206 research outputs found
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
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
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
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
The SU(2) and SU(3) chiral phase transitions within Chiral Perturbation Theory
The SU(2) and SU(3) chiral phase transitions in a hot gas made of pions,
kaons and etas are studied within the framework of Chiral Perturbation Theory.
By using the meson meson scattering phase shifts in a second order virial
expansion, we are able to describe the temperature dependence of the quark
condensates. We have estimated the critical temperatures where the different
condensates melt. In particular, the SU(3) formalism yields a lower critical
temperature for the non-strange condensates than within SU(2), and also
suggests that the strange condensate may melt at a somewhat higher temperature,
due to the different strange and non-strange quark masses.Comment: 4 pages, two figures. Final version to appear in Phys Rev D. Complete
model independent calculation. Unitarized ChPt only used to check
extrapolation at high T. References added and numerical bug correcte
Chiral dynamics in the presence of bound states: kaon-nucleon interactions revisited
We study the S-wave kaon-nucleon interactions for strangeness S=-1 in a novel
relativistic chiral unitary approach based on coupled channels. Dispersion
relations are used to perform the necessary resummation of the lowest order
relativistic chiral Lagrangian. A good description of the data in the K^- p,
\pi \Sigma and \pi \Lambda channels is obtained. We show how this method can be
systematically extended to higher orders, emphasizing its applicability to any
scenario of strong self-interactions where the perturbative series diverges
even at low energies. Discussions about the differences to existing approaches
employing pseudo-potentials in a regulated Lippmann-Schwinger equation are
included. Finally, we describe the resonance content of our meson-baryon
amplitudes and discuss its nature.Comment: 12 pp, LaTeX2e, FZJ-IKP(TH)-2000-2
The Nambu-Jona-Lasinio Model at O(1/N^2)
We write down the anomalous dimensions of the fields of the
Nambu--Jona-Lasinio model or chiral Gross Neveu model with a continuous global
chiral symmetry for the two cases and
at in a expansion.Comment: 9 latex pages, 4 figures (available on request from the author),
LTH-308, (2 eqns corrected
Baryon polarization in low-energy unpolarized meson-baryon scattering
We compute the polarization of the final-state baryon, in its rest frame, in
low-energy meson--baryon scattering with unpolarized initial state, in
Unitarized BChPT. Free parameters are determined by fitting total and
differential cross-section data (and spin-asymmetry or polarization data if
available) for , and scattering. We also compare our
results with those of leading-order BChPT
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.
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
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