19,625 research outputs found
Chiral SU(3) Symmetry and Strangeness
In this talk we review recent progress on the systematic evaluation of the
kaon and antikaon spectral functions in dense nuclear matter based on a chiral
SU(3) description of the low-energy pion-, kaon- and antikaon-nucleon
scattering data.Comment: 9 pages, 4 figures, invited talk given by M.F.M.L. at the SQM2001
conferenc
Effective chiral theory of kaon-nucleon scattering
We apply the relativistic chiral SU(3) Lagrangian density to kaon-nucleon
scattering imposing constraints from the pion-nucleon s- and p-wave threshold
parameters at chiral order . The s and u channel decouplet baryon exchange
is included explicitly and is found to play a crucial role in understanding the
empirical s- and p-wave nuclear kaon dynamics quantitatively.Comment: 12 pages, 5 figures, invited talk "International Workshop XXVII on
Gross Properties of Nuclei and Nuclear Excitations", Hirschegg, Austria,
January, 200
Covariant meson-baryon scattering with chiral and large N_c constraints
We give a review of recent progress on the application of the relativistic
chiral SU(3) Lagrangian to meson-baryon scattering. It is shown that a combined
chiral and 1/N_c expansion of the Bethe-Salpeter interaction kernel leads to a
good description of the kaon-nucleon, antikaon-nucleon and pion-nucleon
scattering data typically up to laboratory momenta of p_lab about 500 MeV. We
solve the covariant coupled channel Bethe-Salpeter equation with the
interaction kernel truncated to chiral order Q^3 where we include only those
terms which are leading in the large N_c limit of QCD.Comment: 27 pages, 5 figures, Invited talk given by M.F.M.L. at the IARD 2000
meetin
Charmed meson resonances from chiral coupled-channel dynamics
Charmed meson resonances with quantum numbers J^P=0^+ and J^P=1^+ are
generated in terms of chiral coupled-channel dynamics. At leading order in the
chiral expansion a parameter-free prediction is obtained for the scattering of
Goldstone bosons off charmed pseudo-scalar and vector mesons. The recently
announced narrow open charm states observed by the BABAR and CLEO
collaborations are reproduced. We suggest the existence of states that form an
anti-triplet and a sextet representation of the SU(3) group. In particular, so
far unobserved narrow isospin-singlet states with negative strangeness are
predicted.Comment: Presented at Hadron 03: 10th International Conference on Hadron
Spectroscopy, Aschaffenburg, Germany, 31 Aug - 6 Sep 200
Chiral symmetry, strangeness and resonances
We review the important role played by the chiral SU(3) symmetry in
predicting the properties of antikaons and hyperon resonances in cold nuclear
matter. Objects of crucial importance are the meson-baryon scattering
amplitudes obtained within the chiral coupled-channel effective field theory.
The formation of baryon resonances as implied by chiral coupled-channel
dynamics is discussed. Results for antikaon and hyperon-resonance spectral
functions are presented for isospin symmetric and asymmetric matter.Comment: invited talk presented by M.F.M.L. at the 18th Nishinomiya Yukawa
Memorial Symposium, 21 pages, 12 figure
Two-nucleon scattering: merging chiral effective field theory with dispersion relations
We consider two-nucleon scattering close to threshold. Partial-wave
amplitudes are obtained by an analytic extrapolation of subthreshold reaction
amplitudes calculated in a relativistic formulation of chiral perturbation
theory. The constraints set by unitarity are used in order to stabilize the
extrapolation. Neutron-proton phase shifts are analyzed up to laboratory
energies MeV based on the
next-to-next-to-next-to-leading order expression for the subthreshold
amplitudes. We find a reasonably accurate description of the empirical S- and
P-waves and a good convergence of our approach. These results support the
assumption that the subthreshold nucleon-nucleon scattering amplitude may be
computed perturbatively by means of the chiral expansion. The intricate soft
scales that govern the low-energy nucleon-nucleon scattering are generated
dynamically via a controlled analytic continuation.Comment: 10 pages, 5 figures, version accepted for publication, a more
detailed discussion of the results is adde
Two-nucleon scattering: merging chiral effective field theory with dispersion relations
We consider two-nucleon scattering close to threshold. Partial-wave
amplitudes are obtained by an analytic extrapolation of subthreshold reaction
amplitudes calculated in a relativistic formulation of chiral perturbation
theory. The constraints set by unitarity are used in order to stabilize the
extrapolation. Neutron-proton phase shifts are analyzed up to laboratory
energies MeV based on the
next-to-next-to-next-to-leading order expression for the subthreshold
amplitudes. We find a reasonably accurate description of the empirical S- and
P-waves and a good convergence of our approach. These results support the
assumption that the subthreshold nucleon-nucleon scattering amplitude may be
computed perturbatively by means of the chiral expansion. The intricate soft
scales that govern the low-energy nucleon-nucleon scattering are generated
dynamically via a controlled analytic continuation.Comment: 10 pages, 5 figures, version accepted for publication, a more
detailed discussion of the results is adde
Quark-mass dependence of baryon resonances
We study the quark-mass dependence of J^P = \frac12^- s-wave and J^P =
\frac32^- d-wave baryon resonances. Parameter-free results are obtained in
terms of the leading order chiral Lagrangian. In the 'heavy' SU(3) limit with
m_\pi =m_K \simeq 500 MeV the s-wave resonances turn into bound states forming
two octets plus a singlet representations of the SU(3) group. Similarly the
d-wave resonances turn into bound states forming an octet and a decuplet in
this limit. A contrasted result is obtained in the 'light' SU(3) limit with
m_\pi =m_K \simeq 140 MeV for which no resonances exist.Comment: 8 pages, three figures, talk presented at HYP200
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