齊藤英治, 東北大学
[第三回KEK連携コロキウム] スピン流とスピントロニクスの物理
つくばキャンパス3号館1階セミナー ホール/東海キャンパス(TV会議中継) 東海1号館324号室 スピン流は物質中のスピン角運動量の流れです。最新のナノテクノロジーにより、スピン流を実験的に捉えることができるようになり、スピンを用いたエレクトロニクス「スピントロニクス」が急速に進展しました。
スピン流は物質中のスピン角運動量の流れです。最新のナノテクノロジーにより、スピン流を実験的に捉えることができるようになり、スピンを用いたエレクトロニクス「スピントロニクス」が急速に進展しました。
スピン流の基礎物理は幾何学的位相や相対論など物理学の面白く美しい部分と深く繋がっていることが明らかになり、他方でスピン流の概念はメモリデバイス開発等へ応用が進み、その一部は実用化に至っています。
講演では、スピン流の基礎概念を紹介し、研究の現場の活気とともに最新の成果のいくつかを紹介する予定です。
Kazuo Hosomichi, National Defense Academy
Supersymmetric vortex defects in two dimensions
Meeting room1, Kenkyu honkan 1F, slides (kek.jp only)
We study codimension-two BPS defects in 2d N=(2,2) supersymmetric gauge theories, focusing especially on those characterized by vortex-like singularities in the dynamical or non-dynamical gauge field. We classify possible SUSY-preserving boundary conditions on charged matter fields around the vortex defects, and derive a formula for defect correlators on the squashed sphere. We also prove an equivalence relation between vortex defects and 0d-2d coupled systems. Our defect correlators are shown to be consistent with the mirror symmetry duality between Abelian gauged linear sigma models and Landau-Ginzburg models, as well as that between the minimal model and its orbifold. We also study the vortex defects inserted at conical singularities.
Yasha Neiman, Okinawa Institute of Science and Technology
From infinity to the horizon through twistor space
Meeting room 1, Kenkyu honkan 1F
I will outline an ongoing research program, aimed at deriving the physics inside an observable patch of de Sitter space from dS/CFT. The approach is a marriage between the higher-spin realization of dS_4/CFT_3 by Strominger et.al. and the suggestion by Verlinde et.al. to consider a folded-in-half version of de Sitter space, where the information content in a causal patch is the same as at the asymptotic boundary. I will briefly describe two threads of results. The first is a completed dictionary between the CFT and the bulk causal-patch physics, in the limit of free bulk fields. The second is a new dictionary between the full boundary theory and twistor space, which should take us beyond the linearized bulk limit.
Jnanadeva Maharana, Institute of Physics, Bhubaneswar
Analyticity of Scattering Amplitude in Higher Dimensional Theories
Seminar room, Kenkyu honkan 3F, slides (kek.jp only)
Theories in higher spacetime dimensions (D>4) have been topics of research for several years. Moreover, there are models where the extra compact dimension might have large radius and we might discover new phenomena even at LHC. I shall discuss field theories in higher dimensions and derive analyticity property of scattering amplitude within the frame works of LSZ formalism. The analog of Froissart bound will be derived.
Toyokazu Sekiguchi, Tokyo University, RESCEU
[Cosmophysics group seminar] Cosmological applications of axion electrodynamics
Meeting room 3, Kenkyu honkan 1F
The axion and axion-like particles originate from a variety of UV theories based on QFT as well as string theory. Couplings of those axions with U(1) gauge fields are fairly ubiquitous. They are known to offer rich phenomenology in the very early Universe, for instance, inflation and preheating. In my talk I’m going to focus on their rolls at later epoch when the Universe is dominated by the radiation. In the first part of my talk, such an axion is identified with the QCD axion. It is recently argued that coupling of the axion to a hidden U(1) field suppresses the axion CDM abundance, which can open up the axion window up to the GUT scale. The claim postulates that production of the axion fluctuations is negligible. We revisit the argument by performing 3d lattice simulations of the axion electrodynamics, where the nonlinear dynamics in the coevolution of the axion fluctuations and gauge field is incorporated to the full extent. We show production of the axion fluctuations plays a crucial roll and the suppression is moderated significantly. In the latter part, I will discuss an application to the cosmological relaxation, which we show can be compatible with reheating temperature higher than the electroweak scale.
Marcus Sperling, University of Vienna
Covariant fuzzy spaces, matrix models and higher spin
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
In this talk, I will discuss the generalised and basic fuzzy 4-sphere in the context of the IKKT matrix model. These spaces arise as SO(5)-equivariant projections of quantised SO(6) coadjoint orbits and exhibit full SO(5) covariance. I will sketch how (basic and generalised) 4-sphere arise as solutions in a Yang-Mills matrix model, such that the fluctuations on the 4-sphere lead to a higher-spin gauge theory.
Yasuhiro Yamaguchi, RIKEN Nishina Center
Hidden-charm meson-baryon molecules coupled with five-quark states
Meeting room 1, Kenkyu honkan 1F
We investigate the hidden-charm pentaquarks as $¥bar{D}^{(¥ast)}¥Lambda_{¥rm c}$ and $¥bar{D}^{(¥ast)}¥Sigma^{(¥ast)}_{¥rm c}$ molecules coupled to the compact five-quark states. The coupling to the five-quark states is treated as the short range potential, where the relative strength for the meson-baryon channels is determined by the structure of the five-quark states. Introducing the five-quark state potential and the one pion exchange potential, the coupled-channel Schrodinger equations are solved. We found that resonant and bound states appear, where the five-quark state potential plays an important role to produce these states. We also report the results in the hidden-bottom sector.
濱村一航, 京都大学
量子論の合成系の構造
Seminar room, Kenkyu honkan 3F
近年、量子情報理論の進展に伴い量子論の公理を物理的あるいは情報的に意味のあるものに書き換えよういう試みが盛んになっている。「量子状態はヒルベルト空間を用いて表される」という公理の導出は最も重要であるが、それだけで他の全ての公理が直ちに導出できるというわけではなく、「合成系はヒルベルト空間のテンソル積で表される」という合成系の公理は明らかではない。ここでは量子論の局所系はヒルベルト空間で表されることを認めた上で、合成系の候補を絞っていくことを考えた。特に情報因果律など多くの物理的要請を満たす最大テンソル積状態空間を状態空間の候補から除外するため、状態について定義されていたエンタングルメントを物理量に拡張した。物理量のエンタングルメントと最大テンソル積状態空間は相容れない。測定出力として二値を取る物理量のエンタングルメントを検出することを考え、セパラブルな二値測定について成り立つBell-CHSH不等式の双対版を示した。
Daiki Suenaga, Nagoya University
Spectral functions for D and D0* mesons in nuclear matter with partial restoration of chiral symmetry
Seminar room, Kenkyu honkan 3F
We investigate the in-medium masses of a $¥bar{D}$ $(0^-)$ meson and a $¥bar{D}^*_0$ $(0^+)$ meson, and spectral functions for $¥bar{D}$ and $¥bar{D}_0^*$ meson channels in nuclear matter. These mesons are introduced as chiral partners in the chiral-symmetry-broken vacuum, hence they are useful to explore the partial restoration of the broken chiral symmetry in nuclear matter. We consider the linear sigma model to describe the chiral symmetry breaking and to investigate a qualitative tendency of changes of $¥bar{D}$ mesons at low density. Our study shows that the loop corrections to $¥bar{D}$ and $¥bar{D}_0^*$ meson masses provide a smaller mass splitting at finite density than that in vacuum, a result that indicates a tendency of the restoration of the chiral symmetry. We investigate also the spectral function for $¥bar{D}_0^*$ meson channel, and find three peaks. The first peak, which corresponds to the resonance of the $¥bar{D}_0^*$ meson, is broadened by collisions with nucleons in medium, and the peak position shifts to lower mass due to the partial restoration of chiral symmetry as the density increases. The second peak is identified as a threshold enhancement which shows a remarkable enhancement as the density increases. The third peak is Landau damping. The obtained properties of $¥bar{D}$ and $¥bar{D}_0^*$ mesons in nuclear matter will provide useful information for experiments.
Takashi Hiramatsu, Rikkyo University
Field-theoretic simulations of cosmic strings
Meeting Room 3, Kenkyu-Honkan Building 1F, slides (kek.jp only)
