Differential reduction of generalized hypergeometric functions from Feynman diagrams: One-variable case

The differential-reduction algorithm, which allows one to express generalized hypergeometric functions with parameters of arbitrary values in terms of the same functions with parameters whose values differ from the original ones by integers, is discussed in the context of evaluating Feynman diagrams. Where this is possible, we compare our results with those obtained using standard techniques. It is shown that the criterion of reducibility of multiloop Feynman integrals can be reformulated in terms of the criterion of reducibility of hypergeometric functions. The relation between the numbers of master integrals obtained by differential reduction and integration by parts is discussed.     

Diffractive photoproduction of jets with a direct pomeron coupling at HERA

We investigate in detail the effect of a direct pomeron coupling to quarks on the production of jets inep scattering with almost real photons. Jet production via a direct pomeron coupling is compared with the resolved-pomeron mechanism. We consider both direct and resolved photoproduction. Rapidity and transverse momentum distributions are calculated and compared with preliminary H1 and ZEUS data.     

Strong-coupling constant with flavor thresholds at five loops in the modified minimal-subtraction scheme

We present in analytic form the matching conditions for the strong-coupling constant alphas(nf) (mu) at the flavor thresholds to four loops in the modified minimal-subtraction scheme. Taking into account the present knowledge on the coefficient beta4 of the Callan-Symanzik beta function of quantum chromodynamics, we thus derive a five-loop formula for alphas(nf) (mu) together with appropriate relationships between the asymptotic scale parameters Lamda(nf) for different numbers of flavors nf.     

Small-x behavior of the structure function and its slope for “frozen” and analytic strong-coupling constants

Using the leading-twist approximation of the Wilson operator product expansion with “frozen” and analytic versions of the strong-coupling constant, we show that the Bessel-inspired behavior of the structure function F₂ and its slope ∂lnF₂/∂ln(1/x) at small values of x, obtained for a flat initial condition in the DGLAP evolution equations, leads to good agreement with experimental data of deep-inelastic scattering at DESY HERA.     

Large-x resummation in Q2 evolution

The standard analytic solution to the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equation in Mellin space is improved by resumming the large-x divergences. Explicit results are given to next-to-leading order and next-to-leading logarithmic accuracy, which significantly reduce the parton density functions' theoretical uncertainties, more than the inclusion of next-to-next-to-leading order corrections in some cases, and is, therefore, of paramount importance for the reliable interpretation of ongoing and future experiments with hadron beams or targets, including those at the CERN Large Hadron Collider.     

Width and partial widths of unstable particles

In the gauge theory context, a definition of branching ratios and partial widths of unstable particles is proposed that satisfies the basic principles of additivity and gauge independence. A simpler definition, similar to the conventional one, is examined in the Z0-boson case. In order to establish contact with experiment, we show that it leads to a peak cross section that justifies the expression used by the LEP Electroweak Working Group through next-to-next-to-leading order, provided that the pole rather than the on-shell mass and width of the Z0 boson is employed.     

Strong coupling constant from scaling violations in fragmentation functions

We present a new determination of the strong coupling constant alpha(s) through the scaling violations in the fragmentation functions for charged pions, charged kaons, and protons. In our fit we include the latest e+e- annihilation data from CERN LEP1 and SLAC SLC on the Z-boson resonance and older, yet very precise, data from SLAC PEP at center-of-mass energy sqaure root of s = 29 GeV. At next-to-leading order, we find alpha(s)(5)(M(Z)) = 0.1170+/-0.0073. A new world average of alpha(s) is given.     

Counting master integrals: Integration-by-parts procedure with effective mass

We show that the new relation between master integrals recently obtained in M.Yu. Kalmykov and B.A. Kniehl (2011) [1] can be reproduced using the integration-by-parts technique implemented with an effective mass. In fact, this relation is recovered as a special case of a whole family of new relations between master integrals.     

Radiative corrections toe + e −→Zh 0 andZ→γh 0 in the minimal supersymmetric theory

The Higgs sector of the minimal supersymmetric extension of the standard model (MSSM) becomes phenomenologically hard to distinguish from the standard model (SM) in the limit that the CP-odd scalar,A ⁰, is much heavier than theZ boson. If, in addition, all the superpartners lie outside the kinematic reach of present-day (or near-future) colliders the only experimental evidence for supersymmetry (SUSY) might be through internal loops involving superpartners. We have calculated sfermion-induced radiative corrections toe ⁺ e ^?→Zh ⁰ andZ→γh ⁰ in the MSSM, which are enhanced for highm _t .