Electroweak Constraints on Effective Theories with U(2)xU(1) Flavor Symmetry

In a previous analysis presented in hep-ph/0412166, electroweak constraints were given on arbitrary linear combinations of a set of dimension-6 operators. Flavor universality and thus U(3)^5 flavor symmetry were assumed for the operators. In this article, we expand the analysis to account for the flavor-dependent theories that distinguish the third generation of fermions from the light two generations. We still assume flavor universality for the light two generations to avoid large FCNCs. Consequently, the U(3)^5 flavor symmetry is relaxed to [U(2)xU(1)]^5, and therefore more operators are added. We calculate the corrections to electroweak precision observables, assuming arbitrary coefficients for the operators. The corrections are combined with the standard model predictions and the experimental data to obtain the chi^2 distribution as a function of the operator coefficients. We apply our result to constrain two flavor-dependent extensions of the standard model: the simplest little Higgs model and a model with an SU(2)xSU(2)xU(1) gauge group.Comment: 11 pages, 2 figure

Electroweak Constraints on Effective Theories

We discuss electroweak constraints on TeV scale extensions of the standard model. To obtain model-independent results, effective theory approach is adopted. Constraints are given on arbitrary linear combinations of a set of dimension-6 operators that respect the SM gauge symmetry, as well as CP, lepton and baryon number conservation. Applications of the results are also discussed.Comment: To appear in Proceedings of SUSY06, the 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions, UC Irvine, California, 12-17 June 200

Little Higgs Models and Electroweak Measurements

Using effective field theory approach, we study the constraints from electroweak data on the SU(5)/SO(5), SU(6)/SP(6), SU(3)xU(1) little Higgs models and their variations. We construct an effective theory valid above the electroweak symmetry breaking scale in these models that includes dimension-six operators induced by integrating out heavy fields. We calculate the constraints on the models using the results of hep-ph/0412166, where bounds on arbitrary linear combinations of flavor and CP conserving dimension-six operators are given. We present the constraints in terms of the bounds on the masses of heavy fermions and heavy gauge bosons. The constraints are often stringent, but in some regions of the parameter space the constraints are mild enough and do not imply significant fine-tuning.Comment: Small changes to the plots due to the change in numerical results in hep-ph/0412166, text unchange