岡本亮, 京都大学
量子系の時間発展と弱値
Meeting room 3, Kenkyu honkan 1F
量子系では，「観測」がその後の量子状態の時間発展に大きな影響を及ぼす．例えば，ある時刻に，光子の位置の射影測定を行った場合，その後の光子の位置の時間発展は，測定を行わなかった場合と大きく異なってしまう．同様に，光子の位置の射影測定を行った後，運動量の射影測定を行ったとしても，位置測定以前の運動量の正確な情報を得ることはできない．従って，射影測定を用いて，光子が辿る軌跡を問うこと無意味である．一方，射影測定ではなく，「弱測定」と呼ばれる測定手法，および弱測定結果から得られる「弱値」を用いると，この問いに答えることができる．例えば，トロント大学の研究グループは，2重スリットの実験において，弱測定を用いることで，光子の軌跡を記録することに成功している．また，位置と運動量のような，非可換な観測量の同時測定が，連続的な弱測定によって実現されている．これにより，パラドキシカルな弱値の間の関係性といった従来アクセスできなかった情報を得ることが可能になっている．本講演では，時間発展する量子系の弱値について，光子を用いた実験を軸に概観するとともに，最近の我々の研究結果について紹介する．
Yusuke Yamada, Research center for the early universe (RESCEU), University of Tokyo
Nonlinear realization in supergravity and its application
Meeting room 3, Kenkyu honkan 1F
Spontaneously broken supersymmetry plays important roles in supergravity model buildings. Below the supersymmetry breaking scale, the effective theory is well described by nonlinear realizations of supergravity. We show two applications of nonlinearly realized supergravity: One is the effective action of anti-D3 brane in KKLT background. The KKLT model is well known as the string realization of de Sitter vacua. The anti-D3 brane plays an important role in uplifting the vacuum. We show that the world volume fields on anti-D3 brane and their couplings are described in terms of the constrained superfields (nonlinear realizations). Secondly, we show that the nonlinear realization is useful to realize non-supersymmetric models within supergravity. As an example, we show the embedding of the Horndeski model into supergravity, which describes the most general ghost-free scalar-tensor system.
Takumi Doi, RIKEN Nishina Center for Accelerator-Based Science
Nuclear Physics from Lattice QCD
Meeting Room 1, Kenkyu honkan 1F
One of the most fundamental questions in nuclear physics is how nuclear physics itself emerges from the underlying theory, quantum chromodynamics (QCD), and the determination of baryon forces from QCD plays a crucial role to answer this question. In this talk, I review the first-principles lattice QCD calculation of baryon forces as well as general hadron-hadron interactions. I introduce a novel theoretical framework, HAL QCD method, and present the latest lattice QCD results, in particular, those obtained near the physical point. The physical implications for exotic dibaryons, equation of state of high dense matter and the structure of neutron stars are also discussed and future prospects will be given.
Sota Nakajima, Osaka City University
Exponentially suppressed cosmological constant with enhanced gauge symmetry in heterotic interpolating models
Meeting room 1, Kenkyu honkan 1F
An interpolating model is a (D－ d)-dimensional string model that continuously relates two D-dimensional string models. A few nine-dimensional interpolating models with two parameters are constructed and the massless spectra are studied by considering compactification of heterotic strings on a twisted circle with Wilson line. It is found that there are some conditions between radius R and Wilson line A under which the gauge symmetry is enhanced. In particular, when the gauge symmetry is enhanced to SO(18) \times SO(14), the cosmological constant is exponentially suppressed. We also construct a non-supersymmetric string model which is tachyon-free in all regions of moduli space and whose gauge symmetry involves E_8. This talk will be based on the work with H. Itoyama, arXiv: 1905.10745.
小川和久, 北海道大学
プローブを用いない弱値の直接測定法
Seminar room, Kenkyu honkan 3F
事前・事後選択されたシステム（事前・事後選択系）における弱い値は、典型的には弱測定によって測定され、そこではプローブ系は被測定系と弱い相互作用をする。しかし弱測定では、プローブ系として被測定系の他に追加の自由度を準備する必要性があるため、弱値測定のための実験系は一般に複雑になる。本研究では、事前・事後選択系がほとんど乱されないという従来の弱測定が持つ条件を保ちながら、プローブを用いずに弱値を直接測定する方法を提案する。この方法では、事前選択と事後選択の間に小さな変換が与えた時に、選択後の確率振幅の変化に小さな変換の微分の弱値が現れる。この方法は基本的に弱値を測定する全ての実験に適用することができ、弱値測定のための実験系を単純化することができる。
Shohei Saga, JSPS Fellow, Yukawa Institute for Theoretical Physics
The vector mode in the observational cosmology
Meeting room 1, Kenkyu honkan 1F In the context of the cosmological perturbation theory, perturbations can be decomposed into the scalar, vector, and tensor modes. Current observations strongly support only the scalar mode. It is known that the vector mode does not arise from the linear perturbation theory in the standard cosmology.
In the context of the cosmological perturbation theory, perturbations can be decomposed into the scalar, vector, and tensor modes. Current observations strongly support only the scalar mode. It is known that the vector mode does not arise from the linear perturbation theory in the standard cosmology.
In this talk, I will introduce the second-order vector mode, which is inevitably generated in the standard cosmology. I also show the way to observe the vector-mode signature. Finally, I will mention a role of the second-order vector mode in observational cosmology.
Kouichi Hagino, Department of Physics, Graduate School of Science, Tohoku University
Perspectives on nuclear reaction theory and superheavy elements
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
The nuclear fusion reaction plays an important role in several phenomena in physics, such as the energy production in stars, nucleosynthesis, and a synthesis of superheavy elements. In particular, heavy-ion fusion reactions at energies around the Coulomb barrier are intriguing phenomena showing strong interplays between nuclear structure and nuclear reaction. For example, in medium-heavy systems, it has been known that fusion cross sections are largely enhanced relative to a prediction of a simple potential model, which has been interpreted in terms of quantum tunneling with many degrees of freedom. In this seminar, I will discuss quantum many-body dynamics of heavy-ion fusion reactions. To this end, I will summarize the current status of the field and will discuss future developments of nuclear reaction theory. I will put some emphasis on nuclear reaction for superheavy elements and will discuss future directions from a view point of multi-disciplinary science for systems in a strong Coulomb field.
Yoshimasa Hidaka, RIKEN
Kinetic theory with spin for massless and massive particles
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
We consider kinetic theory with spin (or helicity) degrees of freedom and its application. The spin plays an important role when particles are in a large magnetic or rotational field. This is the case in heavy-ion collision experiments, where the peripheral collision is expected to produce these large fields. In such a situation, anomalous transport phenomena (e.g., chiral magnetic and vortical effects) will occur due to the coupling between the spin and the magnetic field or the vorticity of fluid. We construct the kinetic theory for massless and massive particles based on quantum field theory and show the novel transport phenomena caused by interactions.
Hiroyuki Kitamoto, National Center for Theoretical Sciences
No-go theorem of anisotropic inflation via Schwinger mechanism
Seminar room, Kenkyu honkan 3F, slides (kek.jp only)
In the inflation theory with a dilatonic coupling between the inflaton and the U(1) gauge field, a persistent electric field (and then an anisotropic inflation) is obtained as a solution of the classical field equations. We studied the pair production of charged scalar particles in the inflaton-driven electric field. In particular, we evaluated the induced current due to the pair production. Solving the field equations with the induced current, we showed that the first-order backreaction screens the electric field with the cosmic expansion. This result indicates that the no-go theorem of anisotropic inflations holds true regardless of whether the dilatonic coupling is present or not. If time allows, we also comment on future directions of this topic, i.e. i) induced current on general backgrounds, ii) pair productions of charged fermions. This talk is based on Phys. Rev. D98 (2018) 103512 and work in progress
横田一広, 日本大学
弱値の基礎と応用
Meeting room 1, Kenkyu honkan 1F
