776 research outputs found
The impact of photoproduction on the resonance spectrum
The J\"ulich-Bonn coupled-channel framework is extended to
photoproduction. The spectrum of nucleon and resonances is extracted
from simultaneous fits to several pion-induced reactions in addition to pion,
eta and photoproduction off the proton. More than 40,000 data
points up to a center-of-mass energy of E2.3 GeV including recently
measured double-polarization observables are analyzed. The influence of the
channel on the extracted resonance parameters and the
appearance of states not seen in other channels is investigated. The
J\"ulich-Bonn model includes effective three-body channels and guarantees
unitarity and analyticity, which is a prerequisite for a reliable determination
of the resonance spectrum in terms of poles and residues.Comment: 21 pages, 11 figures. Minor modifications, additional information in
the appendix. Accepted for publication in Eur. Phys. J.
Chiral Dynamics and S-wave Contributions in Semileptonic B decays
The flavor-changing neutral current process is beneficial to
testing the standard model and hunting for new physics scenarios. In exclusive
decay modes like , the S-wave effects may not be
negligible and thus have to be reliably estimated. Using the scalar form
factors derived from dispersion relations in two channels and matched to Chiral
Perturbation Theory, we investigate the S-wave contributions in , with the invariant mass lying in the vicinity of the
mass of , and the with .
We find that the S-wave will modify differential decay widths by about 10% in
the process of and about 5% in . A forward-backward asymmetry for the charged kaon in the final state
arises from the interference between the S-wave and P-wave contributions. The
measurement of this asymmetry offers a new way to determine the variation of
the S-wave phase versus the invariant mass.Comment: 26 pages, 10 figure
Cusps in K_L --> 3 pi decays
The pion mass difference generates a pronounced cusp in K --> 3 pi decays,
the strength of which is related to the pi pi S-wave scattering lengths. We
apply an effective field theory framework developed earlier to evaluate the
amplitudes for K_L --> 3 pi decays in a systematic manner, where the strictures
imposed by analyticity and unitarity are respected automatically. The
amplitudes for the decay eta --> 3 pi are also given.Comment: 15 pages, 3 figures, uses Elsevier styl
On the chiral effective meson-baryon Lagrangian at third order
We show that the recently constructed complete and ``minimal'' third order
meson-baryon effective chiral Lagrangian can be further reduced from 84 to 78
independent operators.Comment: 6 pp, accepted for publication in Eur. Phys. J.
Scalar mesons in a finite volume
Using effective field theory methods, we discuss the extraction of the mass
and width of the scalar mesons f0(980) and a0(980) from the finite-volume
spectrum in lattice QCD. In particular, it is argued that the nature of these
states can be studied by invoking twisted boundary conditions, as well as
investigating the quark mass dependence of the spectrum.Comment: 18 pages, 3 figure
Neutron-proton mass difference in nuclear matter
Isospin-breaking effects in nuclear matter are studied in the framework of a
medium-modified Skyrme model. The proposed effective Lagrangian incorporates
both the medium influence of the surrounding nuclear environment on the single
nucleon properties and an explicit isospin-breaking effect in the mesonic
sector. The approach predicts that the neutron-proton mass difference decreases
in isospin-symmetric nuclear matter but by a very small amount only.Comment: 8 pages, 4 figures, revised versio
Complete phase diagram for the integrable chain with alternating spins in the sectors with competing interactions
We investigate the anisotropic integrable spin chain consisting of spins
and by means of thermodynamic Bethe ansatz for the anisotropy
, where the analysis of the Takahashi conditions leads to a more
complicated string picture. We give the phase diagram with respect to the two
real coupling constants and , which contains a new region
where the ground state is formed by strings with infinite Fermi zones. In this
region the velocities of sound for the two physical excitations have been
calculated from the dressed energies. This leads to an additional line of
conformal invariance not known before.Comment: 13 pages, LaTeX, uses ioplppt.sty and epsfig.sty, figure 3 correcte
Isospin-breaking two-nucleon force with explicit Delta-excitations
We study the leading isospin-breaking contributions to the two-nucleon
two-pion exchange potential due to explicit Delta degrees of freedom in chiral
effective field theory. In particular, we find important contributions due to
the delta mass splittings to the charge symmetry breaking potential that act
opposite to the effects induced by the nucleon mass splitting.Comment: 10 pages, 4 figure
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