Technicolour and precision electroweak data revisited

We examine the present status of technicolour (TC) models in the light of recent improvements both in theory and experiment. First we present an updated model-independent fit of high-energy precision electroweak data, and emphasize their compatibility with the Standard Model. We then compare the model-independent fit with a one-generation TC model with Ntc = 2, degenerate techniquarks and either a Dirac or a Majorana technineutrino, not necessarily degenerate with the technielectron. The results are charted in a way which clearly shows how data disfavour simple TC models, unless judicious combinations of additional effects (induced by the dynamics and/or the spectrum) are allowed. Techniquark mass splitting is shown to be fatal to the Dirac case. Even allowing for theoretical uncertainties, a pattern of stringent constraints on TC models is seen to emerge.