737 research outputs found
Isospin symmetry breaking and the neutron-proton mass difference
QCD sum rules using polynomial kernels are used to evaluate the strong part
of the proton-neutron mass difference DeltaM_np in a model independent fashion.
The result for the mass difference turns out to depend sensitively on the value
of the four quark condensate and reproduces the experimental value of
DeltaM_np for ~ 2^2.Comment: Arguments detailed. Two references added. Version to appear in
Physical Review C. DOI:10.1103/PhysRevC.00.00520
New Sum Rule Determination of the Nucleon Mass
A new QCD calculation of the mass of the nucleon is presented. It makes use
of a polynomial kernel in the dispersion integrals tailored to practically
eliminate the contribution of the unknown 1/2+ and 1/2- continuum. This
approach avoids the arbitrariness and other drawbacks attached to the Borel
kernel used in previous sum rules calculations. Our method yields stable
results for the nucleon mass and coupling for standard values of the
condensates. The prediction of the nucleon mass m_{N}=(0.945 \pm .045) GeV is
in good agreement with experiment.Comment: 7 page
Isovector Meson Masses from QCD Sum Rules
We present a calculation of the masses of the isovector mesons ( vector,
scalar and pseudoscalar including the established recurrences) using a new
method of finite energy QCD sum rules. The method is based on the idea of
choosing a suitable integration kernel which minimizes the occurring integral
over the cut in the complex energy (squared) plane. We obtain remarkably stable
results in a wide range R, where R is the radius of the integration contour.
The sum rule predictions agree with the experimental values within the expected
accuracy showing that QCD describes single resonances.Comment: Typos and misprints correcte
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