88,328 research outputs found

    Lepton flavor-changing Scalar Interactions and Muon g2g-2

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    A systematic investigation on muon anomalous magnetic moment and related lepton flavor-violating process such as \m\to e\g, \t\to e\g and \t\to \m\g is made at two loop level in the models with flavor-changing scalar interactions. The two loop diagrams with double scalar exchanges are studied and their contributions are found to be compatible with the ones from Barr-Zee diagram. By comparing with the latest data, the allowed ranges for the relevant Yukawa couplings YijY_{ij} in lepton sector are obtained. The results show a hierarchical structure of Y_{\m e, \t e} \ll Y_{\m \t} \simeq Y_{\m\m} in the physical basis if Δaμ\Delta a_{\mu} is found to be >50×1011>50\times 10^{-11}. It deviates from the widely used ansatz in which the off diagonal elements are proportional to the square root of the products of related fermion masses. An alternative Yukawa coupling matrix in the lepton sector is suggested to understand the current data. With such a reasonable Yukawa coupling ansatz, the decay rate of \t\to \m\g is found to be near the current experiment upper bound.Comment: 15 pages, Revtex, 9 figures, published version in EPJ

    Random Walk over Basins of Attraction to Construct Ising Energy Landscapes

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    An efficient algorithm is developed to construct disconnectivity graphs by a random walk over basins of attraction. This algorithm can detect a large number of local minima, find energy barriers between them, and estimate local thermal averages over each basin of attraction. It is applied to the SK spin glass Hamiltonian where existing methods have difficulties even for a moderate number of spins. Finite-size results are used to make predictions in the thermodynamic limit that match theoretical approximations and recent findings on the free energy landscapes of SK spin glasses.Comment: 2 Figures and 1 Table. To be published in Physical Review Letter

    Charmless decays B->pipi, piK and KK in broken SU(3)symmetry

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    Charmless B decay modes Bππ,πKB \to \pi \pi, \pi K and KKKK aresystematically investigated with and without flavor SU(3) symmetry. Independent analyses on ππ\pi \pi and πK\pi K modes both favor a large ratio between color-suppressed tree (CC) and tree (T)T) diagram, which suggests that they are more likely to originate from long distance effects. The sizes of QCD penguin diagrams extracted individually from ππ\pi\pi, πK\pi K and KKKK modes are found to follow a pattern of SU(3) breaking in agreement with the naive factorization estimates. Global fits to these modes are done under various scenarios of SU(3)relations. The results show good determinations of weak phase γ\gamma in consistency with the Standard Model (SM), but a large electro-weak penguin (P_{\tmop{EW}}) relative to T+CT + C with a large relative strong phase are favored, which requires an big enhancement of color suppressed electro-weak penguin (P_{\tmop{EW}}^C) compatible in size but destructively interfering with P_{\tmop{EW}} within the SM, or implies new physics. Possibility of sizable contributions from nonfactorizable diagrams such as WW-exchange (EE), annihilation(AA) and penguin-annihilation diagrams(PAP_A) are investigated. The implications to the branching ratios and CP violations in KKK Kmodes are discussed.Comment: 27 pages, 9 figures, reference added, to appear in Phy.Rev.

    First-principles study of phenyl ethylene oligomers as current-switch

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    We use a self-consistent method to study the distinct current-switch of 22^{'}-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol, from the first-principles calculations. The numerical results are in accord with the early experiment [Reed et al., Sci. Am. \textbf{282}, 86 (2000)]. To further investigate the transport mechanism, we calculate the switching behavior of p-terphenyl with the rotations of the middle ring as well. We also study the effect of hydrogen atom substituting one ending sulfur atom on the transport and find that the asymmetry of I-V curves appears and the switch effect still lies in both the positive and negative bias range.Comment: 6 pages, 6 figure