"Confronting electroweak precision measurements with new physics models"


Abstract:

The precision experiments at LEP and SLC consolidated the validity of
the electroweak Standard Model (SM) with high accuracy and one of the
key questions is: to what extent does this rule out or constrain the
parameter space of New Physics extensions of the SM ?  The usual way
to derive bounds on new physics starts from the SM together with its
substantial radiative corrections and treats the ``extension sector''
as a tree level perturbation, presuming that higher order corrections
from the new sector are numerically small.  However, for most of the
extended models this kind of ``strategy'' leads to misleading
conclusions. The reason is that the SM radiative corrections are
unstable with respect to extended tree level perturbations.
Typically, phenomenological fits to new physics models, in general,
fix parameters in such a way that gauge hierarchies are spoiled.  I
will present a few examples and discuss the drawback for the
interpretation of precision experiments.