88,328 research outputs found

### Lepton flavor-changing Scalar Interactions and Muon $g-2$

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 $Y_{ij}$ 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 $\Delta a_{\mu}$ is found to be $>50\times 10^{-11}$. 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

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

Charmless B decay modes $B \to \pi \pi, \pi K$ and $KK$ aresystematically
investigated with and without flavor SU(3) symmetry. Independent analyses on
$\pi \pi$ and $\pi K$ modes both favor a large ratio between color-suppressed
tree ($C$) and tree ($T)$ diagram, which suggests that they are more likely to
originate from long distance effects. The sizes of QCD penguin diagrams
extracted individually from $\pi\pi$, $\pi K$ and $KK$ 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 $\gamma$ in
consistency with the Standard Model (SM), but a large electro-weak penguin
(P_{\tmop{EW}}) relative to $T + C$ 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 $W$-exchange ($E$),
annihilation($A$) and penguin-annihilation diagrams($P_A$) are investigated.
The implications to the branching ratios and CP violations in $K K$modes are
discussed.Comment: 27 pages, 9 figures, reference added, to appear in Phy.Rev.

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

We use a self-consistent method to study the distinct current-switch of
$2^{'}$-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

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