23,233 research outputs found
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
Unitary and causal dynamics based on the chiral Lagrangian
Pion-nucleon scattering, pion photoproduction, and nucleon Compton scattering
are analyzed within a scheme based on the chiral Lagrangian. Partial-wave
amplitudes are obtained by an analytic extrapolation of subthreshold reaction
amplitudes computed in chiral perturbation theory, where the constraints set by
electromagnetic-gauge invariance, causality and unitarity are used to stabilize
the extrapolation. Experimental data are reproduced up to energies
MeV in terms of the parameters relevant at order . A
striking puzzle caused by an old photon asymmetry measurement close to the pion
production threshold is discussed.Comment: Invited plenary talk at Chiral 10 Workshop, Valencia (Spain), June
21-24, 201
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
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