56 research outputs found

    The coupling constant gρσγ_{\rho\sigma\gamma} as derived from QCD sum rules

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    We employ QCD sum rules to calculate the coupling constant gρσγ_{\rho\sigma\gamma} by studying the three point ρσγ{\rho\sigma\gamma}-correlation function. Our results is consistent with the value of this coupling constant obtained using vector meson dominance of the electromagnetic current and the experimental ρ0\rho^0-photoproduction data.Comment: 10 pages RevTex, 3 postscript figure

    Decay constants, light quark masses and quark mass bounds from light quark pseudoscalar sum rules

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    The flavor udud and usus pseudoscalar correlators are investigated using families of finite energy sum rules (FESR's) known to be very accurately satisfied in the isovector vector channel. It is shown that the combination of constraints provided by the full set of these sum rules is sufficiently strong to allow determination of both the light quark mass combinations mu+mdm_u+m_d, ms+mum_s+m_u and the decay constants of the first excited pseudoscalar mesons in these channels. The resulting masses and decay constants are also shown to produce well-satisfied Borel transformed sum rules, thus providing non-trivial constraints on the treatment of direct instanton effects in the FESR analysis. The values of mu+mdm_u+m_d and ms+mum_s+m_u obtained are in good agreement with the values implied by recent hadronic τ\tau decay analyses and the ratios obtained from ChPT. New light quark mass bounds based on FESR's involving weight functions which strongly suppress spectral contributions from the excited resonance region are also presented.Comment: 28 pages, 10 figure

    Evaluating the Effects of SARS-CoV-2 Spike Mutation D614G on Transmissibility and Pathogenicity

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    Global dispersal and increasing frequency of the SARS-CoV-2 spike protein variant D614G are suggestive of a selective advantage but may also be due to a random founder effect. We investigate the hypothesis for positive selection of spike D614G in the United Kingdom using more than 25,000 whole genome SARS-CoV-2 sequences. Despite the availability of a large dataset, well represented by both spike 614 variants, not all approaches showed a conclusive signal of positive selection. Population genetic analysis indicates that 614G increases in frequency relative to 614D in a manner consistent with a selective advantage. We do not find any indication that patients infected with the spike 614G variant have higher COVID-19 mortality or clinical severity, but 614G is associated with higher viral load and younger age of patients. Significant differences in growth and size of 614G phylogenetic clusters indicate a need for continued study of this variant
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