175 research outputs found
Resonances, Chiral Symmetry, Coupled Channel Unitarity and Effective Lagrangians
By means of a coupled channel non-perturbative unitary approach, it is
possible to extend the strong constrains of Chiral Perturbation Theory to
higher energies. In particular, it is possible to reproduce the lowest lying
resonances in meson-meson scattering up to 1.2 GeV using the parameters of the
O(p^2) and O(p^4) Chiral Lagrangian. We report on an update of these results
examining their possible relevance for meson spectroscopy.Comment: To appear in the proceedings of the 8th International Conference on
Hadron Spectroscopy, HADROn 99, August 24-28, 1999, Beijing, China. Four
pages, uses espcrc1.sty (included
A Non-Perturbative Chiral Approach for Meson-Meson Interactions
A non-perturbative method which combines constraints from chiral symmetry
breaking and coupled channel unitarity is used to describe meson-meson
interactions up to \sqrt{s}\lesssim 1.2 GeV, extending in this way the range of
applicability of the information contained in Chiral Perturbation Theory (\chi
PT), since this perturbative series is typically restricted to \sqrt{s}\lesssim
500 MeV. The approach uses the O(p^2) and O(p^4) \chiPT Lagrangians. The seven
free parameters resulting from the O(p^4) Lagrangian are fitted to the
experimental data. The approach makes use of the expansion of T^{-1} instead of
the amplitude itself as done in \chiPT. The former expansion is suggested by
analogy with the effective range approximation in Quantum Mechanics and it
appears to be very useful. The results, in fact, are in good agreement with a
vast amount of experimental analyses.Comment: 4 pages, 2 figures, LaTeX, Talk given at PANIC99, Uppsala (Sweden),
June 10-16, 199
Chiral unitary approach to S-wave meson baryon scattering in the strangeness S=0 sector
We study the S-wave interaction of mesons with baryons in the strangeness S=0
sector in a coupled channel unitary approach. The basic dynamics is drawn from
the lowest order meson baryon chiral Lagrangians. Small modifications inspired
by models with explicit vector meson exchange in the t-channel are also
considered. In addition the pi pi N channel is included and shown to have an
important repercussion in the results, particularly in the isospin 3/2 sector.Comment: 23 pages, LaTeX, 21 figure
Dynamical Generation of Hyperon Resonances
In this talk we report on how, using a chiral unitary approach for the
meson--baryon interactions, two octets of baryon states and a
singlet are generated dynamically, resulting in the case of strangeness
in two poles of the scattering matrix close to the nominal
resonance. We suggest experiments which could show evidence for the existence
of these states.Comment: Invited talk in the VIII International Conference on Hypernuclei and
Strange Particle Physic
Hadron resonances generated from the dynamics of the lightest scalar ones
We have studied the interactions of the scalar resonances f_0(980) and
a_0(980) with the vector resonance \phi(1020) and with the lightest
pseudoscalars \pi, K, \eta and \eta'. We first obtain the interaction kernels
without including any new free parameter. Afterwards, the interaction kernels
are unitarized and the final S-wave amplitudes result. We find that these
interactions are very rich and generate a large amount of pseudoscalar
resonances including the K(1460), \pi(1300), \pi(1800), \eta(1475) and X(1835)
resonances. The f_0(980)\phi(1020) self-interactions give rise to the
\phi(2170) resonance. For realistic choices of the parameters we also obtain an
isovector companion in the same mass region from the a_0(980) \phi(1020)
interactions.Comment: 4 pafes, 4 figures. Invited talk at QCD 10 (25th anniversary), 15th
International QCD Conference, 28th June - 3rd July 2010 Montpellier (France).
To be published in Nucl. Phys. B (Proc. Suppl.
Chiral Perturbation Theory and the f2(1270) resonance
Within Chiral Perturbation Theory, we study elastic pion scattering in the
I=0, J=2, channel, whose main features are the f2(1270) resonance and the
vanishing of the lowest order. By means of a chiral model that includes an
explicit resonance coupled to pions, we describe the data and calculate the
resonance contribution to the O(p^4) and O(p^6) chiral parameters. We also
generalize the Inverse Amplitude Method to higher orders, which allows us to
study channels with vanishing lowest order. In particular, we apply it to the
I=0,J=2 case, finding a good description of the f2(1270) resonance, as a pole
in the second Riemann sheet.Comment: 4 pages,1 figur
Chiral dynamics in U(3) unitary chiral perturbation theory
We perform a complete one-loop calculation of meson-meson scattering, and of
the scalar and pseudoscalar form factors in U(3) chiral perturbation theory
with the inclusion of explicit resonance fields. This effective field theory
takes into account the low-energy effects of the QCD U_A(1) anomaly explicitly
in the dynamics. The calculations are supplied by non-perturbative
unitarization techniques that provide the final results for the meson-meson
scattering partial waves and the scalar form factors considered. We present
thorough analyses on the scattering data, resonance spectroscopy, spectral
functions, Weinberg-like sum rules and semi-local duality. The last two
requirements establish relations between the scalar spectrum with the
pseudoscalar and vector ones, respectively. The Nc extrapolation of the various
quantities is studied as well. The fulfillment of all these non-trivial aspects
of the QCD dynamics by our results gives a strong support to the emerging
picture for the scalar dynamics and its related spectrum.Comment: To match the version accepted by Phys.Lett.
Photoproduction of meson and baryon resonances in a chiral unitary approach
By means of a coupled channel non-perturbative unitary approach, it is
possible to extend the strong constrains of Chiral Perturbation Theory to
higher energies. In particular, it is possible to reproduce the lowest lying
resonances in meson-meson scattering up to 1.2 GeV using the parameters of the
O(p^2) and O(p^4) Chiral Lagrangian. The meson baryon sector can also be
tackled along similar lines. We report on an update of these results showing
some examples of photon induced reactions where the techniques have been
recently applied.Comment: Contribution to the Erice Summer School of Nuclear Physics, 21th
course: Electromagnetic Probes and the Structure of Hadrons and Nuclei
September 17th - 25th, 1999, Erice/Sicily/Ital
J/\Psi \to \phi \pi \pi (K \bar{K}) decays, chiral dynamcis and OZI violation
We have studied the invariant mass distributions of the \pi\pi and K \bar{K}
systems for invariant masses up to 1.2 GeV from the J/\Psi \to \phi
\pi\pi(K\bar{K}) decays. The approach exploits the connection between these
processes and the \pi\pi and K\bar{K} strange and non-strange scalar form
factors by considering the \phi meson as a spectator. The calculated scalar
form factors are then matched with the ones from next-to-leading order chiral
perturbation theory, including the calculation of the the K\bar{K} scalar form
factors. Final state interactions in the J/\Psi \to \phi \pi\pi (K\bar{K})
processes are taken into account as rescattering effects in the system of the
two pseudoscalar mesons. A very good agreement with the experimental data from
DM2 and MARK-III is achieved. Furthermore, making use of SU(3) symmetry, the
S-wave contribution to the \pi^+\pi^- event distribution in the J/\Psi \to
\omega \pi^+\pi^- reaction is also given and the data up to energies of about
0.7 GeV are reproduced. These decays of the J/\Psi to a vector and a pair of
pseudoscalars turn out to be very sensitive to OZI violating physics which we
parametrize in terms of a direct OZI violation parameter and the chiral
perturbation theory low energy constants L_4^r and L_6^r. These constants all
come out very different from zero, lending further credit to the statement that
the OZI rule is not operative in the scalar 0^{++} channel.Comment: revtex, 21 pages, 10 figures, extended discussion of the model in
section 2 and some minor corrections, version accepted for publication in
Nucl. Phys.
Radiative open charm decay of the Y(3940), Z(3930), X(4160) resonances
We determine the radiative decay amplitudes for decay into and , or and of some of the charmonium like
states classified as X,Y,Z resonances, plus some other hidden charm states
which are dynamically generated from the interaction of vector mesons with
charm. The mass distributions as a function of the or
invariant mass show a peculiar behavior as a consequence of
the nature of these states. The experimental search of these
magnitudes can shed light on the nature of these states.Comment: 18 pages, 9 figure
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