Antonio Pich

K → πℓ+ℓ− decays in the effective chiral lagrangian of the standard model

Abstract The decay amplitudes of K → π l + l − transitions (l = e or μ ) are calculated in chiral perturbation theory to lowest non-trivial order. This includes one-loop contributions as well as contributions from all possible tree level counterterms to the corresponding order in momenta and meson masses. After relating the local counterterms in the chiral realization to the lowest dimensional local transition operator at the quark level, only one combination of counterterm coupling constants appearing in the decay amplitudes remains unknown. Two possible solutions for this constant are found from a comparison with the experimentally known K + → π + e + e − decay rate. Predictions are then obtained for the rates of K + → π + μ + μ − , K s 0 → π 0 e + e − and K s 0 → π 0 μ + μ − decays as well as for the corresponding spectra in the invariant mass of the lepton pair. The CP -violating transition K L 0 → π 0 ‘γ’ → π 0 l + l − is also discussed.

K-K mixing in the standard model

Abstract We present a new calculation of the B parameter which governs the short distance contribution to the K 0 - K 0 off-diagonal mass matrix. The calculation combines the information provided by the effective chiral lagrangian realization of QCD at long distances with the perturbative behaviour of QCD at short distances via the local duality approach. The result exhibits an explicit renormalization scale dependence which exactly cancels with the corresponding dependence in the Wilson coefficient.

The decay K+→φ+φ0 in the standard model

Abstract We present a direct calculation of the ΔI = 3 2 amplitude which governs the K + →φ + φ 0 . The calculational procedure is similar to the one which has been recently used by two of us to evaluate the B -parameter of K 0 K 0 mixing. The succesful result we find reinforces our belief in the value of the B -parameter obtained previously by two of us.

Problem with the |ΔI| = 12 rule in the standard model

34 paginas, 9 figuras, 5 tablas.-- Trabajo presentado al 23o International Conference On High-Energy Physics celebrado del 16 al 23 de Julio de 1986 en Berkeley (USA).

CP phases in the charged current and Higgs sectors for Majorana neutrinos

The diagonalization of the leptonic mass matrices is performed in the framework of the triplet model to generate Majorana mass terms for neutrinos. This allows the understanding of the role played by the CP-violating phases in the Higgs sector and their relation with those of the charged-current Lagrangian. It is shown that all the leptonic mixings, including those of the Higgs couplings, can be given in terms of a Kobayashi-Maskawa matrix and the relative Majorana phases of the neutrino fields. The characteristic Majorana phases, always appearing together with the neutrino mass, are present in |ΔL|=2 pieces and they show up in processes with a) neutrino-antineutrino propagation, and/or b) at least two different neutrinos as asymptotic states, and/or c) a vertex with a doubly-charged scalar. The phenomenological implications for processes with these characteristics are given.

|V(us)| and m(s) from hadronic tau decays

Recent experimental results on hadronic tau decays into strange particles by the OPAL Collaboration are employed to determine V(us) and m(s) from moments of the invariant mass distribution. Our results are V(us)=0.2208+/-0.0034 and m(s)(2 GeV)=81+/-22 MeV. The error on V(us) is dominated by experiment and should be improvable in the future. Nevertheless, already now our result is competitive with the standard extraction of V(us) from K(e3) decays, and it is compatible with unitarity.

The hierarchy problem in the scalar triplet model

Abstract We investigate the possibility of maintaining the hierarchy of the gauge and lepton number symmetry breakdown in the context of the Gelmini-Roncadelli model of electroweak interactions. Calculating the effective potential in the one-loop approximation, we find the additional constraints one must impose on the scalar self-couplings to protect the tree level hierarchy from dangerous radiative corrections.

π0–η mixing and CP violation

We discuss π0–ηmixing and its implication for e′/e to next-to-leading order in the low-energy expansion. The big effect due to η–η′ mixing is shown to be largely cancelled by other contributions occurring at the same order in the chiral expansion.

Quark-hadron duality violation in QCD Sum Rules with hadronic \tau data

We study the Quark-Hadron Duality Violation in Finite Energy Sum Rules (FESRs) with the LR correlator, through an analysis of the possible high-energ y behavior of the LR spectral function, taking into account the experimental hadronic τ-decay data and the known short-distance constraints. We show that the pinched weights allow to determine with precision the dimension six and eight contributions in the Operator-Product Expansion, O6 = −4.3 +0.9 −0.7

From Hadronic τ Decays to the Chiral Couplings and

6 paginas, 2 figuras.-- Comunicacion presentada al 10o International Workshop on Tau Lepton Physics, celbrado del 22 al 25 de Septiembre de 2008 en Novosibirsk (Rusia).-- arXiv:0812.1943v1.