セミナー 2019年

Noriyuki Sogabe, Keio U

Triangle anomalies and nonrelativistic Nambu-Goldstone modes of generalized global symmetries

Meeting room 1, Kenkyu honkan 1F
In massless QCD coupled to QED in an external magnetic field, a photon with the linear polarization in the direction of the external magnetic field mixes with the charge neutral pion through the triangle anomaly, leading to one gapless mode with the quadratic dispersion relation ω?k^2 and one gapped mode. In this talk, we show that this gapless mode can be interpreted as the so-called type-B Nambu-Goldstone (NG) mode associated with the spontaneous breaking of the generalized global symmetries and that its presence is solely dictated by the anomalous commutator in the symmetry algebra. We also argue a possible realization of such nonrelativistic NG modes in 3-dimensional Dirac semimetals.

Syuhei Iguro, Nagoya University

Testing the 2HDM explanation of the muon g-2 anomaly at the LHC

Meeting room 3, Kenkyu honkan 1F
The discrepancy between the measured value and the Standard Model prediction for the muon anomalous magnetic moment is one of the important issues in the particle physics. In this talk, we consider a two Higgs doublet model (2HDM) where the extra Higgs doublet couples to muon and tau in lepton flavor violating (LFV) way and the one-loop correction involving the scalars largely contributes to the muon anomalous magnetic moment. The couplings should be sizable to explain the discrepancy, so that the extra Higgs bosons would dominantly decay into μτ LFV modes, which makes the model testable at the LHC through multi-lepton signatures even though they are produced via the electroweak interaction. We discuss the current status and the future prospect for the extra Higgs searches at the LHC, and demonstrate the reconstruction of the mass spectrum using the multi-lepton events.

Shintaro Eijima, KEK

Sterile neutrino dark matter and heavy neutral leptons

Meeting room 1, Kenkyu honkan 1F
Sterile neutrino as a possible dark matter candidate is reviewed. I will give an overview of the current status of the research on the dark matter particle, and discuss the motivation and limits obtained through astrophysical observations. Originally the thermal production via mixing was suggested which, however, is ruled out in current constraints. I will introduce different mechanisms to produce the dark matter. In particular a resonant production with lepton asymmetry in thermal plasma and the asymmetry originated by heavy neutral leptons are explained.

Etsuko Itou, Keio University

Two-colour QCD phases and the topology at low temperature and high density

Meeting room 1, Kenkyu honkan 1F
>We delineate equilibrium phase structure and topological charge distribution of dense two-colour QCD at low temperature by using a lattice simulation with two-flavour Wilson fermions that has a chemical potential μ and a diquark source j incorporated. We systematically measure the diquark condensate, the Polyakov loop, the quark number density and the chiral condensate with improved accuracy and j→0 extrapolation over earlier publications; the known qualitative features of the low temperature phase diagram, which is composed of the hadronic, Bose-Einstein condensed (BEC) and BCS phases, are reproduced. In addition, we newly find that around the boundary between the hadronic and BEC phases, nonzero quark number density occurs even in the hadronic phase in contrast to the prediction of the chiral perturbation theory (ChPT), while the diquark condensate approaches zero in a manner that is consistent with the ChPT prediction. At the highest μ, which is of order the inverse of the lattice spacing, all the above observables change drastically, which implies a lattice artifact. Finally, at temperature of order 0.45Tc, where Tc is the chiral transition temperature at zero chemical potential, the topological susceptibility is calculated from a gradient-flow method and found to be almost constant for all the values of μ ranging from the hadronic to BCS phase. This is a contrast to the case of 0.89Tc in which the topological susceptibility becomes small as the hadronic phase changes into the quark-gluon plasma phase. This talk is based on arXiv:1910.07872.

Daisuke Nomura, KEK

[IPNS Physics Seminar] The muon g-2: a new data-analysis

Room 345, bldg. 4
Following updates in the compilation of e^+ e^- –> hadrons data, I will talk about re-evaluations of the hadronic vacuum polarization contributions to the anomalous magnetic moment of the muon (a_¥mu). Combining the results for the hadronic vacuum polarization contributions with recent updates for the hadronic light-by-light corrections, the electromagnetic and the weak contributions, the deviation between the measured value of a_¥mu and its Standard Model prediction amounts to ¥Delta a_¥mu = (28.02 +/- 7.37) x 10^{-10}, corresponding to a muon g-2 discrepancy of 3.8 ¥sigma.

Gerald V. Dunne, University of Connecticut

[12th KEK joint colloquium] Decoding the Path Integral: Resurgence and Non-Perturbative Physics

Kobayashi hall, Kenkyu honkan 1F
There are several important conceptual and computational questions concerning the Minkowski space path integral, which have recently been approached from a new perspective motivated by “resurgent asymptotics”, which is a novel mathematical formalism that seeks to unify perturbative and non-perturbative physics. In this general talk, I will introduce the basic ideas, report on some examples in quantum mechanics and quantum field theory, and discuss future prospects.

Natsumi Nagata, Department of Physics, University of Tokyo

Limit on the Axion Decay Constant from the Cooling Neutron Star in Cassiopeia A

Meeting room 3, Kenkyu honkan 1F
The observed rapid cooling of the neutron star (NS) located at the center of the supernova remnant Cassiopeia A (Cas A) can be explained in the minimal NS cooling scenario. This consequence may be changed if there exists an extra cooling source, such as axion emission. In this talk, I will first give a brief review on the standard NS cooling theory. I will then discuss the Cas A NS cooling in the presence of axion emission. It turns out that we can obtain a lower limit on the axion decay constant from the Cas A NS cooling observation, which is as strong as existing limits set by other astrophysical observations such as SN1987A. I will also talk about some recent progress on the limits on the axion decay constant from NS surface temperature observations.

Andreas Crivellin, Paul Scherrer Institut

Discovering New Physics with Flavour

Meeting room 3, Kenkyu honkan 1F, slides (kek.jp only)
In the last years very intriguing hints for New Physics (NP) in the flavour sector have been accumulated. In particular, deviations from the Standard Model predictions in semi-leptonic B decays were discovered, pointing strongly towards the violating of lepton flavour universality (LFU). These hints for NP could be related to the long standing discrepancy in the anomalous magnetic moment of the muon which also measures LFU violation. Furthermore, there are interesting tensions in direct CP violating observables in meson decays, i.e. epsilon’/epsilon and B->Kpi. Even though these observables are not directly related to LFU violation, they could be correlated in a UV complete model. After reviewing the current experimental und theoretical situation, I will discuss possible NP models which can explain the anomalies. As it turns out, leptoquarks are prime candidates for such an explanation und I will present some interesting UV completions, including one based on the famous Pati-Salam gauge group.

Martin Hoferichter, Institute for Nuclear Theory, University of Washington

Searching for physics beyond the Standard Model with lepton dipole moments

Meeting room 3, Kenkyu Honkan 1F
The longstanding discrepancy between measurement and Standard Model prediction for the anomalous magnetic moment (g-2)/2 of the muon, as well as the recently emerging tension in the electron g-2, could be considered indications that physics beyond the Standard Model is lurking in lepton dipole moments. To decide this issue conclusively, both improved measurements and theoretical predictions are required. In view of the expected improvement by a factor of 4 at the Fermilab muon g-2 experiment, as well as the upcoming Muon g-2/EDM experiment at J-PARC, this presents a challenge to theory, with current uncertainties almost exclusively dominated by hadronic corrections to about equal parts from hadronic vacuum polarization and hadronic light-by-light scattering. In the talk, I will review the present status of the magnetic dipole moments, especially their Standard Model prediction, and discuss possible connections with electric dipole moments.

初貝安弘氏, 筑波大学 

[11th KEK joint colloquium] 仮想と実在をつなぐバルクエッジ対応

Seminar hall 4 go-kan / Room 324 1 go-kan Tokai campus(TV link)
2016年度のノーベル物理学賞の対象となり、近年多くの興味を集めているトポロジカル相はその名の通りトポロジカルな量で相が特定されることを最大の特徴とする。しかし実は多くの場合、そのトポロジカルな量は実験では直接観測できない。つまり、見えない! 実際に観測されるのは表面状態などのいわゆるエッジ状態(局在状態)であり、境界を見てバルクを想像するのである。トポロジカル絶縁体の角度分解光電子分光(ARPES)実験で観測する表面状態がその典型例である。

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