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
弱測定(weak measurement)は、量子系を乱さずに物理量を得る測定手法として、 1988年にY.Aharonovたちによって提唱された。弱測定の結果、測定器がアンサン ブル平均として示す値は弱値(weak value)と呼ばれる。 弱測定及び弱値は、量子基礎に対する新しいアプローチを提供するものとして、 近年注目されている。特に、量子の取り得る状態確率を古典粒子のように推論す るとパラドックスに陥るという「量子パラドックス」について、弱測定による実 験検証がなされてきた。本発表ではその例として「３つの箱のパラドックス」と 「ハーディのパラドックス」を取り上げる。量子パラドックスにおける弱値の一 部には、もはや確率とは見なせない－１という特異な値が見られ、全体としてパ ラドックスを回避するのに重要な役割を果たしている。そこで、このような特異 な弱値が、弱測定という文脈によらずに、物理的に意味のある指標となりうるか についても議論したい。 基礎研究の一方、弱測定と弱値については、新しい測定技術への応用の可能性も 見出されており、信号増幅による高感度測定や直接的状態トモグラフィーが盛ん に議論されている。後者について、単一ピクセルを用いた圧縮イメージング技術 を用いて、弱値による波動関数（波面）測定を行った研究が最近報告された。 我々の研究室でも現在、この圧縮イメージング技術を立ち上げようとしており、 弱値を使った応用を検討しているところである。本発表では、この先行研究につ いて紹介し、今後の応用研究について、幅広くご意見を伺えたらと考えている。
Tomo Takahashi, Saga University
Aspects of non-minimal inflation
Meeting room 1, Kenkyu honkan 1F
We discuss models of inflation where the inflaton is non-minimally coupled to gravity in some general setting, focusing on their predictions on inflationary observables such as the spectral index and tensor-to-scalar ratio. We consider both metric and Palatini formalisms of gravity and argue that how some inflation models can be alleviated by introducing a non-minimal coupling to gravity. The issues of distinguishing variants of such models are also discussed.
Andrew Lytle, INFN, Sezione di Roma Tor Vergata
b->c semileptonic decays and phenomenology
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
There are at the moment a number of long-standing discrepancies between observables in b->c semileptonic decays and their Standard Model predictions. In addition there is the long-standing tension between inclusive and exclusive determinations of Vcb, the latter being obtained from these same decays. Here I will discuss the state-of-the-art lattice simulations addressing these issues. After reviewing the status of B->D(*) form factors I will discuss in more detail new results from HPQCD that treat the ‘b’ quark fully relativistically.
Keisuke Yanagi, Department of Physics, University of Tokyo
Dark Matter Heating vs. Rotochemical Heating in Old Neutron Stars
Seminar room, Kenkyu honkan 3F
Dark matter (DM) particles in the Universe accumulate in neutron stars (NSs) through their interactions with ordinary matter. It has been known that their annihilation inside the NS core causes late-time heating, with which the surface temperature becomes a constant value of Ts≃(2−3)×10^3 K for the NS age t≳10^{6−7} years. This conclusion is, however, drawn based on the assumption that the beta equilibrium is maintained in NSs throughout their life, which turns out to be invalid for rotating pulsars. The slowdown in the pulsar rotation drives the NS matter out of beta equilibrium, and the resultant imbalance in chemical potentials induces late-time heating, dubbed as rotochemical heating. This effect can heat a NS up to Ts≃10^6 K for t≃10^{6−7} years. In fact, recent observations found several old NSs whose surface temperature is much higher than the prediction of the standard cooling scenario and is consistent with the rotochemical heating. Motivated by these observations, in this letter, we reevaluate the significance of the DM heating in NSs, including the effect of the rotochemical heating. We then show that the signature of DM heating can still be detected in old ordinary pulsars, while it is concealed by the rotochemical heating for old millisecond pulsars. To confirm the evidence for the DM heating, however, it is necessary to improve our knowledge on nucleon pairing gaps as well as to evaluate the initial period of the pulsars accurately. In any cases, a discovery of a very cold NS can give a robust constraint on the DM heating, and thus on DM models. To demonstrate this, as an example, we also discuss the case that the DM is the neutral component of an electroweak multiplet, and show that an observation of a NS with Ts≲10^3 K imposes a stringent constraint on such a DM candidate.
Kazunobu Maruyoshi, Seikei University
Landscape of Superconformal Field Theories in 4d
Meeting room 1, Kenkyu honkan 1F
Abstract: Classification of superconformal field theories (SCFTs) is an important question in theoretical physics. We would like to (partially) answer this question focusing on SCFTs in four dimensions realized in the fixed points of the renormalization group flow induced by certain deformations of “known” SCFTs. The deformations include all possible relevant deformations and F-term couplings to gauge-singlet chiral multiplets. By “known” we mean we know the superconformal index in enough higher order. With this knowledge our deformation program is well defined and produces various fixed points. As simple examples, we see the deformations of the N=2 Argyres-Douglas theory, and of N=1 supersymmetric SU(2) gauge theory coupled to an adjoint and two fundamental chiral multiplets. In particular, from the latter theory, we find 34 fixed points, which cover all the known (low central charge) SCFTs and the interesting unknown ones, and 36 candidate fixed points possessing unphysical operators, including one with (a, c)=(0.20, 0.22), that need further investigation.
Mark Barton (NAOJ）
Design and status of KAGRA
Seminar room, Kenkyu honkan 3F
