129,449 research outputs found
Multiple Gamma Lines from Semi-Annihilation
Hints in the Fermi data for a 130 GeV gamma line from the galactic center
have ignited interest in potential gamma line signatures of dark matter.
Explanations of this line based on dark matter annihilation face a parametric
tension since they often rely on large enhancements of loop-suppressed cross
sections. In this paper, we pursue an alternative possibility that dark matter
gamma lines could arise from "semi-annihilation" among multiple dark sector
states. The semi-annihilation reaction with a single final state photon is
typically enhanced relative to ordinary annihilation into photon pairs.
Semi-annihilation allows for a wide range of dark matter masses compared to the
fixed mass value required by annihilation, opening the possibility to explain
potential dark matter signatures at higher energies. The most striking
prediction of semi-annihilation is the presence of multiple gamma lines, with
as many as order N^3 lines possible for N dark sector states, allowing for dark
sector spectroscopy. A smoking gun signature arises in the simplest case of
degenerate dark matter, where a strong semi-annihilation line at 130 GeV would
be accompanied by a weaker annihilation line at 173 GeV. As a proof of
principle, we construct two explicit models of dark matter semi-annihilation,
one based on non-Abelian vector dark matter and the other based on retrofitting
Rayleigh dark matter.Comment: 15 pages of text, 8 figures. v2: refs adde
Non-invasive detection of molecular bonds in quantum dots
We performed charge detection on a lateral triple quantum dot with star-like
geometry. The setup allows us to interpret the results in terms of two double
dots with one common dot. One double dot features weak tunnel coupling and can
be understood with atom-like electronic states, the other one is strongly
coupled forming molecule-like states. In nonlinear measurements we identified
patterns that can be analyzed in terms of the symmetry of tunneling rates.
Those patterns strongly depend on the strength of interdot tunnel coupling and
are completely different for atomic- or molecule-like coupled quantum dots
allowing the non-invasive detection of molecular bonds.Comment: 4 pages, 4 figure
Coplanar Repeats by Energy Minimization
This paper proposes an automated method to detect, group and rectify
arbitrarily-arranged coplanar repeated elements via energy minimization. The
proposed energy functional combines several features that model how planes with
coplanar repeats are projected into images and captures global interactions
between different coplanar repeat groups and scene planes. An inference
framework based on a recent variant of -expansion is described and fast
convergence is demonstrated. We compare the proposed method to two widely-used
geometric multi-model fitting methods using a new dataset of annotated images
containing multiple scene planes with coplanar repeats in varied arrangements.
The evaluation shows a significant improvement in the accuracy of
rectifications computed from coplanar repeats detected with the proposed method
versus those detected with the baseline methods.Comment: 14 pages with supplemental materials attache
Symmetry sensitivities of Derivative-of-Gaussian filters
We consider the measurement of image structure using linear filters, in particular derivative-of-Gaussian (DtG) filters, which are an important model of V1 simple cells and widely used in computer vision, and whether such measurements can determine local image symmetry. We show that even a single linear filter can be sensitive to a symmetry, in the sense that specific responses of the filter can rule it out. We state and prove a necessary and sufficient, readily computable, criterion for filter symmetry-sensitivity. We use it to show that the six filters in a second order DtG family have patterns of joint sensitivity which are distinct for 12 different classes of symmetry. This rich symmetry-sensitivity adds to the properties that make DtG filters well-suited for probing local image structure, and provides a set of landmark responses suitable to be the foundation of a nonarbitrary system of feature categories
Generalized intrinsic symmetry detection
In this paper, we address the problem of detecting partial symmetries in 3D objects. In contrast to previous work, our algorithm is able to match deformed symmetric parts: We first develop an algorithm for the case of approximately isometric deformations, based on matching graphs of surface feature lines that are annotated with intrinsic geometric properties. The sensitivity to non-isometry is controlled by tolerance parameters for each such annotation. Using large tolerance values for some of these annotations and a robust matching of the graph topology yields a more general symmetry detection algorithm that can detect similarities in structures that have undergone strong deformations. This approach for the first time allows for detecting partial intrinsic as well as more general, non-isometric symmetries. We evaluate the recognition performance of our technique for a number synthetic and real-world scanner data sets
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