Precision Electroweak TestsMy earlier research emphasized studying the effects of non-standard-model physics on precision electroweak measurements. These measurements are important for constraining and ruling out a variety of models that purport to be more fundamental than the standard model of particle physics. This work has often involved building effective field theories to describe the most important degrees of freedom at a particular energy, and relating the properties of such theories to the underlying dynamics.

Early on I studied the effects of technicolor interactions on precision electroweak measurements. Such contributions to electroweak vacuum polarizations are now conventionally described by the parameters

S, andT. TheSparameter describes a momentum-dependent (kinetic) mixing of the electroweak gauge bosons, while theTparameter involves isospin breaking, which splits theWandZmasses. We found that QCD-like technicolor models give large corrections toZphysics; in other words, they give contributions toSof order 1. Current measurements ofScan thus rule out a large class of technicolor models.Present data tend to give central values for

SandTwhich are small, or negative. Most theories of non-standard physics give rise to positive values forSandT. I also showed that heavy Majorana fermions (i.e. fermions whose masses violate the conservation of fermion number) can give negative contributions to theSandTparametersI have also examined corrections from extended technicolor theories that are complementary to

SandT. The corrections fromSandTare flavor blind, since they arise from vacuum polarization effects. Thus measurements ofSandTare insensitive to new, flavor-dependent, physics that can appear in vertex corrections. Generally we expect the heaviest family of fermions to couple most strongly to flavor physics. Generically, extended technicolor gauge boson corrections decrease the partial width from the standard model expectation, so a large class of such models can be ruled out by current measurements. I have also looked at models where two gauge groups mix to produce the electroweak gauge group. In these models, the extended technicolor corrections increase the partial width ofZdecaying to b quarks, and cancel to a large extent with the corrections from the extra electroweak gauge bosons, and thus can be consistent with current data.Most of the work described above has been done with collaborators at several universities; I expect that these very fruitful collaborations will continue in the future.