34,638 research outputs found
Co-rich decagonal Al-Co-Ni: predicting structure, orientational order, and puckering
We apply systematic methods previously used by Mihalkovic et al. to predict
the structure of the `basic' Co-rich modification of the decagonal Al70 Co20
Ni10 layered quasicrystal, based on known lattice constants and previously
calculated pair potentials. The modelling is based on Penrose tile decoration
and uses Monte Carlo annealing to discover the dominant motifs, which are
converted into rules for another level of description. The result is a network
of edge-sharing large decagons on a binary tiling of edge 10.5 A. A detailed
analysis is given of the instability of a four-layer structure towards
-doubling and puckering of the atoms out of the layers, which is applied to
explain the (pentagonal) orientational order.Comment: IOP LaTex; 7 pp, 2 figures. In press, Phil. Mag. A (Proc. Intl. Conf.
on Quasicrystals 9, Ames Iowa, May 2005
Radiative Neutrino Mass, Dark Matter and Leptogenesis
We propose an extension of the standard model, in which neutrinos are Dirac
particles and their tiny masses originate from a one-loop radiative diagram.
The new fields required by the neutrino mass-generation also accommodate the
explanation for the matter-antimatter asymmetry and dark matter in the
universe.Comment: 4 pages, 3 figures. Revised version with improved model. Accepted by
PR
A left-right symmetric model with SU(2)-triplet fermions
We consider an
left-right symmetric model with three Higgs scalars including an
doublet, an doublet and an bidoublet. In
addition to usual SU(2)-doublet fermions, our model contains SU(2)-triplet
fermions with Majorana masses. The neutral components of the left-handed
triplets can contribute a canonical seesaw while the neutral components of the
right-handed triplets associated with the right-handed neutrinos can contribute
a double/inverse-type seesaw. Our model can be embedded into an SO(10) grand
unification theory where the triplets belong to the representations.Comment: 4 pages. To appear in Phys. Rev.
Neutrino masses, leptogenesis and dark matter in hybrid seesaw
We suggest a hybrid seesaw model where relatively ``light''right-handed
neutrinos give no contribution to the neutrino mass matrix due to a special
symmetry. This allows their Yukawa couplings to the standard model particles to
be relatively strong, so that the standard model Higgs boson can decay
dominantly to a left and a right-handed neutrino, leaving another stable
right-handed neutrino as cold dark matter. In our model neutrino masses arise
via the type-II seesaw mechanism, the Higgs triplet scalars being also
responsible for the generation of the matter-antimatter asymmetry via the
leptogenesis mechanism.Comment: 4 page
Radiative seesaw in left-right symmetric model
There are some radiative origins for the neutrino masses in the conventional
left-right symmetric models with the usual bi-doublet and triplet Higgs
scalars. These radiative contributions could dominate over the tree-level
seesaw and could explain the observed neutrino masses.Comment: 5 pages, 3 figures. Revised version with minor change. Accepted by
PR
Ground-State Entanglement in Interacting Bosonic Graphs
We consider a collection of bosonic modes corresponding to the vertices of a
graph Quantum tunneling can occur only along the edges of
and a local self-interaction term is present. Quantum entanglement of one
vertex with respect the rest of the graph is analyzed in the ground-state of
the system as a function of the tunneling amplitude The topology of
plays a major role in determining the tunneling amplitude
which leads to the maximum ground-state entanglement. Whereas in most of the
cases one finds the intuitively expected result we show that it
there exists a family of graphs for which the optimal value of is pushed
down to a finite value. We also show that, for complete graphs, our bi-partite
entanglement provides useful insights in the analysis of the cross-over between
insulating and superfluid ground statesComment: 5 pages (LaTeX) 5 eps figures include
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