295 research outputs found
Linear meson and baryon trajectories in AdS/QCD
An approximate holographic dual of QCD is constructed and shown to reproduce
the empirical linear trajectories of universal slope on which the square masses
of radially and orbitally excited hadrons join. Conformal symmetry breaking and
other IR effects are described exclusively by deformations of the anti-de
Sitter background metric. The predictions for the light hadron spectrum include
new relations between ground state masses and trajectory slopes and are in good
overall agreement with experimental data.Comment: 4 page
The Strangeness Radius and Magnetic Moment of the Nucleon Revisited
We update Jaffe's estimate of the strange isoscalar radius and magnetic
moment of the nucleon. We make use of a recent dispersion--theoretical fit to
the nucleon electromagnetic form factors and an improved description of
symmetry breaking in the vector nonet. We find ~n.m.
and ~fm. The strange formfactor follows
a dipole with a cut--off mass of 1.46~GeV, . These numbers should be considered as upper limits on the
strange vector current matrix--elements in the nucleon.Comment: 8 pp, LaTeX, uses epsf, 1 figure in separate fil
Scalar Spectrum from a Dynamical Gravity/Gauge model
We show that a Dynamical AdS/QCD model is able to reproduce the linear Regge
trajectories for the light-flavor sector of mesons with high spin and also for
the scalar and pseudoscalar ones. In addition the model has confinement by the
Wilson loop criteria and a mass gap. We also calculate the decay amplitude of
scalars into two pion in good agreement to the available experimental data.Comment: Presented in the 4th International Workshop on Astronomy and
Relativistic Astrophysic
K* nucleon hyperon form factors and nucleon strangeness
A crucial input for recent meson hyperon cloud model estimates of the nucleon
matrix element of the strangeness current are the nucleon-hyperon-K* (NYK*)
form factors which regularize some of the arising loops. Prompted by new and
forthcoming information on these form factors from hyperon-nucleon potential
models, we analyze the dependence of the loop model results for the
strange-quark observables on the NYK* form factors and couplings. We find, in
particular, that the now generally favored soft N-Lambda-K* form factors can
reduce the magnitude of the K* contributions in such models by more than an
order of magnitude, compared to previous results with hard form factors. We
also discuss some general implications of our results for hadronic loop models.Comment: 9 pages, 8 figures, new co-author, discussion extended to the
momentum dependence of the strange vector form factor
Representing and Computing Uncertainty in Phonological Reconstruction
Despite the inherently fuzzy nature of reconstructions in historical
linguistics, most scholars do not represent their uncertainty when proposing
proto-forms. With the increasing success of recently proposed approaches to
automating certain aspects of the traditional comparative method, the formal
representation of proto-forms has also improved. This formalization makes it
possible to address both the representation and the computation of uncertainty.
Building on recent advances in supervised phonological reconstruction, during
which an algorithm learns how to reconstruct words in a given proto-language
relying on previously annotated data, and inspired by improved methods for
automated word prediction from cognate sets, we present a new framework that
allows for the representation of uncertainty in linguistic reconstruction and
also includes a workflow for the computation of fuzzy reconstructions from
linguistic data.Comment: To appear in: Proceedings of the 4th Workshop on Computational
Approaches to Historical Language Chang
Mesonic Spectrum from a Dynamical Gravity/Gauge model
Within a formulation of a Dynamical AdS/QCD model we calculate the spectrum
of light flavored mesons. The background fields of the model correspond to an
IR deformed Anti de Sitter metric coupled to a dilaton field. Confinement comes
as a consequence of the dilaton dynamics coupled to gravity. Additionally to
the Regge-like spectrum of light- scalar, vector and higher spin mesons, we
obtain the decay width of scalar mesons into two pions.Comment: Talk given at Light Cone 2009: Relativistic Hadronic and Particle
Physics (LC 2009), Sao Jose dos Campos, Brazil, 8-13 Jul 2009
Meson-Baryon-Baryon Vertex Function and the Ward-Takahashi Identity
Ohta proposed a solution for the well-known difficulty of satisfying the
Ward-Takahashi identity for a photo-meson-baryon-baryon amplitude (MBB)
when a dressed meson-baryon-baryon (MBB) vertex function is present. He
obtained a form for the MBB amplitude which contained, in addition to
the usual pole terms, longitudinal seagull terms which were determined entirely
by the MBB vertex function. He arrived at his result by using a Lagrangian
which yields the MBB vertex function at tree level. We show that such a
Lagrangian can be neither hermitian nor charge conjugation invariant. We have
been able to reproduce Ohta's result for the MBB amplitude using the
Ward-Takahashi identity and no other assumption, dynamical or otherwise, and
the most general form for the MBB and MBB vertices. However, contrary
to Ohta's finding, we find that the seagull terms are not robust. The seagull
terms extracted from the MBB vertex occur unchanged in tree graphs,
such as in an exchange current amplitude. But the seagull terms which appear in
a loop graph, as in the calculation of an electromagnetic form factor, are, in
general, different. The whole procedure says nothing about the transverse part
of the (MBB) vertex and its contributions to the amplitudes in
question.Comment: A 20 pages Latex file and 16 Postscript figures in an uuencoded
format. Use epsf.sty to include the figures into the Latex fil
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