Finite Anomalous Magnetic Moment in the Gauge-Higgs Unification

We show that the anomalous magnetic moment of fermion in the gauge-Higgs unification is finite in any spacetime dimensions, which is a new predictive physical observable similar to the Higgs mass.Comment: 12 pages, 2 eps files, final version to appear in PR

Flavor Mixing in the Gauge-Higgs Unification

Gauge-Higgs unification is the fascinating scenario solving the hierarchy problem without supersymmetry. In this scenario, the Standard Model (SM) Higgs doublet is identified with extra component of the gauge field in higher dimensions and its mass becomes finite and stable under quantum corrections due to the higher dimensional gauge symmetry. On the other hand, Yukawa coupling is provided by the gauge coupling, which seems to mean that the flavor mixing and CP violation do not arise at it stands. In this talk, we discuss that the flavor mixing is originated from simultaneously non-diagonalizable bulk and brane mass matrices. Then, this mechanism is applied to various flavor changing neutral current (FCNC) processes via Kaluza-Klein (KK) gauge boson exchange at tree level and constraints for compactification scale are obtained.Comment: 5 pages, prepared for the proceedings of the International Workshop on Grand Unified Theories (GUT2012) held at Yukawa Institute for Theoretical Physics, March 15-17 2012, Kyoto, Japa

Temperature dependence of the band gap shrinkage due to electron-phonon interaction in undoped n-type GaN

The photoluminescence spectra of band-edge transitions in GaN is studied as a function of temperature. The parameters that describe the temperature dependence red-shift of the band-edge transition energy and the broadening of emission line are evaluated using different models. We find that the semi-empirical relation based on phonon-dispersion related spectral function leads to excellent fit to the experimental data. The exciton-phonon coupling constants are determined from the analysis of linewidth broadening

Hybrid functionals within the all-electron FLAPW method: implementation and applications of PBE0

We present an efficient implementation of the PBE0 hybrid functional within the full-potential linearized augmented-plane-wave (FLAPW) method. The Hartree-Fock exchange term, which is a central ingredient of hybrid functionals, gives rise to a computationally expensive nonlocal potential in the one-particle Schroedinger equation. The matrix elements of this exchange potential are calculated with the help of an auxiliary basis that is constructed from products of FLAPW basis functions. By representing the Coulomb interaction in this basis the nonlocal exchange term becomes a Brillouin-zone (BZ) sum over vector-matrix-vector products. We show that the Coulomb matrix can be made sparse by a suitable unitary transformation of the auxiliary basis, which accelerates the computation of the vector-matrix-vector products considerably. Additionally, we exploit spatial and time-reversal symmetry to identify the nonvanishing exchange matrix elements in advance and to restrict the k summations for the nonlocal potential to an irreducible set of k points. Favorable convergence of the self-consistent-field cycle is achieved by a nested density-only and density-matrix iteration scheme. We discuss the convergence with respect to the parameters of our numerical scheme and show results for a variety of semiconductors and insulators, including oxide materials, where the PBE0 hybrid functional improves the band gaps and the description of localized states in comparison with the PBE functional. Furthermore, we find that in contrast to conventional local exchange-correlation functionals ferromagnetic EuO is correctly predicted to be a semiconductor.Comment: 15 pages, 6 figures, 2 table

Linear-response theory of the longitudinal spin Seebeck effect

We theoretically investigate the longitudinal spin Seebeck effect, in which the spin current is injected from a ferromagnet into an attached nonmagnetic metal in a direction parallel to the temperature gradient. Using the fact that the phonon heat current flows intensely into the attached nonmagnetic metal in this particular configuration, we show that the sign of the spin injection signal in the longitudinal spin Seebeck effect can be opposite to that in the conventional transverse spin Seebeck effect when the electron-phonon interaction in the nonmagnetic metal is sufficiently large. Our linear-response approach can explain the sign reversal of the spin injection signal recently observed in the longitudinal spin Seebeck effect.Comment: Proc. of ICM 2012 (Accepted for publication in J. Korean Phys. Soc.), typos correcte

Electronic structures of B-2p and C-2p of boron-doped diamond film by soft X-ray absorption and emission spectroscopy

X-ray absorption (XAS) and emission (XES) spectroscopy near B-K and C-K edges have been performed on metallic (~1at%B, B-diamond) and semiconducting (~0.1at%B and N, BN-diamond) doped-diamond films. Both B-K XAS and XES spectra shows metallic partial density of state (PDOS) with the Fermi energy of 185.3 eV, and there is no apparent boron-concentration dependence in contrast to the different electric property. In C-K XAS spectrum of B-diamond, the impurity state ascribed to boron is clearly observed near the Fermi level. The Fermi energy is found to be almost same with the top of the valence band of non-doped diamond, E_V, 283.9 eV. C-K XAS of BN-diamond shows both the B-induced shallow level and N-induced deep-and-broad levels as the in-gap states, in which the shallow level is in good agreement with the activation energy (E_a=0.37 eV) estimated from the temperature dependence of the conductivity, namely the change in C-2p PDOS of impurity-induced metallization is directly observed. The electric property of this diamond is mainly ascribed to the electronic structure of C-2p near the Fermi level. The observed XES spectra are compared with the DVX-alpha cluster calculation. The DVX-alpha result supports the strong hybridization between B-2p and C-2p observed in XAS and XES spectra, and suggests that the small amount of borons (<1at%) in diamond occupy the substitutional site rather than interstitial site.Comment: submitted to Phys. Rev. B, 5 pages and 5 figure