163,560 research outputs found
Z_{12-I} Orbifold Compactification toward SUSY Standard Model
We explain the orbifold compactification in string models and present a
Z_{12-I} orbifold compactification toward supersymmetric standard models. We
also point out an effective R-parity from this string construction. The VEVs of
gauge singlets are chosen such that phenomenological constraints are satisfied.Comment: 13 pages with 5 figure. Talk presented at "CTP Symposium on SUSY at
LHC", Cairo, 11-14 March 200
Brane gravity, massless bulk scalar and self-tuning of the cosmological constant
We show that a self-tuning mechanism of the cosmological constant could work
in 5D non-compact space-time with a symmetry in the presence of a
massless scalar field. The standard model matter fields live only on the 4D
brane. The change of vacuum energy on the brane (brane cosmological constant)
by, for instance, electroweak and QCD phase transitions, just gives rise to
dynamical shifts of the profiles of the background metric and the scalar field
in the extra dimension, keeping 4D space-time flat without any fine-tuning. To
avoid naked singularities in the bulk, the brane cosmological constant should
be negative. We introduce an additional brane-localized 4D Einstein-Hilbert
term so as to provide the observed 4D gravity with the non-compact extra
dimension. With a general form of brane-localized gravity term allowed by the
symmetries, the low energy Einstein gravity is successfully reproduced on the
brane at long distances. We show this phenomenon explicitly for the case of
vanishing bulk cosmological constant.Comment: 1+15 pages, no figure, Version to appear in PR
Cramer-Rao Lower Bound for Point Based Image Registration with Heteroscedastic Error Model for Application in Single Molecule Microscopy
The Cramer-Rao lower bound for the estimation of the affine transformation
parameters in a multivariate heteroscedastic errors-in-variables model is
derived. The model is suitable for feature-based image registration in which
both sets of control points are localized with errors whose covariance matrices
vary from point to point. With focus given to the registration of fluorescence
microscopy images, the Cramer-Rao lower bound for the estimation of a feature's
position (e.g. of a single molecule) in a registered image is also derived. In
the particular case where all covariance matrices for the localization errors
are scalar multiples of a common positive definite matrix (e.g. the identity
matrix), as can be assumed in fluorescence microscopy, then simplified
expressions for the Cramer-Rao lower bound are given. Under certain simplifying
assumptions these expressions are shown to match asymptotic distributions for a
previously presented set of estimators. Theoretical results are verified with
simulations and experimental data
Subwavelength localization and toroidal dipole moment of spoof surface plasmon polaritons
We experimentally and theoretically demonstrate subwavelength scale localization of spoof surface plasmon polaritons at a point defect in a two-dimensional groove metal array. An analytical expression for dispersion relation of spoof surface plasmon polaritons substantiates the existence of a band gap where a defect mode can be introduced. A waveguide coupling method allows us to excite localized spoof surface plasmon polariton modes and measure their resonance frequencies. Numerical calculations confirm that localized modes can have a very small modal volume and a high Q factor both of which are essential in enhancing light-matter interactions. Interestingly, we find that the localized spoof surface plasmon polariton has a significant toroidal dipole moment, which is responsible for the high Q factor, as well as an electric quadrupole moment. In addition, the dispersion properties of spoof surface plasmon polaritons are analyzed using a modal expansion method and numerical calculations
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