Search

We extend the results of [arXiv:1006.0207 [hep-lat]] by computing the S-parameter at two loops in the perturbative region of the conformal window. Consistently using the expression for the location of the infra-red fixed point at the two-loop order we express the S-parameter in terms of the number of flavors, colors and matter representation. We show that S, normalized to the number of flavors, increases as we decrease the number of flavors. Our findings support the conjecture presented in [arXiv:1006.0207 [hep-lat]] according to which the normalized value of the S-parameter at the upper end of the conformal window constitutes the lower bound across the entire phase diagram for the given underlying asymptotically free gauge theory. We also show that the non-trivial dependence on the number of flavors merges naturally with the non-perturbative estimate of the S-parameter close to the lower end of the conformal window obtained using gauge duality [arXiv:1007.0254 [hep-ph]]. Our results are natural benchmarks for lattice computations of the S-parameter for vector-like gauge theories., Comment: Version to match the one published in Phys. Lett. B. The file is prepared in the 2-columns RevTeX format has 9 pages, 4 figures and one table

Near conformal dynamics is employed in different extensions of the standard model of particle interactions as well as in cosmology. Many of its interesting properties are either conjectured or determined using model computations. We introduce a relevant four dimensional gauge theory template allowing us to investigate such dynamics perturbatively. The gauge theory we consider is quantum chromodynamics with the addition of a meson-like scalar degree of freedom as well as an adjoint Weyl fermion. At the two-loop level, and in the Veneziano limit, we firmly establish the existence of several fixed points of which one is all directions stable in the infrared. An interesting feature of the model is that this fixed point is lost, within the perturbatively trustable regime, by merging with another fixed point when varying the number of quark flavors. We show the emergence of the Miransky scaling and determine its properties. We are also able to determine the walking region of the theory which turns out to be, at large number of colors, about 12% of the conformal window. Furthermore, we determine highly relevant quantities for near conformal dynamics such as the anomalous dimension of the fermion masses., Comment: 17 pages, 8 figures

We provide a complete extension of Minimal Walking Technicolor able to account for the standard model fermion masses. The model is supersymmetric at energies greater or equal to the technicolor compositeness scale. We integrate out, at the supersymmetry breaking scale, the elementary Higgses. We use the resulting four-fermion operators to derive the low energy effective theory. We then determine the associated tree-level vacuum and low energy spectrum properties. Furthermore we investigate the phenomenological viability of the model by comparing its predictions with electroweak precision tests and experimental bounds on the mass spectrum. We then turn to the composite Higgs phenomenology at the LHC and show that current data are already constraining the parameter space of the model., Comment: 43 pages, 13 figures. Version published on NPB. Typos corrected, results unchanged

We provide a pedagogical introduction to extensions of the Standard Model in which the Higgs is composite. These extensions are known as models of dynamical electroweak symmetry breaking or, in brief, Technicolor. Material covered includes: motivations for Technicolor, the construction of underlying gauge theories leading to minimal models of Technicolor, the comparison with electroweak precision data, the low energy effective theory, the spectrum of the states common to most of the Technicolor models, the decays of the composite particles and the experimental signals at the Large Hadron Collider. The level of the presentation is aimed at readers familiar with the Standard Model but who have little or no prior exposure to Technicolor. Several extensions of the Standard Model featuring a composite Higgs can be reduced to the effective Lagrangian introduced in the text. We establish the relevant experimental benchmarks for Vanilla, Running, Walking, and Custodial Technicolor, and a natural fourth family of leptons, by laying out the framework to discover these models at the Large Hadron Collider., LaTeX, 102 pages. Version to match the published version