179 research outputs found
The light-cone gauge and the calculation of the two-loop splitting functions
We present calculations of next-to-leading order QCD splitting functions,
employing the light-cone gauge method of Curci, Furmanski, and Petronzio (CFP).
In contrast to the `principal-value' prescription used in the original CFP
paper for dealing with the poles of the light-cone gauge gluon propagator, we
adopt the Mandelstam-Leibbrandt prescription which is known to have a solid
field-theoretical foundation. We find that indeed the calculation using this
prescription is conceptionally clear and avoids the somewhat dubious
manipulations of the spurious poles required when the principal-value method is
applied. We reproduce the well-known results for the flavour non-singlet
splitting function and the N_C^2 part of the gluon-to-gluon singlet splitting
function, which are the most complicated ones, and which provide an exhaustive
test of the ML prescription. We also discuss in some detail the x=1 endpoint
contributions to the splitting functions.Comment: 41 Pages, LaTeX, 8 figures and tables as eps file
Lattice energy-momentum tensor with Symanzik improved actions
We define the energy-momentum tensor on lattice for the and
for the nonlinear -model Symanzik tree-improved actions, using Ward
identities or an explicit matching procedure. The resulting operators give the
correct one loop scale anomaly, and in the case of the sigma model they can
have applications in Monte Carlo simulations.Comment: Self extracting archive fil
A Rigourous Treatment of the Lattice Renormalization Problem of F_B
The -meson decay constant can be measured on the lattice using a
expansion. To relate the physical quantity to Monte Carlo data one has to know
the renormalization coefficient, , between the lattice operators and their
continuum counterparts. We come back to this computation to resolve
discrepancies found in previous calculations. We define and discuss in detail
the renormalization procedure that allows the (perturbative) computation of
. Comparing the one-loop calculations in the effective Lagrangian approach
with the direct two-loop calculation of the two-point -meson correlator in
the limit of large -quark mass, we prove that the two schemes give
consistent results to order . We show that there is, however, a
renormalization prescription ambiguity that can have sizeable numerical
consequences. This ambiguity can be resolved in the framework of an
improved calculation, and we describe the correct prescription in that case.
Finally we give the numerical values of that correspond to the different
types of lattice approximations discussed in the paper.Comment: 27 pages, 2 figures (Plain TeX, figures in an appended postscript
file
Características epidemiológicas y clínicas de mortalidad materna en el Hospital Eleazar Guzmán Barrón. Nuevo Chimbote, 2006-2015
El objetivo planteado en esta investigación básica fue determinar las características epidemiológicas y clínicas que inciden en la mortalidad materna en el Hospital Regional Eleazar Guzmán Barrón de Nuevo Chimbote, Provincia del Santa-Ancash-Perú durante el período 2006-2015. Metodología: el estudio cuantitativo, descriptivo, retrospectivo, transversal, utilizó una ficha de registro, la cual se validó por juicio de expertos teniendo como fuentes de información las historias clínicas. Constituye el diagnóstico de una Propuesta de Macroproyecto de Investigación en Salud Pública de la USP. Posteriormente se determinarán factores asociados y formulará un Proyecto de Intervención con énfasis en capacitación de grupos de interés y población vulnerable, evaluación de impacto social y planteamientos para evitar y prevenir la mortalidad materna. Dada la magnitud del problema, continúa la propuesta educativa para gestantes. Resultados: las características epidemiológicas fueron: muertes ocurridas en etapa de vida joven entre 20 a 29 años de edad (67%); nivel educativo secundaria 33%, estado civil: convivientes en 50%; ocupación: 88,9% se dedicaban a labores del hogar; procedencia: urbana en el 61%; las características clínicas fueron: el 61% no presentó antecedentes patológicos; el 39% tuvo entre 37 a 40 semanas de gestación; fueron multíparas el 33%; multigestas con 56%; en el 67% no se registró datos sobre aborto; periodo intergenésico no registrado en 33%; no tuvieron ninguna atención prenatal en el 45%; planificación familiar: no usaron ningún método 72%. El diagnóstico de ingreso 72% fueron de gestantes; en cuanto a las características clínicas durante el parto se identificó la eclampsia en 5,6% y en patologías del puerperio se identificó la infección puerperal con 17%. La causa básica de muerte materna fue la hemorragia en 22%, el tipo de muerte materna fue directa en 56% y el momento reproductivo fue en el embarazo: 72%. Conclusión: Existen características epidemiológicas y clínicas que inciden en la mortalidad materna en el HREGB durante el período 2006-2015. Las características epidemiológicas más relevantes fueron: edad, estado civil y ocupación y las características clínicas más relevantes fueron: paridad, gravidez, atención prenatal, planificación familiar, edad gestacional, diagnóstico de ingreso y patologías del puerperio. La mayoría de muertes maternas fueron de tipo directas (causas obstétricas) y la causa básica fue por hemorragia en primer lugar, infección en segundo lugar y por enfermedad hipertensiva del embarazo. Las hemorragias se debieron a atonía uterina, embarazo ectópico y mola hidatidiforme.Trabajo de investigació
Perturbative Renormalization Factors of Bilinear Quark Operators for Improved Gluon and Quark Actions in Lattice QCD
We calculate one-loop renormalization factors of bilinear quark operators for
gluon action including six-link loops and -improved quark action in the
limit of massless quark. We find that finite parts of one-loop coefficients of
renormalization factors diminish monotonically as either of the coefficients
or of the six-link terms are decreased below zero. Detailed
numerical results are given, for general values of the clover coefficient, for
the tree-level improved gluon action in the Symanzik approach and for the choices suggested by Wilson and by Iwasaki and from renormalization-group analyses. Compared with the case of
the standard plaquette gluon action, finite parts of one-loop coefficients are
reduced by 10--20% for the Symanzik action, and approximately by a factor two
for the renormalization-group improved gluon actions.Comment: 19 pages, REVTeX, with 3 epsf figure
Topological aspects of QCD
We review recent results from lattice on topological aspects of QCD: most of
the results refer to monopoles and to instantons. We discuss in detail the
evidence for condensation of monopoles in the vacuum and confinement of colour
by dual superconductivity, and the major role of monopoles in dynamics
(monopole dominance). As for instantons we review the problem, a
possible determination of the spin content of the proton, and new lattice data
relevant to instanton liquid models.Comment: 8 pages, to be published in the Proceedings of Lattice 95, uuencoded
postscript file. IFUP-TH 49/9
Non-singlet structure functions beyond the next-to-next-to leading order
We study the evolution of the flavour non-singlet deep-inelastic structure
functions F_{2,NS} and F_3 at the next-to-next-to-next-to-leading order (N^3LO)
of massless perturbative QCD. The present information on the corresponding
three-loop coefficient functions is used to derive approximate expressions of
these quantities which prove completely sufficient for values x > 10^{-2} of
the Bjorken variable. The inclusion of the N^3LO corrections reduces the
theoretical uncertainty of alpha_s determinations from non-singlet scaling
violations arising from the truncation of the perturbation series to less than
1%. We also study the predictions of the soft-gluon resummation, of
renormalization-scheme optimizations by the principle of minimal sensitivity
(PMS) and the effective charge (ECH) method, and of the Pade' summation for the
structure-function evolution kernels. The PMS, ECH and Pade' approaches are
found to facilitate a reliable estimate of the corrections beyond N^3LO.Comment: 29 pages, LaTeX, 12 eps-figure
Joint resummation in electroweak boson production
We present a phenomenological application of the joint resummation formalism
to electroweak annihilation processes at measured boson momentum Q_T. This
formalism simultaneously resums at next-to-leading logarithmic accuracy large
threshold and recoil corrections to partonic scattering. We invert the impact
parameter transform using a previously described analytic continuation
procedure. This leads to a well-defined, resummed perturbative cross section
for all nonzero Q_T, which can be compared to resummation carried out directly
in Q_T space. From the structure of the resummed expressions, we also determine
the form of nonperturbative corrections to the cross section and implement
these into our analysis. We obtain a good description of the transverse
momentum distribution of Z bosons produced at the Tevatron collider.Comment: 27 pages, LaTeX, 8 figures as eps files. Some additions to earlier
version, this version as published in Phys. Rev. D66 (2002) 01401
Scheme dependence of NLO corrections to exclusive processes
We apply the so-called conformal subtraction scheme to predict perturbatively
exclusive processes beyond leading order. Taking into account evolution
effects, we study the scheme dependence for the photon-to-pion transition form
factor and the electromagnetic pion form factor at next-to-leading order for
different pion distribution amplitudes. Relying on the conformally covariant
operator product expansion and using the known higher order results for
polarized deep inelastic scattering, we are able to predict perturbative
corrections to the hard-scattering amplitude of the photon-to-pion transition
form factor beyond next-to-leading order in the conformal scheme restricted to
the conformal limit of the theory.Comment: RevTeX, 25 pages, 2 figures, 5 tables, minor changes, to be published
in Phys. Rev.
Complete next-to-leading order perturbative QCD prediction for the pion electromagnetic form factor
We present the results of a complete leading-twist next-to-leading order
(NLO) QCD analysis of the spacelike pion electromagnetic form factor at large
momentum transfer Q. We have studied their dependence on the form of the pion
distribution amplitude. For a given distribution amplitude, we have examined
the sensitivity of the predictions to the choice of the renormalization and
factorization scales. Theoretical uncertainty of the LO results related to the
renormalization scale ambiguity has been significantly reduced by including the
NLO corrections. Adopting the criteria according to which a NLO prediction is
considered reliable if, both, the ratio of the NLO to LO contributions and the
strong coupling constant are reasonably small, we find that reliable
perturbative predictions for the pion electromagnetic form factor with all
distribution amplitudes considered can already be made at a momentum transfer
Q<10 GeV, with corrections to the LO results being typically of the order of ~
20%. To check our predictions and to discriminate between the distribution
amplitudes, it is necessary to obtain experimental data extending to higher
values of Q.Comment: 39 pages, RevTex, 17 figures included; revised version (an error in
the analytical expression for T_H corrected, numerical results correspondigly
modified; presentation of the results modified to some extent and some points
discussed in more detail after referees reports
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