Measuring Vacuum Polarization with Josephson Junctions

We argue that the vacuum polarization by the virtual electron-positron pairs can be measured by studying a Josephson junction in a strong magnetic field. The vacuum polarization results in a weak dependence of the Josephson constant on the magnetic field strength which is within the reach of the existing experimental techniques.Comment: 4 pages, 2 figures, LaTe

Next-to-next-to-leading order vacuum polarization function of heavy quark near threshold and sum rules for bbˉb \bar b system

A correlator of the vector current of a heavy quark is computed analytically near threshold in the next-to-next-to-leading order in perturbative and relativistic expansion that includes \al_s^2, \al_sv and $v^2$ corrections in the coupling constant and velocity of the heavy quark to the nonrelativistic Coulomb approximation. Based on this result, the numerical values of the $b$-quark pole mass and the strong coupling constant are determined from the analysis of sum rules for the $\Upsilon$ system. The next-to-next-to-leading corrections are found to be of order of next-to-leading ones.Comment: 12 pages Latex, misprints in the formulae for the nonrelativistic Green function are correcte

Third order Coulomb correction to ttbar threshold cross section

We report on our result of third order Coulomb correction to the cross section sigma(ee -> ttbar) near threshold. Analytic expression for the Coulomb energy and wave function at the origin are obtained. We discuss the significance of the Coulomb correction to the threshold cross section and heavy quarkonium phenomenology.Comment: To appear in the proceedings of the 7th International Symposium on Radiative Corrections(RADCOR05), Shonan Village, Japana Oct. 200

On the light quark mass effects in Higgs boson production in gluon fusion

Production of Higgs bosons at the LHC is affected by the contribution of light quarks, that mediate the gg \to Hg transition. Although their impact is suppressed by small Yukawa couplings, it is enhanced by large logarithms of the ratio of the Higgs boson mass or its transverse momentum to light quark masses. We study the origin of this enhancement, focusing on the abelian corrections to gg \to Hg amplitudes of the form (C_F alphas L^{2})^n, where $L \in { ln(s/mb^2), ln(p_\perp^2/mb^2) }. We show how these non-Sudakov double logarithmic terms can be resummed to all orders in the strong coupling constant. Interestingly, we find that the transverse momentum dependence of these corrections is very weak due to a peculiar cancellation between different logarithmic terms. Although the abelian part of QCD corrections is not expected to be dominant, it can be used to estimate missing higher-order corrections to light quark contributions to Higgs boson production at the LHC.Comment: 18 pages, 2 figure

Coulomb Artifacts and Breakdown of Perturbative Matching in Lattice NRQCD

By studying an explicit analytical solution of the Coulomb problem on the lattice we demonstrate a breakdown of perturbative matching for the description of the Coulomb artifacts in lattice NRQCD, which leads to a large systematic error in the predictions for the heavy quarkonium spectrum. The breakdown is a result of a fine interplay between the short and long distance effects specific to the lattice regularization of NRQCD. We show how the problem can be solved within the Schrodinger matching procedure.Comment: 11 pages, 1 figure. Journal version (minor revisions implemented

Bottom Quark Mass from Υ\Upsilon Sum Rules to O(αs3){\cal O}(\alpha_s^3)

We use the ${\cal O}(\alpha_s^3)$ approximation of the heavy-quark vacuum polarization function in the threshold region to determine the bottom quark mass from nonrelativistic $\Upsilon$ sum rules. We find very good stability and convergence of the perturbative series for the bottom quark mass in $\rm\overline{MS}$ renormalization scheme. Our final result is $\overline{m}_b(\overline{m}_b)=4.169\pm 0.008_{th}\pm 0.002_{\alpha_s}\pm 0.002_{exp}$.Comment: 23 pages, 6 figures, journal versio

Spin Dependence of Heavy Quarkonium Production and Annihilation Rates: Complete Next-to-Next-to-Leading Logarithmic result

The ratio of the photon mediated production or annihilation rates of spin triplet and spin singlet heavy quarkonium states is computed to the next-to-next-to-leading logarithmic accuracy within the nonrelativistic renormalization group approach. The result is presented in analytical form and applied to the phenomenology of $t\bar{t}$, $b\bar{b}$ and $c\bar{c}$ systems. The use of the nonrelativistic renormalization group considerably improves the behaviour of the perturbative expansion and is crucial for accurate theoretical analysis. For bottomonium decays we predict $\Gamma(\eta_b(1S) \to \gamma\gamma)=0.659\pm 0.089 ({\rm th.}) {}^{+0.019}_{-0.018} (\delta \alpha_{\rm s})\pm 0.015 ({\rm exp.}) {\rm keV}$. Our results question the accuracy of the existing extractions of the strong coupling constant from the bottomonium annihilation. As a by-product we obtain novel corrections to the ratio of the ortho- and parapositronium decay rates: the corrections of order $\alpha^4\ln^2\alpha$ and $\alpha^5\ln^3\alpha$.Comment: Appendices A.4, A.5 and B correcte