Asymptotic neutrino-nucleon cross section and saturation effects

In this paper we present a simple analytic expression for the (spin-averaged) neutrino-nucleon cross section for ultra-high energies at twist-2, obtained as the asymptotic limit of our previous findings. This expression gives values for the cross section in remarkable numerical agreement with the previous numerical evaluation in the energy region relevant for forthcoming neutrino experiments. Moreover, we discuss the role and the relevance of saturation and recombination effects in our approach, in comparison with other recent suggestions.Comment: 19 pages, 2 figure

Master integrals for the two-loop light fermion contributions to gg→Hgg \to H and H→γγH \to \gamma\gamma

We give the analytic expressions of the eight master integrals entering our previous computation of two-loop light fermion contributions to $gg \to H$ and $H \to \gamma\gamma$. The results are expressed in terms of generalized harmonic polylogarithms with maximum weight four included.Comment: 9 pages, 6 figure

Small x behavior of the slope dlnF_2/dln(1/x) in the framework of perturbative QCD

Using an analytical parameterization for the behavior of the x slope of the structure function F_2 at small x in perturbative QCD, at the leading twist approximation of the Wilson operator product expansion, and applying a flat initial condition in the DGLAP evolution equations, we found very good agreement with new precise deep inelastic scattering experimental data from HERA.Comment: 13 pages, 3 figures, late

Q2-evolution of parton densities at small-x values

In the leading twist approximation of the Wilson operator product expansion with "frozen" and analytic strong coupling constants we show that Bessel-inspired behavior of the structure function F2 at small x, obtained for a flat initial condition in the DGLAP evolution equations, leads to good agreement with the deep inelastic scattering experimental data from HERA.Comment: 19 pages, 5 figures, published in the Proceedings of Workshop on Physics of Fundamental Interactions, Institute of High Energy Physics, Protvino, Russia, 22--25 December 2008 (Phys.Atom.Nucl. in press

Small x behavior of parton distributions. A study of higher twist effects

Higher twist corrections to the structure function F_2 at small x are studied for the case of a flat initial condition for the twist-two QCD evolution in the next-to-leading order approximation. We present an analytical parameterization of the contributions from the twist-two and higher twist operators of the Wilson operator product expansion. Higher twist terms are evaluated using two different approaches, one motivated by BFKL and the other motivated by the renormalon formalism. The results of the latter approach are in very good agreement with deep inelastic scattering data from HERA.Comment: 46 pages, 9 figures, typeset using REVTeX. Misprints corrected, new results, discussions, references and acknowledgements added, 2 pictures replaced. The conclusions remain unchange

Two-Loop N_F =1 QED Bhabha Scattering: Soft Emission and Numerical Evaluation of the Differential Cross-section

Recently, we evaluated the virtual cross-section for Bhabha scattering in pure QED, up to corrections of order alpha^4 (N_F =1). This calculation is valid for arbitrary values of the squared center of mass energy s and momentum transfer t; the electron and positron mass m was considered a finite, non vanishing quantity. In the present work, we supplement the previous calculation by considering the contribution of the soft photon emission diagrams to the differential cross-section, up to and including terms of order alpha^4 (N_F=1). Adding the contribution of the real corrections to the renormalized virtual ones, we obtain an UV and IR finite differential cross-section; we evaluate this quantity numerically for a significant set of values of the squared center of mass energy s.Comment: 24 pages, 15 figures. Formulas in Appendix B corrected, changes in Section 3, references adde

Calculation of a Class of Three-Loop Vacuum Diagrams with Two Different Mass Values

We calculate analytically a class of three-loop vacuum diagrams with two different mass values, one of which is one-third as large as the other, using the method of Chetyrkin, Misiak, and M\"{u}nz in the dimensional regularization scheme. All pole terms in \epsilon=4-D (D being the space-time dimensions in a dimensional regularization scheme) plus finite terms containing the logarithm of mass are kept in our calculation of each diagram. It is shown that three-loop effective potential calculated using three-loop integrals obtained in this paper agrees, in the large-N limit, with the overlap part of leading-order (in the large-N limit) calculation of Coleman, Jackiw, and Politzer [Phys. Rev. D {\bf 10}, 2491 (1974)].Comment: RevTex, 15 pages, 4 postscript figures, minor corrections in K(c), Appendix B removed, typos corrected, acknowledgements change

Two-loop light fermion contribution to Higgs production and decays

We compute the electroweak corrections due to the light fermions to the production cross section $\sigma(g g \to H)$ and to the partial decay widths $\Gamma (H \to \gamma \gamma)$ and $\Gamma (H \to g g)$. We present analytic results for these corrections that are expressed in terms of Generalized Harmonic Polylogarithms. We find that for the gluon fusion production cross section and for the decay width $\Gamma (H \to g g)$ the corrections are large in the Higgs mass region below 160 GeV where they reach up to 9% of the lowest order term. For the decay width $\Gamma (H \to \gamma \gamma)$ the corrections for Higgs mass above 160 GeV can reach $-$10% of the lowest order term.Comment: 12 pages, 4 figure

Bjorken sum rule with analytic coupling at low Q2 values

The experimental data obtained for the polarized Bjorken sum rule \Gamma^{(p-n)}_1(Q^2) for small values of Q2 are approximated by the predictions obtained in the framework of analytic QCD up to the 5th order perturbation theory, whose coupling constant does not contain the Landau pole. We found an excellent agreement between the experimental data and the predictions of analytic QCD, as well as a strong difference between these data and the results obtained in the framework of standard QCD.Comment: 9 pages, 1 figur