15,697 research outputs found
Grand Unification and Proton Stability Near the Peccei-Quinn Scale
We show that in an model with a DSF-like invisible axion
it is possible to obtain (i) the convergence of the three gauge coupling
constants at an energy scale near the Peccei-Quinn scale; (ii) the correct
value for ; (iii) the stabilization of the proton by
the cyclic symmetries which also stabilize the axion as a
solution to the strong CP problem. Concerning the convergence of the three
coupling constants and the prediction of the weak mixing angle at the -peak,
this model is as good as the minimal supersymmetric standard model with
. We also consider the standard model with six and seven
Higgs doublets. The main calculations were done in the 1-loop approximation but
we briefly consider the 2-loop contributions.Comment: 12 pages, 4 figure
Naturally light invisible axion in models with large local discrete symmetries
We show that by introducing appropriate local symmetries in
electroweak models it is possible to implement an automatic Peccei-Quinn
symmetry keeping at the same time the axion protected against gravitational
effects. Although we consider here only an extension of the standard model and
a particular 3-3-1 model, the strategy can be used in any kind of electroweak
model. An interesting feature of this 3-3-1 model is that if: {\it i)} we add
right-handed neutrinos, {\it ii)} the conservation of the total lepton number,
and {\it iii)} a symmetry, the and the chiral Peccei-Quinn
are both accidental symmetries in the sense that they are not
imposed on the Lagrangian but they are just the consequence of the particle
content of the model, its gauge invariance, renormalizability and Lorentz
invariance. In addition, this model has no domain wall problem.Comment: Some changes and a new reference added, 7 page
Naturally light invisible axion and local Z_{13} times Z_3 symmetries
We show that by imposing local symmetries in an
electroweak model we can implement an invisible axion in
such a way that (i) the Peccei-Quinn symmetry is an automatic symmetry of the
classical Lagrangian; and (ii) the axion is protected from semi classical
gravitational effects. In order to be able to implement such a large discrete
symmetry, and at the same time allow a general mixing in each charge sector, we
introduce right-handed neutrinos and enlarge the scalar sector of the model.
The domain wall problem is briefly considered.Comment: PQ charges and typos correcte
Noise correction on LANDSAT images using a spline-like algorithm
Many applications using LANDSAT images face a dilemma: the user needs a certain scene (for example, a flooded region), but that particular image may present interference or noise in form of horizontal stripes. During automatic analysis, this interference or noise may cause false readings of the region of interest. In order to minimize this interference or noise, many solutions are used, for instane, that of using the average (simple or weighted) values of the neighboring vertical points. In the case of high interference (more than one adjacent line lost) the method of averages may not suit the desired purpose. The solution proposed is to use a spline-like algorithm (weighted splines). This type of interpolation is simple to be computer implemented, fast, uses only four points in each interval, and eliminates the necessity of solving a linear equation system. In the normal mode of operation, the first and second derivatives of the solution function are continuous and determined by data points, as in cubic splines. It is possible, however, to impose the values of the first derivatives, in order to account for shapr boundaries, without increasing the computational effort. Some examples using the proposed method are also shown
Dynamically Induced Spontaneous Symmetry Breaking in 3-3-1 Models
We show that in SU(3)_C X SU(3)_L X U(1)_N (3-3-1) models embedded with a
singlet scalar playing the role of the axion, after imposing scale invariance,
dynamical symmetry breaking of Peccei-Quinn symmetry occurs through the
one-loop effective potential for the singlet field. We, then, analyze the
structure of spontaneous symmetry breaking by studying the new scalar potential
for the model, and verify that electroweak symmetry breaking is tightly
connected to the 3-3-1 breaking by the strong constraints among their vacuum
expectation values. This offers a valuable guide to write down the correct
pattern of symmetry breaking for multi-scalar theories. We also obtained that
the accompanying massive pseudo-scalar, instead of acquiring mass of order of
Peccei-Quinn scale as we would expect, develops a mass at a much lower scale, a
consequence solely of the dynamical breaking.Comment: 12 pages, typos corrected, improved text, conclusions unchange
A method of open cluster membership determination
A new method for the determination of open cluster membership based on a
cumulative effect is proposed. In the field of a plate the relative x and y
coordinate positions of each star with respect to all the other stars are
added. The procedure is carried out for two epochs t_1 and t_2 separately, then
one sum is subtracted from another. For a field star the differences in its
relative coordinate positions of two epochs will be accumulated. For a cluster
star, on the contrary, the changes in relative positions of cluster members at
t_1 and t_2 will be very small. On the histogram of sums the cluster stars will
gather to the left of the diagram, while the field stars will form a tail to
the right. The procedure allows us to efficiently discriminate one group from
another. The greater the distance between t_1 and t_2 and the more cluster
stars present, the greater is the effect. The accumulation method does not
require reference stars, determination of centroids and modelling the
distribution of field stars, necessary in traditional methods. By the proposed
method 240 open clusters have been processed, including stars up to m<13. The
membership probabilities have been calculated and compared to those obtained by
the most commonly used Vasilevskis-Sanders method. The similarity of the
results acquired the two different approaches is satisfactory for the majority
of clusters.Comment: 10 pages, 5 figure
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