理論物理学セミナー
140 イベント
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セミナー
Forming primordial black holes
2024年11月11日(月) 14:00 - 15:30
Zachary Picker (Postdoctoral Researcher, University of California, Los Angeles, USA)
Primordial black holes (PBHs) are black holes which form in the early universe. Not only are PBHs good dark matter candidates, but they have a wide range of fascinating phenomenology (even if they are only a fraction of the dark matter). In this talk I will review a somewhat under-discussed aspect of the PBH gospel---their formation mechanisms. In fact, there is a wide variety of ways to form PBHs of different sizes and abundances, and many of our favorite BSM theories can have PBHs in their spectra. I will then discuss some of our particular upcoming research on PBH formation, where attractive Yukawa forces in a dark sector can lead to the early formation of dense dark structures called Fermi balls which can collapse to black holes, with novel cosmological implications.
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
Quantum signature kernels
2024年10月30日(水) 14:00 - 15:00
Samuel Crew (Postdoctoral Fellow, Imperial College London, UK)
Arising from rough path theory, the signature transform captures features of time-series data by constructing a so-called path signature. This feature has proven valuable for various machine learning tasks. However, computing the associated signature kernel classically remains computationally intensive. In this talk, I will present recent developments in generalising the signature kernel to randomised Lie group path developments. I will discuss a quantum approach via matrix models with an associated unitary quantum signature kernel to propose a quantum algorithm for its computation.
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
Holographic Gubser flow
2024年10月29日(火) 13:30 - 14:30
Sukrut Mondkar (Postdoctoral Researcher, Harish-Chandra Research Institute, India)
Gubser flow is an evolution with cylindrical and boost symmetries, which can be best studied by mapping the future wedge of Minkowski space ℝ^{(3,1)} to dS_3 × ℝ in a conformal relativistic theory. Here, we sharpen the analytic results of Banerjee, Mitra, Mukhopadhyay Soloviev, EPJC (2024) and validate them via the first numerical exploration of the Gubser flow in a holographic conformal field theory. Remarkably, the leading generic behavior at large de Sitter time is free-streaming in transverse directions and the sub-leading behavior is that of a color glass condensate. We also show that Gubser flow can be smoothly glued to the vacuum outside the future Minkowski wedge generically given that the energy density vanishes faster than any power when extrapolated to early proper time or to large distances from the central axis. We find that at intermediate times the ratio of both the transverse and longitudinal pressures to the energy density converge approximately to a fixed point which is hydrodynamic only for large initial energy densities. We argue that our results suggest that the Gubser flow is better applied to collective behavior in jets rather than the full medium in the phenomenology of heavy ion collisions and can reveal new clues to the mechanism of confinement. The talk will be based on Mitra, Mondkar, Mukhopadhyay, Soloviev, arxiv:2408.04001/hep-th (accepted for publication in JHEP).
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
Open Effective Field Theories for primordial cosmology
2024年10月18日(金) 13:30 - 15:00
Thomas Colas (Postdoc, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK)
Imprints of new physics on observable cosmology may require the modelling of dissipation and noise. In this talk, I will present an open effective field theory for primordial cosmology where the inflaton sector interacts with an unknown environment. The approach recovers the usual effective field theory of inflation in a certain limit and extends it to account for local dissipation and noise. Non-Gaussianities are generated that peak in the equilateral configuration for large dissipation and in the folded configurations for small dissipation. The construction provides an embedding for local dissipative models of inflation and a framework to study dissipative and stochastic effects in cosmology.
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
Application of Complex Scaling Method to Scattering Calculations of Atomic Systems
2024年10月8日(火) 13:30 - 15:00
佐野 大志 (早稲田大学 理工学研究科 物理学及応用物理学専攻 辻川研究室 修士課程)
Based on our paper [1], this presentation will show the application of complex scaling method(CSM) to scattering calculations of atomic systems. While CSM has been extensively used to study resonance states, the application of CSM to scattering calculations was proposed recently with applications in nuclear physics. In our study, we apply the CSM scattering calculation to atomic systems and propose an effective correction to avoid the problem of slow convergence to the number of complex eigen energies. Our results with the effective correction agree well with those reported in the literature for positron scattering with the targets Ne, Ar, Kr, Xe, H, He, He+, and Li2+. In this presentation, we introduce the framework of phase-shift calculation using the CSM together with the examples of the positron scattering, and advantages and features of this approach. [This seminar is co-hosted by Few-body Systems in Physics Laboratory, RIKEN Nishina Center.]
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
Algebraic curves and parametric resurgence
2024年7月29日(月) 16:30 - 17:45
Samuel Crew (Postdoctoral Fellow, Imperial College London, UK)
In this talk I will discuss recent work together with Ines Aniceto (Southampton) on algebraic examples of parametric resurgence. We discuss a simple example to elucidate the so-called higher order Stokes phenomena and discuss how a Borel inner-outer matching procedure allows us to view parametric resurgence as a series of non-parametric resurgence problems.
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
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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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
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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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
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
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
Magnonic spin current and shot noise in an itinerant Fermi gas
2024年6月25日(火) 13:30 - 15:00
テイユ・チョウ (東京大学 大学院理学系研究科 物理学専攻 博士課程)
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.
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
Grassmann Tensor Renormalization Group for two-flavor Schwinger model with a theta term
2024年6月24日(月) 16:00 - 17:00
菅野 颯人 (理化学研究所 仁科加速器科学研究センター (RNC) 理研BNL研究センター 理論研究グループ 基礎科学特別研究員)
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.
会場: via Zoom / セミナー室 (359号室)
イベント公式言語: 英語
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セミナー
Boundary-induced transitions in Möbius quenches of holographic BCFT
2024年5月15日(水) 16:00 - 17:30
Dongsheng Ge (大阪大学 大学院理学研究科 特任研究員)
Boundary effects play an interesting role in finite-size physical systems. In this work, we study the boundary-induced properties of 1+1-dimensional critical systems driven by inhomogeneous Möbius-like quenches. We focus on the entanglement entropy in BCFTs with a large central charge and a sparse spectrum of low-dimensional operators. We find that the choice of boundary conditions leads to different scenarios of dynamical phase transitions. We also derive these results in a holographic description in terms of intersecting branes in AdS3, and find a precise match.
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
Role of self-gravity on the central halo structure of fuzzy dark matter
2024年4月30日(火) 13:30 - 15:00
間仁田 侑典 (京都大学 基礎物理学研究所 協力研究員)
Fuzzy dark matter (FDM) is a dark matter model that is characterized by the ultralight masses around 10−22 eV. As FDM has the wave-like nature, the self-gravitating structure is described by the Schrödinger-Poisson equation. Previous simulations based on the Schrödinger-Poisson equation have demonstrated that soliton-like structure having a high-density flat core is formed at the central region of the FDM halos, and the size of such a core is typically determined by the de Broglie wavelength. Away from the central core, the density profile of the FDM halos resembles that of the cold dark matter halos on average, and is shown to be described by the Navarro-Frenk-White (NFW) profile. In this paper, we study the role of the self-gravity of the soliton core, and its relation to the bulk halo properties by solving the Schrödinger-Poisson equation in a simplified setup. The findings indicate that the contribution from the soliton self-gravity must dominate over the NFW potential in order to sustain the soliton.
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
A night out with ghosts
2024年4月24日(水) 16:00 - 17:30
Veronica Errasti Diez (Research Fellow, Faculty of Physics, Ludwig-Maximilians-Universität München, Germany)
Field theories are the chief theoretical framework for physics. For instance, the Standard Model and General Relativity are widely accepted as accounting for subatomic particle and gravitational behavior, respectively. Nonetheless, even such acclaimed field theories have their limitations, such as the mysterious neutrino masses and dark sector. A natural and popular way around the hurdles consists in generalizations of field theories, via the inclusion of non-linear and/or higher-order corrections. Unless painstakingly avoided, these corrections lead to the propagation of negative kinetic energy modes, or ghosts for short. Ghosts have earned an appalling fame: kill, exorcise, avoid… No efforts are spared to guarantee their absence. In this talk, we will delve into the root causes for the ill name of ghosts. As a result, we will take up the cudgels for ghosts. While they do have a strong tendency to yield ill-behaved theories, ghosts are not intrinsically pathological. As we will see, good-natured ghosts open the door to multi-disciplinary tantalizing opportunities…! And ghosts make excellent party-goers, so make sure not to miss this appointment!
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
Short-Lived Hawking Radiation Under Stringy Effects
2024年4月11日(木) 13:30 - 15:00
ウェイシャン・シャオ (Ph.D. Student, Department of Physics, National Taiwan University, Taiwan)
A UV theory is required in order to describe the origin of late-time Hawking radiation. In this talk, I will explore Hawking radiation in a non-local model of the radiation field inspired by Witten's open string field theory. An attempt at extracting the correlators of this theory will be discussed, which leads to a space-time uncertainty relation. As a result, the characteristics of trans-Planckian field modes differ significantly from that in the standard low-energy effective theory, and I will argue that this ultimately results in the termination of Hawking radiation around the scrambling time of the black hole.
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
Brane field theory with higher-form symmetry
2024年3月12日(火) 14:00 - 15:30
川名 清晴 (Research Fellow, Korea Institute for Advanced Study (KIAS), Republic of Korea)
We propose field theory for branes with higher-form symmetry as a generalization of ordinary Landau theory. The field \psi[C_p^{}] becomes a functional of p-dimensional closed brane Cp embedded in a spacetime. As a natural generalization of ordinary field theory, we call this theory brane field theory. In order to construct an action that is invariant under higher-form transformation, we first generalize the concept of “derivative” for higher-dimensional objects. Then, we discuss various fundamental properties of the brane field based on the higher-form invariant action. It is shown that the classical solution exhibits the area law in the unbroken phase of U(1) p-form symmetry, while it indicates a constant behavior in the broken phase for the large volume limit of Cp. In the latter case, the low-energy effective theory is described by the p-form Maxwell theory. If time permits, we also discuss brane-field theories with a discrete higher-form symmetry and show that the low-energy effective theory becomes a BF-type topological field theory, resulting in topological order.
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
Stochastic tunneling in de Sitter spacetime
2024年2月28日(水) 16:00 - 17:30
宮地 大河 (神戸大学 大学院理学研究科 物理学専攻 宇宙論研究室 博士課程)
The formulation of tunneling in real time formalism is discussed. In the case of de Sitter spacetime, there is a method called the stochastic approach, which is known to reproduce the tunneling predicted by Hawking and Moss in the imaginary time formalism. In the case of accelerated expansion of space, the short-wavelength modes are stretched and transformed into long-wavelength modes. In the stochastic approach, such UV-IR transition is incorporated as quantum noise, and the dynamics of the long-wavelength modes are described by stochastic differential equations. In this talk, we construct a Schwinger-Keldysh path integral that reproduces this stochastic differential equation and reformulate the tunneling probability. We also reproduce the Hawking-Moss tunneling probabilities by using the saddle point approximation.
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
140 イベント