Juan José Sanz-Cillero

Quantum loops in the resonance chiral theory: The Vector form-factor

We present a calculation of the Vector Form Factor at the next-to-leading order in the 1/NC expansion, within the framework of Resonance Chiral Theory. The calculation is performed in the chiral limit, and with two dynamical quark flavours. The ultraviolet behaviour of quantum loops involving virtual resonance propagators is analyzed, together with the kind of counterterms needed in the renormalization procedure. Using the lowest-order equations of motion, we show that only a few combinations of local couplings appear in the final result. The low-energy limit of our calculation reproduces the standard Chiral Perturbation Theory formula, allowing us to determine the resonance contribution to the chiral low-energy couplings, at the next-to-leading order in 1/NC, keeping a full control of their renormalization scale dependence.

Rho meson properties in the chiral theory framework

Abstract. We study the mass, width and couplings of the lightest resonance multiplet with I (JPC) = 1 (1-) quantum numbers. Effective field theories based on chiral symmetry are employed in order to describe the form factor associated with the two pseudoscalar matrix element of the QCD vector current. The bare poles of the intermediate resonances are regularized through a Dyson-Schwinger-like summation. We explore the role of the resonance width in physical observables and make a coupled-channel analysis of the final-state interactions. This provides many interesting properties, like the pole mass

Viability of strongly coupled scenarios with a light Higgs-like boson.

M_\rho^{\mathrm{pole}}= 764.1\pm 2.7^{+4.0}_{-2.5}

One-Loop Calculation of the Oblique S Parameter in Higgsless Electroweak Models

MeV. At energies

The vector form factor at the next-to-leading order in 1/NC: chiral couplings L9(μ) and C88(μ) − C90(μ)

E\gtrsim 1

Towards a determination of the chiral couplings at NLO in 1/N(C): L**r(8)(mu)

GeV, a second 1 (1-) resonance multiplet is considered in order to describe the data in a more consistent way. From the phenomenologically extracted resonance couplings, we obtain the chiral coupling

Low-energy signals of strongly-coupled electroweak symmetry-breaking scenarios

L_9^{\mathrm{r}}(\mu_0)= (7.04\pm 0.05^{+0.19}_{-0.27})\cdot 10^{-3}

Long distance chiral corrections in B meson amplitudes

, at

Uncertainty estimates of the σ-pole determination by Padé approximants

\mu_0 = 770

Traces of resonances in electroweak effective Lagrangians

MeV, and show how the running with the scale μ affects the resonance parameters. A 1/NC counting is adopted in this work and the consistency of the large-NC expansion is tested. Finally, we make an estimation of the contribution from diagrams with resonances in crossed channels.