セミナー 2013年

Keiju Murata, Keio U

Electric Field Quench in AdS/CFT

Meeting room 1, Kenkyu honkan 1F
An electric field quench, a suddenly applied electric field, can induce nontrivial dynamics in confining systems which may lead to thermalization as well as a deconfinement transition. In order to analyze this nonequilibrium transitions, we use the AdS/CFT correspondence for N=2 supersymmetric QCD that has a confining meson sector. We find that the electric field quench causes the deconfinement transition even when the magnitude of the applied electric field is smaller than the critical value for the static case (which is the QCD Schwinger limit for quark-antiquark pair creation). The time dependence is crucial for this phenomenon, and the gravity dual explains it as the weakly turbulent instability of a D-brane in the bulk AdS spacetime. Interestingly, the d econfinement time takes only discrete values as a function of the magnitude of the electric field. We advocate that the new deconfinement phenomenon is analogous to the exciton Mott transition.

Satoshi Nakamura, Osaka University

[Paricle and Nuclear Physics Seminar at J-PARC] Neutrino-induced meson productions off nucleon in resonance region

Tokai 1st building 115
Future neutrino experiments are planned to address questions such as leptonic CP violation and mass hierarchy. For this purpose, it is essential to have more quantitative understanding of the neutrino-nucleus scattering. The neutrino energy spans rather wide range including the nucleon resonance region for which we have been working. We have developed a dynamical coupled-channels (DCC) model that describes piN, gamma N -> piN, etaN, KLambda, KSigma reactions. We extend the DCC model to work on the neutrino reactions. In this presentation, I explain the DCC model, and show the quality of the fit to the piN and gammaN data. Then I discuss our strategy for extending the DCC model to the neutrino reactions. As a first step, we study the forward neutrino-induced meson productions using the PCAC hypothesis, for which I present numerical results.

Yoichi Iwasaki, KEK

Global Structure of Conformal Theories in the SU(3) Gauge Theory

Meeting room1, Kenkyu honkan 1F
We investigate SU(3) gauge theories in four dimensions with N_f fundamental fermions, on a lattice using the Wilson fermion. We first introduce a new concept “conformal theories with an IR cutoff’, after pointing out that the following two categories in SU(3) gauge theories with fundamental N_f fermions possess an IR fixed point: Large N_f (N_f^c ≦ N_f ≦ 16) QCD within the conformal window (referred as Conformal QCD) and small N_f (1 ≦ N_f ≦ N_f^c-1) QCD at temperature T/T_c > 1 (referred as High Temperature QCD). In the case of Conformal QCD in the continuum limit, the compact space and/or time gives an IR cutoff. In the case of High Temperature QCD, the temperature T plays a role of an IR cutoff together with a cutoff due to possible compact space, depending on how to take the continuum limit. We note any lattice calculation is performed on a finite lattice. Thus any calculation on a lattice possesses an IR cutoff. In the conformal theories with an IR cutoff there exists the “conformal region” together with the confining region and the deconfining region. We verify numerically on a lattice of the size 16^3×64 the existence of the conformal region and the non-trivial Z(3) structure of the vacuum and the Yukawa-type decay form of meson propagators in the conformal region. We stress that High Temperature QCD is intrinsically accompanied with an IR cutoff. Therefore the understanding the vacuum structure and the property of correlation functions is the key to resolve long standing issues in High Temperature QCD. We further argue that there is a precise correspondence between Conformal QCD and High Temperature QCD in the temporal propagators under the change of the parameters N_f and T/T_c respectively: the one boundary is close to meson states and the other is close to free quark states. In particular, we find the correspondence between Conformal QCD with N_f = 7 and High Temperature QCD with N_f=2 at T~2, T_c being in close relation to a meson unparticle model. From this we estimate the anomalous mass dimension γ* = 1.2 (1) for N_f=7.

Shion Chen, University of Tokyo

コライダー実験における崩壊粒子の運動量エンタング ルメントを用いたベル不 等式検証

Seminar Room, Kenkyu Honkan 3F
ベルの不等式は 2 粒子間の相関について、古典論が満たすべき上限を与える式である。量子論の下では、 エンタングル状態など特定の条件下で不等式が破れることが知られており、いわば古典論と量子論の判別式のようなものである。これまで既に多数の光学実験において破れが報告され、量子論の「勝利」はほぼ確定したが、フェルミオンや質量のある粒子系での実験例は依然として少ない。しかし量子力学の普遍性検証という観点において、また一般に重い粒子は古典性が強いという点で、これらの系での検証は非常に興味深い。また、未だよく理解されてない量子力学の非局所性などの性質を探る上でも重要である。
高エネルギーコライダー実験で生成される不安定粒子は、その崩壊で様々なエンタングル状態を生じるため、これらの検証手段として有望である。 我々は今回チャーモニウム崩壊J/ψ, ηc, χc0→ΛΛ→pπpπに主に着目した。チャーモニウムから崩壊したΛΛのペアはヘリシティー・エンタングル状態を形成する。ΛΛ対は続けて弱崩壊Λ→pπ-, Λbar→pbar π+を行うが、この崩壊では崩壊角分布が親粒子の偏極の方向と相関を持つ。従って終状態のπ+π-は親粒子の性質を引き継いで互いの運動量がエンタングルし、量子論では2つπの方向が古典論の予言を超えた大きな相関を予想する。この性質を用いたベル不等式および量子力学の検証は1980年代に提案されたが、BES実験などのチャームファクトリーの登場により近年になって理論・実験双方からのアプローチが盛んになってきた。今回講演ではこれらに関する近年のアクティビティや、我々が行った新しいベルの不等式検証の定式化および実験可能性について論ずる。さらに同様の崩壊構造を持つZ→ττ→πνπν、H→τ
τ→πνπνに関しても検討し、超高エネルギー実験における量子力学基礎実験のポテンシャルについても考えてみようと思う。(これはHiggs bosonを応用する初の試みである!)

Toshifumi Noumi, RIKEN

Effects of heavy fields during inflation

Meeting room 3, Kenkyu honkan 1F
Effects of heavy fields during inflation will be discussed. Inflationary models based on high energy theories, such as supergravity and superstring theory, generically contain heavy scalar fields in addition to the inflaton. Such heavy scalar fields could be therefore used as a probe of high energy physics. In this talk, I will discuss multi-field inflation models with a turning background trajectory, as a possible scenario heavy fields can affect inflationary dynamics. When heavy fields are excited after the turn and oscillate around the bottom of the potential, the following two effects are generically induced: deformation of the inflationary background spacetime and conversion interactions between adiabatic and isocurvature perturbations. I will discuss such effects on primordial power spectra of curvature perturbations.

Tomohiro Nakama, RESCEU

Revealing the formation condition of primordial black holes by numerical simulations

Meeting room 1, Kenkyu honkan 1F
Primordial black holes (PBHs) are an important tool in cosmology to probe the primordial spectrum of small-scale curvature perturbations that reenter the cosmological horizon during radiation domination epoch. We numerically solve the evolution of spherically symmetric highly perturbed configurations to clarify the criteria of PBHs formation using an extremely wide class of curvature profiles characterized by five parameters, (in contrast to only two parameters used in all previous papers) which specify the curvature profiles not only at the central region but also at the outer boundary of configurations. It is shown that formation or non-formation of PBHs is determined entirely by only two master parameters one of which can be presented as an integral of curvature over initial configurations and the other is presented in terms of the position of the core and the boundary.

Noriaki Kitazawa, Tokyo Metropolitan University

Towards constructing realistic string models with D-branes

Meeting Room 1, Kenkyu-Honkan 1F
In the first part of the seminar some basic ingredients of the string models of particle physics are reviewed. The mechanisms to obtain chiral fermion spectrum at the intersection of D-branes or on the D-branes at a singularity are briefly explained. An attempt to construct a model with non-trivial Yukawa couplings is introduced. In the second part of the seminar two systems of D-branes without supersymmetry are introduced; the system of D-branes at non-supersymmetric orbifold fixed point, and the system of so called “brane supersymmetry breaking”. The NS-NS tadpole problem of non-supersymmetric system is discussed. The possible spontaneous gauge symmetry breaking in two concrete models, corresponding to the above two systems, is discussed.

川合光, 京都大学

砂漠と自然性 -場の理論をこえて-

Meeting room 1, Kenkyu honkan 1F
LHCの結果によると、超対称性は低エネルギーには見当たらず、しかもHiggs粒子は基本粒子と考えてもよい。そうすると次に問題となるのは、どれくらい大きいエネルギースケールまで標準模型が有効かということであるが、Higgs質量が決定されたため精度のよい解析ができるようになった。まだ、トップクォーク質量の誤差からくるあいまいさはあるが、弱電磁スケールからプランクスケールの間には なにもない砂漠である可能性がでてきた。これは、標準模型の物理とプランクスケールの物理が直接つながっているということであり、それらの統合をはかることが素粒子物理学の次の目標であることを意味している。そのための重要な手掛かりとなるのが宇宙項およびスカラー質量の自然性の問題である。従来、自然性は超対称性との関連で議論されることが多かったが、上記の実験結果はより広い視野から議論しなおす必要性を示している。自然性問題を再考するため、従来の結果を損なうことなく、場の理論を少しはみ出すいくつかの試みについて議論する。

Takahisa Igata, Osaka City U

Stable Bound Orbits of Massless Particles in Myers-Perry Black Holes

Meeting room 1, 3 go-kan 1F
No stable circular orbits of a particle exist in higher-dimensional Schwarzschild black holes because of the dependence of gravitational potential on spacetime dimensions. We find, however, that stable bound orbits of a particle in Myers-Perry black holes appear as black hole spin increases. In this talk we discuss the appearance of stable bound orbits of a massless particle in six-dimensional Myers-Perry black hole and some application.

Ryosuke Sato, KEK

Effective gravitational interactions of dark matter axions

Meeting Room 1, Kenkyu Honkan 1F
We investigate the structure of gravitational self interactions of coherently oscillating axions in the general relativistic framework. A generic action for a massive scalar field in the Friedmann-Robertson-Walker background is first introduced based on the effective field theory approach to cosmological perturbations. Using the obtained setup, we evaluate the effective gravitational interaction of the massive scalar field, i.e. scalar quartic interactions mediated by metric perturbations. Applying the results to the system of dark matter axions, we estimate the self interaction rate of them, and discuss its implications for axion Bose-Einstein condensate dark matter scenario. Leading contributions for gravitational interactions of axions are given by the process mediated by the dynamical graviton field, which is essentially the Newtonian potential induced by fluctuations of the background fluids. We find that it leads to the same order of magnitude for the interaction rate of dark matter axions in the condensed regime, compared with the result of previous studies using the Newtonian approximation.

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