Seminar
646 events

Seminar
The role of demographic stochasticity in the evolution of spite and altruism
July 9 (Tue) at 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

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
Recent progress of microscopic equation of state for hyperonmixed nuclear matter
July 4 (Thu) at 14:00  15:00, 2024
Togashi Hajime (Specially Appointed Assistant Professor, Research Center for Nuclear Physics, Osaka University)
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 threebody forces including hyperons on the structure and particle composition of (proto) neutron stars.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Worldline Path Integrals for the Graviton and 1Loop Divergences in Quantum Gravity
June 28 (Fri) at 16:00  17:20, 2024
Fiorenzo Bastianelli (Professor, University of Bologna, Italy)
In this talk, I will discuss perturbative quantum gravity at the 1loop 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 SchwingerDeWitt 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 oneloop divergences in quantum gravity with a cosmological constant in arbitrary dimensions. When evaluated onshell, these calculations yield a set of gaugeinvariant 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

Seminar
Challenging conventional wisdom in binary evolution
June 28 (Fri) at 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 higherorder 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 Xray 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 longstanding problems. The topics are as follows: 1. impact of supernova ejecta on companion star evolution, 2. wind accretion onto black holes, 3. commonenvelope 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

Seminar
Ychromosome turnover in Drosophila – Escaping from an evolutionary deadend?
June 28 (Fri) at 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 deadend 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 oneway path to deadend but by a circular process, i.e., “sexchromosome cycle.”
Venue: Hybrid Format (3F #359 and Zoom), Main Research Building
Event Official Language: English

Seminar
Inferring collective behavior from social interactions to population coding
June 27 (Thu) at 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 steadystate 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 colocalization 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

Magnonic spin current and shot noise in an itinerant Fermi gas
June 25 (Tue) at 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 stronglycorrelated interfaces play central roles in fundamental physics as well as spintronic applications. Although the spinflip tunneling process, a key mechanism of spin transport, has been extensively studied in solidstate 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 spinflip 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

Seminar
Grassmann Tensor Renormalization Group for twoflavor Schwinger model with a theta term
June 24 (Mon) at 16:00  17:00, 2024
Hayato Kanno (Special Postdoctoral Researcher, Theory Group, RIKEN BNL Research Center, RIKEN Nishina Center for AcceleratorBased 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 twodimensional 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 twoflavor 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

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
Quantum Computation Study Group Seminars
June 18 (Tue) at 13:30  15:00, 2024
Yuta Kikuchi (Research Scientist, Quantum algorithms and machine learning, Quantinuum K.K.)
Ermal Rrapaj (HPC Architecture and Performance Engineer, National Energy Research Scientific Computing Center (NERSC), Lawrence Berkeley National Laboratory (LBNL), USA)Speaker: Yuta Kikuchi Title: Simulating Floquet scrambling circuits on trappedion quantum computers Abstract: Complex quantum manybody dynamics spread initially localized quantum information across the entire system. Information scrambling refers to such a process, whose simulation is one of the promising applications of quantum computing. We demonstrate the HaydenPreskill recovery protocol and the interferometric protocol for calculating outoftimeordered correlators to study the scrambling property of a onedimensional kickedIsing model on 20qubit trappedion quantum processors. The simulated quantum circuits have a geometrically local structure that exhibits the ballistic growth of entanglement, resulting in the circuit depth being linear in the number of qubits for the entire state to be scrambled. We experimentally confirm the growth of signals in the HaydenPreskill recovery protocol and the decay of outoftimeordered correlators at late times. As an application of the created scrambling circuits, we also experimentally demonstrate the calculation of the microcanonical expectation values of local operators adopting the idea of thermal pure quantum states. Speaker: Ermal Rrapaj Title: Exact block encoding of imaginary time evolution with universal quantum neural networks Abstract: Quantum computers have been widely speculated to offer significant advantages in obtaining the ground state of difficult Hamiltonian in chemistry and physics. The imaginarytime evolution method is a wellknown approach used for obtaining the ground state in quantum manybody problems on a classical computer. In this work we develop a practical method for such purpose. We develop a constructive approach to generate quantum neural networks capable of representing the exact thermal states of all manybody qubit Hamiltonians. The Trotter expansion of the imaginarytime propagator is implemented through an exact block encoding by means of a unitary, restricted Boltzmann machine architecture. Marginalization over the hiddenlayer neurons (auxiliary qubits) creates the nonunitary action on the visible layer. Then, we introduce a unitary deep Boltzmann machine architecture, in which the hiddenlayer qubits are allowed to couple laterally to other hidden qubits. We prove that this wave function ansatz is closed under the action of the imaginarytime propagator and, more generally, can represent the action of a universal set of quantum gate operations. We provide analytic expressions for the coefficients for both architectures, thus enabling exact network representations of thermal states without stochastic optimization of the network parameters. In the limit of large imaginary time, the ansatz yields the ground state of the system. The number of qubits grows linearly with the system size and total imaginary time for a fixed interaction order. Both networks can be readily implemented on quantum hardware via midcircuit measurements of auxiliary qubits. If only one auxiliary qubit is measured and reset, the circuit depth scales linearly with imaginary time and system size, while the width is constant. Alternatively, one can employ a number of auxiliary qubits linearly proportional to the system size, and circuit depth grows linearly with imaginary time only.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

The speciationlatitude relationship in ferns
June 6 (Thu) at 16:00  17:00, 2024
José Said GutiérrezOrtega (Special Postdoctoral Researcher, 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 interglaciationglaciation) 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 macroecological research
Venue: via Zoom
Event Official Language: English

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

Seminar
Lipid Peroxidation Structure Selectivity: A Clue to Coal Workers' Pneumoconiosis
May 30 (Thu) at 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 subtypespecific metabolic processes were identified. These findings suggest that coalderived 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 coalderived 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

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
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