Ref HAL: hal-00378183_v1
Ref Arxiv: 0904.2555
DOI: 10.1016/j.physletb.2009.08.039
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30 citations
Abstract:

We extract the K+K- couplings of the isoscalar scalar mesons sigma/f_0(600)and f_0(980) from pi pi to pi pi / K K scatterings and found: |g_{sigma K+K-}|/|g_{sigma pi+pi-}|= 0.8 and |g_{f_0 K+K-}|/ |g_{f_0 pi+pi-}|= 1.7. Theseresults, together with the tiny "direct" gamma gamma width of the sigma and itslarge hadronic width, are a strong indication for the gluonium/glueball natureof the sigma-meson, as predicted by QCD spectral sum rules (QSSR) + somelow-energy theorems (LET), while some other assignements (pi pi molecule,tetraquark state and ordinary qq meson) do not satisfy simultaneously theserequirements from the data. These properties suggest that the sigma can be ascalar meson associated to the U(1)V conformal anomaly like is the eta'-mesonfor the U(1)A anomaly.

Ref HAL: hal-00378180_v1
Ref Arxiv: 0903.2266
DOI: 10.1016/j.physletb.2009.04.012
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29 citations
Abstract:

We systematically re-examine the extraction of the masses and couplings ofthe 1^{-+} hybrid, four-quark and molecule mesons from QCD spectral sum rules(QSSR). To NLO for the perturbative and power corrections, the hybrid mass isM_H=1.81(6) GeV and M_H < 2.2(2) GeV from the positivity of the spectralfunction. In the same way, but to LO, the four-quark state mass is M_{4q}=1.70(4) GeV and M_{4q} < 2.4(1) GeV, while the molecule mass is about 1.3(1)GeV. The observed \pi_1(1400) and \pi_1(1600) might be explained by atwo-component mixing with the set of input masses (1.2-1.3 ; 1.70-1.74) GeV andwith a mixing angle \theta= -(11.7+- 2.2)^0, which slightly favours amolecule/four-quark mixing, and which eventually suggests that the \pi_1(2015)is mostly an hybrid meson. Isospin and non-exotic partners of the previousstates and some of their radial excitations are also expected to be found inthe energy region around 2 GeV. Further tests of this phenomenological scenarioare required.

Ref HAL: hal-00378178_v1
Ref Arxiv: 0902.1322
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Abstract:

This part of the talk aims to present briefly the biodata and the exceptionalcareer of Paco Yndurain who left us suddenly in June 2008. The scientific part:Light Scalar Mesons in QCD is published in the proceedings of QCD 08(Montpellier 7-12th july 2008: arXiv:0811.0563 [hep-ph]).

Comments: 7 pages, Invited Plenary Talk given at Confinement8, 1-6 sept., Mainz (DE) (bug corrected)

Ref HAL: hal-00378175_v1
Ref Arxiv: 0901.3823
DOI: 10.1016/j.physletb.2009.01.062
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89 citations
Abstract:

We re-examine recent determinations of power corrections from tau-decay andconfront the results with the existing ones from QCD spectral sum rules (QSSR).We conclude that contrary to the QSSR analysis, which lead to =(6.8+-1.3)10^{-2} GeV^4, tau-decay is not a good place for extracting thegluon condensate due to its extra alpha_s^2 coefficient which suppresses itscontribution in this process. Results from e^+e^- sum rules and tau-decay: rhoalpha_s^2= (4.5+-0.3)10^{-4}GeV^6, where rho=3.0+-0.2 confirm the deviationfrom the vacuum saturation estimate of the four-quark condensate."Non-standard"power corrections (direct instantons, duality violation and tachyonic gluonmass) beyond the SVZ-expansion, partially cancel out in the V+A hadronictau-decay channel, which gives at order alpha_s^4:alpha_s(M_tau)=0.3249(29)_{ex}(75)_{th} leading to als(M_Z)|_tau=0.1192(4)_{ex}(9)_{th},in remarkable agreement with (but more accurate than)alpha_s(M_Z)|_Z=0.1191(27)obtained at the same alpha_s^4 order from the Z-widthand the global fit of electroweak data. Finally, the role of the tachyonicgluon mass in the determinations of |V_{us}|from tau-decay and of m_s fromtau-decay, e^+e^- and (pseudo)scalar channels is emphasized.

Ref HAL: hal-00378089_v1
Ref Arxiv: 0811.0563
DOI: 10.1016/j.nuclphysbps.2008.12.069
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19 citations
Abstract:

I present a mini-review of the masses and couplings of the bare (unmixed)light scalar mesons : $\bar qq, (\overline{qq})(qq), (\bar qq)(\bar qq), gg$from QCD spectral sum rules (QSSR) and low-energy theorems (LET) which wecompare with recent lattice calculations when available. Some unbiased commentson the different scenarios are given. The possiblity for the $\sigma (0.6)$ tobe mostly a gluonium/glueball with a huge violation of the OZI rule in itsdecay is discussed. This review complements and updates the ones presentedearlier [1]. Despite some progresses, the internal structure of the lightscalar mesons remain puzzling, and some further efforts are required. It willbe more fun at LHC if the Higgs of the Standard Model is a $\sigma$-likeresonance.

Comments: Scientific part of the invited talk for a tribute to Paco Yndurain at Confinement (3-7th september, Mainz)

Ref HAL: hal-00378072_v1
Ref Arxiv: 0807.2830
DOI: 10.1016/j.physletb.2008.08.060
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25 citations
Abstract:

We confront the recent improved measurements of the D_{(s)} (semi) leptonicdecays with lattice QCD (LQCD) with n_f=3 flavours and QCD spectral sum rules(QSSR) predictions. D\to\mu\nu_\mu leptonic width data compared withtheoretical determinations of f_D, leads to the value of the CKM mixing angle :|V_cd|= 0.230 (10)_exp (9)_th. Measured ratio of the D semi-leptonic widthscombined with LQCD and QSSR predictions leads to the average |V_cd|/|V_cs|=0.2175(88), and then to |V_cs|= 1.068(47). We consider the previousdeterminations as improvements of the existing estimates. Using the averagedata of the D_s\to \mu\nu_\mu (resp. D_s\to \tau\nu_\tau) branching ratios, oneobtains : |V_cs|f_{D_s}^\mu= (259 +- 12) {MeV} (resp) |V_cs|f_{D_s}^\tau= (274+- 13) {MeV}, which can be compared with the average of the Standard Model (SM)values from LQCD and QSSR f_{D_s}=(240 +- 7) MeV. If one uses the presentdetermination of |V_cs|, there is an agreement with the SM prediction within1\sigma. If instead, we impose the unitarity constraint |V_cs|< 1, or assume(as frequently done) |V_cs|=|V_ud|, we would obtain a deviation from the SMexpectations ranging from 1.5 to 3 \sigma, eventually signaling some NewPhysics beyond the SM.

Ref HAL: hal-00378070_v1
Ref Arxiv: 0806.4092
DOI: 10.1016/j.nuclphysbps.2008.09.043
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10 citations
Abstract:

We analyse data on pi pi and gamma gamma scattering below 700 MeV within animproved analytic K-matrix model. This model is based on an effective theorywith couplings between resonances, hadrons and photons. The two-photon decay ofa resonance can proceed through intermediate transition into charged hadrons(here: pi^+ pi^-) and their subsequent annihilation or through a ``direct''transition into photons. Our analysis confirms the rather large total radiativewidth of the sigma/f_0(600) resonance which we find as (3.9 \pm 0.6) keV butsuggests its dominance by the pi pi rescattering process. This process is notsensitive to the internal structure of the resonance contrary to the directcomponent which we find small, (0.13 \pm 0.05) keV, and well consistent withthe expectations for an unmixed glueball according to the QCD sum rulecalculations.

Comments: Talk (W.O.) at the International Workshop on e+e- collisions from phi to psi, Frascati, April 2008.