835 research outputs found
Dispersive representation of the pion vector form factor in decays
We propose a dispersive representation of the charged pion vector form factor
that is consistent with chiral symmetry and fulfills the constraints imposed by
analyticity and unitarity. Unknown parameters are fitted to the very precise
data on decays obtained by Belle, leading to a
good description of the corresponding spectral function up to a
squared invariant mass GeV. We discuss the effect of isospin
corrections, and obtain the values of low energy observables. For larger values
of , this representation is complemented with a phenomenological description
to allow its implementation in the new TAUOLA hadronic currents.Comment: 22 pages, 4 figures. Determination of rho(770) pole parameters
substantially improved using a new method, based on rational approximants.
Other results unchanged. Version to be published in EPJ
Flavor changing neutral currents in models
We consider flavor changing neutral current effects coming from the
exchange in 3-3-1 models. We show that the mass of this extra neutral vector
boson may be less than 2 TeV and discuss the problem of quark family
discrimination.Comment: REVTEX 10 pages, IFT-P.026/93, IC/93/174 (revised and extended
version
The hadronic off-shell width of meson resonances
Within the resonance chiral effective theory we study the dressed propagators
of the spin-1 fields, as arise from a Dyson-Schwinger resummation
perturbatively constructed from loop diagrams with absorptive contributions in
the s-channel. We apply the procedure to the vector pion form factor and the
elastic pion-pion scattering to obtain the off-shell width of the rho_0 meson.
We adopt a definition of the off-shell width of spin-1 meson resonances that
satisfies the requirements of analyticity, unitarity, chiral symmetry and
asymptotic behaviour ruled by QCD. To fulfil these constraints the resummation
procedure cannot consist only of self-energy diagrams. Our width definition is
shown to be independent of the formulation used to describe the spin-1 meson
resonances.Comment: 1+12 pages, 4 figures. Minor changes in text. Conclusions unchanged.
Version accepted for publication in Phys. Rev.
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