On threshold resummation beyond leading 1-x order

We check against exact finite order three-loop results for the non-singlet F_2 and F_3 structure functions the validity of a class of momentum space ansaetze for threshold resummation at the next-to-leading order in 1-x, which generalize results previously obtained in the large-\beta_0 limit. We find that the ansaetze do not work exactly, pointing towards an obstruction to threshold resummation at this order, but still yield correct results at the leading logarithmic level for each color structures, as well as at the next-to-next-to-leading logarithmic level for the specific C_F^3 color factor. A universality of the leading logarithm contributions to the physical evolution kernels of F_2 and F_3 at the next-to-leading order in 1-x is observed.Comment: v1:18 pages; v2: 26 pages, expanded version with new results for the F_3 structure function and added references; v3: more concise sections 3 and 4, improved discussion in section 5, added references, to be published in JHE

Constant terms in threshold resummation and the quark form factor

We verify to order alpha_s^4 two previously conjectured relations, valid in four dimensions, between constant terms in threshold resummation (for Deep Inelastic Scattering and the Drell-Yan process) and the second logarithmic derivative of the massless quark form factor. The same relations are checked to all orders in the large beta_0 limit; as a byproduct a dispersive representation of the form factor is obtained. These relations allow to compute in a symmetrical way the three-loop resummation coefficients B_3 and D_3 in terms of the three-loop contributions to the virtual diagonal splitting function and to the quark form factor, confirming results obtained in the literature.Comment: 39 pages, no figure; version 2: same content, but improved presentation, with a new section devoted to the variety of resummation procedures; version 3: journal version, where a remark about the all orders validity of the conjecture in the DIS case is reporte

Initial design and evaluation of automatic restructurable flight control system concepts

Results of efforts to develop automatic control design procedures for restructurable aircraft control systems is presented. The restructurable aircraft control problem involves designing a fault tolerance control system which can accommodate a wide variety of unanticipated aircraft failure. Under NASA sponsorship, many of the technologies which make such a system possible were developed and tested. Future work will focus on developing a methodology for integrating these technologies and demonstration of a complete system

A Conceptual Framework to Guide Leader and Follower Education, Development, and Assessment

Leader and follower education and development is essential, yet a challenging task. It is helpful to have a conceptual framework with specific elements to determine where to sustain and improve efforts. A leaderfollower conceptual framework was recently developed to include four “C” elements (Character, Competence, Context, Communication) across four psychosocial levels of interactions (Personal, Interpersonal, Team, Organizational). This framework guides the who, what, when, where, and how of effective and adaptive leadership and followership. The leader-follower conceptual framework can be used in any professional field as a guide to develop sessions, curriculum, programs, and assessments for individuals, teams, and organizations

Infrared renormalons and analyticity structure in pQCD

Relation between the infrared renormalons, the Borel resummation prescriptions, and the analyticity structure of Green functions in perturbative QCD (pQCD) is investigated. A specific recently suggested Borel resummation prescription resulted in the Principal Value and an additional power-suppressed correction that is consistent with the Operator Product Expansion. Arguments requiring the finiteness of the result for any power coefficient of the leading infrared renormalon, and the consistency in the case of the absence of that renormalon, require that this prescription be modified. The apparently most natural modification leads to the result represented by the Principal Value. The analytic structure of the amplitude in the complex coupling plane, obtained in this way, is consistent with that obtained in the literature by other methods.Comment: 6 pages, revtex4, 1 eps-figure; improved version - the paragraph containing Eqs.(18) and (19) is new, as well as the next paragraph; the Title modified; some references added; version to appear in Phys. Rev.

Fixing the renormalisation scheme in NNLO perturbative QCD using conformal limit arguments

We discuss how the renormalisation scheme ambiguities in QCD can be fixed, when two observables are related, by requiring the coefficients in the perturbative expansion relating the two observables to have their conformal limit values, i.e. to be independent of the $\beta$-function of the renormalised coupling. We show how the next-to-leading order BLM automatic scale fixing method can be extended to next-to-next-to-leading order to fix both the renormalisation scale and $\beta_2$ in a unique way. As an example we apply the method to the relation between Bjorken's sum rule and $R_{e+e-}$ and compare with experimental data as well as other scheme fixing methods.Comment: 14 pages LaTeX, uses revtex.sty, 1 encapsulated PostScript figur

Relating Physical Observables in QCD without Scale-Scheme Ambiguity

We discuss the St\"uckelberg-Peterman extended renormalization group equations in perturbative QCD, which express the invariance of physical observables under renormalization-scale and scheme-parameter transformations. We introduce a universal coupling function that covers all possible choices of scale and scheme. Any perturbative series in QCD is shown to be equivalent to a particular point in this function. This function can be computed from a set of first-order differential equations involving the extended beta functions. We propose the use of these evolution equations instead of perturbative series for numerical evaluation of physical observables. This formalism is free of scale-scheme ambiguity and allows a reliable error analysis of higher-order corrections. It also provides a precise definition for $\Lambda_{\overline{\rm MS}}$ as the pole in the associated 't Hooft scheme. A concrete application to $R(e^+e^- \to {\rm hadrons})$ is presented.Comment: Plain TEX, 4 figures (available upon request), 22 pages, DOE/ER/40322-17

The Meson Production in Proton-Proton Collisions in Next-To-Leading Order and Infrared Renormalons

In this article, we investigate the next-to-leading order contribution of the higher-twist Feynman diagrams to the large-$p_T$ inclusive pion production cross section in proton-proton collisions and present the general formulae for the higher-twist differential cross sections in the case of the running coupling and frozen coupling approaches. We compared the resummed next-to-leading order higher-twist cross sections with the ones obtained in the framework of the frozen coupling approach and leading-twist cross section. The structure of infrared renormalon singularities of the higher twist subprocess cross section and it's resummed expression (the Borel sum) are found. It is shown that the resummed result depends on the choice of the meson wave functions used in the calculations. We discuss the phenomenological consequences of possible higher-twist contributions to the meson production in proton-proton collisions in next-to-leading order at RHIC.Comment: 33 pages, 15 figures, 4 table

QCD Corrections to t anti-b H^- Associated Production in e^+ e^- Annihilation

We calculate the QCD corrections to the cross section of e^+ e^- -> t anti-b H^- and its charge-conjugate counterpart within the minimal supersymmetric extension of the Standard Model. This process is particularly important if m_t b H^+ and e^+ e^- -> H^+ H^- are not allowed kinematically. Large logarithmic corrections that arise in the on-mass-shell scheme of quark mass renormalization, especially from the t anti-b H^- Yukawa coupling for large values of tan(beta), are resummed by adopting the modified minimal-subtraction scheme, so that the convergence behavior of the perturbative expansion is improved. The inclusion of the QCD corrections leads to a significant reduction of the theoretical uncertainties due to scheme and scale dependences.Comment: 21 pages (Latex), 8 figures (Postscript); detailed discussion of scheme and scale dependences adde

Commensurate Scale Relations in Quantum Chromodynamics

We use the BLM method to show that perturbatively-calculable observables in QCD can be related to each other without renormalization scale or scheme ambiguity. We define and study the commensurate scale relations. We show that the commensurate scales satisfy the renormalization group transitivity rule which ensures that predictions in PQCD are independent of the choice of an intermediate renormalization scheme. We generalize the BLM procedure to higher order. The application of this procedure to relate known physical observables in QCD gives surprisingly simple results. In particular, the annihilation ratio $R_{e^+e^-}$ and the Bjorken sum rule for polarized electroproduction are related through simple coefficients, which reinforces the idea of a hidden symmetry between these two observables.Comment: 35 pages (RevTeX), one PostScript figure included at the end. SLAC-PUB-6481, UMD Preprint #94-13