1,777 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
Pseudoscalar pole light-by-light contributions to the muon in Resonance Chiral Theory
We have studied the transition form-factors
() within a chiral invariant framework that allows us to
relate the three form-factors and evaluate the corresponding contributions to
the muon anomalous magnetic moment , through pseudoscalar pole
contributions. We use a chiral invariant Lagrangian to describe the
interactions between the pseudo-Goldstones from the spontaneous chiral symmetry
breaking and the massive meson resonances. We will consider just the lightest
vector and pseudoscalar resonance multiplets. Photon interactions and flavor
breaking effects are accounted for in this covariant framework. This article
studies the most general corrections of order within this setting.
Requiring short-distance constraints fixes most of the parameters entering the
form-factors, consistent with previous determinations. The remaining ones are
obtained from a fit of these form-factors to experimental measurements in the
space-like () region of photon momenta. The combination of data,
chiral symmetry relations between form-factors and high-energy constraints
allows us to determine with improved precision the on-shell -pole
contribution to the Hadronic Light-by-Light scattering of the muon anomalous
magnetic moment: we obtain for
our best fit. This result was obtained excluding BaBar data, which our
analysis finds in conflict with the remaining experimental inputs. This study
also allows us to determine the parameters describing the system
in the two-mixing angle scheme and their correlations. Finally, a preliminary
rough estimate of the impact of loop corrections () and higher vector
multiplets (asym) enlarges the uncertainty up to .Comment: 43 pages, 5 figures. Accepted for publication in JHEP. New subsection
involving error analysis and some minor change
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