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)
Cosmic strings had been studied originally as potential seeds of the large-scale structure of the Universe, which had eventually been replaced by inflation, but the recent concern on them would be an aspect as a possible source of gravitational waves. The cosmic strings have a network structure spread over superhorizon scales, and their reconnection process is crucial for their networks to evade the strong observational constraints and thus to survive in the present time. In this talk, we show our recent numerical works on the reconnection process and the time-evolution of cosmic strings networks based on the 3D field-theoretic simulations. Furthermore, we introduce some preliminary results on the gravitational waves radiated from the cosmic strings networks.
Miguel Vazquez-Mozo, Universidad de Salamanca
Planar Zeros in Field and String Theory Amplitudes
Meeting room 3, Kenkyu honkan 1F, slides (kek.jp only)
Planar zeros are an interesting feature of certain scattering amplitudes with one or more gauge bosons radiated, consisting in the vanishing of the amplitude for configurations where all momenta lie on a single plane. In this talk I shall study these planar zeros in various field theories at tree-level. In the case of theories with gauge invariance, the zeros are determined by the vanishing of a homogeneous polynomial in the stereographic coordinates determining the direction of flight of the particles involved. This projective property is absent in pure scalar theories. In gravitational theories, on the other hand, amplitudes vanish whenever the scattering is planar. String theory corrections to the field theory amplitudes spoil the projective nature of gauge planar zeros, as well as the vanishing of gravitational planar amplitudes.
中村孝明, 高知工科大学
グラフ上の非線形シュレディンガー方程式
Seminar room, Kenkyu honkan 3F 非線形シュレディンガー方程式 (Nonlinear Schrödinger equation)は、ボーズ＝アインシュタイン凝縮系を記述すると同時に、渦糸、光ファイバー中パルス波等の様々な物理系にも現れる。近年、単純な系であるグラフ上での非線形シュレディンガー方程式の研究が盛んになっている。この講演では、非線形シュレディンガー方程式の基礎的性質の解説とともに、フロップ筒井型点欠陥を課したリング上での系の固有値の安定性の議論を紹介する。またこの系の数値的な解析から得られた、順位交差や反発、新奇量子ホロノミーやベリー位相の存在について論じ、さらには、線形系には見られないエネルギー準位の一部消滅といった現象についても解説する。
非線形シュレディンガー方程式 (Nonlinear Schrödinger equation)は、ボーズ＝アインシュタイン凝縮系を記述すると同時に、渦糸、光ファイバー中パルス波等の様々な物理系にも現れる。近年、単純な系であるグラフ上での非線形シュレディンガー方程式の研究が盛んになっている。この講演では、非線形シュレディンガー方程式の基礎的性質の解説とともに、フロップ筒井型点欠陥を課したリング上での系の固有値の安定性の議論を紹介する。またこの系の数値的な解析から得られた、順位交差や反発、新奇量子ホロノミーやベリー位相の存在について論じ、さらには、線形系には見られないエネルギー準位の一部消滅といった現象についても解説する。
References:T.Nakamura, T. Cheon, “Spectral properties of nonlinear Schro dinger equation on a ring” to be published in J. Phys. Soc. Jpn. (arXiv: 1706.08695)
Masazumi Honda, Weizmann Institute of Science
Recent progress on resurgence
Meeing room 1, Kenkyu honkan 1F I will review recent progress on a resummation technique called “resurgence”, which has received much attention in the past 5 years in the context of weak coupling perturbative series in quantum field theory. I will begin with general expectation on perturbative series in quantum field theory and explain an idea of resurgence with some simple examples. Then I will ask whether we can apply resurgence to interesting quantum field theories such as QCD.
I will review recent progress on a resummation technique called “resurgence”, which has received much attention in the past 5 years in the context of weak coupling perturbative series in quantum field theory. I will begin with general expectation on perturbative series in quantum field theory and explain an idea of resurgence with some simple examples. Then I will ask whether we can apply resurgence to interesting quantum field theories such as QCD.
Although this is still open question, I will discuss what should be done to answer this question and introduce recent ideas, which may be useful for this problem.
Masaru Hongo, RIKEN
Relativistic hydrodynamics from quantum field theory
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only) Hydrodynamics is a low-energy effective theory which describes a long-distance and long-time behavior of many-body systems. It is applicable not only to a non-relativistic weakly-interacting dilute gas but also a relativistic strongly-interacting dense liquid such as the quark-gluon plasma created in ultra relativistic heavy-ion collision experiments. Although relativistic hydrodynamics itself is well-established formalism, its foundation from underlying microscopic theories, or quantum field theories, remains unclear. In this study, based on the recent development of non-equilibrium statistical mechanics, we provide the field-theoretical derivation of the relativistic Navier-Stokes equation [1]. We show that the procedure to derive hydrodynamic equations is similar to the so-called renormalized/optimized perturbation theory. Furthermore, we give a path-integral formula for local thermal equilibrium which results in the emergence of thermally induced curved spacetime [2]. Based on these results, we perform the derivative expansion and derive the first-order hydrodynamic equation (the Navier-Stokes equation) with the Green-Kubo formulas for transport coefficients.
Hydrodynamics is a low-energy effective theory which describes a long-distance and long-time behavior of many-body systems. It is applicable not only to a non-relativistic weakly-interacting dilute gas but also a relativistic strongly-interacting dense liquid such as the quark-gluon plasma created in ultra relativistic heavy-ion collision experiments. Although relativistic hydrodynamics itself is well-established formalism, its foundation from underlying microscopic theories, or quantum field theories, remains unclear. In this study, based on the recent development of non-equilibrium statistical mechanics, we provide the field-theoretical derivation of the relativistic Navier-Stokes equation [1]. We show that the procedure to derive hydrodynamic equations is similar to the so-called renormalized/optimized perturbation theory. Furthermore, we give a path-integral formula for local thermal equilibrium which results in the emergence of thermally induced curved spacetime [2]. Based on these results, we perform the derivative expansion and derive the first-order hydrodynamic equation (the Navier-Stokes equation) with the Green-Kubo formulas for transport coefficients.
References:
[1] T. Hayata, Y. Hidaka, M. Hongo, and T. Noumi, Phys. Rev. D 92, 065008 (2015)
[1] M. Hongo, Annals of Physics, 383, 1 (2017)
Ippei Danshita, YITP Kyoto University
A proposal for experimental realization of the Sachdev-Ye-Kitaev model with ultracold gases
Seminar room, Kenkyu honkan 3F The Sachdev-Ye-Kitaev (SYK) model consists of Q fermions with an all-to-all random two-body hopping [1,2]. Its static state is a non-Fermi liquid with nonzero entropy at vanishing temperature, which is called the Sachdev-Ye (SY) state [3]. Since the SY state has been conjectured to be holographically dual to charged black holes with two-dimensional anti-de Sitter horizons, the SYK model has attracted much attention as a new theoretical tool for studying quantum gravity (see, e.g., Ref. [4]). In this work, we propose a possible route for realizing the SYK model experimentally with use of ultracold gases in optical lattices [5]. We also show how to measure out-of-time-order correlators of the SYK model, which may allow for capturing one of the most crucial characteristics of a black hole, namely maximally chaotic property.
The Sachdev-Ye-Kitaev (SYK) model consists of Q fermions with an all-to-all random two-body hopping [1,2]. Its static state is a non-Fermi liquid with nonzero entropy at vanishing temperature, which is called the Sachdev-Ye (SY) state [3]. Since the SY state has been conjectured to be holographically dual to charged black holes with two-dimensional anti-de Sitter horizons, the SYK model has attracted much attention as a new theoretical tool for studying quantum gravity (see, e.g., Ref. [4]). In this work, we propose a possible route for realizing the SYK model experimentally with use of ultracold gases in optical lattices [5]. We also show how to measure out-of-time-order correlators of the SYK model, which may allow for capturing one of the most crucial characteristics of a black hole, namely maximally chaotic property.
[1] A. Y. Kitaev, “A simple model of quantum holograpy”, KITP string seminar and Entanglement 2015 program (Feb. 12, April 7, and May 27, 2015). http://online.kitp.ucsb.edu/online/entangled15/.
[2] S. Sachdev, Phys. Rev. X 5, 041025 (2015).
[3] S. Sachdev and J. Ye, Phys. Rev. Lett. 70, 3339 (1993).
[4] J. Maldacena and D. Stanford, Phys. Rev. D 94, 106002 (2016).
[5] I. Danshita, M. Hanada, and M. Tezuka, arXiv:1606.02454v2 [cond-mat.quant-gas], to appear in PTEP.
Jianwei Qiu, Jefferson Lab
Explore hadron structure from the first principle lattice QCD calculations
Seminar room, Kenkyu honkan 3F
Parton distribution and correlation functions describe the relation between a hadron and the quarks and gluons (or partons) within it, and carry rich information on hadron’s partonic structure. They cannot be calculated by QCD perturbation theory, and have been extracted from experimental data of high energy scattering cross sections with the aid of QCD factorization. Parton distribution functions are the simplest of all correlation functions. Without them, we would not be able to understand the hard probes in hadronic collisions, including the Higgs discovery at the LHC. In this talk, I will discuss how can the QCD factorization help extract the same parton distribution and correlation functions from various “lattice cross sections” – hadron matrix elements that can be systematically calculated by using lattice QCD techniques. With the ab initio lattice QCD calculations, complementary to the experimental measurements, I argue that we are entering a new era of exploring hadron’s internal structure in terms of the dynamics of quarks and gluons.
Heng-Yu Chen, National Taiwan University
Aspects of Spinning CFT correlators and Witten Diagrams
Seminar room, Kenkyu honkan 3F
