46 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
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
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
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
All-order results for soft and collinear gluons
I briefly review some general features and some recent developments
concerning the resummation of long-distance singularities in QCD and in more
general non-abelian gauge theories. I emphasize the field-theoretical tools of
the trade, and focus mostly on the exponentiation of infrared and collinear
divergences in amplitudes, which underlies the resummation of large logarithms
in the corresponding cross sections. I then describe some recent results
concerning the conformal limit, notably the case of N = 4 superymmetric
Yang-Mills theoryComment: 15 pages, invited talk presented at the 10th Workshop in High Energy
Physics Phenomenology (WHEPP X), Chennai, India, January 200
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
Anomalous Neutrino Reactions at HERA
We study the sensitivity of HERA to new physics using the helicity suppressed
reaction , where the final neutrino can be a standard
model one or a heavy neutrino. The approach is model independent and is based
on an effective lagrangian parametrization. It is shown that HERA will put
significant bounds on the scale of new physics, though, in general, these are
more modest than previously thought. If deviations from the standard model are
observed in the above processes, future colliders such as the SSC and LHC will
be able to directly probe the physics responsible for these discrepancies}Comment: 11 Pages + 2 figures is TOPDRAWER (included at the end or available
by mail). Report UCRHEP-T113 (requires the macropackage PHYZZX). A line in
the TeX file requesting an input file has been removed, it caused problem
The KLN Theorem and Soft Radiation in Gauge Theories: Abelian Case
We present a covariant formulation of the Kinoshita, Lee, Nauenberg (KLN)
theorem for processes involving the radiation of soft particles. The role of
the disconnected diagrams is explored and a rearrangement of the perturbation
theory is performed such that the purely disconnected diagrams are factored
out. The remaining effect of the disconnected diagrams results in a simple
modification of the usual Feynman rules for the S-matrix elements. As an
application, we show that when combined with the Low theorem, this leads to a
proof of the absense of the corrections to inclusive processes (like the
Drell-Yan process). In this paper the abelian case is discussed to all orders
in the coupling.Comment: 27 pages, LaTeX, 14 figure