[en] We investigate the reliability of the analytic continuation by duality (ACD) technique in estimating the electroweak S parameter for technicolor theories. The ACD technique, which is an application of finite energy sum rules, relates the S parameter for theories with unknown particle spectra to known OPE coefficients. We identify the sources of error inherent in the technique and evaluate them for several toy models to see if they can be controlled. The evaluation of errors is done analytically and all relevant formulas are provided in appendixes including analytical formulas for approximating the function 1/s with a polynomial in s. The use of analytical formulas protects us from introducing additional errors due to numerical integration. We find that it is very difficult to control the errors even when the momentum dependence of the OPE coefficients is known exactly. In realistic cases in which the momentum dependence of the OPE coefficients is only known perturbatively, it is impossible to obtain a reliable estimate. (c) 2000 The American Physical Society

[en] We use 106 pb^-1 of data collected with the Collider Detector at Fermilab to search for narrow-width, vector particles decaying to a top and an antitop quark. Model independent upper limits on the cross section for narrow, vector resonances decaying to tt are presented. At the 95% confidence level, we exclude the existence of a leptophobic Z^' boson in a model of top-color-assisted technicolor with mass M_Z^'<480 GeV/c² for natural width Γ=0.012M_Z^' , and M_Z^'<780 GeV/c² for Γ=0.04M_Z^' . (c) 2000 The American Physical Society

[en] We have carried out numerical studies of vacuum alignment in technicolor models of electroweak and flavor symmetry breaking. The goal is to understand alignment implications for strong and weak CP nonconservation in quark interactions. In this first part, we restrict our attention to the technifermion sector of simple models. We find several interesting phenomena, including (1) the possibility that all observable phases in the technifermions' unitary vacuum-alignment matrix are integer multiples of π/N^' where N^'≤N, the number of technifermion doublets, and (2) the possibility of exceptionally light pseudo Goldstone technipions. (c) 2000 The American Physical Society

[en] Using a manifestly gauge-invariant approach we show that the set of low-energy constants in the electroweak chiral Lagrangian currently used in the literature is redundant. In particular, by employing the equations of motion for the gauge fields, one can choose to remove two low-energy constants which contribute to the self-energies of the gauge-bosons. The relation of this result to the experimentally determined values for the oblique parameters S, T and U is discussed. We then evaluate the matching relation between gauge-invariant Green's functions in the full and the effective theory for the case of the standard model with a heavy Higgs boson and compare the results for the independent low-energy constants with those for a simple technicolor model. Since the pattern of the low-energy constants is very different in these two models it may be misleading to mimic any strongly interacting symmetry breaking sector by a heavy Higgs boson. From our investigation we conclude that current electroweak precision data do not really rule out such strongly interacting models. (orig.)