Tatsuhiro Misumi, Akita University
Central-branch Wilson fermion, Spin chain and Aoki phase
Meeting room 1, Kenkyu honkan 1F In this talk, we first discuss the central-branch Wilson fermion, which is defined by imposing a specific relation between the mass and the Wilson parameter [1]. This setup gives two massless Dirac fermions in the continuum limit, and it turns out that no fine-tuning of m is required because the extra U(1) symmetry at the central branch prohibits the additive mass renormalization [2,3]. We show that Dirac determinant is positive semi-definite and this formulation is free from the sign problem, so the Monte Carlo simulation of the path integral is possible. By identifying the symmetry at low energy, we find that this lattice model has the mixed ’t Hooft anomaly between the extra U(1) symmetry, lattice translation, and lattice rotation, which means that the trivially gapped phase is forbidden at the central branch [4]. We discuss its relation to the anomaly of half-integer anti-ferromagnetic spin chains, so our lattice gauge theory is suitable for numerical simulation of Haldane conjecture. We also argue that it gives new and strict understanding on parity-broken phase (Aoki phase) of 2d Wilson fermion [4]. Furthermore, we show that our study can be extended to 4d lattice QCD with Wilson fermion, leading to a novel insight into the question which of Aoki-phase or Sharpe-Singleton scenarios is valid.
In this talk, we first discuss the central-branch Wilson fermion, which is defined by imposing a specific relation between the mass and the Wilson parameter [1]. This setup gives two massless Dirac fermions in the continuum limit, and it turns out that no fine-tuning of m is required because the extra U(1) symmetry at the central branch prohibits the additive mass renormalization [2,3]. We show that Dirac determinant is positive semi-definite and this formulation is free from the sign problem, so the Monte Carlo simulation of the path integral is possible. By identifying the symmetry at low energy, we find that this lattice model has the mixed ’t Hooft anomaly between the extra U(1) symmetry, lattice translation, and lattice rotation, which means that the trivially gapped phase is forbidden at the central branch [4]. We discuss its relation to the anomaly of half-integer anti-ferromagnetic spin chains, so our lattice gauge theory is suitable for numerical simulation of Haldane conjecture. We also argue that it gives new and strict understanding on parity-broken phase (Aoki phase) of 2d Wilson fermion [4]. Furthermore, we show that our study can be extended to 4d lattice QCD with Wilson fermion, leading to a novel insight into the question which of Aoki-phase or Sharpe-Singleton scenarios is valid.
[References]
[1] M. Creutz, T. Kimura, T. Misumi, Phys. Rev. D83 (2011) 094506, [arXiv:1101.4239].
[2] T. Kimura, S. Komatsu, T. Misumi, T. Noumi, S. Torii, S. Aoki, JHEP 01 (2012) 048, [arXiv:1111.0402].
[3] T. Misumi, PoS LATTICE2012 (2012) 005, [arXiv:1211.6999].
[4] T. Misumi, Y. Tanizaki, [arXiv:1910:09604].
Sanefumi Moriyama, Osaka City University
ABJM Matrix Model and 2D Toda Lattice Hierarchy
Meeting room 1, Kenkyu honkan 1F
It was known that the worldvolume of multiple M2-branes is described by 3D supersymmetric Chern-Simons theory (known as ABJM theory). After moving to the grand canonical ensemble, it was found in our previous works that the vacuum expectation values of half-BPS Wilson loops in the ABJM theory satisfy Giambelli relations and Jacobi-Trudi relations, which imply integrability directly. To investigate the integrable structure, we further defined two-point functions in ABJM matrix model and identified the structure as 2D Toda lattice hierarchy. In this talk I will give an overview of the recent progress on integrability in the ABJM theory.
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.
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.
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)
