81 research outputs found
The structure functions of longitudinal virtual photon at low virtualities
The structure functions of longitudinal virtual photon at low virtualities
are calculated in the framework of chiral pertubation theory(ChPT) in the zero
and first order of ChPT. It is assumed that the virtuality of target
longitudinal photon is much less than the virtuality of the hard projectile
photon and both are less than the characteristic ChPT scale.Comment: 16 pages, 8 figure
The asymptotic Sâmatrix, massâshell anomalies and observables
Asymptotic Sâmatrix techniques are applied to the identification of a Standard Model background to polarized deepâinelastic scattering experiments at HERA in search of Rightâhanded Charged Currents. It is also pointed out that the Asymptotic Sâmatrix produces finite observables free of MassâShell Anomalies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87409/2/297_1.pd
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Theoretical aspects of top quark production at hadron collider
We summarize our calculation of the total cross section for top quark production at hadron colliders within the context of perturbative quantum chromodynamics, including resummation of the effects of initial-state soft gluon radiation to all orders in the strong coupling strength
Radiative background to the search for right-handed charged currents
The probability for an electron to emit a collinear, hard photon while undergoing helicity flip is finite in the limit that the electron mass tends to zero. We point out that this provides a background of order [alpha] to tests of the Standard Model, which may affect the search for right-handed, charged currents in deeply inelastic scattering, especially at HERA. It would appear to be exceedingly difficult to discriminate against this background in practice and may make it difficult to improve substantially the mass limits on a right-handed charged vector boson.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29981/1/0000345.pd
Physical consequences of mass singularities
We argue that the perturbation expansion of massless field theories are uniquely and unambiguously defined for properly formed observables. In so doing, we generalize the Kinoshita-Lee-Nauenberg theorem to show that there are no observable "mass-shell anomalies". Paradoxically, in realistic circumstances, massive electrons give rise to non-intuitive, enhanced effects, for example, an unexpected background to the search for right-handed charged currents at HERA.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30154/1/0000531.pd
Threshold Resummation of the Total Cross Section for Heavy Quark Production in Hadronic Collisions
We discuss calculations of the inclusive total cross section for heavy quark
production at hadron collider energies within the context of perturbative
quantum chromodynamics, including resummation of the effects of initial-state
soft gluon radiation to all orders in the strong coupling strength. We resum
the universal leading-logarithm contributions, and we restrict our integrations
to the region of phase space that is demonstrably perturbative. We include a
detailed comparison of the differences between ours and other methods. We
provide predictions of the physical cross section as a function of the heavy
quark mass in proton-antiproton reactions at center-of-mass energies of 1.8 and
2.0 TeV, and we discuss estimated uncertainties.Comment: 31 pages, RevTeX, 7 figure
Power Corrections in QCD: A Matter of Energy Resolution
We consider power-like corrections in QCD which can be viewed as power
surpressed infrared singularities. We argue that the presence of these
singularities depends crucially on the energy resolution. In case of poor
energy resolution, i.e., inclusive cross sections, there are constraints on
infrared singularities expressed by the Kinoshita-Lee-Nauenberg (KLN) theorem.
We rewrite the theorem in covariant notations and argue that the KLN theorem
implies the extension of the Bloch-Nordsieck cancellation of logarithmic
singularities to the case of linear corrections.Comment: 11 pages, Latex file, uses epsf.sty, 5 figures in a uufil
An operator expansion for the elastic limit
A leading twist expansion in terms of bi-local operators is proposed for the
structure functions of deeply inelastic scattering near the elastic limit , which is also applicable to a range of other processes. Operators of
increasing dimensions contribute to logarithmically enhanced terms which are
supressed by corresponding powers of . For the longitudinal structure
function, in moment () space, all the logarithmic contributions of order
are shown to be resummable in terms of the anomalous dimension of
the leading operator in the expansion.Comment: 9 pages, 1 figure, uses REVTEX 3.1 and axodra
Asymptotic Dynamics in Quantum Field Theory
A crucial element of scattering theory and the LSZ reduction formula is the
assumption that the coupling vanishes at large times. This is known not to hold
for the theories of the Standard Model and in general such asymptotic dynamics
is not well understood. We give a description of asymptotic dynamics in field
theories which incorporates the important features of weak convergence and
physical boundary conditions. Applications to theories with three and four
point interactions are presented and the results are shown to be completely
consistent with the results of perturbation theory.Comment: 18 pages, 3 figure
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