We show that it is possible to construct explicit models of electroweak symmetry breaking in which the number of techniflavors needed to enter the conformal phase of the theory is small and weakly dependent on the number of technicolors. Surprisingly, the minimal model with {\it just} two (techni)flavors, together with a suitable gauge dynamics, can be made almost conformal. The theories we consider are generalizations of orientifold type gauge theories, in which the fermions are in either two index symmetric or antisymmetric representation of the gauge group, as the underlying dynamics responsible for the spontaneous breaking of the electroweak symmetry. We first study their phase diagram, and use the fact that specific sectors of these theories can be mapped into supersymmetric Yang-Mills theory to strengthen our results. This correspondence allows us also to have information on part of the nonperturbative spectrum. We propose and investigate some explicit models while briefly exploring relevant phenomenological consequences. Our theories not only can be tested at the next collider experiments but, due to their simple structure, can also be studied via current lattice simulations.Comment: RevTex, 4 pages, 2-column format and 2 eps figures. Final version to match the one which will appear in the Rapid Communication section of Physical Review

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Abstract:We study the ultraviolet behaviour of four-dimensional quantum field theories involving non-abelian gauge fields, fermions and scalars in the Veneziano limit. In a regime where asymptotic freedom is lost, we explain how the three types of fields cooperate to develop fully interacting ultraviolet fixed points, strictly controlled by perturbation theory. Extensions towards strong coupling and beyond the large-N limit are discussed.

We investigate theories in which the technifermions in higher dimensional representations of the technicolor gauge group dynamically break the electroweak symmetry of the standard model.Somewhat surprisingly, for the two-index symmetric representation of the gauge group the lowest number of techniflavors needed to render the underlying gauge theory quasi conformal is two. This is exactly one doublet of technifermions with respect to the weak interactions promoting these theories to ideal candidates of "walking" type technicolor models. From the point of view of the weak interactions the two techniflavor theory has a Witten anomaly, which we cure by introducing a fourth family of leptons. An elegant feature of this model is that the techniquarks * Electronic address: dietrich@nbi.dk † Electronic address: francesco.sannino@nbi.dk ‡ Electronic address: kimmo.tuominen@phys.jyu.fi

We propose an all orders beta function for ordinary Yang-Mills theories with or without fermions inspired by the Novikov-Shifman-Vainshtein-Zakharov beta function of N = 1 supersymmetric gauge theories. The beta function allows us to bound the conformal window. When restricting to one adjoint Weyl fermion we show how the proposed beta function matches the one of supersymmetric Yang-Mills theory. The running of the pure Yang-Mills coupling is computed and the deviation from the two loop result is presented. We then compare the deviation with the one obtained from lattice data also with respect to the two loop running. * Electronic address: ryttov@nbi.dk † Electronic address: sannino@ifk.sdu.dk