37,594 research outputs found
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
Bipartite graph partitioning and data clustering
Many data types arising from data mining applications can be modeled as
bipartite graphs, examples include terms and documents in a text corpus,
customers and purchasing items in market basket analysis and reviewers and
movies in a movie recommender system. In this paper, we propose a new data
clustering method based on partitioning the underlying bipartite graph. The
partition is constructed by minimizing a normalized sum of edge weights between
unmatched pairs of vertices of the bipartite graph. We show that an approximate
solution to the minimization problem can be obtained by computing a partial
singular value decomposition (SVD) of the associated edge weight matrix of the
bipartite graph. We point out the connection of our clustering algorithm to
correspondence analysis used in multivariate analysis. We also briefly discuss
the issue of assigning data objects to multiple clusters. In the experimental
results, we apply our clustering algorithm to the problem of document
clustering to illustrate its effectiveness and efficiency.Comment: Proceedings of ACM CIKM 2001, the Tenth International Conference on
Information and Knowledge Management, 200
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
Speed of Sound in the Mass Varying Neutrinos Scenario
We discuss about the speed of sound squared in the Mass Varying Neutrinos
scenario (MaVaNs). Recently, it was argued that the MaVaNs has a catastrophic
instability which is the emergence of an imaginary speed of sound at the
non-relativistic limit of neutrinos. As the result of this instability, the
neutrino-acceleron fluid cannot act as the dark energy. However, it is found
that the speed of sound squared in the neutrino-acceleron fluid could be
positive in our model. We examine the speed of sound in two cases of the scalar
potential. One is the small fractional power-law potential and another is the
logarithmic one. The power-law potential model with the right-handed neutrinos
gives a stable one.Comment: 17 pages, References added, minor modification
Entangled-state cycles from conditional quantum evolution
A system of cascaded qubits interacting via the oneway exchange of photons is
studied. While for general operating conditions the system evolves to a
superposition of Bell states (a dark state) in the long-time limit, under a
particular resonance condition no steady state is reached within a finite time.
We analyze the conditional quantum evolution (quantum trajectories) to
characterize the asymptotic behavior under this resonance condition. A distinct
bimodality is observed: for perfect qubit coupling, the system either evolves
to a maximally entangled Bell state without emitting photons (the dark state),
or executes a sustained entangled-state cycle - random switching between a pair
of Bell states while emitting a continuous photon stream; for imperfect
coupling, two entangled-state cycles coexist, between which a random selection
is made from one quantum trajectory to another.Comment: 12 pages, 10 figure
Glassy Dynamics in a Frustrated Spin System: Role of Defects
In an effort to understand the glass transition, the kinetics of a spin model
with frustration but no quenched randomness has been analyzed. The
phenomenology of the spin model is remarkably similiar to that of structural
glasses. Analysis of the model suggests that defects play a major role in
dictating the dynamics as the glass transition is approached.Comment: 9 pages, 5 figures, accepted in J. Phys.: Condensed Matter,
proceedings of the Trieste workshop on "Unifying Concepts in Glass Physics
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