8,193 research outputs found
Production of the Y(4260) State in B Meson Decay
We calculate the branching ratio for the production of the meson in
the decay . We use QCD sum rules approach and we consider
the to be a mixture between charmonium and exotic tetraquark,
, states with . Using the value of the
mixing angle determined previously as: , we get the
branching ratio , which
allows us to estimate an interval on the branching fraction in agreement with the experimental
upper limit reported by Babar Collaboration.Comment: 5 pages, 2 figures, 1 table. arXiv admin note: text overlap with
arXiv:1105.134
A Neural Network Gravitational Arc Finder based on the Mediatrix filamentation Method
Automated arc detection methods are needed to scan the ongoing and
next-generation wide-field imaging surveys, which are expected to contain
thousands of strong lensing systems. Arc finders are also required for a
quantitative comparison between predictions and observations of arc abundance.
Several algorithms have been proposed to this end, but machine learning methods
have remained as a relatively unexplored step in the arc finding process. In
this work we introduce a new arc finder based on pattern recognition, which
uses a set of morphological measurements derived from the Mediatrix
Filamentation Method as entries to an Artificial Neural Network (ANN). We show
a full example of the application of the arc finder, first training and
validating the ANN on simulated arcs and then applying the code on four Hubble
Space Telescope (HST) images of strong lensing systems. The simulated arcs use
simple prescriptions for the lens and the source, while mimicking HST
observational conditions. We also consider a sample of objects from HST images
with no arcs in the training of the ANN classification. We use the training and
validation process to determine a suitable set of ANN configurations, including
the combination of inputs from the Mediatrix method, so as to maximize the
completeness while keeping the false positives low. In the simulations the
method was able to achieve a completeness of about 90% with respect to the arcs
that are input to the ANN after a preselection. However, this completeness
drops to 70% on the HST images. The false detections are of the order of
3% of the objects detected in these images. The combination of Mediatrix
measurements with an ANN is a promising tool for the pattern recognition phase
of arc finding. More realistic simulations and a larger set of real systems are
needed for a better training and assessment of the efficiency of the method.Comment: Updated to match published versio
Comment on ``Casimir force in compact non-commutative extra dimensions and radius stabilization''
We call attention to a series of mistakes in a paper by S. Nam [JHEP 10
(2000) 044, hep-th/0008083].Comment: 6 pages, LaTeX, uses JHEP.cl
Y(4260) as a mixed charmonium-tetraquark state
Using the QCD sum rule approach we study the Y(4260) state assuming that it
can be described by a mixed charmonium-tetraquark current with
quantum numbers. For the mixing angle around , we obtain a value for the mass which is in good agreement with the
experimental mass of the Y(4260). However, for the decay width we find the
value \Ga_Y \approx (1.0\pm 0.2) MeV which is not compatible with the
experimental value \Ga \approx (88\pm 23) MeV. Therefore, we conclude that,
although we can explain the mass of the Y(4260), this state cannot be described
as a mixed charmonium-tetraquark state since, with this assumption, we can not
explain its decay width.Comment: 9 pages, 6 figure
Anisotropic Lifshitz Point at
We present the critical exponents , and
for an -axial Lifshitz point at second order in an expansion.
We introduced a constraint involving the loop momenta along the -dimensional
subspace in order to perform two- and three-loop integrals. The results are
valid in the range . The case corresponds to the usual
Ising-like critical behavior.Comment: 10 pages, Revte
O valor do substratos de nidificação para as abelhas sem ferrão (Meliponini) no cerrado (Maranhão, Brasil) e a meliponicultura como ferramenta de sustentabilidade e conservação.
Lifshitz-point critical behaviour to
We comment on a recent letter by L. C. de Albuquerque and M. M.
Leite (J. Phys. A: Math. Gen. 34 (2001) L327-L332), in which results to
second order in were presented for the critical
exponents , and
of d-dimensional systems at m-axial Lifshitz points.
We point out that their results are at variance with ours. The discrepancy is
due to their incorrect computation of momentum-space integrals. Their
speculation that the field-theoretic renormalization group approach, if
performed in position space, might give results different from when it is
performed in momentum space is refuted.Comment: Latex file, uses the included iop stylefiles; Uses the texdraw
package to generate included figure
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