16 research outputs found
Target normal single-spin asymmetry in inclusive electron-nucleon scattering in the 1/Nc expansion
The target normal single-spin asymmetry in inclusive electron-nucleon
scattering is studied in the low-energy regime that includes the
resonance. The particular interest in the asymmetry resides in that it is
driven by two-photon exchange effects. It probes the spin-dependent absorptive
part of the two-photon exchange amplitude, which is free of infrared and
collinear singularities and represents the most pristine expression of
two-photon exchange dynamics. The study presented here uses the 1/Nc expansion
of QCD, which combines the and through the emergent SU(4)
spin-flavor symmetry in the baryon sector and allows for a systematic
construction of the transition EM currents. The analysis includes the first
subleading corrections in the 1/Nc expansion and presents results for elastic
and inelastic final states. The asymmetry is found to be in the range
. The resonance plays an important role as an
intermediate state in the elastic asymmetry and as a final state in the
inclusive asymmetry
QCD angular momentum in transitions
transitions offer new possibilities for exploring the
isovector component of the QCD quark angular momentum (AM) operator causing the
flavor asymmetry in the nucleon. We extend the concept of QCD AM to
transitions between baryon states, using light-front densities of the
energy-momentum tensor in transversely localized states. We calculate the transition AM in the expansion, connect it with the
flavor asymmetry in the nucleon, and estimate the values using
lattice QCD results. In the same setup we connect the transition AM to the
transition GPDs sampled in hard exclusive electroproduction processes with transitions, enabling experimental study of the transition
AM.Comment: 7 pages, 1 figur
Induced pseudoscalar coupling of the proton weak interaction
The induced pseudoscalar coupling is the least well known of the weak
coupling constants of the proton's charged--current interaction. Its size is
dictated by chiral symmetry arguments, and its measurement represents an
important test of quantum chromodynamics at low energies. During the past
decade a large body of new data relevant to the coupling has been
accumulated. This data includes measurements of radiative and non radiative
muon capture on targets ranging from hydrogen and few--nucleon systems to
complex nuclei. Herein the authors review the theoretical underpinnings of
, the experimental studies of , and the procedures and uncertainties
in extracting the coupling from data. Current puzzles are highlighted and
future opportunities are discussed.Comment: 58 pages, Latex, Revtex4, prepared for Reviews of Modern Physic