586 research outputs found
Leading Logarithms in Field Theory
We consider the Sudakov form factor in effective theories and we show that
one can derive correctly the double logarithms of the original, high-energy,
theory. We show that in effective theories it is possible to separate
explicitely soft and hard dynamics being these two regimes related to velocity
conserving and to velocity changing operators respectively. A new effective
theory is sketched which extracts the leading collinear singularities of the
full theory amplitudes. Finally, we show how all leading logarithmic effects in
field theory can be obtained by means of simple effective theories, where they
correspond to a renormalization effect.Comment: Latex file, 20 pages, no figures, corrected some typo
The Resummation of Soft Gluon in Hadronic Collisions
We compute the effects of soft gluon resummation for the production of high
mass systems in hadronic collisions. We carefully analyse the growth of the
perturbative expansion coefficients of the resummation formula. We propose an
expression consistent with the known leading and next-to-leading resummation
results, in which the coefficients grow much less than factorially. We apply
our formula to Drell--Yan pair production, heavy flavour production, and the
production of high invariant mass jet pairs in hadronic collisions. We find
that, with our formula, resummation effects become important only fairly close
to the threshold region. In the case of heavy flavour production we find that
resummation effects are small in the experimental configurations of practical
interest.Comment: 45 pages, Latex, epsfig, 10 figures. Minor corrections to text,
notation and references. The previously quoted HERAb NLO bottom production
cross section was wrong, and it has been fixed. Accepted for Publication on
Nucl. Phys.
Searches for Clean Anomalous Gauge Couplings effects at present and future colliders
We consider the virtual effects of a general type of Anomalous (triple) Gauge
Couplings on various experimental observables in the process of
electron-positron annihilation into a final fermion-antifermion state. We show
that the use of a recently proposed "-peak subtracted" theoretical
description of the process allows to reduce substantially the number of
relevant parameters of the model, so that a calculation of observability limits
can be performed in a rather simple way. As an illustration of our approach, we
discuss the cases of future measurements at LEP2 and at a new 500 GeV linear
collider.Comment: 23 pages incl. 5 figures (e-mail [email protected]
A new approach to evaluate the leading hadronic corrections to the muon g-2
We propose a novel approach to determine the leading hadronic corrections to
the muon g-2. It consists in a measurement of the effective electromagnetic
coupling in the space-like region extracted from Bhabha scattering data. We
argue that this new method may become feasible at flavor factories, resulting
in an alternative determination potentially competitive with the accuracy of
the present results obtained with the dispersive approach via time-like data.Comment: 7 pages, 3 figures. Version accepted for publication in Phys. Lett.
Hadronic Cross Sections in Electron-Positron Annihilation with Tagged Photon
Events with tagged photons in the process of electron-positron annihilation
into hadrons are considered. The initial state radiation is suggested to scan
the hadronic cross section with the energy. QED radiative corrections are taken
into account. The results for the total and exclusive cross sections are given
in an analytic form. Some numerical estimates are presented.Comment: 12 pages, 2PS figures, the final journal versio
Pair Production in Small-Angle Bhabha Scattering
Radiative corrections due to the production of virtual as well as real soft
and hard pairs in small-angle Bhabha scattering are calculated analytically.
Both the collinear and the semi-collinear kinematical regions of hard pair
production are considered. The calculation, within the leading and
next-to-leading logarithmic approximation, provides an accuracy of O(0.1%).
Numerical results show that the effects of pair production have to be taken
into account for a luminosity determination accurate to O(0.1%) at LEP.Comment: Latex. 20 page
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