Effect of the Zero-Mode on the Response of a Trapped Bose-Condensed Gas

The dynamical response of a trapped Bose-Einstein condensate (BEC) is formulated consistently with quantum field theory and is numerically evaluated. We regard the BEC as a manifestation of the breaking of the global phase symmetry. Then, the Goldstone theorem implies the existence of a zero energy excitation mode (the zero-mode). We calculate the effect of the zero-mode on the response frequency and show that the contribution of the zero-mode to the first excitation mode is not so important in the parameter set realized in the existing experiment. This is the reason that experimental results can be described using the Bogoliubov prescription, although it breaks the consistency of the description in quantum field theory.Comment: 18 pages, 3 figure

Dark Left-Right Model: CDMS, LHC, etc

The Standard Model of particle interactions is extended to include fermion doublets (n,e)_R transforming under the gauge group SU(2)_R such that n is a Dirac scotino (dark-matter fermion), with odd R parity. Based on recent CDMS data, it is shown how this new dark left-right model (DLRM2) favors a Z' gauge boson at around 1 or 2 TeV and be observable at the LHC. The new W_R gauge bosons may also contribute significantly to lepton-flavor-changing processes such as mu to e gamma and mu-e conversion in a nucleus or muonic atom.Comment: 7 pages, 4 figures, typo corrected, talk at Dark Side of Universe 2010, Leon, Mexic

Quark tensor charge and electric dipole moment within the Schwinger-Dyson formalism

We calculate the tensor charge of the quark in the QCD-like theory in the Landau gauge using the Schwinger-Dyson formalism. It is found that the dressed tensor charge of the quark is significantly suppressed against the bare quark contribution, and the result agrees qualitatively with the analyses in the collinear factorization approach and lattice QCD. We also analyze the quark confinement effect with the phenomenological strong coupling given by Richardson, and find that this contribution is small. We show that the suppression of the quark tensor charge is due to the superposition of the spin flip of the quark arising from the successive emission of gluons which dress the tensor vertex. We also consider the relation between the quark and the nucleon electric dipole moments by combining with the simple constituent quark model.Comment: 16 pages, 11 figures. arXiv admin note: text overlap with arXiv:1401.285

Anomalous behavior of the energy gap in the one-dimensional quantum XY model

We re-examine the well-studied one dimensional spin-1/2 $XY$ model to reveal its nontrivial energy spectrum, in particular the energy gap between the ground state and the first excited state. In the case of the isotropic $XY$ model -- the $XX$ model -- the gap behaves very irregularly as a function of the system size at a second order transition point. This is in stark contrast to the usual power-law decay of the gap and is reminiscent of the similar behavior at the first order phase transition in the infinite-range quantum $XY$ model. The gap also shows nontrivial oscillatory behavior for the phase transitions in the anisotropic model in the incommensurate phase. We observe a close relation between this anomalous behavior of the gap and the correlation functions. These results, those for the isotropic case in particular, are important from the viewpoint of quantum annealing where the efficiency of computation is strongly affected by the size dependence of the energy gap.Comment: 25 pages, 8 figures. arXiv admin note: substantial text overlap with arXiv:1501.0292

Quark scalar, axial, and pseudoscalar charges in the Schwinger-Dyson formalism

We calculate the scalar, axial, and pseudoscalar charges of the quark in the Schwinger-Dyson formalism of Landau gauge QCD. It is found that the dressed quark scalar density of the valence quark is significantly enhanced against the bare quark contribution, and the result explains qualitatively the phenomenologically known value of the pion-nucleon sigma term and also that given by lattice QCD. Moreover, we show that the Richardson's interquark potential suppresses the quark scalar density in the Higashjima-Miransky approximation. This fact suggests that the quark scalar density is an observable that is sensitive to quark confinement. For the quark axial charge, we find that it is suppressed due to the gluon dynamics. The result of the quenched analysis agrees qualitatively with the experimental data of the isovector axial coupling constant $g_A$. We show that the suppression of the quenched axial charge is due to a mechanism similar to that of the quark tensor charge. In the Schwinger-Dyson equation with the leading unquenching quark-loop contribution the quark axial charge is more suppressed, due to the anomaly effect. The quark pseudoscalar density is found to be large, and is divergent as the bare quark becomes massless. This result is in agreement with the phenomenological current algebraic analysis, and explains well the dominance of the pion-pole contribution.Comment: 28 pages, 22 figure

Long life stau in the minimal supersymmetric standard model

We study the stau lifetime in a scenario with the LSP taken to be a neutralino and the NLSP being a stau, based on the minimal supersymmetric Standard Model. The mass difference between the LSP and NLSP, $\delta m$, must satisfy $\delta m/m_{\tilde{\chi}} \sim$ a few % or less for coannihilation to occur, where $m_{\tilde{\chi}}$ is the neutralino mass. We calculate the stau lifetime from the decay modes $\tilde{\tau}\to \tilde{\chi}\tau$, $\tilde{\chi}\nu_\tau\pi$, and $\tilde{\chi}\nu_\tau\mu(e)\nu_{\mu(e)}$ and discuss its dependence on various parameters. We find that the lifetime is in the range $10^{-22}$--$10^{16}$ sec for $10^{-2} \le \delta m \le 10$ GeV. We also discuss the connection with lepton flavor violation if there is mixing between sleptons.Comment: 15 pages, 5 figure