Abstract: We present a one-loop calculation of the oblique S parameter within Higgsless models of electroweak symmetry breaking and analyze the phenomenological implications of the available electroweak precision data. We use the most general effective Lagrangian with at most two derivatives, implementing the chiral symmetry breaking SU(2)(L) circle times SU(2)(R) -> SU(2)(L+R) with Goldstones, gauge bosons and one multiplet of vector and axial-vector massive resonance states. Using the dispersive representation of Peskin and Takeuchi and imposing the short-distance constraints dictated by the operator product expansion, we obtain S at the NLO in terms of a few resonance parameters. In asymptotically-free gauge theories, the final result only depends on the vector-resonance mass and requires M-V > 1.8TeV (3.8TeV) to satisfy the experimental limits at the 3 sigma (1 sigma) level; the axial state is always heavier, we obtain M-A > 2.5TeV (6.6TeV) at 3 sigma (1 sigma). In strongly-coupled models, such as walking or conformal technicolour, where the second Weinberg sum rule does not apply, the vector and axial couplings are not determined by the short-distance constraints; but one can still derive a lower bound on S, provided the hierarchy M-V < M-A remains valid. Even in this less constrained situation, we find that in order to satisfy the experimental limits at 3 sigma one needs M-V,M-A > 1.8TeV.

Abstract: The couplings of the electroweak effective theory contain information on the heavy-mass scales which are no-longer present in the low-energy Lagrangian. We build a general effective Lagrangian, implementing the electroweak chiral symmetry breaking SU(2)(L) circle times SU(2)(R) -> SU(2)(L+R), which couples the known particle fields to heavier states with bosonic quantum numbers J(P) = 0(+/-) and 1(+/-). We consider colour-singlet heavy fields that are in singlet or triplet representations of the electroweak group. Integrating out these heavy scales, we analyze the pattern of low-energy couplings among the light fields which are generated by the massive states. We adopt a generic non-linear realization of the electroweak symmetry breaking with a singlet Higgs, without making any assumption about its possible doublet structure. Special attention is given to the different possible descriptions of massive spin-1 fields and the differences arising from naive implementations of these formalisms, showing their full equivalence once a proper short-distance behaviour is required.

Abstract: Using the spectral functions measured in tau decays, we investigate the actual numerical impact of duality violations on the extraction of the strong coupling. These effects are tiny in the standard alpha(s)(m(tau)(2)) determinations from integrated distributions of the hadronic spectrum with pinched weights, or from the total tau hadronic width. The pinched-weight factors suppress very efficiently the violations of duality, making their numerical effects negligible in comparison with the larger perturbative uncertainties. However, combined fits of alpha(s) and duality-violation parameters, performed with non-protected weights, are subject to large systematic errors associated with the assumed modelling of duality-violation effects. These uncertainties have not been taken into account in the published analyses, based on specific models of quark-hadron duality.

Abstract: Recent lattice data on pi pi -scattering phase shifts in the vector-isovector channel, pseudoscalar meson masses and decay constants for strange-quark masses smaller or equal to the physical value allow us to study the strangeness dependence of these observables for the first time. We perform a global analysis on two kind of lattice trajectories depending on whether the sum of quark masses or the strange-quark mass is kept fixed to the physical point. The quark mass dependence of these observables is extracted from unitarized coupled-channel one-loop Chiral Perturbation Theory. This analysis guides new predictions on the rho (770) meson properties over trajectories where the strange-quark mass is lighter than the physical mass, as well as on the SU(3) symmetric line. As a result, the light- and strange-quark mass dependence of the rho (770) meson parameters are discussed and precise values of the Low Energy Constants present in unitarized one-loop Chiral Perturbation Theory are given. Finally, the current discrepancy between two- and three-flavor lattice results for the rho (770) meson is studied.

Abstract: The tau -> pi pi pi nu(tau) decay is driven by the hadronization of the axial-vector current. Within the resonance chiral theory, and considering the large-N-C expansion, this process has been studied in Ref. [1] (D. Gomez Dumm, A. Pich, J. Portoles, 2004). In the light of later developments we revise here this previous work by including a new off-shell width for the lightest a(1) resonance that provides a good description of the tau -> pi pi pi nu(tau) spectrum and branching ratio. We also consider the role of the rho(1450) resonance in these observables. Thus we bring in an overall description of the tau -> pi pi pi nu(tau) process in excellent agreement with our present experimental knowledge.