79 research outputs found
Radiative Decays, the Topological Susceptibility and the Witten-Veneziano Mass Formula
The formulae describing the radiative decays \eta'(\eta)\rta\c\c in QCD
beyond the chiral limit are derived. The modifications of the conventional PCAC
formulae due to the gluonic contribution to the axial anomaly in the flavour
singlet channel are precisely described. The decay constants are found to
satisfy a modified Dashen formula which generalises the Witten--Veneziano
formula for the mass of the . Combining these results, it is shown how
the topological susceptibility in QCD with massive, dynamical quarks may be
extracted from measurements of \eta'(\eta)\rta\c\c.Comment: TeX, 21 pages, no figures, uses harvma
Phenomenological evidence for the energy dependence of the mixing angle
A phenomenological analysis on various decay processes is performed using an
energy-dependent mixing angle scheme. Special attention is given
to the radiative couplings between lowest-lying vector and pseudoscalar mesons.
The agreement between our predictions and the experimental values is
remarkable. This analysis opens a connection to two-angle fits in the
sector.Comment: 13 pages. Introduction slightly modified. A second Table added.
Conclusions remain unchange
The number of colors in the decays pi^0, eta, eta-prime -> gamma gamma
The decays pi^0, eta, eta-prime -> gamma gamma are investigated up to
next-to-next-to-leading order in the framework of the combined 1/N_c and chiral
expansions. Without mixing of the pseudoscalar mesons the N_c independence of
the pi^0 and eta decay amplitudes is shown to persist at the one-loop level,
although the contribution of the Wess-Zumino-Witten term to the pertinent
vertices is not canceled by the N_c dependent part of a Goldstone-Wilczek term.
The decay amplitude of the singlet field, on the other hand, depends strongly
on N_c and yields under the inclusion of mixing also a strong N_c dependence
for the eta decay. Both the eta and eta-prime decay are suited to confirm the
number of colors to be N_c=3.Comment: 18 pages, 1 figur
Matching of U_L(3) x U_R(3) and SU_L(3) x SU_R(3) Chiral Perturbation Theories
The heavy singlet field is integrated out from the U_L(3) x U_R(3) Chiral
Perturbation Theory and it is shown how its effects on the low-energy dynamics
are reduced to effective vertices for the light mesons. The results are matched
against the standard SU_L(3) x SU_R(3) Chiral Perturbation Theory in order to
establish the relations between the coupling constants from both theories to
one-loop level accuracy.Comment: 10 pages, 1 eps figure. Some comments rephrase
The electric dipole moment of the neutron in chiral perturbation theory
We calculate the electric dipole moments of the neutron and the Lambda within
the framework of heavy baryon chiral perturbation theory. They are induced by
strong CP-violating terms of the effective Lagrangian in the presence of the
vacuum angle theta_0. The construction of such a Lagrangian is outlined and we
are able to give an estimate for theta_0.Comment: 17 pages, 2 figure
Short- and long-distance contributions to the rare decay K_L-->mu+ mu-
The interplay between short- and long-distance contributions to the K_L-->mu+
mu- decay amplitude is analyzed. The long-distance piece is estimated using
chiral perturbation theory techniques and large-N_C considerations, leading to
a consistent description of the pi^0-->e+ e-, eta-->mu+ mu- and K_L-->mu+ mu-
branching ratios.Comment: 4 pages, 1 figure, talk given at the Euroconference QCD 98,
Montpellier, France, July 199
The eta' in baryon chiral perturbation theory
We include in a systematic way the eta' in baryon chiral perturbation theory.
The most general relativistic effective Lagrangian describing the interaction
of the lowest lying baryon octet with the Goldstone boson octet and the eta' is
presented up to linear order in the derivative expansion and its heavy baryon
limit is obtained. As explicit examples, we calculate the baryon masses and the
pi N sigma-term up to one-loop order in the heavy baryon formulation. A
systematic expansion in the meson masses is possible, and appearing divergences
are renormalized.Comment: 16 pages, 2 figure
Hadronic eta and eta-prime decays
The hadronic decays eta, eta-prime -> 3 pi and eta-prime -> eta pi pi are
investigated within the framework of U(3) chiral effective field theory in
combination with a relativistic coupled-channels approach. Final state
interactions are included by deriving s- and p-wave interaction kernels for
meson-meson scattering from the chiral effective Lagrangian and iterating them
in a Bethe-Salpeter equation. Very good overall agreement with currently
available data on decay widths and spectral shapes is achieved.Comment: 28 pages, 5 figures, 8 table
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