Probing exotic leptons through oblique parameters

Abstract: In order to build realistic models in which electroweak symmetry is dynamically broken we should explain the smallness of the Peskin-Takeuchi {ital S} and {ital T} parameters. In accordance with the decoupling theorem, these parameters must be suppressed by SU(2){sub {ital L}}{times}U(1){sub {ital Y}} invariant masses. From this fact we can expect that if fermions with large SU(2){sub {ital L}}{times}U(1){sub {ital Y}} invariant masses undergo condensation and break electroweak symmetry, the {ital S} and {ital T} parameters can be small. It is intersting that not only the {ital S} but also the {ital T} parameter can become small even if there exists a large isospin violation in fermion condensation. In this paper we examine the possibility that, by the strong four-Fermi interaction, massive vectorlike fields undergo condensation and break electroweak symmetry. The model becomes almost the same as the standard model at a low energy scale and predicts a heavy Higgs boson. Moreover, we discuss a model in which the four-Fermi interaction can be induced by massive gauge boson exchange. In this model, the masses of ordinary matter fermions (quark and lepton) are enhanced.

Abstract: We show that an integral S over the spectral function of spin-1 states of the Higgs sector is constrained by precision weak-interaction measurements. Current data exclude large technicolor models; asymmetry measurements at the CERN ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ collider LEP and the SLAC Linear Collider will soon provide more stringent limits on Higgs-boson strong interactions.

Abstract: The effects of new physics on vacuum polarization corrections to electroweak processes can in general be parametrized in terms of six real constants, in the limit of neglecting terms which vanish for Λ→∞, with Λ being the scale of new physics. Three of these parameters can be reabsorbed in the definitions of α, GF and mZ, while the remaining three are observables. On the basis of simple models, it is shown that all three can be important and should be kept in a model-independent analysis of the data. This is equivalent to treating Δr, Δϱ and s2w (an effective sin2θw fro on-shell Z couplings) as independent observables. By now available data allow a separate model-independent determination of these quantities. Implications for technicolour and supersymmetric models and anomalous γWW or ZWW couplings are discussed.

Abstract: We set the framework for a model-independent analysis of the data on electroweak precision tests. Starting from three basic observables, the mass ratio m w / m z , the Z partial width and the forward-backward asymmetry for changed leptons, we define three dimensionless parameters ϵ 1 , ϵ 2 and ϵ 3 which contain the snall radiative correction effects one is interested in, with large m t -effects only appearing in ϵ 1 . The results on the epsilons implied by the present experimental data are discussed as well as the predictions of the Standard Model, as functions of m t and m H , with special attention to evaluating the theoretical errors. We formulate a hierarchy of simple and general assumptions, valid in large classes of models, which are needed in order to relate the epsilons to an increasingly larger set of observables including the τ-polarisation asymmetry, the forward-backward asymmetry for the b-quark, deep inelastic neutrino scattering and atomic parity violation. Correspondingly the analysis of present data is performed in stages and the conclusions are examined at each stage. Finally the case of the Standard Model is recovered as a very relevant particular example.

Abstract: We study the leading radiative corrections to various weak interaction parameters due to new heavy particles. We use an effective chiral lagrangian and input from low energy QCD to confirm the large size of these effects in technicolor theories.

Abstract: Effects of physics beyond the standard model on electroweak observables ares studied using the Peskin-Takeuchi isospin-conserving, S, and -breaking, T, parametrization of ``new'' quantum loop corrections Experimental constraints on S and T are presented Atomic parity-violating experiments are shown to be particularly sensitive to S with existing data giving S=-27\ifmmode\pm\else\textpm\fi{}20\ifmmode\pm\else\textpm\fi{}11 That constraint has important implications for generic technicolor models which predict S\ensuremath{\simeq}01${\mathit{N}}_{\mathit{T}}$${\mathit{N}}_{\mathit{D}}$ (${\mathit{N}}_{\mathit{T}}$ is the number of technicolors, ${\mathit{N}}_{\mathit{D}}$ is the number of technidoublets)