1,819 research outputs found
Pole structure and compositeness
We present in this talk a series of new results on the nature of a bound
state or resonance based on the calculation of the expectation values of the
number operators of the free particles in the state of interest. In this way, a
new universal criterion for the elementariness of a bound state emerges. In the
case of large particle wavelengths compared to the range of their interaction,
a new closed formula for the compositeness of a bound state in a two-particle
continuum is obtained. The extension of these results to resonances with
respect to the open channels can be given by making use in addition of suitable
phase-factor transformations as also reviewed here. We end with a discussion on
the as possible double- or triple-pole virtual state, which would be
the first case in particle phenomenology.Comment: 10 pages, 4 figures. Plenary talk at Hadron201
Final State Interactions in Hadronic D decays
We show that the large corrections due to final state interactions (FSI) in
the D^+\to \pi^-\pi^+\pi^+, D^+_s\to \pi^-\pi^+\pi^+, and D^+\to K^-\pi^+\pi^+
decays can be accounted for by invoking scattering amplitudes in agreement with
those derived from phase shifts studies. In this way, broad/overlapping
resonances in S-waves are properly treated and the phase motions of the
transition amplitudes are driven by the corresponding scattering matrix
elements determined in many other experiments. This is an important step
forward in resolving the puzzle of the FSI in these decays. We also discuss why
the \sigma and \kappa resonances, hardly visible in scattering experiments, are
much more prominent and clearly visible in these decays without destroying the
agreement with the experimental \pi\pi and K\pi low energy S-wave phase shifts.Comment: 22 pages, 6 figures, 5 tables. Minor changes. We extend the discusion
when quoting a reference and we include a new one. Some typos are fixe
Unitarization Technics in Hadron Physics with Historical Remarks
We review a series of unitarization techniques that have been used during the
last decades, many of them in connection with the advent and development of
current algebra and later of Chiral Perturbation Theory. Several methods are
discussed like the generalized effective-range expansion, K-matrix approach,
Inverse Amplitude Method, Pad\'e approximants and the N/D method. More details
are given for the latter though. We also consider how to implement them in
order to correct by final-state interactions. In connection with this some
other methods are also introduced like the expansion of the inverse of the form
factor, the Omn\'es solution, generalization to coupled channels and the
Khuri-Treiman formalism, among others.Comment: 45 pages, 2 figures. Invited contribution to a special issue on
"Effective Field Theories - Chiral Perturbation Theory and Non-relativistic
QFT". Updated to match the published versio
Scalar Mesons and Chiral Symmetry
It is the purpose of the present manuscript to emphasize those aspects that
make the scalar sector with vacuum quantum numbers rather unique. Chiral
symmetry is the basic tool for our study together with a resummation of Chiral
Perturbation Theory (CHPT) that stresses the role of unitarity but also allows
one to include explicit resonance fields and to match with the CHPT expansion
at low energies.Comment: 8 pages,2 figures. Invited talk at the -meson workshop,
Kyoto, June 200
Aspects of Strangeness -1 Meson-Baryon Scattering
We consider meson-baryon interactions in S-wave with strangeness -1. This is
a sector populated by plenty of resonances interacting in several two-body
coupled channels. We consider a large set of experimental data, where the
recent experiments are remarkably accurate. This requires a sound theoretical
description to account for all the data and we employ Unitary Chiral
Perturbation Theory up to and including O(p^2). The spectroscopy of our
solutions is studied within this approach, discussing the rise from the pole
content of two \Lambda(1405) resonances and of the \Lambda(1670),
\Lambda(1800), \Sigma(1480), \Sigma(1620) and \Sigma(1750). We finally argue
about our preferred fit.Comment: 6 figures, 3 figures, talk given in the IVth International Conference
on Quarks and Nuclear Physics (QNP06), Madrid June 5th and 10th, 2006. One
reference is update
Identification of a Scalar Glueball
We have performed a coupled channel study of the meson-meson S-waves
involving isospins (I) 0, 1/2 and 3/2 up to 2 GeV. For the first time the
channels \pi\pi, K\bar{K}, \eta\eta, \sigma\sigma, \eta\eta', \eta'\eta',
\rho\rho, \omega\omega, \omega\phi$, \phi\phi, a_1\pi and \pi^*\pi are
considered. All the resonances with masses below 2 GeV for I=0 and 1/2 are
generated by the approach. We identify the f_0(1710) and a pole at 1.6 GeV,
which is an important contribution to the f_0(1500), as glueballs. This is
based on an accurate agreement of our results with predictions of lattice QCD
and the chiral suppression of the coupling of a scalar glueball to \bar{q}q.
Another nearby pole, mainly corresponding to the f_0(1370), is a pure octet
state not mixed with the glueball.Comment: 5 pages, 1 figure. More data are included and reproduced. Some
discussions have been rephrase
Scalar-Pseudoscalar scattering and pseudoscalar resonances
The interactions between the f_0(980) and a_0(980) scalar resonances and the
lightest pseudoscalar mesons are studied. We first obtain the interacting
kernels, without including any ad hoc free parameter, because the lightest
scalar resonances are dynamically generated. These kernels are unitarized,
giving the final amplitudes, which generate pseudoscalar resonances, associated
with the K(1460), \pi(1300), \pi(1800), \eta(1475) and X(1835). We also
consider the exotic channels with I=3/2 and I^G=1^+ quantum numbers. The former
could be also resonant in agreement with a previous prediction.Comment: 3 pages, 2 figures; Contributed oral presentation in (QCHS09) The IX
International Conference on Quark Confinement and Hadron Spectrum - Madrid,
Spain, 30 Aug 2010 - 03 Sep 201
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