histories. Finally, I will discuss our on-going largest sample study of interacting supernovae and emerging pictures of dramatic dying breaths of massive stars.
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Quantum Error Transmutation
2024年7月17日(水) 10:30 - 11:30
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.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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講演会・レクチャー
Differential Topology Seminar: Rigidity and Flexibility of Isometric Embeddings
2024年7月16日(火) 15:00 - 16:30
Dominik Inauen (Academic Staff, University of Leipzig, Germany)
The problem of embedding abstract Riemannian manifolds isometrically (i.e. preserving the lengths) into Euclidean space stems from the conceptually fundamental question of whether abstract Riemannian manifolds and submanifolds of Euclidean space are the same. As it turns out, such embeddings have a drastically different behaviour at low regularity (i.e. C1) than at high regularity (i.e. C2). For example, by the famous Nash--Kuiper theorem it is possible to find C1 isometric embeddings of the standard 2-sphere into arbitrarily small balls in R3, and yet, in the C2 category there is (up to translation and rotation) just one isometric embedding, namely the standard inclusion. Analoguous to the Onsager conjecture in fluid dynamics, one might ask if there is a sharp regularity threshold in the Holder scale which distinguishes these flexible and rigid behaviours. In my talk I will review some known results and argue why the Holder exponent 1/2 can be seen as a critical exponent in the problem.
会場: 京都大学 理学研究科 6号館609号室
イベント公式言語: 英語
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セミナー
Mapping the Phase Space of toric Calabi-Yau 3-folds using Explainable Machine Learning
2024年7月16日(火) 13:30 - 14:30
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.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Topological recursion and twisted Higgs bundles
2024年7月16日(火) 10:30 - 12:00
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.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語
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Discovering Physical Laws with Artificial Intelligence
2024年7月12日(金) 10:00 - 11:30
刘 子鸣 (Ph.D. Student, Department of Physics, Massachusetts Institute of Technology, USA)
Deep neural networks have been extremely successful in language and vision tasks. However, their black-box nature makes them undesirable for scientific tasks. In this talk, I will show how we can make these black-box AI models more interpretable and transparent and use them to discover physical laws, including conservation laws (AI Poincare), symmetries, phase transitions and symbolic relations (Kolmogorov-Arnold Networks). Ziming is a physicist and a machine learning researcher. Ziming received BS in physics from Peking Univeristy in 2020, and is current a fourth-year PhD student at MIT and IAIFI, advised by Max Tegmark. His research interests lie generally in the intersection of artificial intelligence (AI) and physics (science in general).
会場: via Zoom
イベント公式言語: 英語
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セミナー
Tensionless Strings in a Kalb-Ramond Background
2024年7月10日(水) 16:00 - 17:00
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
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
The role of demographic stochasticity in the evolution of spite and altruism
2024年7月9日(火) 16:00 - 17:00
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.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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第26回 MACSコロキウム
2024年7月8日(月) 14:45 - 18:00
田口 聡 (京都大学 大学院理学研究科 地球惑星科学専攻 教授)
野田口 理孝 (京都大学 大学院理学研究科 生物科学専攻 教授)14:45-15:00 ティータイムディスカッション 15:00-16:00 田口 聡 博士(京都大学理学研究科地球惑星科学専攻 教授 / 附属サイエンス連携探索セン ター センター長)「太陽風が奥深く入ってくる場所での地球の大気とプラズマの振る舞い」 16:15-17:15 野田口 理孝 博士(京都大学大学院理学研究科生物科学専攻植物学系 教授)「植物科学のために挑んだ学際融合」 17:15-18:00 継続討論会
会場: 理学研究科セミナーハウス(建物配置図(北部構内)【10】の建物)
イベント公式言語: 日本語
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セミナー
Dynamics of the very early universe: towards decoding its signature through primordial black hole abundance, dark matter, and gravitational waves.
2024年7月5日(金) 14:00 - 15:15
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.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Recent progress of microscopic equation of state for hyperon-mixed nuclear matter
2024年7月4日(木) 14:00 - 15:00
富樫 甫 (大阪大学 核物理研究センター 特任助教)
The presence of hyperons in the neutron star interior have been investigated by many researchers using both phenomenological and microscopic approaches for the equation of state (EOS) of neutron star matter with hyperons. However, hyperon fractions in nuclear matter are still far from being understood, since there are relatively large uncertainties in hyperon interactions due to the small amount of the experimental data. Furthermore, recently observed masses of massive pulsars impose severe constraints on the hyperon EOS. In this seminar, I will review the recent results of microscopic nuclear EOS including hyperons and its applications to astrophysical compact objects to discuss the possible signatures of the presence of hyperons in compact star interiors. In particular, I will discuss the effect of three-body forces including hyperons on the structure and particle composition of (proto) neutron stars.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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その他
SLMath Summer Graduate School "h-principle"
2024年7月1日(月) - 12日(金)
会場: 東北大学片平キャンパス 知の館
イベント公式言語: 英語
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Worldline Path Integrals for the Graviton and 1-Loop Divergences in Quantum Gravity
2024年6月28日(金) 16:00 - 17:20
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.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語
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セミナー
Challenging conventional wisdom in binary evolution
2024年6月28日(金) 14:00 - 15:15
Ryosuke Hirai (理化学研究所 開拓研究本部 (CPR) 長瀧天体ビックバン研究室 基礎科学特別研究員)
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.
会場: via Zoom
イベント公式言語: 英語
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セミナー
Y-chromosome turnover in Drosophila – Escaping from an evolutionary dead-end?
2024年6月28日(金) 14:00 - 16:00
野澤 昌文 (東京都立大学 准教授)
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.”
会場: 研究本館 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Inferring collective behavior from social interactions to population coding
2024年6月27日(木) 16:00 - 17:30
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.
会場: via Zoom
イベント公式言語: 英語
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講演会・レクチャー
Obstructions to Lagrangian surgery
2024年6月27日(木) 15:00 - 17:00
Emmy Murphy (Professor, Princeton University, USA)
Given a Lagrangian immersion with a transverse double point, we can surger this point to obtain an embedded Lagrangian with more complicated topology. As a classical example, both the Clifford and Chekanov tori in C2 are obtained via Lagrangian surgery on a immersed sphere called the Whitney sphere. In the talk we'll discuss a Floer-theoretic obstruction to this: that is, showing that a Lagrangian cannot be realized as a surgery. An interesting dilemma is that PH invariants of an immersed Lagrangian itself cannot detect the fact that it is immersed. Instead, we have to consider families of Floer invariants coming from all possible surgeries, and use properties specific to SFT Lagrangian cobordism maps.
会場: 京都大学数理解析研究所
イベント公式言語: 英語
179件のイベント / 2024年
イベント
カテゴリ
シリーズ
- iTHEMSコロキウム
- MACSコロキウム
- iTHEMSセミナー
- iTHEMS数学セミナー
- Dark Matter WGセミナー
- iTHEMS生物学セミナー
- 理論物理学セミナー
- 情報理論SGセミナー
- Quantum Matterセミナー
- ABBL-iTHEMSジョイントアストロセミナー
- Math-Physセミナー
- Quantum Gravity Gatherings
- RIKEN Quantumセミナー
- Quantum Computation SGセミナー
- Asymptotics in Astrophysics SG Seminar
- GW-EOS WGセミナー
- DEEP-INセミナー
- NEW WGセミナー
- Lab-Theory Standing Talks
- 場の量子論セミナー
- STAMPセミナー
- QuCoInセミナー
- Number Theory Seminar
- 産学連携数理レクチャー
- Berkeley-iTHEMSセミナー
- iTHEMS-仁科センター中間子科学研究室ジョイントセミナー
- RIKEN Quantumレクチャー
- 作用素環論
- iTHEMS集中講義-Evolution of Cooperation
- 公開鍵暗号概論
- 結び目理論
- iTHES理論科学コロキウム
- SUURI-COOLセミナー
- iTHESセミナー