R-parity-violating signals for chargino production at LEP II

We study chargino pair production at LEP II in supersymmetric models with spontaneously broken R-parity. We perform signal and background analyses, showing that a large region of the parameter space of these models can be probed through chargino searches at LEP II. In particular, we determine the attainable limits on the chargino mass as a function of the magnitude of the effective bilinear R-parity violation parameter ∈, demonstrating that LEP II is able to unravel the existence of charginos with masses almost up to their kinematical limit even in the case of R-parity violation. This requires the study of several final state topologies since the usual MSSM chargino signature is recovered as ∈ → 0. Moreover, for sufficiently large ∈ values, for which the chargino decay mode χ ± → τ ± J dominates, we find through a dedicated Monte Carlo analysis that the χ ± mass bounds are again very close to the kinematic limit. Our results establish the robustness of the chargino mass limit, in the sense that it is basically model-independent. They also show that LEP II can establish the existence of spontaneous R-parity violation in a large region of parameter space should charginos be produced. © 1999 Elsevier Science B.V.

Strangeness content and structure function of the nucleon in a statistical quark model

The strangeness content of the nucleon is determined from a statistical model using confined quark levels, and is shown to have a good agreement with the corresponding values extracted from experimental data. The quark levels are generated in a Dirac equation that uses a linear confining potential (scalar plus vector). With the requirement that the result for the Gottfried sum rule violation, given by the New Muon Collaboration (NMC), is well reproduced, we also obtain the difference between the structure functions of the proton and neutron, and the corresponding sea quark contributions.

Variational studies and replica symmetry breaking in the generalization problem of the binary perceptron

We analyze the average performance of a general class of learning algorithms for the nondeterministic polynomial time complete problem of rule extraction by a binary perceptron. The examples are generated by a rule implemented by a teacher network of similar architecture. A variational approach is used in trying to identify the potential energy that leads to the largest generalization in the thermodynamic limit. We restrict our search to algorithms that always satisfy the binary constraints. A replica symmetric ansatz leads to a learning algorithm which presents a phase transition in violation of an information theoretical bound. Stability analysis shows that this is due to a failure of the replica symmetric ansatz and the first step of replica symmetry breaking (RSB) is studied. The variational method does not determine a unique potential but it allows construction of a class with a unique minimum within each first order valley. Members of this class improve on the performance of Gibbs algorithm but fail to reach the Bayesian limit in the low generalization phase. They even fail to reach the performance of the best binary, an optimal clipping of the barycenter of version space. We find a trade-off between a good low performance and early onset of perfect generalization. Although the RSB may be locally stable we discuss the possibility that it fails to be the correct saddle point globally. ©2000 The American Physical Society.

Exploring neutrino mixing with low energy superbeams

We explore the features of neutrino oscillation which are relevant for measurements of the leptonic CP violating phase δ and the sign of Delta;m13 2 in experiments with low-energy conventional superbeams. Toward the goal, we introduce a new powerful tool called the CP trajectory diagram in bi-probability space which allows us to represent pictorially the three effects, the effects of (a) genuine CP violation due to the sin δ term, (6) CP conserving cos δ term, and (c) fake CP violation due to earth matter, separately in a single diagram. By using the diagram, we observe that there is a two-fold ambiguity in the determination of S which is related with the sign of Delta;m13 2. Possible ways of resolving the ambiguity are discussed. In particular, we point out that an in situ simultaneous measurement of δ and the sign of Delta;m13 2 can be carried out at distances of about 700 km, or at the Phase II of the JHF experiment provided that sin δ ·Delta;m13 2 < 0, both with a megaton class water Cherenkov detector.

Physical parameters and basis transformations in the two-Higgs-doublet model

A direct connection between physical parameters of general two-Higgs-doublet model (2HDM) potentials after electroweak symmetry breaking (EWSB) and the parameters that define the potentials before EWSB is established. These physical parameters, such as the mass matrix of the neutral Higgs bosons, have well-defined transformation properties under basis transformations transposed to the fields after EWSB. The relations are also explicitly written in a basis covariant form. Violation of these relations may indicate models beyond 2HDMs. In certain cases the whole potential can be defined in terms of the physical parameters. The distinction between basis transformations and reparametrizations is pointed out. Some physical implications are discussed. © 2008 The American Physical Society.

Conflict between the classical equivalence principle and quantum mechanics

As far as external gravitational fields described by Newton's theory are concerned, theory shows that there is an unavoidable conflict between the universality of free fall (Galileo's equivalence principle) and quantum mechanics - a result confirmed by experiment. Is this conflict due perhaps to the use of Newton's gravity, instead of general relativity, in the analysis of the external gravitational field? The response is negative. To show this we compute the low corrections to the cross-section for the scattering of different quantum particles by an external gravitational field, treated as an external field, in the framework of Einstein's linearized gravity. To first order the cross-sections are spin-dependent; if the calculations are pushed to the next order they become dependent upon energy as well. Therefore, the Galileo's equivalence and, consequently, the classical equivalence principle, is violated in both cases. We address these issues here.

Una metodología eficiente para manejo de restricciones en algoritmos evolutivos multi-objetivo

This paper presents a new approach for solving constraint optimization problems (COP) based on the philosophy of lexicographical goal programming. A two-phase methodology for solving COP using a multi-objective strategy is used. In the first phase, the objective function is completely disregarded and the entire search effort is directed towards finding a single feasible solution. In the second phase, the problem is treated as a bi-objective optimization problem, turning the constraint optimization into a two-objective optimization. The two resulting objectives are the original objective function and the constraint violation degree. In the first phase a methodology based on progressive hardening of soft constraints is proposed in order to find feasible solutions. The performance of the proposed methodology was tested on 11 well-known benchmark functions.

Statistical quark model for the nucleon structure function

A statistical quark model, with quark energy levels given by a central linear confining potential is used to obtain the light sea-quark asymmetry, d̄/ū, and also for the ratio d/u, inside the nucleon. After adjusting a temperature parameter by the Gottfried sum rule violation, and chemical potentials by the valence up and down quark normalizations, the results are compared with experimental data available. © 2009 American Institute of Physics.

The Owner Share scheduler for a distributed system

In large distributed systems, where shared resources are owned by distinct entities, there is a need to reflect resource ownership in resource allocation. An appropriate resource management system should guarantee that resource's owners have access to a share of resources proportional to the share they provide. In order to achieve that some policies can be used for revoking access to resources currently used by other users. In this paper, a scheduling policy based in the concept of distributed ownership is introduced called Owner Share Enforcement Policy (OSEP). OSEP goal is to guarantee that owner do not have their jobs postponed for longer periods of time. We evaluate the results achieved with the application of this policy using metrics that describe policy violation, loss of capacity, policy cost and user satisfaction in environments with and without job checkpointing. We also evaluate and compare the OSEP policy with the Fair-Share policy, and from these results it is possible to capture the trade-offs from different ways to achieve fairness based on the user satisfaction. © 2009 IEEE.

Improved statistical quark model for the nucleon structure function

An improved statistical quark model, with quark energy levels given by a central linear confining potential, is used to obtain the light sea-quark asymmetry, d̄/ū, and also for the corresponding difference d̄-ū, inside the nucleon. In the model, a temperature parameter is adjusted by recent results obtained for the Gottfried sum rule violation, with two chemical potentials adjusted by the valence up and down quark normalizations. The results are compared with available recent experimental data. © 2010 American Institute of Physics.

Statistical quark models for the nucleon structure functions

We consider some existing relativistic models for the nucleon structure functions, relying on statistical approaches instead of perturbative ones. These models are based on the Fermi-Dirac distribution for the confined quarks, where a density of energy levels is obtained from an effective confining potential. In this context, it is presented some results obtained with a recent statistical quark model for the sea-quark asymmetry in the nucleon. It is shown, within this model, that experimental available observables, such as the ratio and difference between proton and neutron structure functions, are quite well reproduced with just three parameters: two chemical potentials used to reproduce the valence up and down quark numbers in the nucleon, and a temperature that is being used to reproduce the Gottfried sum rule violation. © 2010 American Institute of Physics.

A heuristic algorithm based on multi-assignment procedures for nurse scheduling

This paper tackles a Nurse Scheduling Problem which consists of generating work schedules for a set of nurses while considering their shift preferences and other requirements. The objective is to maximize the satisfaction of nurses' preferences and minimize the violation of soft constraints. This paper presents a new deterministic heuristic algorithm, called MAPA (multi-assignment problem-based algorithm), which is based on successive resolutions of the assignment problem. The algorithm has two phases: a constructive phase and an improvement phase. The constructive phase builds a full schedule by solving successive assignment problems, one for each day in the planning period. The improvement phase uses a couple of procedures that re-solve assignment problems to produce a better schedule. Given the deterministic nature of this algorithm, the same schedule is obtained each time that the algorithm is applied to the same problem instance. The performance of MAPA is benchmarked against published results for almost 250,000 instances from the NSPLib dataset. In most cases, particularly on large instances of the problem, the results produced by MAPA are better when compared to best-known solutions from the literature. The experiments reported here also show that the MAPA algorithm finds more feasible solutions compared with other algorithms in the literature, which suggest that this proposed approach is effective and robust. © 2013 Springer Science+Business Media New York.

Utilização de redes neurais recorrentes na caracterização de cargas não lineares em sistemas elétricos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Jornalismo e cidadania: uma análise comparativa de coberturas de violações de direitos do adolescente

Pós-graduação em Comunicação - FAAC

As responsabilidades decorrentes do desvio de poder na Administração Pública

Pós-graduação em Direito - FCHS