492 research outputs found
Neutrinos Have Mass - So What?
In this brief review, I discuss the new physics unveiled by neutrino
oscillation experiments over the past several years, and discuss several
attempts at understanding the mechanism behind neutrino masses and lepton
mixing. It is fair to say that, while significant theoretical progress has been
made, we are yet to construct a coherent picture that naturally explains
non-zero, yet tiny, neutrino masses and the newly revealed, puzzling patterns
of lepton mixing. I discuss what the challenges are, and point to the fact that
more experimental input (from both neutrino and non-neutrino experiments) is
dearly required - and that new data is expected to reveal, in the next several
years, new information. Finally, I draw attention to the fact that neutrinos
may have only just begun to reshape fundamental physics, given the fact that we
are still to explain the LSND anomaly and because the neutrino oscillation
phenomenon is ultimately sensitive to very small new-physics effects.Comment: invited brief review, 15 pages, 1 eps figure, typo corrected,
reference adde
Low Temperature Static and Dynamic Behavior of the Two-Dimensional Easy-Axis Heisenberg Model
We apply the self-consistent harmonic approximation (SCHA) to study static
and dynamic properties of the two-dimensional classical Heisenberg model with
easy-axis anisotropy. The static properties obtained are magnetization and spin
wave energy as functions of temperature, and the critical temperature as a
function of the easy-axis anisotropy. We also calculate the dynamic correlation
functions using the SCHA renormalized spin wave energy. Our analytical results,
for both static properties and dynamic correlation functions, are compared to
numerical simulation data combining cluster-Monte Carlo algorithms and Spin
Dynamics. The comparison allows us to conclude that far below the transition
temperature, where the SCHA is valid, spin waves are responsible for all
relevant features observed in the numerical simulation data; topological
excitations do not seem to contribute appreciably. For temperatures closer to
the transition temperature, there are differences between the dynamic
correlation functions from SCHA theory and Spin Dynamics; these may be due to
the presence of domain walls and solitons.Comment: 12 pages, 14 figure
Right-handed Sneutrinos as Nonthermal Dark Matter
When the minimal supersymmetric standard model is augmented by three
right-handed neutrino superfields, one generically predicts that the neutrinos
acquire Majorana masses. We postulate that all supersymmetry (SUSY) breaking
masses as well as the Majorana masses of the right-handed neutrinos are around
the electroweak scale and, motivated by the smallness of neutrino masses,
assume that the lightest supersymmetric particle (LSP) is an almost-pure
right-handed sneutrino. We discuss the conditions under which this LSP is a
successful dark matter candidate. In general, such an LSP has to be nonthermal
in order not to overclose the universe, and we find the conditions under which
this is indeed the case by comparing the Hubble expansion rate with the rates
of the relevant thermalizing processes, including self-annihilation and
co-annihilation with other SUSY and standard model particles.Comment: 17 pages v.2: References adde
Importance of Numerical Implementation and Clustering Analysis in Force-Directed Algorithms for Accurate Community Detection
Peer reviewedPostprin
Deviation of Atmospheric Mixing from Maximal and Structure in the Leptonic Flavor Sector
I attempt to quantify how far from maximal one should expect the atmospheric
mixing angle to be given a neutrino mass-matrix that leads, at zeroth order, to
a nu_3 mass-eigenstate that is 0% nu_e, 50% nu_mu, and 50% nu_tau. This is done
by assuming that the solar mass-squared difference is induced by an
"anarchical" first order perturbation, an approach than can naturally lead to
experimentally allowed values for all oscillation parameters. In particular,
both |cos 2theta_atm| (the measure for the deviation of atmospheric mixing from
maximal) and |U_e3| are of order sqrt(Delta m^2_sol/Delta m^2_atm) in the case
of a normal neutrino mass-hierarchy, or of order Delta m^2_sol/Delta m^2_atm in
the case of an inverted one. Hence, if any of the textures analyzed here has
anything to do with reality, next-generation neutrino experiments can see a
nonzero cos 2theta_atm in the case of a normal mass-hierarchy, while in the
case of an inverted mass-hierarchy only neutrino factories should be able to
see a deviation of sin^2 2theta_atm from 1.Comment: 12 pages, no figures, references and acknowledgments adde
Seiberg Duality and e+ e- Experiments
Seiberg duality in supersymmetric gauge theories is the claim that two
different theories describe the same physics in the infrared limit. However,
one cannot easily work out physical quantities in strongly coupled theories and
hence it has been difficult to compare the physics of the electric and magnetic
theories. In order to gain more insight into the equivalence of two theories,
we study the ``e+ e-'' cross sections into ``hadrons'' for both theories in the
superconformal window. We describe a technique which allows us to compute the
cross sections exactly in the infrared limit. They are indeed equal in the
low-energy limit and the equality is guaranteed because of the anomaly matching
condition. The ultraviolet behavior of the total ``e+ e-'' cross section is
different for the two theories. We comment on proposed non-supersymmetric
dualities. We also analyze the agreement of the ``\gamma\gamma'' and ``WW''
scattering amplitudes in both theories, and in particular try to understand if
their equivalence can be explained by the anomaly matching condition.Comment: 24 pages, 2 figures, uses psfi
Neutrino Masses and Lepton Flavour Violation in Thick Brane Scenarios
We address the issue of lepton flavour violation and neutrino masses in the
``fat-brane'' paradigm, where flavour changing processes are suppressed by
localising different fermion field wave-functions at different positions (in
the extra dimensions) in a thick brane. We study the consequences of
suppressing lepton number violating charged lepton decays within this scenario
for lepton masses and mixing angles. In particular, we find that charged lepton
mass matrices are constrained to be quasi-diagonal. We further consider whether
the same paradigm can be used to naturally explain small Dirac neutrino masses
by considering the existence of three right-handed neutrinos in the brane, and
discuss the requirements to obtain phenomenologically viable neutrino masses
and mixing angles. Finally, we examine models where neutrinos obtain a small
Majorana mass by breaking lepton number in a far away brane and show that, if
the fat-brane paradigm is the solution to the absence of lepton number
violating charged lepton decays, such models predict, in the absence of flavour
symmetries, that charged lepton flavour violation will be observed in the next
round of rare muon/tau decay experiments.Comment: 33 pages, 9 eps figure
Vortices in the presence of a nonmagnetic atom impurity in 2D XY ferromagnets
Using a model of nonmagnetic impurity potential, we have examined the
behavior of planar vortex solutions in the classical two-dimensional XY
ferromagnets in the presence of a spin vacancy localized out of the vortex
core. Our results show that a spinless atom impurity gives rise to an effective
potential that repels the vortex structure.Comment: 6 pages, 2 figures, RevTex
Automatic Patent Clustering using SOM and Bibliographic Coupling
Patents are usually organized in classes generated by the offices responsible for patents protection, to create a useful format to the information retrieval process. The complexity of patent taxonomies is a challenge for the automation of patent classification. Beside this, the high numbers of subgroups makes the classification in deeper levels more difficult. This work proposes a method to cluster patents using Self Organizing Maps (SOM) networks and bibliographic coupling. To validate the proposed method, an empirical experiment used a patent database from a specific classification system. The obtained results show that patents clusters were successfully identified by SOM through their cited references, and that SOM results were similar to k-Means algorithm results to perform this task. This study can contribute to the development of the knowledge organization systems by evaluating the use of citation analysis in the automatic clustering of patents in a constrained knowledge domain, at the subgroup level of current patent classification systems
Proteomic analysis of soybean leaves in a compatible and an incompatible interaction with Phakopsora pachyrhizi.
Asian soybean rust (ASR), which is incited by the fungus Phakopsora pachyrhizi, is considered one of the most aggressive diseases to the soybean culture. There are no commercial cultivars immune to the pathogen and the control measure currently used is the application of fungicides that harms the environment and increases production costs. For a better understanding of the host?s response to the pathogen at the molecular level, two soybean genotypes were analyzed (PI561356, resistant to ASR and Embrapa 48, susceptible) at 72 hours and 192 hours after inoculation with spores of P. pachyrhizi. Leaf protein profiles of the plants were compared by two-dimensional electrophoresis associated with mass spectrometry (MS). Twenty-two protein spots presented different levels when the two treatments were compared (inoculated vs. non-inoculated). From those, twelve proteins were identified by MS analysis. Some of them are involved in metabolic pathways related to plant defense against pathogens, as in the case of carbonic anhydrase, 1-deoxy-D-xylulose- 5-phosphate reductoisomerase, fructose-bisphosphate aldolase and glutamine synthetase. The possible biochemical-physiological meanings of our findings are discussed
- âŠ