16 research outputs found
The Ward Identities of the Gauge Invariant Three Boson Vertices
We outline the pinch technique for constructing gauge invariant Green's
functions in gauge theories and derive the Ward identities that must be
satisfied by the gauge invariant three boson vertices of the standard model.
They are generalizations of their tree level Ward identities and are shown to
be crucial for the delicate gauge cancellations of the S-matrix.Comment: 6 pages Latex, uses revtex[aps,aipbook,floats]. To appear in the
proceedings of the International Symposium on Vector Boson Self Interactions,
Feb. 1-3, 1995 UCLA, Los Angeles, California US
The dual gauge fixing property of the S matrix
The -matrix is known to be independent of the gauge fixing parameter to
all orders in perturbation theory. In this paper by employing the pinch
technique we prove at one loop a stronger version of this independence. In
particular we show that one can use a gauge fixing parameter for the gauge
bosons inside quantum loops which is different from that used for the bosons
outside loops, and the -matrix is independent from both. Possible
phenomenological applications of this result are briefly discussed.Comment: 17 pages, Late
A method for determining anomalous gauge boson couplings from e^{+}e^{-} experiments
We present a model-independent method for determining anomalous gauge boson
couplings from ongoing and future e^{+}e^{-} -> W^{+} W^{-} experiments. First
we generalize an already existing method, which relies on the study of four
observables constructed through appropriate projections of the unpolarized
differential cross-section. In particular, we retain both linear and quadratic
terms in the unknown couplings, and compute contributions to these observables
originating from anomalous couplings which do not separately conserve the
discrete C, P, and T symmetries. Second, we combine the above set of
observables with three additional ones, which can be experimentally obtained
from the total cross-sections for polarized final state W bosons. The resulting
set of seven observables may provide useful information for constraining, and
in some cases for fully determining, various of the possible anomalous gauge
boson couplings.Comment: 15 pages, Latex, 1 Figure, uses axodra
A set of sum rules for anomalous gauge boson couplings
The dependence of the differential cross-section for on-shell W-pair
production on the anomalous trilinear gauge couplings invariant under C and P
is examined. It is shown that the contributions of the anomalous magnetic
moments of the W boson due to the photon and the Z can be individually
projected out by means of two appropriately constructed polynomials. The
remaining four anomalous couplings are shown to satisfy a set of
model-independent sum rules. Specific models which predict special relations
among the anomalous couplings are then studied; in particular, the composite
model of Brodsky and Hiller, and the linear and non-linear effective Lagrangian
approaches. The relations predicted by these models, when combined with the
aforementioned sum rules, give rise to definite predictions, particular to each
model. These predictions can be used, at least in principle, in order to
exclude or constrain such models.Comment: 19 pages, 2 figures, uses axodraw.st
Consistency Condition for the Pinch Technique Self-Energies at Two Loops
A simple and testable necessary condition for the gauge independence of the
Pinch Technique self-energies at two loops is discussed. It is then shown that,
in the case of the and self-energies, the condition is indeed satisfied
by the Papavassiliou-Pilaftsis formulation.Comment: 7 pages, Latex, 1 PostScript figur
The heavy quark decomposition of the S-matrix and its relation to the pinch technique
We propose a decomposition of the S-matrix into individually gauge invariant
sub-amplitudes, which are kinematically akin to propagators, vertices, boxes,
etc. This decompsition is obtained by considering limits of the S-matrix when
some or all of the external particles have masses larger than any other
physical scale. We show at the one-loop level that the effective gluon
self-energy so defined is physically equivalent to the corresponding gauge
independent self-energy obtained in the framework of the pinch technique. The
generalization of this procedure to arbitrary gluonic -point functions is
briefly discussed.Comment: 11 uuencoded pages, NYU-TH-94/10/0
Application of the Pinch Technique to Neutral Current Amplitudes and the Concept of the Z Mass
The pinch technique (PT) is applied to neutral current amplitudes, focusing
on the mixing problem. Extending recent arguments due to Papavassiliou and
Pilaftsis, it is shown that the use of the PT self-energies does not shift the
complex-valued position of the pole through order {\cal O}(). This leads
(to the same accuracy) to a simple interpretation of , the mass measured
at LEP, in terms of the PT self-energies. It is pointed out that the PT
approach provides a convenient and rather elegant formalism to discuss
important neutral current amplitudes, such as those relevant to four-fermion
processes and LEP2.Comment: 13 pages, Latex, 3 PostScript figure
LEADING VACUUM-POLARIZATION CONTRIBUTIONS TO THE RELATION BETWEEN POLE AND RUNNING MASSES
The vacuum--polarization contributions of {\cal O}(b^{n-1} \al_s^n) to the
relation between the pole--mass of a quark and the \MS parameter \mh (M)
are evaluated by a straightforward method. They are found to approximate very
well the exact answer, known through {\cal O}(\al_s^2), thus providing a
simple physical interpretation. Results are also given for the cases when the
vacuum--polarization contributions are defined by the pinch technique
prescription and specific background field gauges. Assuming that the terms are also dominant, we evaluate , compare the
results with those of optimization methods, briefly discuss M_b/\mh_b (M_b),
and estimate the irreducible errors in the perturbative series. Implications
for the electroweak amplitude are emphasized. An update of the QCD
corrections to this amplitude, including an estimate of the theoretical error,
is given.Comment: 27 pages, 1 figure and 5 tables all included in the text in a
compressed ps fil
Two-loop electroweak corrections to the parameter beyond the leading approximation
We show that in the framework of the pinch technique the universal part of
the parameter can be meaningfully defined, beyond one loop. The
universal part so obtained satisfies the crucial requirements of
gauge-independence, finiteness, and process-independence, even when subleading
contributions of the top quark are included. The mechanism which enforces the
aforementioned properties is explained in detail, and several subtle field
theoretical issues are discussed. Explicit calculations of the sub-leading
two-loop corrections of order are carried
out in the context of an model, with , and various
intermediate and final results are reported.Comment: 40 pages, TeXsis, uu encoded ps files, 14 figures include