901 research outputs found
Threshold and pseudothreshold values of the sunset diagram
Analytic results for the threshold and pseudothreshold values of the sunset
diagram with arbitrary masses are obtained in terms of dilogarithms of ratios
of the masses.Comment: 11 pages, plain LaTe
Small-threshold behaviour of two-loop self-energy diagrams: two-particle thresholds
The behaviour of two-loop two-point diagrams at non-zero thresholds
corresponding to two-particle cuts is analyzed. The masses involved in a cut
and the external momentum are assumed to be small as compared to some of the
other masses of the diagram. By employing general formulae of asymptotic
expansions of Feynman diagrams in momenta and masses, we construct an algorithm
to derive analytic approximations to the diagrams. In such a way, we calculate
several first coefficients of the expansion. Since no conditions on relative
values of the small masses and the external momentum are imposed, the threshold
irregularities are described analytically. Numerical examples, using diagrams
occurring in the Standard Model, illustrate the convergence of the expansion
below the first large threshold.Comment: 28 pages (including 23 pages of text in latex and 5 pages with 6
figures in a separate postcript file
One Loop Multiphoton Helicity Amplitudes
We use the solutions to the recursion relations for double-off-shell fermion
currents to compute helicity amplitudes for -photon scattering and
electron-positron annihilation to photons in the massless limit of QED. The
form of these solutions is simple enough to allow {\it all}\ of the
integrations to be performed explicitly. For -photon scattering, we find
that unless , the amplitudes for the helicity configurations (+++...+) and
(-++...+) vanish to one-loop order.Comment: 27 pages + 4 uuencoded figures (included), Fermilab-Pub-93/327-T,
RevTe
Target normal spin asymmetry and charge asymmetry for elastic scattering and the crossed processes
Two kinds of asymmetry arise from the interference of the Born amplitude and
the box-type amplitude corresponding to two virtual photons exchange, namely
charge-odd and one spin asymmetries. In case of unpolarized particles the
charge-odd correlation is calculated. It can be measured in combination of
electron muon and positron muon scattering experiments. The forward-backward
asymmetry is the corresponding quantity which can be measured for the crossed
processes. In the case of polarized muon the one-spin asymmetry for
annihilation and scattering channels has been calculated. The additional
structure function arising from the interference is shown to suffer from
infrared divergencies. The background due to electroweak interaction is
discussed.Comment: 19 pages, 5 figure
Radiative muon pair production in high energy electron-positron annihilation process
The lowest order radiative correction to the differential cross-section of
process of muon pair production with emission of hard photon at high energy
electron-positron annihilation are calculated. Taking into account the emission
of additional soft and hard photon the cross-section can be put in the form of
Drell-Yan process in leading logarithmical approximation. Applying the crossing
transformation we obtain the cross section of radiative electron-muon
high-energy scattering process. Virtual and soft photon emission contributions
of non-leading form are tabulated for several typical kinematical points. The
limit of small invariant mass of muon pair is in agreement with our previous
analysis.Comment: 9 pages, 2 figure
Special case of sunset: reduction and epsilon-expansion
We consider two loop sunset diagrams with two mass scales m and M at the
threshold and pseudotreshold that cannot be treated by earlier published
formula. The complete reduction to master integrals is given. The master
integrals are evaluated as series in ratio m/M and in epsilon with the help of
differential equation method. The rules of asymptotic expansion in the case
when q^2 is at the (pseudo)threshold are given.Comment: LaTeX, 13 pages, 1 figur
Prospects of Open Charm Production at GSI-FAIR and J-PARC
We present a detailed phenomenological study of the prospects of open charm
physics at the future and facilities GSI-FAIR and J-PARC,
respectively. In particular, we concentrate on differential cross sections and
the charge and longitudinal double-spin asymmetries at next-to-leading order
accuracy. Theoretical uncertainties for the proposed observables are estimated
by varying the charm quark mass and the renormalization and factorization
scales.Comment: 11 pages, 13 figure
Towards a common origin of the elliptic flow, ridge and alignment
It is claimed that elliptic flow, ridge and alignment are effects of
azimuthal asymmetry, which have a common origin evolving with primary energy
and stemming from the general structure of field-theoretical matrix elements.
It interrelates a new ridge-phenomenon, recently found at the LHC and RHIC,
with known coplanarity feature observed in collider jet physics as well as in
cosmic ray studies.Comment: 4 pages, few typos fixed, reference added, version published in JETP
Letter
Prevalence of Anemia and Related Deficiencies in the First Year following Laparoscopic Gastric Bypass for Morbid Obesity
Background. Anemia associated with deficiencies in iron, folic acid, and vitamin B12 are very common after Laparoscopic Roux-en-Y Gastric Bypass (LRYGB) surgery for morbid obesity. This study was conducted to evaluate the prevalence of anemia after LRYGB. Patients and Methods. A total of 377 morbid obese patients were included in our study. All patients underwent a LRYGB. Hematologic parameters were obtained prior to and after surgery on standardized time intervals. Results. Anemia was present in 21 (P = 0.02) patients after surgery. Iron, folic acid, and vitamin B12 deficiencies were diagnosed in 66%, 15%, and 50% of patients, respectively. In 86% of patients, anemia was accompanied by one of these deficiencies. Conclusion. These results show that anemia and deficiencies for iron, folic acid deficiency, and vitamin B12 are very common within the first year after LRYGB. We advise a minimal daily intake of 65 mg of iron in male and 100 mg in female patients, 350 μg of vitamin B12, and 400 μg of folic acid. Patients undergoing LRYGB must be closely monitored for deficiencies pre- and postoperative and supplemented when deficiencies occur
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