L. DelBuono

Radiative decays, nonet symmetry, and SU(3) breaking

We reexamine the problem of simultaneously describing in a consistent way all radiative and leptonic decays of light mesons (V{r_arrow}P{gamma}, P{r_arrow}V{gamma}, P{r_arrow}{gamma}{gamma}, V{r_arrow}e{sup +}e{sup {minus}}). For this purpose, we rely on the hidden local symmetry model in both its anomalous and non-anomalous sectors. We show that the SU(3) symmetry breaking scheme proposed by Bando, Kugo and Yamawaki, supplemented with nonet symmetry breaking in the pseudoscalar sector, allows one to reach a nice agreement with all data, except for the K{sup {asterisk}{plus_minus}} radiative decay. An extension of this breaking pattern allows one to account for this particular decay mode too. Considered together, the whole set of radiative decays provides a pseudoscalar mixing angle {theta}{sub P}{approx_equal}{minus}11{degree} and a value for {theta}{sub V} which is {approx_equal}3{degree} from that of ideal mixing. We also show that it is impossible, in a practical sense, to disentangle the effects of nonet symmetry breaking and those of glue inside the {eta}{sup {prime}}, using only light meson decays. {copyright} {ital 1999} {ital The American Physical Society}

The dipion mass spectrum in e+e- annihilation and τ decay: a dynamical (ρ, ω, φ) mixing approach

We readdress the problem of finding a simultaneous description of the pion form factor data in e+e- annihilations and in τ decays. For this purpose, we work in the framework of the hidden local symmetry Lagrangian and modify the vector meson mass term by including the pion and kaon loop contributions. This leads us to define the physical ρ, ω and φ fields as linear combinations of their ideal partners, with coefficients being meromorphic functions of s, the square of the four-momentum flowing into the vector meson lines. This allows us to define a dynamical, i.e. s-dependent, vector meson mixing scheme. The model is overconstrained by extending the framework in order to include the description of all meson radiative (VPγ and Pγγ couplings) and leptonic (Ve+e- couplings) decays and also the isospin breaking (ω/φ→π+π-) decay modes. The model provides a simultaneous, consistent and good description of the e+e- and τ dipion spectra. The expression for the pion form factor in the latter case is derived from those in the former case by switching off the isospin breaking effects specific to e+e- and switching on those for τ decays. Besides, the model also provides a good account of all decay modes of the form VPγ and Pγγ as well as the isospin breaking decay modes. It leads us to propose new reference values for the ρ0→e+e- and ω→π+π- partial widths, which are part of our description of the pion form factor. Other topics (φ→KK̄, the ρ meson mass and width parameters) are briefly discussed. As the e+e- data are found to be perfectly consistent with τ data up to identified isospin breaking effects, one finds no reason to cast any doubt on them and, therefore, on the theoretical estimate of the muon anomalous moment aμ derived from them. Therefore, our work turns out to confirm the relevance of the reported 3.3σ discrepancy between this theoretical estimate of aμ and its direct BNL measurement.

Upgraded breaking of the HLS model: a full solution to the τ−e + e − and ϕ decay issues and its consequences on g−2 VMD estimates

The muon anomalous magnetic moment aμ and the hadronic vacuum polarization are examined using data analyzed within the framework of a suitably broken HLS model. The analysis relies on all available scan data samples and leaves provisionally aside the existing ISR data. Our HLS model based global fit approach allows for a better check of consistency between data sets and we investigate how results depend on different strategies which may be followed. Relying on global fit qualities, we find several acceptable solutions leading to ambiguities in the reconstructed value for (aμ)th. Among these, the most conservative solution is

A global treatment of VMD physics up to the φ; I: e + e − annihilations, anomalies and vector meson partial widths

a_{\mu}^{\mathrm{had,LO}}[\mathrm{HLS\ improved}]=687.72(4.63) \times10^{-10}

An update of the HLS estimate of the muon g−2

and (aμ)th=11 659 175.37(5.31)×10−10 corresponding to a 4.1σ significance for the difference Δaμ=(aμ)exp−(aμ)th. It is also shown that the various contributions accessible through the model yield uniformly a factor 2 improvement of their uncertainty. The breaking procedure implemented in the HLS model is an extension of the former procedure based on a mechanism defined by Bando, Kugo and Yamawaki (BKY). This yields a quite satisfactory simultaneous description of most e+e− annihilation channels up to and including the ϕ meson (π+π−, π0γ, ηγ, π+π−π0, K+K−,

VMD, the WZW Lagrangian and ChPT: The Third Mixing Angle

K^{0} \overline{K}^{0}

Muon g - 2 estimates: can one trust effective Lagrangians and global fits?

) and of a set of 10 (mostly radiative) decay widths of light mesons. It also allows to achieve the proof of consistency between the e+e−→π+π− annihilation and the τ±→π±π0ν decay and gives a solution to the reported problem concerning the measured partial width ratio

A global treatment of VMD physics up to the φ: II. τ decay and hadronic contributions to g−2

\varGamma(\phi\to K^{+}K^{-})/\varGamma(\phi\to K^{0} \overline{K}^{0})

The dipion mass spectrum in e+e- annihilation and tau decay: Isospin symmetry breaking effects from the (rho, omega, phi) mixing

. Prospects for improving the VMD based estimates of aμ are emphasized.

A global treatment of VMD physics up to the f : II. t decayandhadronic contributions

The HLS Model, equipped with a mechanism providing the breaking of U(3)/SU(3) symmetry and an isospin symmetry breaking leading naturally to vector meson mixing, has been recently shown to successfully account for the e+e−→π+π− cross section and for the dipion spectrum in τ decay. The present study shows that the full anomalous sector of the HLS model can be considered and is validated by the experimental data. Indeed, this extended model provides a successful simultaneous fit to the e+e−→π+π− data together with the available data on the e+e−→π0γ, e+e−→ηγ and e+e−→π0π+π− cross sections. It is shown that the fit of these data sets also predicts an accurate description of the η/η′→π+π−γ decays fully consistent with the reported information on their branching fractions and spectra. Finally, one also derives from our global fits products of widths of the form Γ(V→f1)Γ(V→e+e−) and ratios of the form Γ(V→f1)/Γ(V→f2) describing decays of vector mesons to several non-leptonic final states.