682 research outputs found
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
Semiquantitative Assessment of Bowel Habits and Its Relation with Calcium Metabolism after Gastric Bypass Surgery: A Retrospective Study
Background. Calcium malabsorption after bariatric surgery may be harmful to skeletal health and demands for optimal skeletal management. Methods. 103 Patients were evaluated retrospectively at 12 months after surgery. The evaluation included a questionnaire about stool frequency and consistency and laboratory assessments. Results. 103 Patients, 27 males and 76 females, were included in the study. 83 Patients had an alimentary limb of 100 cm and 20 patients one of 150 cm. At 12 months after surgery, 77.7% reported changes of bowel habits, albumin adjusted calcium levels were normal in all but 2 patients, and PTH levels were increased in 35%. Correlations between semiquantified bowel scores (fecal scores) and data from the laboratory demonstrated increasing PTH values along with more frequent and softer/watery stools (RR 30.5, CI 6.2–149.2, P < .001). There was a trend for higher PTH levels in patients with an alimentary limb of 150 cm. Normal PTH levels were more frequently found in case of calcium and vitamin D3 use (RR 14.3, CI 3.6–56.5, P < .001). Conclusion. This study demonstrates interrelationships between semi-quantified fecal scores, PTH levels, and the compliance of taking calcium/vitamin D3 suppletion. However, prospective randomized studies are necessary to show causal relationships
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
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
Quantum Corrections to the Reissner-Nordstrom and Kerr-Newman Metrics: Spin 1
A previous evaluation of one-photon loop corrections to the energy-momentum
tensor has been extended to particles with unit spin and speculations are
presented concerning general properties of such forms.Comment: 21 pages, 1 Figur
On Observing Top Quark Production at the Tevatron
A technique for separating top quark production from Standard Model
background events is introduced. It is applicable to the channel in which one
top quark decays semi-leptonically and its anti-quark decays hadronically into
three jets, or vice versa. The method is shown to discriminate dramatically
between Monte Carlo generated events with and without simulated top quarks of
mass around 120 GeV and above. The simulations were performed with CDF detector
characteristics incorporated, showing that the method is applicable to existing
data.Comment: 8 pages, TUFTS-TH-92-G01 (Two minor TeX mistakes corrected
Graviton-induced Bremsstrahlung
We discuss photon Bremsstrahlung induced by virtual graviton exchange in
proton-proton interactions at hadronic colliders, resulting from the exchange
of Kaluza-Klein excitations of the graviton. The relevant subprocesses, gg to G
to e^+e^-gamma and q barq to e^+e^-gamma are discussed in both the ADD and the
RS scenarios. Although two-body final states (or real graviton emission) would
presumably be the main discovery channels, a search for three-body final states
could be worthwhile since such events have characteristic features that could
provide additional confirmation. In particular, the k_perp-distribution of the
photon is in both scenarios harder than that of the Standard-model background.Comment: 24 pages, including figures. v2: Including initial-state
Bremsstrahlung and photon k_perp spectra. Version to appear in PR
Signatures of HyperCharge Axions in Colliders
If in addition to the standard model fields, a new pseudoscalar field that
couples to hypercharge topological number density, the hypercharge axion,
exists, it can be produced in colliders in association with photons or Z
bosons, and detected by looking for its decay into photons or Z's. For a range
of masses below a TeV and coupling above a fraction of 1/TeV, existing data
from LEP II and the Tevatron can already put interesting constraints, and in
future colliders accessible detection range is increased significantly. The
hypercharge axion can help in explaining the matter-antimatter asymmetry in the
universe.Comment: 11 pages, 8 figures, uses axodraw.st
Compton and double Compton scattering processes at colliding electron-photon beams
Radiative corrections (RC) to the Compton scattering cross section are
calculated in the leading and next-to leading logarithmic approximation to the
case of colliding high energy photon-electron beams.
RC to the double Compton scattering cross section in the same experimental
set-up are calculated in the leading logarithmic approximation.
We consider the case when no pairs are created in the final state. We show
that the differential cross section can be written in the form of the Drell-Yan
process cross-section.
Numerical values of the -factor and the leading order distribution on the
scattered electron energy fraction and scattering angle are presented
Bremsstrahlung photon polarization for , and high energy collisions
The polarization of bremsstrahlung photon in the processes , and is calculated for peripheral
kinematics, in the high energy limit where the cross section does not decrease
with the incident energy. When the initial electron is
unpolarized(longitudinally polarized) the final photon can be linearly
(circularly) polarized. The Stokes parameters of the photon polarization are
calculated as a function of the kinematical variables of process: the energy of
recoil particle, the energy fraction of scattered electron, and the polar and
azimuthal angles of photon. Numerical results are given in form of tables, for
typical values of the relevant kinematic variables.Comment: 9 pages, 3 figure
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