8,556 research outputs found
Searching for galactic sources in the Swift GRB catalog
Since the early 1990s Gamma Ray Bursts have been accepted to be of
extra-galactic origin due to the isotropic distribution observed by BATSE and
the redshifts observed via absorption line spectroscopy. Nevertheless, upon
further examination at least one case turned out to be of galactic origin. This
particular event presented a Fast Rise, Exponential Decay (FRED) structure
which leads us to believe that other FRED sources might also be Galactic. This
study was set out to estimate the most probable degree of contamination by
galactic sources that certain samples of FREDs have. In order to quantify the
degree of anisotropy the average dipolar and quadripolar moments of each sample
of GRBs with respect to the galactic plane were calculated. This was then
compared to the probability distribution of simulated samples comprised of a
combination of isotropically generated sources and galactic sources. We observe
that the dipolar and quadripolar moments of the selected subsamples of FREDs
are found more than two standard deviations outside those of random
isotropically generated samples.The most probable degree of contamination by
galactic sources for the FRED GRBs of the Swift catalog detected until February
2011 that do not have a known redshift is about 21 out of 77 sources which is
roughly equal to 27%. Furthermore we observe, that by removing from this sample
those bursts that may have any type of indirect redshift indicator and multiple
peaks gives the most probable contamination increases up to 34% (17 out of 49
sources). It is probable that a high degree of contamination by galactic
sources occurs among the single peak FREDs observed by Swift.Comment: Published to A&A, 4 pages, 5 figures, this arXiv version includes
appended table with all the bursts considered in this stud
Noncommutative 6D Gauge Higgs Unification Models
The influence of higher dimensions in noncommutative field theories is
considered. For this purpose, we analyze the bosonic sector of a recently
proposed 6 dimensional SU(3) orbifold model for the electroweak interactions.
The corresponding noncommutative theory is constructed by means of the
Seiberg-Witten map in 6D. We find in the reduced bosonic interactions in 4D
theory, couplings which are new with respect to other known 4D noncommutative
formulations of the Standard Model using the Seiberg-Witten map.
Phenomenological implications due to the noncommutativity of extra dimensions
are explored. In particular, assuming that the commutative model leads to the
standard model values, a bound -5.63 10^{-8} GeV^{-2}< theta <1.06
10^{-7}GeV^{-2} on the corresponding noncommutativity scale is derived from
current experimental constraints on the S and T oblique parameters. This bound
is used to predict a possibly significant impact of noncommutativity effects of
extra dimensions on the rare Higgs boson decay H-> gamma gamma.Comment: Latex file, 11 pages, 1 figur
New optical solitons of Kundu-Eckhaus equation via λ-symmetry
New closed-form exact solutions for the nonlinear Kundu-Eckahus (KE) equation with generalized coefficients are obtained. A travelling wave transformation reduces the KE equation to a second-order ordinary differential equation that is completely integrated by using the λ-symmetry approach. A one-parameter family of singular solutions of the reduced equation provides a unified expression for a class of solutions for the KE equation which contains, as particular cases, most of the exact solutions derived during the last years by using a great variety of powerful integration methods. The general solution of the reduced equation permits to construct a two-parameter family of exact solutions for the KE equation, providing a rich class of new exact solutions that, to the best or our knowledge, have not been reported before
Hints on the quadrupole deformation of the (1232)
The E2/M1 ratio (EMR) of the (1232) is extracted from the world data
in pion photoproduction by means of an Effective Lagrangian Approach (ELA).This
quantity has been derived within a crossing symmetric, gauge invariant, and
chiral symmetric Lagrangian model which also contains a consistent modern
treatment of the (1232) resonance. The \textit{bare} s-channel
(1232) contribution is well isolated and Final State Interactions (FSI)
are effectively taken into account fulfilling Watson's theorem. The obtained
EMR value, EMR%, is in good agreement with the latest lattice
QCD calculations [Phys. Rev. Lett. 94, 021601 (2005)] and disagrees with
results of current quark model calculations.Comment: Enlarged conclusions and explanations on the E2/M1 ratio. Figure 3
improved. References updated. 5 pages. 3 figures. 2 tables. Accepted for
publication in Physical Review
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