Ref HAL: hal-00489469_v1
Ref Arxiv: 0804.1252
DOI: 10.1142/S0217751X08041694
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23 citations
Résumé:

We have computed the one-loop electroweak expression of diagonal and non diagonal stop-antistop and sbottom-antisbottom production from initial state gluons at LHC. We have investigated the possibility that the one-loop effects exhibit a dependence on "extra" supersymmetric parameters different from the final squark masses. Our results, given for a choice of twelve SUSY benchmark points in the MSSM with mSUGRA symmetry breaking, show that in some cases a mild dependence might arise, at the percent relative level, of not simple experimental detection.

Commentaires: 44 pages, 23 eps figures

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

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.

Commentaires: 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
Résumé:

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
Résumé:

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.

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

Ref HAL: hal-00378066_v1
Ref Arxiv: 0806.2618
DOI: 10.1016/j.physletb.2008.07.083
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30 citations
Résumé:

We reexamine the estimate of the neutron Electric Dipole Moment (NEDM) fromchiral and QCD spectral sum rules (QSSR) approaches. In the former, we evaluatethe pion mass corrections which are about 5% of the leading Log. results.However, the chiral estimate can be affected by the unknown value of therenormalizaton scale nu. For QSSR, we analyze the effect of the nucleoninterpolating currents on the existing predictions. We conclude that previousQSSR results are not obtained within the optimal choice of these operators,which lead to an overestimate of these results by about a factor 4. The weakestupper bound |theta|< 2 10^-9 for the strong CP-violating angle is obtained fromQSSR, while the strongest upper bound |theta|< 1.3 10^-10 comes from the chiralapproach evaluated at the scale \nu=M_N. We also re-estimate the protonmagnetic susceptibility, which is an important input in the QSSR estimate ofthe NEDM.

Ref HAL: hal-00378058_v1
Ref Arxiv: 0804.4452
DOI: 10.1016/j.physletb.2008.06.018
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50 citations
Résumé:

We estimate the I=0 scalar meson sigma/f_0(600) parameters from pi-pi andgamma-gamma scattering data below 700 MeV using an improved analytic K-matrixmodel. A fit of the hadronic data gives a complex pole mass M_sigma= 422-i290MeV, while simultaneous best fits of the gamma-gamma to pi+pi-, pi0pi0 datagive a direct width of (0.13+-0.05)keV, a rescattering component of(2.7+-0.4)keV and a total (direct+rescattering) width of (3.9+-0.6)keV."Running" these results to the physical real axis, the small "direct"gamma-gamma and the large hadronic widths at the "on-shell" mass are compatiblewith QCD spectral sum rules (QSSR) and some low-energy theorems (LET)expectations for an unmixed lowest mass glueball/gluonium sigma_B of a massaround 1 GeV and a large OZI-violation decay into pi-pi.

Ref HAL: hal-00377714_v1
Ref Arxiv: 0803.0696
DOI: 10.1016/j.nuclphysbps.2008.12.047
Ref. & Cit.: NASA ADS
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3 citations
Résumé:

C-odd asymmetry can be studied from an accurate measurement of the angulardistribution due to the interference between the S- and P-waves in e+e- --> pi+pi- at order alpha^3. The asymmetry is dominated by the pion rescatteringdiagram which is enhanced by the presence of the ln(s/m^2_e), and is quitelarge (10% at theta=30^0 and sqrt{s} < M_{f_2}) compared to alpha/pi=0.3%. Thisprocess can also be used for alternatively measuring the size of therescattering term and the phase of the S-wave amplitude, but does not help tosolve the present discrepancy between the hadronic spectral functions from e+e-and tau-decay data.

Commentaires: Proceedings of the QCD 08, 14th High-Energy Physics International Conference On Quantum ChromoDynamics