20 research outputs found
Quantum electrodynamics for vector mesons
Quantum electrodynamics for mesons is considered. It is shown that, at
tree level, the value of the gyromagnetic ratio of the is fixed to 2
in a self-consistent effective quantum field theory. Further, the mixing
parameter of the photon and the neutral vector meson is equal to the ratio of
electromagnetic and strong couplings, leading to the mass difference
at tree order.Comment: 4 pages, 2 figures, REVTeX 4, accepted for publication in PR
Proton and neutron electromagnetic radii and magnetic moments from lattice QCD
We present results for the electromagnetic form factors of the proton and
neutron computed on the -flavor Coordinated Lattice Simulations (CLS)
ensembles including both quark-connected and -disconnected contributions. The
-, pion-mass, lattice-spacing, and finite-volume dependence of our form
factor data is fitted simultaneously to the expressions resulting from
covariant chiral perturbation theory including vector mesons amended by models
for lattice artefacts. From these fits, we determine the electric and magnetic
radii and the magnetic moments of the proton and neutron, as well as the Zemach
radius of the proton. To assess the influence of systematic effects, we average
over various cuts in the pion mass and the momentum transfer, as well as over
different models for the lattice-spacing and finite-volume dependence, using
weights derived from the Akaike Information Criterion (AIC).Comment: 7 pages, 3 figures, contribution to the 16th International Conference
on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2023),
October 15th-20th, 2023, Mainz, Germany. arXiv admin note: substantial text
overlap with arXiv:2401.0540
Electromagnetic form factors of the nucleon from lattice QCD
There is a long-standing discrepancy between different measurements of the
electric and magnetic radii of the proton. Lattice QCD calculations are a
well-suited tool for theoretical investigations of the structure of the nucleon
from first principles. However, all previous lattice studies of the proton's
electromagnetic radii have either neglected quark-disconnected contributions or
were not extrapolated to the continuum and infinite-volume limit. Here, we
present results for the electromagnetic form factors of the proton and neutron
computed on the -flavor Coordinated Lattice Simulations (CLS)
ensembles including both quark-connected and -disconnected contributions. From
simultaneous fits to the -, pion-mass, lattice-spacing, and finite-volume
dependence of the form factors, we determine the electric and magnetic radii
and the magnetic moments of the proton and neutron. For the proton, we obtain
as our final values (stat) (syst) fm,
(stat) (syst) fm, and
(stat) (syst). The magnetic moment is in good agreement with the
experimental value, as is the one of the neutron. On the one hand, our result
for the electric (charge) radius of the proton clearly points towards a small
value, as favored by muonic hydrogen spectroscopy and the recent
-scattering experiment by PRad. Our estimate for the magnetic radius, on
the other hand, is well compatible with that inferred from the A1
-scattering experiment.Comment: 48 pages, 10 figure
Precision calculation of the electromagnetic radii of the proton and neutron from lattice QCD
We present lattice-QCD results for the electromagnetic form factors of the
proton and neutron including both quark-connected and -disconnected
contributions. The parametrization of the -dependence of the form factors
is combined with the extrapolation to the physical point. In this way, we
determine the electric and magnetic radii and the magnetic moments of the
proton and neutron. For the proton, we obtain at the physical pion mass and in
the continuum and infinite-volume limit fm, fm, and , where the errors include all systematics.Comment: 7 pages, 3 figures; for the accompanying paper, see arXiv:2309.06590
[hep-lat]. arXiv admin note: substantial text overlap with arXiv:2309.0659
Infrared renormalization of two-loop integrals and the chiral expansion of the nucleon mass
We describe details of the renormalization of two-loop integrals relevant to
the calculation of the nucleon mass in the framework of manifestly
Lorentz-invariant chiral perturbation theory using infrared renormalization. It
is shown that the renormalization can be performed while preserving all
relevant symmetries, in particular chiral symmetry, and that renormalized
diagrams respect the standard power counting rules. As an application we
calculate the chiral expansion of the nucleon mass to order O(q^6).Comment: Version accepted for publication in Nucl. Phys. A, missing one-loop
diagram added, minor changes in notation, discussion of results improve