Jorge Portolés

Towards a consistent estimate of the chiral low-energy constants☆

Ministerio de Educacion y Ciencia, FPA2004-00996, HU2002-0044, Generalitat Valenciana, GRUPOS03/013, GV04B-594, GV05/015, European Commission, HPRN-CT2002-00311 (EURIDICE)

The Green function and SU(3) breaking in Kl3 decays

Using the 1=/N-C expansion scheme and truncating the hadronic spectrum to the lowest-lying resonances, we match a meromorphic approximation to the Green function onto QCD by imposing the correct large-momentum falloff, both off- shell and on the relevant hadron mass shells. In this way we determine a number of chiral low-energy constants of O(p(6)), in particular the ones governing SU(3) breaking in the K-l3 vector form factor at zero momentum transfer. The main result of our matching procedure is that the known loop contributions largely dominate the corrections of O(p(6)) to f(+)(0). We discuss the implications of our final value f(+)(K0 pi-) (0) = 0.984 +/- 0.012 for the extraction of V-us from K-l3 decays.

Odd-intrinsic-parity processes within the resonance effective theory of QCD

We analyse the most general odd-intrinsic-parity effective lagrangian of QCD valid for processes involving one pseudoscalar with vector mesons described in terms of antisymmetric tensor fields. Substantial information on the odd-intrinsic-parity couplings is obtained by constructing the vector-vector-pseudoscalar Greens three-point function, at leading order in 1/NC, and demanding that its short-distance behaviour matches the corresponding OPE result. The QCD constraints thus enforced allow us to predict the decay amplitudes ω→πγ and ρ→πγ, and the (p6) corrections to π→γγ. Noteworthy consequences concerning the vector meson dominance assumption in the decay ω→3π are also extracted from the previous analysis.

Green function in the resonance region

Abstract We analyze the 〈 V A P 〉 three-point function of vector, axial-vector and pseudoscalar currents. In the spirit of large N C , a resonance dominated Green function is confronted with the leading high-energy behaviour from the operator product expansion. The matching is shown to be fully compatible with a chiral resonance Lagrangian and it allows to determine some of the chiral low-energy constants of O ( p 6 ) .

Hadronic off-shell width of meson resonances

Within the resonance chiral effective theory we study the dressed propagators of the spin-1 fields, which arise from a Dyson-Schwinger resummation perturbatively constructed from loop diagrams with absorptive contributions in the s channel. We apply the procedure to the vector pion form factor and elastic

Vector form factor of the pion from unitarity and analyticity: A model-independent approach

\ensuremath{\pi}\ensuremath{\pi}

The decays K→πl+l− beyond leading order in the chiral expansion

scattering to obtain the off-shell width of the

Short-distance information from B(KL→μ+μ−)

{\ensuremath{\rho}}^{0}

tau ---> pi pi pi nu(tau) decays in the resonance effective theory

meson. We adopt a definition of the off-shell width of spin-1 meson resonances that satisfies the requirements of analyticity, unitarity, chiral symmetry, and asymptotic behavior ruled by QCD. To satisfy these constraints the resummation procedure cannot consist only of self-energy diagrams. Our width definition is shown to be independent of the formulation used to describe the spin-1 meson resonances.

Form factors in the radiative pion decay

We study a model-independent parameterization of the vector pion form factor that arises from the constraints of analyticity and unitarity. Our description should be suitable up to sqrt(s) ~ 1.2 GeV and allows a model-independent determination of the mass of the rho(770) resonance, M(rho) = (775.1 +- 0.5) MeV. We analyse the experimental data on tau(-) -> pion(-) pion(0) neutrino(tau), in this framework, and its consequences on the low-energy observables worked out by chiral perturbation theory. An evaluation of the two-pion contribution to the anomalous magnetic moment of the muon, a_muon, and to the fine structure constant, alpha(M(Z)^2), is also performed.