370 research outputs found
Differential equations and massive two-loop Bhabha scattering: the B5l2m3 case
The two-loop box contributions to massive Bhabha scattering may be reduced to
two-loop box master integrals (MIs) with five, six, and seven internal lines,
plus vertices and self energies. The self-energy and vertex MIs may be solved
analytically by the differential equations (DE) method. This is true for only
few of the box masters. Here we describe some details of the analytical
determination, including constant terms in ep=(4-d)/2, of the complicated
topology B5l2m3 (with 5 lines, 2 of them being massive). With the DE approach,
three of the four coupled masters have been solved in terms of (generalized)
standard Harmonic Polylogarithms.Comment: 5 pages, 2 figures, contribution to RADCOR 2005, Oct 2-7, 2005,
Shonan Village, Japan, to appear in Nucl. B (Proc. Suppl.
Matching perturbative and Parton Shower corrections to Bhabha process at flavour factories
We report on a high-precision calculation of the Bhabha process in Quantum
Electrodynamics, of interest for precise luminosity determination of
electron-positron colliders involved in R measurements in the region of
hadronic resonances. The calculation is based on the matching of exact
next-to-leading order corrections with a Parton Shower algorithm. The accuracy
of the approach is demonstrated in comparison with existing independent
calculations and through a detailed analysis of the main components of
theoretical uncertainty, including two-loop corrections, hadronic vacuum
polarization and light pair contributions. The calculation is implemented in an
improved version of the event generator BABAYAGA with a theoretical accuracy of
the order of 0.1%. The generator is now available for high-precision
simulations of the Bhabha process at flavour factories.Comment: 34 pages, 8 figures, uses elsart.cls. Version to appear on Nuclear
Physics
Electroweak top-quark pair production at the LHC with bosons to NLO QCD in POWHEG
We present the calculation of the NLO QCD corrections to the electroweak
production of top-antitop pairs at the CERN LHC in the presence of a new
neutral gauge boson. The corrections are implemented in the parton shower Monte
Carlo program POWHEG. Standard Model (SM) and new physics interference effects
are properly taken into account. QED singularities, first appearing at this
order, are consistently subtracted. Numerical results are presented for SM and
total cross sections and distributions in invariant mass, transverse
momentum, azimuthal angle and rapidity of the top-quark pair. The remaining
theoretical uncertainty from scale and PDF variations is estimated, and the
potential of the charge asymmetry to distinguish between new physics models is
investigated for the Sequential SM and a leptophobic topcolor model.Comment: 33 pages, 15 figures, 1 table. Discussion added on uncertainties from
parton showers and NLL contribution
Harmonic polylogarithms for massive Bhabha scattering
One- and two-dimensional harmonic polylogarithms, HPLs and GPLs, appear in
calculations of multi-loop integrals. We discuss them in the context of
analytical solutions for two-loop master integrals in the case of massive
Bhabha scattering in QED. For the GPLs we discuss analytical representations,
conformal transformations, and also their transformations corresponding to
relations between master integrals in the s- and t-channel.Comment: 6 pages, latex, uses espcrc2.sty, contrib. to Proc. of X. Int.
Workshop on Advanced Computing and Analysis Techniques in Physics Research
(ACAT), May 22 - 27, 2005, DESY, Zeuthen, Germany, to appear in NI
Master integrals for massive two-loop Bhabha scattering in QED
We present a set of scalar master integrals (MIs) needed for a complete
treatment of massive two-loop corrections to Bhabha scattering in QED,
including integrals with arbitrary fermionic loops. The status of analytical
solutions for the MIs is reviewed and examples of some methods to solve MIs
analytically are worked out in more detail. Analytical results for the pole
terms in epsilon of so far unknown box MIs with five internal lines are given.Comment: 23 pages, 5 tables, 12 figures, references added, appendix B enlarge
On the Soft-Gluon Resummation in Top Quark Pair Production at Hadron Colliders
We uncover a contribution to the NLO/NLL threshold resummed total cross
section for top quark pair production at hadron colliders, which has not been
taken into account in earlier literature. We derive this contribution - the
difference between the singlet and octet hard (matching) coefficients - in
exact analytic form. The numerical impact of our findings on the Sudakov
resummed cross section turns out to be large, and comparable in size to the
current estimates for the theoretical uncertainty of the total cross section. A
rough estimate points toward a few percent decrease of the latter at the LHC.Comment: 11 pages, 1 figur
Two-Loop Planar Corrections to Heavy-Quark Pair Production in the Quark-Antiquark Channel
We evaluate the planar two-loop QCD diagrams contributing to the leading
color coefficient of the heavy-quark pair production cross section, in the
quark-antiquark annihilation channel. We obtain the leading color coefficient
in an analytic form, in terms of one- and two-dimensional harmonic
polylogarithms of maximal weight 4. The result is valid for arbitrary values of
the Mandelstam invariants s and t, and of the heavy-quark mass m. Our findings
agree with previous analytic results in the small-mass limit and numerical
results for the exact amplitude.Comment: 30 pages, 5 figures. Version accepted by JHE
Decays of Scalar and Pseudoscalar Higgs Bosons into Fermions: Two-loop QCD Corrections to the Higgs-Quark-Antiquark Amplitude
As a first step in the aim of arriving at a differential description of
neutral Higgs boson decays into heavy quarks, , to second
order in the QCD coupling , we have computed the
amplitude at the two-loop level in QCD for a general neutral Higgs boson which
has both scalar and pseudoscalar couplings to quarks. This amplitude is given
in terms of a scalar and a pseudoscalar vertex form factor, for which we
present closed analytic expressions in terms of one-dimensional harmonic
polylogarithms of maximum weight 4. The results hold for arbitrary
four-momentum squared, , of the Higgs boson and of the heavy quark mass,
. Moreover we derive the approximate expressions of these form factors near
threshold and in the asymptotic regime .Comment: 56 pages, 2 figure
Nurses and the acceptance of innovations in technology-intensive contexts: the need for tailored management strategies
BACKGROUND: Several technological innovations have been introduced in healthcare over the years, and their implementation proved crucial in addressing challenges of modern health. Healthcare workers have frequently been called upon to become familiar with technological innovations that pervade every aspect of their profession, changing their working schedule, habits, and daily actions. PURPOSE: An in-depth analysis of the paths towards the acceptance and use of technology may facilitate the crafting and adoption of specific personnel policies taking into consideration definite levers, which appear to be different in relation to the age of nurses. APPROACH: The strength of this study is the application of UTAUT model to analyse the acceptance of innovations by nurses in technology-intensive healthcare contexts. Multidimensional Item Response Theory is applied to identify the main dimensions characterizing the UTAUT model. Paths are tested through two stage regression models and validated using a SEM covariance analysis. RESULTS: The age is a moderator for the social influence: social influence, or peer opinion, matters more for young nurse. CONCLUSION: The use of MIRT to identify the most important items for each construct of UTAUT model and an in-depth path analysis helps to identify which factors should be considered a leverage to foster nurses' acceptance and intention to use new technologies (o technology-intensive devices). PRACTICAL IMPLICATIONS: Young nurses may benefit from the structuring of shifts with the most passionate colleagues (thus exploiting the social influence), the participation in ad hoc training courses (thus exploiting the facilitating conditions), while other nurses could benefit from policies that rely on the stressing of the perception of their expectations or the downsizing of their expectancy of the effort in using new technologies
Next-to-next-to-leading soft-gluon corrections for the top quark cross section and transverse momentum distribution
I present results for top quark production in hadronic collisions at LHC and
Tevatron energies. The soft-gluon corrections to the differential cross section
are resummed at next-to-next-to-leading-logarithm (NNLL) accuracy via the
two-loop soft anomalous dimension matrices. Approximate
next-to-next-to-leading-order (NNLO) differential and total cross sections are
calculated. Detailed theoretical predictions are shown for the t tbar cross
section and the top quark p_T distribution at the Tevatron and the LHC.Comment: 23 pages, 14 figures; additional results and figure
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