Production of Heavy Quarks Close to Threshold

We calculate production by vector and axial currents of heavy quark pairs ($c\bar{c}$, $b\bar{b}$, $t\bar{t}$) close to threshold. We take into account strong interaction contributions (including radiative corrections and leading nonperturbative effects) by using the Fermi-Watson final state interaction theorem. We use the results obtained to compare with experiment for open production of $c\bar{c}$, $b\bar{b}$ near threshold, and to give a reliable estimate of the so-called ``threshold effects'' contribution to vector and axial correlators, for $t \bar{t}$, $i.e.$, the contribution of regions close to $4 m_t^2$ to $\Pi(t)$, for small values of $t$ ( 0 < t \lower2pt\hbox{\lesssim} M_Z^2 ).Comment: 36 pages, uses RevTeX, 7 postscript figures available upon reques

Calculation of αˉQ.E.D.\bar{\alpha}_{\rm Q.E.D.} on the Z

We perform a new, detailed calculation of the hadronic contributions to the running electromagnetic coupling, $\bar{\alpha}$, defined on the Z particle (91 GeV). We find for the hadronic contribution, including radiative corrections, 10^5\times \deltav_{\rm had.}\alpha(M_Z^2)= 2740\pm12, or, excluding the top quark contribution, 10^5\times \deltav_{\rm had.}\alpha^{(5)}(M_Z^2)= 2747\pm12. Adding the pure QED corrections we get a value for the running electromagnetic coupling of $$\bar{\alpha}_{\rm Q.E.D.}(M_Z^2)= {{1}\over{128.965\pm0.017}}.$$Comment: Version to appear in Phys. Rev. D. Plain TeX fil

Precision Determination of the Pion Form Factor and Calculation of the Muon g−2g-2

We perform a new calculation of the hadronic contributions, $a({\rm Hadronic})$ to the anomalous magnetic moment of the muon, $a_\mu$. For the low energy contributions of order $\alpha^2$ we carry over an analysis of the pion form factor $F_\pi(t)$ using recent data both on $e^+e^-\to\pi^+\pi^-$ and $\tau^+\to \bar{\nu}_\tau \pi^+\pi^0$. In this analysis we take into account that the phase of the form factor is equal to that of $\pi\pi$ scattering. This allows us to profit fully from analyticity properties so we can use also experimental information on $F_\pi(t)$ at spacelike $t$. At higher energy we use QCD to supplement experimental data, including the recent measurements of $e^+e^-\to {\rm hadrons}$ both around 1 GeV and near the $\bar{c}c$ threshold. This yields a precise determination of the $O(\alpha^2)$ and $O(\alpha^2)+O(\alpha^3)$ hadronic part of the photon vacuum polarization pieces, $$10^{11}\times a^{(2)}({\rm h.v.p.})=6 909\pm64;\quad 10^{11}\times a^{(2+3)}({\rm h.v.p.})=7 002\pm66$$ As byproducts we also get the masses and widths of the $\rho^0, \rho^+$, and very accurate values for the charge radius and second coefficient of the pion. Adding the remaining order $\alpha^3$ hadronic contributions we find $$10^{11}\times a^{\rm theory}(\hbox{Hadronic})= 6 993\pm69\quad(e^+e^- + \tau + {\rm spacel.})$$ The figures given are obtained including $\tau$ decay data. This is to be compared with the recent experimental value, $$10^{11}\times a^{\rm exp.}(\hbox{Hadronic})=7 174\pm150.$$Comment: Plain TeX file. Published version. Correct value for light-by-light include

The Standard Model Prediction of the Muon Anomalous Magnetic Moment

This article reviews and updates the Standard Model prediction of the muon g-2. QED, electroweak and hadronic contributions are presented, and open questions discussed. The theoretical prediction deviates from the present experimental value by 2-3 standard deviations, if e+e- annihilation data are used to evaluate the leading hadronic term.Comment: 30 pages, 8 figures. v2: Updated version to appear in J.Phys.G. Comments and references added, typo corrected in eq.(17