セミナー 2018年

Takasumi Maruyama, KEK

Light Sterile Neutrino: is there any good pictures?

Seminar room, Kenkyu honkan 3F, slides (kek.jp only)
In this seminar, the status of the light sterile neutrino searches and whether there is good and reasonable physics pictures for the neutrinos are discussed. The light sterile neutrino is non-weak interactive neutrino, and it was introduced to explain the results of the LSND experiment. The idea to exist the particle which is sensitive to gravity but not to strong, electromagnetic and weak forces are interesting, however, currently only LSND and MiniBooNE experiments provided positive results. This seminar reviews the status of the sterile neutrino searches in the world, which includes the JSNS2 experiment (J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source). The experiment aims the direct confirmation or refute the LSND results. It will be started from the end of JFY2018.

Xi Yin, Harvard University

Topological Defect Lines and RG Flows in 2D

Seminar room, Kenkyu honkan 3F
Topological defect lines in 2D generalize both global symmetries and Verlinde lines, and provide models of fusion categories without braiding. I will discuss their roles in CFTs and in constraining RG flows, and use them to determine the infrared (fully extended) topological quantum field theory in some examples of massive flows.

Nobuyuki Matsumoto, Kyoto University

Distance between configurations in MCMC simulations and AdS geometry in the simulated tempering algorithm

Seminar room, Kenkyu honkan, slides (kek.jp only)
For a given Markov chain Monte Carlo (MCMC) algorithm, we define distance between configurations, which quantifies difficulty of transition from one configuration to the other. This distance gives a universal form for a class of MCMC algorithms which generate local moves of configurations. The introduction of distance enables us to investigate a relaxation process in a MCMC simulation from a geometrical point of view. We here consider a system whose equilibrium distribution is highly multimodal with a large number of degenerate classical vacua. We show that, when we implement the simulated tempering method for such a system, the anti-de Sitter (AdS) geometry emerges in the extended configuration space. This talk is based on the work with M. Fukuma and N. Umeda [JHEP12(2017)001, work in preparation].

Koutarou Kyutoku, KEK

Initial data of compact object binaries for numerical relativity

Meeting room 1, Kenkyu honkan 1F
Because nonlinear gravity and hydrodynamics play a crucial role, numerical-relativity simulations are necessary to understand accurately the merger stage of compact binary coalescences. In general relativity, valid initial data have to satisfy Hamiltonian and momentum constraints (reminiscent of divergence equations in Maxwell theory). Furthermore, astrophysically realistic time-evolution simulations can be performed only with astrophysically realistic initial data. These facts require us to solve constraint equations imposing realistic conditions. In this seminar, I will review the method to derive desirable initial data of compact object binaries for numerical relativity with a blackboad.
E. Gourgoulhon [gr-qc/0703035] (review)

Tatsuhiro Misumi, Akita University

't Hooft anomaly matching for circle compactification

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
Anomaly matching constrains low-energy physics of strongly-coupled field theories. It has been recently extended to the theories with one-form symmetries including SU(N) Yang-Mills theory with theta=pi. In this talk, we show that we develop a systematic procedure for deriving an ’t Hooft anomaly of the circle-compactified theory starting from the anomaly of the original uncompactified theory without one-form symmetries, where the twisted boundary condition for the compactified direction plays a pivotal role. As an application, we consider ZN-twisted CP^N-1 sigma model and massless ZN-QCD, and compute their anomalies explicitly. We also discuss constraints on finite-(T,mu) phase diagram of ZN-QCD based on the anomaly matching.

Kouji Nakamura, National Astronomical Observatory of Japan

Extension of the input–output relation for a Michelson interferometer to arbitrary coherent-state light sources: --- Gravitational-wave detector and weak-value amplification ---

Seminar room, Kenkyu honkan 3F
An extension of the input–output relation for a conventional Michelson interferometric gravitational-wave detector is carried out to treat an arbitrary coherent state for the injected optical beam. This extension is one of necessary researches toward the clarification of the relation between conventional gravitational-wave detectors and a simple model of a gravitational-wave detector inspired by weak-measurements in [Nishizawa, Phys. Rev. A vol.92 (2015), 032123.]. The derived input–output relation describes not only a conventional Michelson-interferometric gravitational-wave detector but also the situation of weak measurements. As a result, we may say that a conventional Michelson gravitational-wave detector already includes the essence of the weak-value amplification as the reduction of the quantum noise from the light source through the measurement at the dark port.

Nagisa Hiroshima, KEK/U. Tokyo

Modeling evolution of Dark Matter substructure and annihilation boost

Meeting room 1, Kenkyu honkan 1F
We study evolution of dark matter substructures, especially how they lose the mass and change density profile after they fall in gravitational potential of larger host halos. We develop an analytical prescription that models the subhalo mass evolution and calibrate it to results of N-body numerical simulations of various scales from very small (Earth size) to large (galaxies to clusters) halos. We then combine the results with halo accretion histories, and calculate the subhalo mass function that is physically motivated down to Earth-mass scales. Our results — valid for arbitrary host masses and redshifts — show reasonable agreement with those of numerical simulations at resolved scales. Our analytical model also enables self-consistent calculations of the boost factor of dark matter annhilation, which we find to increase from tens of percent at the smallest (Earth) and intermediate (dwarfs) masses to a factor of several at galaxy size, and to become as large as a factor of ?10 for the largest halos (clusters) at small redshifts. Our analytical approach can accommodate substructures in the subhalos (sub-subhalos) in a consistent framework, which we find to give up to a factor of a few enhancement to the annihilation boost. Presence of the subhalos enhances the intensity of the isotropic gamma-ray background by a factor of a few, and as the result, the measurement by Fermi Large Area Telescope excludes the annihilation cross section greater than ?4×10?26 cm3 s?1 for dark matter masses up to ?200 GeV.
arXiv 1803.07691、1403.6827

Fumihiko Sugino, Institute for Basic Science

Highly entangled quantum spin chains and their extensions by semigroups

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
Quantum entanglement is the most surprising feature of quantum mechanics, and plays a crucial role in quantum computation. Ground states of quantum many-body systems typically exhibit the area law behavior in the entanglement entropy, which measures the amount of entanglement between a subsystem and the rest of the system. Recently, a class of solvable one-dimensional spin models with local interactions has been constructed by Mavassagh and Shor and by Salberger and Korepin, in which the ground state is expressed as a superposition of random walks, and has much larger entanglement. Its entanglement entropy is shown to be proportional to the square root of the volume. In this talk, after a brief review of the models, we construct extensions of these models based on the symmetric inverse semigroup, and discuss properties of ground states with the entanglement entropy. As a new feature arising by the extension, there are excited states with Anderson localization properties.

Akihiro Suzuki, National Astronomical Observatory of Japan

Core-collapse supernovae and the final evolutionary states of massive stars

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
Massive stars play important roles in the star-forming history of galaxies throughout cosmic time. They end their lives by producing a violent explosion caused by the gravitational collapse of the iron core, called core-collapse supernovae(CCSNe). They give rise to bright optical emission, thereby making them an important tool to investigating star-forming activities of distant galaxies. One of the fundamental questions on massive star evolution is how to connect massive stars born in a specific environment to various types of CCSNe and compact remnants. This problem is still difficult to solve because of the complex interplay of various physical processes involved in massive star evolution and the explosion mechanism of core-collapse supernova themselves. Therefore, it appears that we still have a long way to go. However, recent observational and theoretical progresses, such as, progenitor detections in HST archival images and numerical modelings of CCSNe by massively parallel supercomputers, have gradually made important steps toward the ultimate goal. In this talk, I review observational features CCSNe and discuss recent topics.

Okuto Morikawa, Department of Physics, Kyushu University

Gradient flow and the Wilsonian renormalization group flow (in Japanese)

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
The gradient flow is the evolution of fields and physical quantities along a dimensionful parameter t, the flow time. We give a simple argument that relates this gradient flow and the Wilsonian renormalization group (RG) flow. We then illustrate the Wilsonian RG flow on the basis of the gradient flow in two examples that possess an infrared fixed point, the 4D many-flavor gauge theory and the 3D O(N) linear sigma model.
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