Updated Analysis of a_1 and a_2 in Hadronic Two-body Decays of B Mesons

Using the recent experimental data of $B\to D^{(*)}(\pi,\rho)$, $B\to D^{(*)} D_s^{(*)}$, $B\to J/\psi K^{(*)}$ and various model calculations on form factors, we re-analyze the effective coefficients a_1 and a_2 and their ratio. QCD and electroweak penguin corrections to a_1 from $B\to D^{(*)}D_s^{(*)}$ and a_2 from $B\to J/\psi K^{(*)}$ are estimated. In addition to the model-dependent determination, the effective coefficient a_1 is also extracted in a model-independent way as the decay modes $B\to D^{(*)}h$ are related by factorization to the measured semileptonic distribution of $B\to D^{(*)}\ell \bar\nu$ at $q^2=m_h^2$. Moreover, this enables us to extract model-independent heavy-to-heavy form factors, for example, $F_0^{BD}(m_\pi^2)=0.66\pm0.06\pm0.05$ and $A_0^{BD^*}(m_\pi^2)=0.56\pm0.03\pm0.04$. The determination of the magnitude of a_2 from $B\to J/\psi K^{(*)}$ depends on the form factors $F_1^{BK}$, $A_{1,2}^{BK^*}$ and $V^{BK^*}$ at $q^2=m^2_{J/\psi}$. By requiring that a_2 be process insensitive (i.e., the value of a_2 extracted from $J/\psi K$ and $J/\psi K^*$ states should be similar), as implied by the factorization hypothesis, we find that $B\to K^{(*)}$ form factors are severely constrained; they respect the relation $F_1^{BK}(m^2_{J/\psi})\approx 1.9 A_1^{BK^*}(m^2_{J/\psi})$. Form factors $A_2^{BK^*}$ and $V^{BK^*}$ at $q^2=m^2_{J/\psi}$ inferred from the measurements of the longitudinal polarization fraction and the P-wave component in $B\to J/\psi K^*$ are obtained. A stringent upper limit on a_2 is derived from the current bound on \ov B^0\to D^0\pi^0 and it is sensitive to final-state interactions.Comment: 33 pages, 2 figures. Typos in Tables I and IX are corrected. To appear in Phys. Rev.

B -> J/psi K^* Decays in QCD Factorization

The hadronic decay B -> J K^* is analyzed within the framework of QCD factorization. The spin amplitudes A_0, A_\parallel and A_\perp in the transversity basis and their relative phases are studied using various different form-factor models for B-K^* transition. The effective parameters a_2^h for helicity h=0,+,- states receive different nonfactorizable contributions and hence they are helicity dependent, contrary to naive factorization where a_2^h are universal and polarization independent. QCD factorization breaks down even at the twist-2 level for transverse hard spectator interactions. Although a nontrivial strong phase for the A_\parallel amplitude can be achieved by adjusting the phase of an infrared divergent contribution, the present QCD factorization calculation cannot say anything definite about the phase phi_\parallel. Unlike B -> J/psi K decays, the longitudinal parameter a_2^0 for B -> J/psi K^* does not receive twist-3 corrections and is not large enough to account for the observed branching ratio and the fraction of longitudinal polarization. Possible enhancement mechanisms for a_2^0 are discussed.Comment: 21 pages, 1 figure, a table and a reference added, some typos correcte

Light-Front Approach for Heavy Pentaquark Transitions

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and parity-odd triplet heavy pentaquark baryons. The theoretical estimate of charmed and bottom pentaquark masses is quite controversial and it is not clear whether the ground-state heavy pentaquark lies above or below the strong-decay threshold. We study the weak transitions of heavy pentaquark states using the light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark transition form factors can be expressed in terms of three Isgur-Wise functions: two of them are found to be normalized to unity at zero recoil, while the third one is equal to 1/2 at the maximum momentum transfer, in accordance with the prediction of the large-Nc approach or the quark model. Therefore, the light-front model calculations are consistent with the requirement of heavy quark symmetry. Numerical results for form factors and Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q, Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+ pi- are estimated to be at the level of 10^{-3} and a few percents, respectively.Comment: 33 pages, 3 figures, version to be published in Phys. Rev.

Thorn-like TiO2 nanoarrays with broad spectrum antimicrobial activity through physical puncture and photocatalytic action

To overcome the conventional limitation of TiO2 disinfection being ineffective under light-free conditions, TiO2 nanowire films (TNWs) were prepared and applied to bacterial disinfection under dark and UV illumination. TNW exhibited much higher antibacterial efficiencies against Escherichia coli (E. coli) under dark and UV illumination conditions compared to TiO2 nanoparticle film (TNP) which was almost inactive in the dark, highlighting the additional contribution of the physical interaction between bacterial membrane and NWs. Such a physical contact-based antibacterial activity was related to the NW geometry such as diameter, length, and density. The combined role of physical puncture and photocatalytic action in the mechanism underlying higher bactericidal effect of TNW was systematically examined by TEM, SEM, FTIR, XPS, and potassium ion release analyses. Moreover, TNW revealed antimicrobial activities in a broad spectrum of microorganisms including Staphylococcus aureus and MS2 bacteriophage, antibiofilm properties, and good material stability. Overall, we expect that the free-standing and antimicrobial TNW is a promising agent for water disinfection and biomedical applications in the dark and/or UV illumination.11Ysciescopu

Vertex functions for d-wave mesons in the light-front approach

While the light-front quark model (LFQM) is employed to calculate hadronic transition matrix elements, the vertex functions must be pre-determined. In this work we derive the vertex functions for all d-wave states in this model. Especially, since both of $^3D_1$ and $^3S_1$ are $1^{--}$ mesons, the Lorentz structures of their vertex functions are the same. Thus when one needs to study the processes where $^3D_1$ is involved, all the corresponding formulas for $^3S_1$ states can be directly applied, only the coefficient of the vertex function should be replaced by that for $^3D_1$. The results would be useful for studying the newly observed resonances which are supposed to be d-wave mesons and furthermore the possible 2S-1D mixing in $\psi'$ with the LFQM.Comment: 12 pages, 2 figures, some typos corrected and more discussions added. Accepted by EPJ

Signatures of Electronic Nematic Phase at Isotropic-Nematic Phase Transition

The electronic nematic phase occurs when the point-group symmetry of the lattice structure is broken, due to electron-electron interactions. We study a model for the nematic phase on a square lattice with emphasis on the phase transition between isotropic and nematic phases within mean field theory. We find the transition to be first order, with dramatic changes in the Fermi surface topology accompanying the transition. Furthermore, we study the conductivity tensor and Hall constant as probes of the nematic phase and its transition. The relevance of our findings to Hall resistivity experiments in the high-$T_c$ cuprates is discussed.Comment: 5 pages, 3 figure

Temperature Dependence of Hall Response in Doped Antiferromagnets

Using finite-temperature Lanczos method the frequency-dependent Hall response is calculated numerically for the t-J model on the square lattice and on ladders. At low doping, both the high-frequency RH* and the d.c. Hall coefficient RH0 follow qualitatively similar behavior at higher temperatures: being hole-like for T > Ts~1.5J and weakly electron-like for T < Ts. Consistent with experiments on cuprates, RH0 changes, in contrast to RH*, again to the hole-like sign below the pseudogap temperature T*, revealing a strong temperature variation for T->0.Comment: LaTeX, 4 pages, 4 figures, submitted to PR

Two-Dimensional Electron Gases at Oxide Interfaces

Two-dimensional electron gases (2DEGs) based on conventional semiconductors such as Si or GaAs have played a pivotal role in fundamental science and technology. The high mobilities achieved in 2DEGs enabled the discovery of the integer and fractional quantum Hall effects and are exploited in high-electron-mobility transistors. Recent work has shown that 2DEGs can also exist at oxide interfaces. These electron gases typically result from reconstruction of the complex electronic structure of the oxides, so that the electronic behavior of the interfaces can differ from the behavior of the bulk. Reports on magnetism and superconductivity in oxide 2DEGs illustrate their capability to encompass phenomena not shown by interfaces in conventional semiconductors. This article reviews the status and prospects of oxide 2DEG

Radiative transitions among the vector and scalar heavy quarkonium states with covariant light-front quark model

In this article, we study the radiative transitions among the vector and scalar heavy quarkonium states with the covariant light-front quark model. In calculations, we observe that the radiative decay widths are sensitive to the constituent quark masses and the shape parameters of the wave-functions, and reproduce the experimental data with suitable parameters.Comment: 11 pages, 7 figure

Mesoscale magnetism at the grain boundaries in colossal magnetoresistive films

We report the discovery of mesoscale regions with distinctive magnetic properties in epitaxial La$_{1-x}$Sr$_{x}$MnO$_{3}$ films which exhibit tunneling-like magnetoresistance across grain boundaries. By using temperature-dependent magnetic force microscopy we observe that the mesoscale regions are formed near the grain boundaries and have a different Curie temperature (up to 20 K {\it higher}) than the grain interiors. Our images provide direct evidence for previous speculations that the grain boundaries in thin films are not magnetically and electronically sharp interfaces. The size of the mesoscale regions varies with temperature and nature of the underlying defect.Comment: 4 pages of text, 4 figure