A numerical test of differential equations for one- and two-loop sunrise diagrams using configuration space techniques

We use configuration space methods to write down one-dimensional integral representations for one- and two-loop sunrise diagrams (also called Bessel moments) which we use to numerically check on the correctness of the second order differential equations for one- and two-loop sunrise diagrams that have recently been discussed in the literature.Comment: 11 pages, no figures, published versio

Heavy quark induced effective action for gauge fields in the SU(N_c) x U(1) model and the low-energy structure of heavy quark current correlators

We calculate the low-energy limit of heavy quark current correlators within an expansion in the inverse heavy quark mass. The induced low-energy currents built from the gluon fields corresponding to the initial heavy quark currents are obtained from an effective action for gauge fields in the one-loop approximation at the leading order of the 1/m expansion. Explicit formulae for the low-energy spectra of electromagnetic and tensor heavy quark current correlators are given. Consequences of the appearance of a nonvanishing spectral density below the two-particle threshold for high precision phenomenology of heavy quarks are discussed quantitatively.Comment: 21 pages in LaTeX, 2 PostScript figures included in the tex

Variations of the high-level Balmer line spectrum of the helium-strong star Sigma Orionis E

Using the high-level Balmer lines and continuum, we trace the density structure of two magnetospheric disk segments of the prototypical Bp star sigma Ori E (B2p) as these segments occult portions of the star during the rotational cycle. High-resolution spectra of the Balmer lines >H9 and Balmer edge were obtained on seven nights in January-February 2007 at an average sampling of 0.01 cycles. We measured equivalent width variations due to the star occultations by two disk segments 0.4 cycles apart and constructed differential spectra of the migrations of the corresponding absorptions across the Balmer line profiles. We first estimated the rotational and magnetic obliquity angles. We then simulated the observed Balmer jump variation using the model atmosphere codes synspec/circus and evaluated the disk geometry and gas thermodynamics. We find that the two occultations are caused by two disk segments. The first of these transits quickly, indicating that the segment resides in a range of distances, perhaps 2.5-6R_star, from the star. The second consists of a more slowly moving segment situated closer to the surface and causing two semi-resolved absorbing maxima. During its transit this segment brushes across the star's "lower" limb. Judging from the line visibility up to H23-H24 during the occultations, both disk segments have mean densities near 10^{12} cm^{-3} and are opaque in the lines and continuum. They have semiheights less than 1/2 of a stellar radius, and their temperatures are near 10500K and 12000K, respectively. In all, the disks of Bp stars have a much more complicated geometry than has been anticipated, as evidenced by their (sometimes) non-coplanarity, de-centerness, and from star to star, differences in disk height.Comment: Accepted by Astron. Astrophys, 13 pages, 4 embedded figure

Analytical calculation of heavy baryon correlators in NLO of perturbative QCD

We present analytical next-to-leading order results for the correlator of baryonic currents at the three-loop level with one finite mass quark. We obtain the massless and the HQET limits of the correlator as particular cases from the general formula, we also give explicit expressions for the moments of the spectral density. Calculations have been performed with an extensive use of the symbolic manipulation programs MATHEMATICA and REDUCE.Comment: 16 pages in LaTeX, including 7 Postscript figures, contribution to the "VII International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT2000)", Oct 16-20, 2000, Fermi National Laboratory, Batavia, Illinois, USA, to appear in the proceeding

An interpolation of the vacuum polarization function for the evaluation of hadronic contributions to the muon anomalous magnetic moment

We propose a simple parameterization of the two-point correlator of hadronic electromagnetic currents for the evaluation of the hadronic contributions to the muon anomalous magnetic moment. The parameterization is explicitly done in the Euclidean domain. The model function contains a phenomenological parameter which provides an infrared cutoff to guarantee the smooth behavior of the correlator at the origin in accordance with experimental data in e+ e- annihilation. After fixing a numerical value for this parameter from the leading order hadronic contribution to the muon anomalous magnetic moment the next-to-leading order results related to the vacuum polarization function are accurately reproduced. The properties of the four-point correlator of hadronic electromagnetic currents as for instance the so-called light-by-light scattering amplitude relevant for the calculation of the muon anomalous magnetic moment are briefly discussed.Comment: 23 pages in LaTeX, 11 PostScript figures included in the tex

Laurent series expansion of sunrise-type diagrams using configuration space techniques

We show that configuration space techniques can be used to efficiently calculate the complete Laurent series \eps-expansion of sunrise-type diagrams to any loop order in D-dimensional space-time for any external momentum and for arbitrary mass configurations. For negative powers of \eps the results are obtained in analytical form. For positive powers of \eps including the finite \eps^0 contribution the result is obtained numerically in terms of low-dimensional integrals. We present general features of the calculation and provide exemplary results up to five loop order which are compared to available results in the literature.Comment: 20 pages, 3 eps-figures include

HEALTH COSTS AND EXTERNALITIES OF PESTICIDE USE IN LOCUST AND GRASSHOPPER CONTROL IN THE SAHEL

To evaluate the economic cost of classical chemical control of locusts, externalities of chemical pesticides in the Sahel are estimated through a farmer survey. The costs of human health, losses in domestic animals and of destroying obsolete pesticides are estimated at $4 per treated ha for chemical control.Environmental Economics and Policy, Health Economics and Policy,

O(\alpha_s) Corrections to Longitudinal Spin-Spin Correlations in e+e- -> q qbar

We calculate the $O(\alpha_s)$ corrections to longitudinal spin-spin correlations in $e^+e^-\to q\bar q$. For top quark pair production the $O(\alpha_s)$ corrections to the longitudinal spin-spin asymmetry amount to less than 1% in the $q^2$-range from above $t\bar t$-treshold up to $\sqrt{q^2}= 1000 GeV$. In the $e^+e^-\to b\bar b$ case the $O(\alpha_s)$ corrections reduce the asymmetry value from its $m=0$ value of -1 to approximately -0.96 for $q^2$-values around the Z-peak. This reduction can be traced to finite anomalous contributions from residual mass effects which survive the $m\to 0$ limit. We discuss the role of the anomalous contributions and the pattern of how they contribute to spin-flip and no-flip terms.Comment: 10 pages, 2 postscript figure