49 research outputs found
The Differential equation method: calculation of vertex-type diagrams with one non-zero mass
The differential equation method is applied to evaluate analytically two-loop
vertex Feynman diagrams. Three on-shell infrared divergent planar two-loop
diagrams with zero thresholds contributing to the processes Z --> bb bar (for
zero b mass) and/or H --> gg are calculated in order to demonstrate a new
application of this method.Comment: 12 pages, LATEX, uses axodray.st
Three-loop massive tadpoles and polylogarithms through weight six
We evaluate the three-loop massive vacuum bubble diagrams in terms of
polylogarithms up to weight six. We also construct the basis of irrational
constants being harmonic polylgarithms of arguments .Comment: 26 pages, 4 ancillary files, v3: version published in JHEP: minor
additions, file with results for massive three-loop form-factor integrals
adde
The transition form factor
We study the transition form factor,
with the local-duality (LD) version of
QCD sum rules. We analyse the extraction of this quantity from two different
correlators, and $,$ with $P,$ $A,$ and $V$ being the
pseudoscalar, axial-vector, and vector currents, respectively. The QCD
factorization theorem for $F_{\eta_c\gamma\gamma}(Q_1^2,Q_2^2)$ allows us to
fix the effective continuum thresholds for the and correlators
at large values of and some fixed value of . We give arguments that, in the region --, the
effective threshold should be close to its asymptotic value such that the LD
sum rule provides reliable predictions for
We show that, for the experimentally
relevant kinematics of one real and one virtual photon, the result of the LD
sum rule for may be
well approximated by the simple monopole formula
where is the
decay constant, is the -quark charge, and the parameter
lies in the mass range of the lowest vector states.Comment: 9 page
Electroweak corrections to -boson hadroproduction at finite transverse momentum
We calculate the full one-loop electroweak radiative corrections, of , to the cross section of single -boson inclusive
hadroproduction at finite transverse momentum (). This includes the corrections to production, the
corrections to production, and certain QCD-electroweak interference
contributions involving a single quark trace. We recover the QCD and purely
weak corrections and study the QED corrections and the QCD-electroweak
interference contributions for the first time. We also consider direct and
resolved photoproduction in elastic and inelastic scattering. We present
and rapidity distributions for the experimental conditions at the Fermilab
Tevatron and the CERN LHC and assess the significance of the various
contributions.Comment: 31 pages, 11 figures; discussion enhanced, figures added, references
added and updated; accepted for publication in Nucl. Phys.
On the -quark running mass in QCD and the SM
We consider electroweak corrections to the relation between the running
mass of the quark in the five-flavor
QCDQED effective theory and its counterpart in the Standard Model (SM).
As a bridge between the two parameters, we use the pole mass of the
quark, which can be calculated in both models. The running mass is not a
fundamental parameter of the SM Lagrangian, but the product of the running
Yukawa coupling and the Higgs vacuum expectation value. Since there exist
different prescriptions to define the latter, the relations considered in the
paper involve a certain amount of freedom. All the definitions can be related
to each other in perturbation theory. Nevertheless, we argue in favor of a
certain gauge-independent prescription and provide a relation which can be
directly used to deduce the value of the Yukawa coupling of the quark at
the electroweak scale from its effective QCD running mass. This approach allows
one to resum large logarithms systematically. Numerical analysis
shows that, indeed, the corrections to the proposed relation are much smaller
than those between and .Comment: 19 pages, 4 figures, misprints corrected (thanks to S. Martin),
results not affecte