8,012 research outputs found
Dark matter coupling to electroweak gauge and Higgs bosons: an effective field theory approach
If dark matter is a new species of particle produced in the early universe as
a cold thermal relic (a weakly-interacting massive particle-WIMP), its present
abundance, its scattering with matter in direct-detection experiments, its
present-day annihilation signature in indirect-detection experiments, and its
production and detection at colliders, depend crucially on the WIMP coupling to
standard-model (SM) particles. It is usually assumed that the WIMP couples to
the SM sector through its interactions with quarks and leptons. In this paper
we explore the possibility that the WIMP coupling to the SM sector is via
electroweak gauge and Higgs bosons. In the absence of an ultraviolet-complete
particle-physics model, we employ effective field theory to describe the
WIMP--SM coupling. We consider both scalars and Dirac fermions as possible
dark-matter candidates. Starting with an exhaustive list of operators up to
dimension 8, we present detailed calculation of dark-matter annihilations to
all possible final states, including gamma gamma, gamma Z, gamma h, ZZ, Zh, W+
W-, hh, and f fbar, and demonstrate the correlations among them. We compute the
mass scale of the effective field theory necessary to obtain the correct
dark-matter mass density, and well as the resulting photon line signals
Charge-impurity-induced Majorana fermions in topological superconductors
We study numerically Majorana fermions (MFs) induced by a charged impurity in
topological superconductors. It is revealed from the relevant Bogoliubov-de
Gennes equations that (i) for quasi-one dimensional systems, a pair of MFs are
bounded at the two sides of one charge impurity and well separated; and (ii)
for a two dimensional square lattice, the charged-impurity-induced MFs are
similar to the known pair of vortex-induced MFs, in which one MF is bounded by
the impurity while the other appears at the boundary. Moreover, the
corresponding local density of states is explored, demonstrating that the
presence of MF states may be tested experimentally.Comment: 5 pages, 5 figure
MR-GNN: Multi-Resolution and Dual Graph Neural Network for Predicting Structured Entity Interactions
Predicting interactions between structured entities lies at the core of
numerous tasks such as drug regimen and new material design. In recent years,
graph neural networks have become attractive. They represent structured
entities as graphs and then extract features from each individual graph using
graph convolution operations. However, these methods have some limitations: i)
their networks only extract features from a fix-sized subgraph structure (i.e.,
a fix-sized receptive field) of each node, and ignore features in substructures
of different sizes, and ii) features are extracted by considering each entity
independently, which may not effectively reflect the interaction between two
entities. To resolve these problems, we present MR-GNN, an end-to-end graph
neural network with the following features: i) it uses a multi-resolution based
architecture to extract node features from different neighborhoods of each
node, and, ii) it uses dual graph-state long short-term memory networks
(L-STMs) to summarize local features of each graph and extracts the interaction
features between pairwise graphs. Experiments conducted on real-world datasets
show that MR-GNN improves the prediction of state-of-the-art methods.Comment: Accepted by IJCAI 201
Symmetry and functional inequalities for stable L\'evy-type operators
In this paper, we provide the sufficient and necessary conditions for the
symmetry of the following stable L\'evy-type operator on
: \mathcal{L}=a(x){\Delta^{\alpha/2}}+b(x)\frac{\d}{\d x},
where are the continuous positive and differentiable functions,
respectively. Under the assumption of symmetry, we further study the criteria
for functional inequalities, including Poincar\'e inequalities, logarithmic
Sobolev inequalities and Nash inequalities. Our proofs rely on the Orlicz space
theory and the estimates of the Green functions
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