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iTHEMS Cosmology Forum 3 - (P)reheating the primordial Universe

2025年3月4日(火) - 5日(水)

榎本 成志 (横浜国立大学 理工学部 博士研究員)
John T. Giblin (Professor, Department of Physics, Kenyon College, USA)
向田 享平 (高エネルギー加速器研究機構 (KEK) 理論センター 助教)

iTHEMS Cosmology Forum Workshop is a series of short workshops, each focusing on an emerging topics in cosmology. The target audience is cosmologists, high-energy physicists and astronomers interested in learning about the subject, not just those who have already worked on the topic. The goal of the workshop is to provide working knowledge of the topic and leave dedicated time for discussions to encourage mutual interactions among participants. The third workshop is devoted to the 'reheating' phase of the early Universe. Reheating bridges the gap between the (almost) empty universe at the end of cosmic inflation and the thermal state of particles, required for Big-Bang nucleosynthesis, and the events of the hot Big-Bang model as a whole, to unfold. It is expected to proceed in different stages starting with a violent parametric resonant creation of particles, dubbed preheating, followed by a redistribution of energy leading to a thermal state. This phase potentially hosts rich phenomenology such as the formation of topoligical defects e.g. solitons, generation of gravitiational wave, and so on. Yet, the very non-linear nature of reheating makes it notoriously hard to describe analytically, and even numerical simulations struggle to follow the whole sequence of events in a given model. Reheating studies have thus yet to reach the degree of compherensiveness and universality that the understanding of cosmic inflation has achieved. This forum will consist of two events. The first, on March 4th, will be in conference format comprising scientific talks on research trends in (P)Reheating. The second, on March 5th, will be a tutorial on numerical aspects of reheating (both theory and hands-on with code) hosted by Tom Giblin of Kenyon College. The workshop will be in English. The workshops are organised by the iTHEMS Cosmology Forum working group, which is the successor of the Dark Matter Working Group at RIKEN iTHEMS. Important dates: Feb. 25th - Registration deadline March 4th - Workshop Day (Room #435-437, Main Research Building 4F) March 5th - Tutorial Day (Room #445-447, Main Research Building 4F) Invited Speakers: John T. Giblin - Kenyon College Kyohei Mukaida - KEK Seishi Enomoto - Yokohama National University Organisers: Kohei Hayashi, Nagisa Hiroshima, Derek Inman, Amaury Micheli, Ryo Namba

会場: 研究本館 4階 435-437号室 / 研究本館 4階 445-447号室

イベント公式言語: 英語

Applications of Geometry of Numbers to Phyllotaxis and Crystallography

2025年2月28日(金) 14:00 - 15:30

富安 亮子 (九州大学 マス・フォア・インダストリ研究所 教授)

The golden angle method, originally known from phyllotaxis in botany, has been used to generate dense point packings on surfaces of revolution. In my recent work, I have extended this method to general surfaces and higher-dimensional manifolds by employing the theories of products of linear forms in number theory, diagonalizable metrics in differential geometry, and local solutions of quasilinear hyperbolic equations. This extension suggests that any biological forms can exhibit phyllotactic patterns locally regardless of their morphology, while the overall pattern is influenced by their global properties in the embedded space. On the algebraic side, it is interesting that the same ideas used for phyllotaxis can also be applied to pseudorandom number generation over F2 = {0, 1}. This work is motivated by my previous research in crystallography. Time permitting, I will also introduce some of the research, which contributes to the analytical foundations of crystallography and is also an application of the geometry of numbers.

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

Genome and Sex Chromosome Analyses of Japanese Frogs Carrying Both XY and ZW Chromosomes Within the Same Species

2025年2月27日(木) 16:00 - 17:00

桂 有加子 (京都大学 京都大学ヒト行動進化研究センター 助教)

The evolution of sex chromosomes, particularly sex chromosome turnover, is a complex and fascinating topic in genetics and evolutionary biology. Sex chromosome turnover refers to the process in which the sex chromosome system changes from XY to ZW (or vice versa), or in which sex chromosomes with different evolutionary origins emerge within the same system (e.g., from one XY system to another XY system). To study sex chromosome turnover, we focus on the Japanese frog (Glandirana rugosa), which possesses both XY and ZW sex chromosomes within the same species, and investigate the molecular mechanisms behind the turnover in the frog (Review: Hayashi et al. JB 2024). Previously, we sequenced the nuclear genome of the ZZ frog (Katsura et al. LSA 2021) and identified sex-linked genes in two populations of the XY and ZW frogs (Miura et al. Mol Ecol 2022). It has been suggested that sex chromosomes originating from at least three different chromosomal lineages have independently emerged within this species. The frogs have a total of 13 chromosomes, and in two populations (Tokai/Eastern Central Japan and Hokuriku-Tohoku/North-Western Japan), chromosome 7 has morphologically differentiated into both ZW and XY chromosomes. However, in other populations, sex chromosomes do not show any morphological differentiation. In this seminar, I introduce the background of our sex chromosome study and present the results of sequence comparisons of morphologically differentiated XY and ZW chromosomes, as well as findings from our analyses of populations, genome, and transcriptome.

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

Asymptotics in astrophysics iTHEMS workshop

2025年2月25日(火) - 28日(金)

This workshop will include overview talks of application of asymptotics and perturbation theory techniques in (wave transport or oscillation related) astrophysics and cosmology eigenvalue problems. In addition, there will be introductory talks about fundamental asymptotics and perturbation theory techniques used in theoretical physics. The purpose of this interdisciplinary workshop is to identify problems in astrophysics and related fields including, but not limited to, stellar structure and evolution, black holes and high-energy physics which can be solved using existing asymptotics and perturbation theory methods in theoretical physics problems (e.g. quantum field theory, gravity), and vice versa.

会場: 融合連携イノベーション推進棟（IIB） 8階

イベント公式言語: 英語

Ubiquity of geometric Brascamp--Lieb data

2025年2月21日(金) 15:00 - 17:00

辻 寛 (埼玉大学 大学院理工学研究科 日本学術振興会 特別研究員 PD)

This talk is based on a joint work with Neal Bez (Nagoya university) and Anthony Gauvan (Saitama university). The Brascamp--Lieb inequality is a futher general inequality involving some data (we call it the Brascamp--Lieb datum), which has been studied in harmonic analysis and convex geometry. For instance, the Hölder inequality and the Young convolution inequality are particular cases. In this talk, we have an interest in geometric Brascamp--Lieb data, which are specific data satisfying nice properties, for which the best constant of the Brascamp--Lieb inequality is well-understood. Our goal in this talk is to show that geomtric Brascamp--Lieb data are dense in general Brascamp--Lieb data in certain sence. Our result substantially follows from the work by Garg, Gurvits, Oliveira and Wigderson.

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

Exploring the evolutionary fate of a mutualistic community using automated microbial culture system

2025年2月20日(木) 16:00 - 17:00

砂川 純也 (北海道大学 大学院生命科学院 生命科学専攻 博士課程)

Microbes are ubiquitous around the world, forming systems where they interact through competition or cooperation. Especially in the form of cooperation, exchange of essential metabolites, known as metabolic cross-feeding, plays a fundamental role in the assembly of microbial communities. An extreme case of metabolic cross-feeding is an obligate mutualism, where one organism can only grow with the help of a partner supplying metabolites (e.g., amino acid). When they face environmental stresses such as antibiotics, it is unclear whether the benefit that causes the formation of obligate ecological mutualism may benefit (or cost) the members to increases (inhibits) resistance through interactions at the evolutionary scale. Another fascinating question is whether an additional benefit (e.g., an enzyme that helps the community persistence against environmental change) will select the community to increase the resistance. Here, I will report my ongoing research progress of obligate cross-feedings involving β-lactamase and discuss the conditions where the benefit can overcome the cost of the obligate interaction. I have started to address this issue by conducting laboratory evolution experiments with an automated culture system which can automatically adjust the strength of the stress (i.e., concentration of the antibiotics), so that the focal microbes have to get evolved. I will also share my story about building this automated culture system.

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

How to define a Majorana fermion?

2025年2月20日(木) 13:00 - 14:30

藤川 和男 (東京大学 名誉教授)

It is fundamental in particle physics if the neutrino is a Dirac fermion or a Majorana fermion, and the seesaw model gives naturally a Majorana neutrino in an extension of the Standard Model. However, the commonly used chirality changing \(pseudo-C symmetry \) \(\nu^{\tilde C}_L=C\overline{\nu_L}^T\) of a chiral fermion is not defined in Lagrangian field theory. Precisely speaking, the neutrinoless double beta decay is not described by the pseudo-C symmetry. The Majorana neutrino obtained after a Bogoliubov-type canonical transformation, which is the one originally defined by Majorana using a Dirac-type fermion, describes consistently all the properties expected for the Majorana neutrino. Physical implication of this fact is briefly discussed.

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

The Topology, Geometry and Physics of non-Hausdorff manifolds

2025年2月19日(水) 15:00 - 17:00

O'Connell David (沖縄科学技術大学院大学 (OIST) 博士課程)

Non-Hausdorff manifolds are manifolds containing "doubled points" that cannot be separated by disjoint open sets. In this talk we will survey some mathematical and physical results surrounding these unusual spaces. As a theme, we will start with their fundamental description as a topological space, and slowly add in more and more structure of interest until we can meaningfully phrase questions of physics. On the mathematical side, we will see descriptions of non- Hausdorff manifolds as colimits of ordinary manifolds, which allows us to describe their geometric features without appealing to arbitrarily- existent partitions of unity. On the physical side, we will consider the inclusion of non-Hausdorff manifolds in a naïve 2d Lorentzian path integral for gravity, and (time permitting) explain how construct quantum fields on a non-Hausdorff background. Ultimately, we will see that these latter two arguments suggest that non-Hausdorff manifolds may be more appropriate than the standard "Trousers space" for the modelling of topology change in Lorentzian signature.

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

New topological quantum order in 2D lattices from non-invertible symmetries

2025年2月18日(火) 15:00 - 16:00

Ayan Mukhopadhyay (Associate Professor, Valparaiso University, Chile)

I will introduce an exactly solvable 2D lattice model which reveals a large number of distinct topological phases with non-invertible (generalized) symmetries. In all these topological phases, which have topological ground state degeneracy, a commutative stabilizer monoid of Hermitian operators leave the ground state invariant and can also distinguish *all* local excitations, (These symmetries are indeed symmetry operations.) There exists novel confined fractonic excitations which change the nature of deconfined excitatons profoundly. The fusion rules form an associative but noncommutative. non-Abelian and non-unital category, and are distinct for each of these phases. A class of these phases are adiabatically connected to a limit which can be described in terms of generalized free field theories. I will describe systematic ways to construct such phases. I will also discuss phases which do not have generalized free field limits. These phases have novel forms of non-local entanglement as many of them share the same topological entanglement entropy. They also violate the entanglement bootstrap axioms. When the phases do not have a generalized free field limit, the violation of the entanglement bootstrap axioms can happen for arbitrary large subregions signifying new forms of long-range entanglement.

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

Operator-algebraic approach to point processes

2025年2月14日(金) 15:00 - 17:00

佐藤 僚亮 (中央大学 理工学部 学振特別研究員PD)

A point process is a mathematical description of a particle system with random interactions, and it naturally appears in various areas of mathematical physics and mathematics, including statistical mechanics, random matrix theory, combinatorics, and representation theory. In particular, a random particle system with repulsive interactions is associated with a determinantal point process, in which the correlation of any number of particles is expressed in terms of the two-particle correlation via a determinant. Furthermore, this determinantal structure enables an algebraic analysis using CAR algebras, which are operator algebras determined by canonical anti-commutation relations. In the first half of the talk, we will review the relationship between determinantal point processes and operator algebras, with a focus on why operator algebras naturally lend themselves to analyses in probability theory and statistical mechanics. In the second half, based on recent work, we will examine the dynamic relationship between point processes and operator algebras, discussing how dynamics on CAR algebras give rise to stochastic processes on determinantal point processes.

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

Linking quantum error correction and gauge theories with quantum reference frames

2025年2月14日(金) 10:30 - 11:30

Philipp Hoehn (沖縄科学技術大学院大学 (OIST) 助教)

Redundancy is the hallmark of both quantum error correction and gauge theories. In this talk, I will show that this analogy is not merely a coincidence but that there is a deeper underlying structural relationship. The key ingredient to this observation is quantum reference frames (QRFs), which constitute a universal tool for dealing with symmetries in quantum systems. They define a split between redundant and physical information in gauge systems, thereby establishing a notion of encoding in that context. This leads to an exact dictionary between (group-based) quantum error correcting codes and QRF setups. In stabilizer codes, this uncovers a correspondence between errors and QRFs: every maximal set of correctable errors generates a unique QRF, and each QRF is associated with a unique class of correctable errors. This allows for a reinterpretation of the Knill-Laflamme condition and novel insights into the relation between correctability and redundancy. The dictionary also reveals a novel error duality, based on Pontryagin duality, and somewhat akin to electromagnetic duality. Time permitting, I will illustrate these findings in surface codes, which can be understood as both codes and lattice gauge theories. These findings may find use in code design and quantum simulations of gauge theories.

会場: 研究本館 3階 345−347号室

イベント公式言語: 英語

Application of genetics and genomics to breeding

2025年2月13日(木) 16:00 - 17:30

ジェフリ・フォーセット (理化学研究所 数理創造プログラム (iTHEMS) 上級研究員)

Humans have domesticated and modified several plants and animals over the course of history to achieve food security. However, drastic changes are required in order to meet the needs of a growing population while facing global warming. In particular, utilizing and improving the productivity of unutilized or underutilized resources such as minor crops, aquatic species, and insects are thought to be essential. Here, I will provide an overview of how humans have been modifying organisms by selective breeding, the role of genetics and genomics in modern selective breeding, and the challenges we are currently facing. This talk will be aimed at non-experts/non-biologists and will cover the basics of genetics.

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

Mathematical Studies on Human Cooperation

2025年2月12日(水) 15:00 - 17:00

村瀬 洋介 (理化学研究所 計算科学研究センター (R-CCS) 離散事象シミュレーション研究チーム 研究員)

Cooperation is a fundamental part of human society. But from an evolutionary perspective, it remains a puzzle—why do people help others even when it costs them? In theory, selfish individuals should have an advantage over cooperators. To explain how cooperative behaviors evolved, researchers have proposed several mechanisms, among which direct and indirect reciprocity play key roles in human interactions. In this talk, I will present my research on the evolution of cooperation, focusing on these two mechanisms. I will begin with an introduction to game theory and evolutionary game theory, which help us understand how people make decisions in strategic situations. Then, I will discuss my study on the repeated Prisoner’s Dilemma, where we discovered a new class of strategies through mathematical analysis and large-scale computations [1]. Finally, I will talk about my research on indirect reciprocity, a process where people cooperate based on reputation [2].

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

Investigating the Crust Urca Process in Accretion Neutron Stars: Implications for Superburst Ignition and Hot Cooling Curve of MAXI J0556-332

2025年2月7日(金) 16:00 - 17:15

Hao Huang (Ph.D. Student, Institute of Modern Physics, China)

This seminar investigates the Urca cooling strength of the 63Fe-63Mn pair, which varies due to uncertainties in the spin-parity of 63Fe, relevant to the Island of Inversion at N = 40. We present simulations that analyze the impact of this cooling mechanism on the thermal evolution of neutron star crusts, focusing on superburst ignition and anomalous hot quiescent phase cooling of MAXI J0556-332. Additionally, we explore the potential crust Urca process through the anomalous cooling curve of MAXI J0556-332, fitting observational data to determine neutron star mass and radius preferences. Preliminary results suggest that neutron stars with a crust Urca process tend to have smaller masses and larger radii, highlighting the need for precise β-decay measurements to further understand these phenomena.

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

Fireworks in the cosmos: The Hidden Power of Nuclear Reactions

2025年2月7日(金) 14:00 - 15:15

Irin Sultana (Ph.D. Student, Department of Physics, Central Michigan University, USA)

Neutron stars in low-mass X-ray binaries, accreting hydrogen- or helium-rich material from a companion star, frequently exhibit thermonuclear runaways on their surfaces known as Type-I X-ray bursts (XRBs). These bursts are powered by nuclear processes, such as the triple-$\alpha$ process, the $\alpha p$ process, and the rapid proton capture process, which play a critical role in model-observation comparisons. In this study, we investigate the impact of nuclear reaction uncertainties on XRBs using the ONEZONE model (Cyburt et al., 2016), considering different accreted compositions and accretion rates for the binary systems that are within the range of observed burst sources. The study is carried out in two stages. First, we determine the burst ignition conditions by simulating the settling of the accreted material with a full reaction network and a semi-analytical model. Second, we perform a sensitivity analysis by varying proton- and alpha-induced reaction rates in JINA REACLIBV2.2 within their estimated uncertainties. We explore the influence of these reactions on the XRBs light curve and the final abundances. The findings highlight key nuclear reactions that significantly affect XRB observables and the final abundances produced, offering guidance for future experimental efforts to improve our understanding of the uncertainties in the reaction rates involved in XRBs.

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

A coarse-grained model of disordered RNA for simulations of biomolecular condensates

2025年2月6日(木) 16:00 - 17:00

安田 一希 (慶應義塾大学 大学院理工学研究科 博士課程)

Protein-RNA condensates are involved in a range of cellular activities. Coarse-grained molecular models of intrinsically disordered proteins have been developed to shed light on and predict single-chain properties and phase separation. An RNA model compatible with such models for disordered proteins would enable the study of complex biomolecular mixtures involving RNA. Here, we present a sequence-independent coarse-grained, two-bead-per-nucleotide model of disordered, flexible RNA based on a hydropathy scale. We parameterize the model, which we term CALVADOS-RNA, using a combination of bottom-up and top-down approaches to reproduce local RNA geometry and intramolecular interactions based on atomistic simulations and in vitro experiments. The model semi-quantitatively captures several aspects of RNA-RNA and RNA-protein interactions. We examined RNA-RNA interactions by comparing calculated and experimental virial coefficients, and non-specific RNA-protein interaction by studying reentrant phase behavior of protein-RNA mixtures. We demonstrate the utility of the model by simulating the formation of mixed condensates consisting of the disordered region of MED1 and RNA chains, and the selective partitioning of disordered regions from transcription factors into these, and compare the results to experiments. Despite the simplicity of our model we show that it captures several key aspects of protein-RNA interactions and may therefore be used as a baseline model to study several aspects of the biophysics and biology of protein-RNA condensates.

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

Mathematics of the Future, Science of the Future: Large Language Models and Their Applications

2025年2月6日(木) 14:00 - 16:00

三内 顕義 (京都大学 大学院理学研究科 特定准教授)

In recent years, the rapid development of large language models (LLMs) such as ChatGPT has given many researchers a strong impression that these systems truly exhibit “intelligence.” In this presentation, we first review the evolution of AI research, explaining how large language models go beyond conventional machine learning by enabling more “general” forms of learning. We then highlight the importance of “sensors” and “mathematical capability” as key factors that allow AI to autonomously carry out scientific tasks such as problem analysis, hypothesis generation, and proofs in fields like mathematics and physics. We also examine how proof assistants can address the issue of hallucinations in LLM outputs, and discuss the role of combinatorial creativity in accelerating interdisciplinary research. Finally, we introduce our “AI Mathematician” agent project, demonstrating how integrating large language models with proof assistants can open new horizons in mathematical sciences.

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

第四回 社会課題は数理科学で解決できる!? − 数理と起業の狭間 −

2025年2月1日(土) 13:00 - 17:00

第4回目の数理科学研究による社会課題の解決の可能性を探るシンポジウムを開催します。過去3年は「数理研究の社会実装―課題と克服」「企業課題と数理研究をつなぐ」「企業における数理研究」というテーマで行いました。近年、世界的にエッジの利いた様々な科学技術をコアとしたスタートアップ支援が活発になっていますが、数理基盤技術がスタートアップにつながった例はそれほど多くありません。一方で、Googleに代表される21世紀を代表するIT企業は数理技術をベースに成功を収めた企業であり、数理がスタートアップのコア技術となるポテンシャルは非常に高いと考えられます。今年度は、大学発のスタートアップ支援を行っている様々な機関や実際に起業を果たした研究者から、お話を伺いこの「数理基盤技術」の「スタートアップ」について参加者とともに学び、それに基づいてこの二つのギャップを埋める方策などについて議論したいと思います。 主催： JST未来社会創造事業「共通基盤」領域 本格研究課題　未来医療を創出する4次元トポロジカルデータ解析数理基盤の開発 共催： 九州大学 マス・フォア・インダストリ研究所 理化学研究所iTHEMS 後援： 株式会社 理研数理 株式会社 JSOL 京都大学 大学院理学研究科 附属サイエンス連携探索センタ−(SACRA) コーディネート： 名古屋大学大学院 理学研究科 生命理学専攻 異分野融合生物学研究室/iBLab 詳細は、関連リンクをご覧下さい。

会場: 名古屋大学 野依記念学術交流館とZoomのハイブリッド開催

イベント公式言語: 日本語

D-modules and the Riemann-Hilbert correspondence as a foundation for mixed Hodge modules

2025年1月31日(金) 14:00 - 16:00

齋藤 隆大 (中央大学 理工学部 助教)

Algebraic analysis is a field which began with the study of differential equations in an algebraic framework, known as D-modules. The Riemann-Hilbert correspondence lies at the heart of this field, which bridges the worlds of analysis and geometry. Thanks to this, some geometric problems can be studied by using D-module theory, and vice versa. Based on D-module theory, Morihiko Saito introduced the concept of mixed Hodge modules, realizing Hodge theory on constructible sheaves, which brings us a functorial treatment of Hodge theory and various applications. In this talk, we will begin with the linear differential equations on the complex plane and introduce monodromy, regularity and Deligne's Riemann-Hilbert correspondence. Then, as a generalization of it, I will explain the basics of the theory of D-modules and the Riemann-Hilbert correspondence. Finally, I will describe the role they play in the theory of Hodge modules and recent progress in this area. For the audience's background knowledge, I will assume basic complex function theory. I will start with a simple example, so people outside the field are welcome.

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

Reheating after a cosmological constant relaxation and gravitational waves lensed by a supermassive black hole

2025年1月30日(木) 14:00 - 15:30

Paul Martens (Postdoctoral Fellow, Department of Physics, The Chinese University of Hong Kong, China)

This presentation will be articulated in two parts. In a first part, I will present the a reheating mechanism that follows a dynamically relaxed cosmological constant. The latter is achieved by the dynamics of a scalar field whose kinetic term is modulated by an inverse power of spacetime curvature. While it is at work against radiative corrections to the dark energy, this process alone would wipe out not only the vacuum energy, but also all other matter contents. A reheating phase is thus introduced, which exploits a null-energy-condition violating sector. In a second part, I shall present a more recent and still ongoing project to describe and characterize the lensing of gravitational waves by an active galactic nuclei (or any supermassive black hole), in the geometric limit. Such systems are simple enough for constraints to be derived with only few assumptions. Yet, they present interesting features that could provide information on e.g. on binary black hole formation mechanisms and quasinormal modes.

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