2 research outputs found
The soft-energy region in the radiative decay of bound states
The orthopositronium decay to three photons is studied in the phase-space
region where one of the photons has an energy comparable to the relative
three-momentum of the e+e- system (w ~ m alpha). The NRQED computation in this
regime shows that the dominant contribution arises from distances ~
1/(mw)^(1/2), which allows to treat the Coulomb interaction perturbatively. The
small-photon energy expansion of the 1-loop decay spectrum from full QED yields
the same result as the effective theory. By doing the threshold expansion of
the 1-loop QED amplitude we confirm that the leading term arises from a
loop-momentum region where q^0 ~ q^2/m ~ w. This corresponds to a new
non-relativistic loop-momentum region, which has to be taken into account for
the description of a non-relativistic particle-antiparticle system that decays
through soft photon emission.Comment: 28 pages, 5 figures; typos corrected, one reference added, published
versio
Odd-intrinsic-parity processes within the Resonance Effective Theory of QCD
We analyse the most general odd-intrinsic-parity effective Lagrangian of QCD
valid for processes involving one pseudoscalar with vector mesons described in
terms of antisymmetric tensor fields. Substantial information on the
odd-intrinsic-parity couplings is obtained by constructing the
vector-vector-pseudoscalar Green's three-point function, at leading order in
1/Nc, and demanding that its short-distance behaviour matches the corresponding
OPE result. The QCD constraints thus enforced allow us to predict the decay
amplitude omega -> pion gamma, and the O(p^6) corrections to pion -> gamma
gamma. Noteworthy consequences concerning the vector meson dominance assumption
in the decay omega -> 3 pions are also extracted from the previous analysis.Comment: 20 pages, 4 figure