Anomalous dimensions of four-quark operators and renormalon structure of mesonic two-point correlators

In this work, we calculate leading-order anomalous dimension matrices for dimension-6 four-quark operators which appear in the operator product expansion of flavour non-diagonal and diagonal vector and axial-vector two-point correlation functions. The infrared renormalon structure corresponding to four-quark operators is reviewed and it is investigated how the eigenvalues of the anomalous dimension matrices influence the singular behaviour of the $u=3$ infrared renormalon pole. It is found that compared to the large-$\beta_0$ approximation where at most quadratic poles are present, in full QCD at $N_f=3$ the most singular pole is more than cubic with an exponent $\kappa\approx 3.2$.Comment: 19 pages, 1 figure; version to appear in JHE

Anomalous Higgs couplings in angular asymmetries of H --> Zl+l- and e+e- --> HZ

We study in detail the impact of anomalous Higgs couplings in angular asymmetries of the crossing-symmetric processes H --> Zl+l- and e+e- --> HZ. Beyond Standard Model physics is parametrized in terms of the SU(3)xSU(2)_LxU(1)_Y dimension-six effective Lagrangian. In the light of present bounds on d = 6 interactions we study how angular asymmetries can reveal non-standard CP-even and CP-odd couplings. We provide approximate expressions to all observables of interest making transparent their dominant dependence on anomalous couplings. We show that some asymmetries may reveal BSM effects that are hidden in other observables. In particular, CP-even and CP-odd d = 6 HZgamma couplings as well as (to a lesser extent) HZll contact interactions can generate asymmetries at the several percent level, while having small or no effects on the di-lepton invariant mass spectrum of H --> Zl+l-. Finally, the higher di-lepton invariant mass probed in e+e- --> HZ leads to interesting differences in the asymmetries with respect to those of H --> Zl+l- that may lead to complementary anomalous coupling searches at the LHC and e+e- colliders.Comment: 34 pages, 14 figures. Minor changes, one additional figure (Fig. 5), one reference added (Ref. [34]). Matches published versio

Dispersive representation of the K pi vector form factor and fits to tau -> K pi nu(tau) and Ke3 data

Recently, we introduced several dispersive representations for the vector $K\pi$ form factor and fitted them to the Belle spectrum of $\tau \to K \pi \nu_\tau$. Here, we briefly present the model and discuss the results for the slope and curvature of $F_+(s)$ arising from the best fit. Furthermore, we compare the pole position of the charged $K^*(892)$ computed from our model with other results in the literature. Finally, we discuss the prospects of a simultaneous fit to $\tau \to K \pi \nu_\tau$ and $K_{e3}$ spectra.Comment: Talk given at "International Workshop on Effective Field Theories: from the pion to the upsilon", February 2009, Valencia, Spain. 7 pages, 2 figures. PoS style. Minor correction in figure

Improving the Kpi vector form factor through Kl3 constraints

The $K\pi$ vector form factor, $F_+^{K\pi}$, used to reproduce the Belle spectrum of \tauKpi decays is described by means of a three-times subtracted dispersion relation also incorporating constraints from $K_{l3}$ decays. The slope and curvature of $F_+^{K\pi}$ are fitted to the data yielding $\lambda_+'=(25.49 \pm 0.31) \times 10^{-3}$ and $\lambda_+"= (12.22 \pm 0.14) \times 10^{-4}$. The pole parameters of the $K^*(892)^\pm$ are found to be $m_{K^*(892)^\pm}= 892.0\pm 0.5$ MeV and $\Gamma_{K^*(892)^\pm}= 46.5 \pm1.1$ MeV. The phase-space integrals relevant for $K_{l3}$ analyses and the $P$-wave isospin-1/2 $K\pi$ phase-shift threshold parameters are also calculated.Comment: 3 pages, uses aipproc style. Talk presented by R. Escribano at the IX International Conference on Quark Confinement and Hadron Spectrum (QCHS09), Madrid, Spain, 30.8-3.9.201