DOI 10.1007/s100520000278
Confronting electroweak precision measurements
with New
Physics
models
M. Czakon1 - J. Gluza1,2 - F. Jegerlehner2 -
M. Zra
ek1
1 Department of Field Theory and Particle Physics,
Institute
of Physics, University of
Silesia, Uniwersytecka 4, 40-007 Katowice, Poland
2 DESY Zeuthen, Platanenallee 6, 15738 Zeuthen, Germany
Received: 9 September 1999 / Published online: 25 February 2000 - © Springer-Verlag 2000
Abstract
Precision experiments, such as those performed at
LEP and SLC,
offer us an excellent opportunity to constrain extended gauge
model
parameters. To this end, it is often assumed that in order to
obtain
more reliable estimates, one should include the sizable one-loop
standard model (SM) corrections, which modify the Z0 couplings
as
well as other observables. This conviction is based on the belief
that
the higher order contributions from the "extension sector''
will be
numerically small. However, the structure of
higher order corrections can be quite different when comparing
the SM with
its extension; thus one should avoid assumptions which do not
take account of
such facts. This is the case for all models with
.
As an example, both the manifest
left-right symmetric model and the
model, with an additional
Z' boson, are discussed, and special attention to the top
contribution to
is given. We conclude
that the only sensible way to confront a model with the
experimental data is to renormalize it self-consistently. If
this is not done, parameters which depend strongly on quantum effects should
be
left free in fits, though essential physics is lost in this way.
We should note that the arguments given here allow us
to state that at the level of loop corrections (indirect effects)
there is nothing like a "model-independent global analysis''
of the data.
Copyright Società Italiana di Fisica, Springer-Verlag 2000
