Ref Arxiv: hep-ph/0009108
Ref. & Cit.: NASA ADS
Abstract:

Within the increasing experimental evidence of the existence of the I=0 scalar low mass and wide \sigma meson, we review the {\it first} analysis of its quark and gluon substructure from QCD spectral sum rules and some low-energy theorems. The present data favour equal components of \bar uu+ \bar dd and of gg in its wave function, which make the wide sigma and the narrow f_0(980) as \eta'-like particles. A coherent picture of the other I=0 scalar mesons spectra within this mixing scheme is shortly discussed. We also expect the a_0(980) to be the lowest isovector \bar ud state, and the K^*_0(1430) its \bar ds partner.

Comments: Plenary talk given at the Workshop on `` Possible existence of the Light $\sigma$-resonance and its applications to hadron physics" (Yukawa Institute for Theoretical Physics, Kyoto, Japan, 11-14th June 2000) and Review talk given at the QCD 00 International Euroconference (15th anniversary) Montpellier, France 6-13th July 2000

Ref Arxiv: hep-ph/0004247
DOI: 10.1016/S0550-3213(00)00618-0
Ref. & Cit.: NASA ADS
45 citations
Abstract:

Firstly, we use the recent ALEPH/OPAL data on the V-A spectral functions for fixing the continuum threshold with which the first and second Weinberg sum rules should be satisfied in the chiral limit. Then, we predict the values of the low-energy constants m_{\pi^+}-m_{\pi^0}, {L}_{10}, and test the values of the electroweak kaon penguin matrix elements _{2\pi} obtained from DMO--like sum rules. Secondly, we use the data on the \tau-total hadronic width R_{\tau,V/A} for extracting , in the {MS}\bar scheme, and propose some new sum rules for < Q_7^{3/2}>_{2\pi} in the chiral limit, where the latter require more accurate data for the spectral functions near the $\tau$-mass. Thirdly, we analyze the effects to the matrix element _{2\pi}, of the S_2\equiv(\bar uu+\bar dd) component of the I=0 scalar meson, with its parameters fixed from QCD spectral sum rules. Our results should stimulate a further attention on the r\^ole of the (expected large) gluonium component of the I=0 scalar meson and of the associated operator in the K--->\pi\pi amplitude. Finally, using our previous determinations, we deduce, in the Standard Model (SM), the conservative upper bound for the CP-violating ratio: \epsilon'/\epsilon < (22\pm 9) 10^{-4}, which is in agreement with the present measurements.

Ref Arxiv: hep-ph/0003151
DOI: 10.1016/S0370-2693(00)00621-3
Ref. & Cit.: NASA ADS
53 citations
Abstract:

Including the radiative perturbative corrections and the short distance tachyonic gluon mass effects which mimic the ones of UV renormalons, we re-estimate the decay amplitudes, masses and widths of light hybrid mesons from QCD spectral sum rules. We show that the effects are tiny and confirm the previous lowest order results. We discuss the phenomenological impacts of our results for the vector hybrids.