Ref HAL: hal-00378066_v1
Ref Arxiv: 0806.2618
DOI: 10.1016/j.physletb.2008.07.083
Ref. & Cit.: NASA ADS
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30 citations
Abstract:

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
Ref. & Cit.: NASA ADS
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50 citations
Abstract:

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
Abstract:

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.

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

Ref HAL: in2p3-00136826_v1
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Ref HAL: hal-00377723_v1
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Comments: Also in Nucl. Phys. B, Proc. Suppl. 174 (2007)

Ref HAL: hal-00377710_v1
Ref Arxiv: 0707.4511
Ref. & Cit.: NASA ADS
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Abstract:

We reanalyse the gamma-gamma scattering data and conclude that in the massregion below 1 GeV the cross section for gamma-gamma to pi^0-pi^0 can belargely explained by the one pion exchange process with pi-pi rescattering. Theradiative width of the sigma is estimated and a model dependent separation intocontributions from direct gamma-gamma decay and decay through rescattering isobtained. We confront these findings with QCD spectral sum rule (QSSR)predictions and conclude that the sigma can have a large gluonium component inits wave function.

Ref HAL: hal-00327555_v1
DOI: 10.1016/j.nuclphysbps.2005.08.001
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Abstract:

Preface