19 research outputs found
Chiral Symmetry and Diffractive Neutral Pion Photo- and Electroproduction
We show that diffractive production of a single neutral pion in
photon-induced reactions at high energy is dynamically suppressed due to the
approximate chiral symmetry of QCD. These reactions have been proposed as a
test of the odderon exchange mechanism. We show that the odderon contribution
to the amplitude for such reactions vanishes exactly in the chiral limit. This
result is obtained in a nonperturbative framework and by using PCAC relations
between the amplitudes for neutral pion and axial vector current production.Comment: 22 pages, 7 figure
Sum Rules for Radiative and Strong Decays of Heavy Mesons
We derive two model-independent sum rules relating the transition matrix
elements for radiative and strong decays of excited heavy mesons to properties
of the lowest-lying heavy mesons. The sum rule for the radiative decays is an
analog of the Cabibbo-Radicati sum rule and expresses the sum of the radiative
widths in terms of the isovector charge radius of the ground state heavy meson.
Using model-dependent estimates and heavy hadron chiral perturbation theory
calculations, we show that this sum rule is close to saturation with states of
excitation energies less than 1 GeV. An analog of the Adler-Weisberger sum rule
gives an useful sum rule for the pionic widths of heavy excited mesons, which
is used to set a model-independent upper bound on the coupling of the P-wave
heavy mesons.Comment: 12 pages, REVTe