18,199 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
Dynamically generated baryon resonances
Identifying a zero-range exchange of vector mesons as the driving force for
the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a
rich spectrum of molecules is formed. We argue that chiral symmetry and
large- considerations determine that part of the interaction which
generates the spectrum. We suggest the existence of strongly bound
crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are
narrow since they can decay only via OZI-violating processes. A narrow nucleon
resonance is found at mass 3.52 GeV. It is a coupled-channel bound state of the
system, which decays dominantly into the
channel. Furthermore two isospin singlet hyperon states at mass
3.23 GeV and 3.58 GeV are observed as a consequence of coupled-channel
interactions of the and states. Most striking is the small width of about 1
MeV of the lower state. The upper state may be significantly broader due to a
strong coupling to the state. The spectrum of crypto-exotic
charm-zero states is completed with an isospin triplet state at 3.93 GeV and an
isospin doublet state at 3.80 GeV. The dominant decay modes involve again the
meson.Comment: Talk presented at N*2005, 10 pages, 1 figur
Hadronic three-body decays of light vector mesons
The decays of light vector mesons into three pseudoscalar mesons are
calculated to leading order in the recently proposed counting scheme that is
based on the hadrogenesis conjecture. Fully differential as well as integrated
decay widths are presented. Since the required parameters have been fixed by
other processes, the considered three-body decays are predictions of the
presented approach. The decay width of the omega meson into three pions agrees
very well with experiment. The partial decay widths of the K^* into its three
K-pi-pi channels are predicted.Comment: 7 page
Large-N_c operator analysis of 2-body meson-baryon counterterms in the chiral Lagrangian
The chiral SU(3) Lagrangian with the baryon octet and decuplet fields is
considered. The Q^2 counterterms involving the decuplet fields are constructed.
We derive the correlation of the chiral parameters implied by the 1/N_c
expansion at leading order in QCD.Comment: 20 pages, 3 figure
Strangeness in the baryon ground states
We compute the strangeness content of the baryon octet and decuplet states
based on an analysis of recent lattice simulations of the BMW, PACS, LHPC and
HSC groups for the pion-mass dependence of the baryon masses. Our results rely
on the relativistic chiral Lagrangian and large- sum rule estimates of the
counter terms relevant for the baryon masses at NLO. A partial summation is
implied by the use of physical baryon and meson masses in the one-loop
contributions to the baryon self energies. A simultaneous description of the
lattice results of the BMW, LHPC, PACS and HSC groups is achieved. From a
global fit we determine the axial coupling constants and in agreement with their values extracted from semi-leptonic
decays of the baryons. Moreover, various flavor symmetric limits of baron octet
and decuplet masses as obtained by the QCDSF-UKQCD group are recovered. We
predict the pion- and strangeness sigma terms and the pion-mass dependence of
the octet and decuplet ground states at different strange quark masses.Comment: 15 pages, 5 tables, 3 figures. There are two significant extensions
in the revised manuscript. First, a precise determination of the axial
coupling constants F and D from the lattice data on the baryon masses is
provided. Second, it is shown that the lattice data of the QCDSF-UKQCD group
on the baryon masses in the flavor symmetric limit are recovered. The 3rd
version is the published versio
On the consistency of recent QCD lattice data of the baryon ground-state masses
In our recent analysis of lattice data of the BMW, LHPC and PACS-CS groups we
determined a parameter set of the chiral Lagrangian that allows a simultaneous
description of the baryon octet and decuplet masses as measured by those
lattice groups. The results on the baryon spectrum of the HSC group were
recovered accurately without their inclusion into our 6 parameter fit. We show
that the same parameter set provides an accurate reproduction of the recent
results of the QCDSF-UKQCD group probing the baryon masses at quite different
quark masses. This shows a remarkable consistency amongst the different lattice
simulations. With even more accurate lattice data in the near future it will
become feasible to determine all low-energy parameters relevant at NLO.Comment: 7 pages, 2 figure
A unitary and causal effective field theory
We report on a novel scheme based on the chiral Lagrangian. It is used to
analyze pion-nucleon scattering, pion photoproduction, and nucleon Compton
scattering. Subthreshold partial-wave amplitudes are calculated in chiral
perturbation theory and analytically extrapolated with constraints imposed by
electromagnetic-gauge invariance, causality and unitarity. Experimental
quantities are reproduced up to energies MeV in terms of
the parameters relevant at order .Comment: 4 pages, contribution to the proceedings of the MENU 2010 conference,
May 31-June 4, 2010, Williamsburg VA, US
- …